Light emitting element driving device

Abstract

A control logic unit (10) transitions from a normal mode to a first limp-home mode (of two limp-home modes) when there is no communication signal from an external microcomputer (35) for more than a first prescribed interval during a normal mode during which a light emission control of light-emitting elements (A1-A24) is performed by a dimmer control unit (15). During the first limp-home mode, the dimmer control unit sets a light-emitting element current setting value on the basis of a terminal current setting value corresponding to the resistance value of a setting resistance (Rextiset 1, 2) and a DC dimmer setting value for each channel set in the register (10A), controls a current driver (11) so as to generate a current at the set light-emitting element current setting value, and controls so as to turn the current driver on and off on the basis of the PWM on-duty setting value for each channel set in the register.

Description

[Technical Field]

[0001] The present disclosure relates to a light emitting element driving device. [Background technology]

[0002] Conventionally, various LED driving devices (LED drivers) that drive LEDs (Light Emitting Diodes) as light emitting elements have been developed. For example, Patent Document 1 discloses an example of an LED driving device having a PWM dimming function. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-179662 Summary of the Invention [Problem to be solved by the invention]

[0004] Recently, limp home has become important as a functional safety measure for in-vehicle devices. Limp home is a mode that maintains functionality in an emergency.

[0005] An object of the present disclosure is to provide a light-emitting element driving device having a limp-home mode that enables highly flexible dimming. [Means for solving the problem]

[0006] For example, the light-emitting element driving device according to the present disclosure includes a current driver that generates current to be passed through each light-emitting element of multiple channels, a dimming control unit that controls the current driver, a control logic unit that includes a register, and an external terminal to which a setting resistor can be externally connected. In a normal mode in which the dimming control unit controls the light emission of the light-emitting element, if there is no communication signal from an external microcomputer for more than a first predetermined period, the control logic unit transitions from the normal mode to a first limp home mode. In the first limp home mode, the dimming control unit sets a light-emitting element current setting value based on a terminal current setting value corresponding to the resistance value of the setting resistor and a DC dimming setting value for each channel set in the register, controls the current driver to generate a current of the set light-emitting element current setting value, and controls the current driver on and off based on a PWM on-duty setting value for each channel set in the register. [Effects of the Invention]

[0007] The light-emitting element driving device according to the present disclosure can have a limp home mode that allows for highly flexible dimming. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating a configuration of an LED driving device according to an exemplary embodiment of the present disclosure. [Figure 2] FIG. 10 is a diagram showing an example of a case where a plurality of LED driving devices are connected and used. [Figure 3] FIG. 1 is a diagram illustrating an example of a system configuration in which an LED driving device is applied to a rear lamp of a vehicle. [Figure 4] FIG. 2 is a diagram showing the main configuration of a dimming control unit and a current driver. [Figure 5] FIG. 2 is a state transition diagram of the LED driving device. [Figure 6] 10 is a table showing the contents of parameters for each mode. [Figure 7] FIG. 10 is a diagram illustrating an example of a register map. [Figure 8] 10 is a table showing an example of correspondence between data values ​​of LHDTYn and PWM dimming on-duty setting values. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, exemplary embodiments of the present disclosure will be described with reference to the drawings. Here, an LED driving device will be described as an example of a light emitting element driving device.

[0010] <1. LED driver configuration> Fig. 1 is a diagram showing the configuration of an LED driving device 20 according to an exemplary embodiment of the present disclosure. The LED driving device 20 shown in Fig. 1 drives LED arrays A1 to A24 of multiple channels (24 channels in this embodiment, for example). The LED driving device 20 is, for example, for use in a vehicle.

[0011] The LED driving device 20 is a semiconductor device having a semiconductor integrated circuit (IC chip) that integrates a DC / DC control unit 1, a UVLO (Under Voltage Lock Out) / TSD (Thermal Shut Down) unit 2, a bandgap reference 3, an internal voltage generation unit 4, an internal voltage generation unit 5, an abnormality notification unit 6, an NMOS transistor 7, an I / O (input / output) port 8, a ring oscillator 9, a control logic unit 10, a current driver 11, a short detection unit 12, an open detection unit 13, and an LED current setting unit 14.

[0012] The LED driving device 20 also has external terminals for establishing electrical connection with the outside, including an SNSN terminal, an SNSP terminal, a BOOT terminal, a GH terminal, a SW terminal, a PGND terminal, a VIN terminal, a VREG5 terminal, a VREG3 terminal, a FAILB terminal, an EN terminal, an RX terminal, a TX terminal, CS0 to CS3 terminals, a PWMIN terminal, an FBV terminal, a MINSELV terminal, LED1 to LED24 terminals, LGND1 to LGND4 terminals, an EXTISET1 terminal, an EXTISET2 terminal, a PWMOUT terminal, and a GND terminal.

[0013] An output stage 25 is arranged outside the LED driver 20 to generate an output voltage Vout from an input voltage Vin by DC / DC conversion and supply the output voltage Vout to the anodes of the LED arrays A1 to A24. The output stage 25 has a switching element N1, a diode D1, an inductor L1, a resistor R1, and an output capacitor Co, which are each discrete components. The switching element N1 is driven and controlled by a DC / DC control unit 1 included in the LED driver 20. The output stage 25 and the DC / DC control unit 1 form a DC / DC converter. In this embodiment, an asynchronous rectification step-down DC / DC converter is particularly configured as the DC / DC converter.

[0014] More specifically, the drain of the switching element N1, which is an NMOS transistor, is connected to the terminal to which the input voltage Vin is applied. A node Nd1, at which the source of the switching element N1 and the cathode of the diode D1 are connected, is connected to the SW terminal. The anode of the diode D1 is connected to the terminal to which the ground potential is applied. The node Nd1 is connected to one end of the inductor L1. The other end of the inductor L1 is connected to one end of the resistor R1 at a node Nd2. The other end of the resistor R1 is connected to one end of the output capacitor Co at a node Nd3. The other end of the output capacitor Co is connected to the terminal to which the ground potential is applied.

[0015] The gate of the switching element N1 is connected to the DC / DC control unit 1 via the GH terminal. The gate of the switching element N1 is driven by a driver (not shown) included in the DC / DC control unit 1. One end of the boot capacitor Cb is connected between the inductor L1 and the node Nd1. The other end of the boot capacitor Cb is connected to the DC / DC control unit 1 via the BOOT terminal.

[0016] When the switching element N1 is on, a current flows through the switching element N1 toward the inductor L1 and resistor R1. When the switching element N1 is turned off, a current flows through the diode D1 toward the inductor L1 and resistor R1. At this time, the boot capacitor Cb is charged by the DC / DC control unit 1.

[0017] When the switching element N1 is turned on, a voltage higher than the input voltage Vin by the voltage generated in the boot capacitor Cb due to charging occurs at the BOOT terminal, which turns on the switching element N1, which is an NMOS transistor.

[0018] By such on / off control of the switching element N1, an output voltage Vout is generated at the node Nd3.

[0019] The output voltage Vout is applied to each anode of the LED arrays A1 to A24. The cathodes of the LED arrays A1 to A24 are connected to the LED1 to LED24 terminals, respectively. A minimum voltage selection unit 1A included in the DC / DC control unit 1 selects the minimum voltage among the terminal voltages (cathode voltages) of the LED1 to LED24 terminals.

[0020] On the other hand, a node Nd2 to which one end of the resistor R1 is connected is connected to the SNSP terminal. A node Nd3 to which the other end of the resistor R1 is connected is connected to the SNSN terminal. The SNSP terminal voltage and the SNSN terminal voltage are input to an amplifier (not shown) included in the DC / DC control unit 1. As a result, the amplifier detects the inductor current flowing through the inductor L1 (resistor R1).

[0021] Based on the output of the amplifier, the DC / DC control unit 1 injects a ripple into the minimum voltage selected by the minimum voltage selection unit 1A, and controls the on / off of the switching element N1 by comparing the voltage after injection with a predetermined threshold. In this way, the DC / DC control unit 1 performs hysteresis control, so that the minimum voltage among the terminal voltages of the LED1 terminal to the LED24 terminal becomes the desired voltage.

[0022] The FBV terminal and the MINSELV terminal are used when multiple LED drivers 20 are connected and used. Fig. 2 shows, as an example, a configuration in which three LED drivers 20 (20m, 20s1, and 20s2) are connected and used. In Fig. 2, the LED driver 20m corresponds to the master, and the LED drivers 20s1 and 20s2 correspond to the slaves.

[0023] The cathodes of the LED arrays A1 to A24 are connected to the LED driving devices 20m, 20s1, and 20s2, respectively. The output voltage Vout generated by the DC / DC function of the LED driving device 20m is applied to the anodes of the LED arrays A1 to A24. The DC / DC function is not used in the LED driving devices 20s1 and 20s2. Note that in FIG. 2, the configuration related to the output of the output voltage Vout is illustrated in a simplified manner for convenience.

[0024] The FBV terminal outputs the minimum voltage selected by the minimum voltage selection unit 1 A from among the cathode voltages of the LED arrays A1 to A24 and the voltages of the MINSELV terminal. The FBV terminal of the external LED driver 20 is connected to the MINSELV terminal.

[0025] 2, the MINSELV terminal of LED driver 20m is connected to the FBV terminal of LED driver 20s1, and the MINSELV terminal of LED driver 20s1 is connected to the FBV terminal of LED driver 20s2. The FBV terminal of LED driver 20m and the MINSELV terminal of LED driver 20s2 are not connected. Note that it is desirable to connect the MINSELV terminal of LED driver 20s2 to an application terminal of a high-gain voltage, such as the reference voltage Vdrv5 generated at the VREG5 terminal of LED driver 20s2, so as not to affect the selection of the minimum voltage.

[0026] As a result, the LED driver 20s2 selects the smallest voltage among the cathode voltages of the LED arrays A1 to A24, and outputs the selected smallest voltage from its own FBV terminal. The LED driver 20s1 selects the smallest voltage among the voltage input to its own MINSELV terminal from the FBV terminal of the LED driver 20s2 and the cathode voltages of the LED arrays A1 to A24, and outputs the selected smallest voltage from its own FBV terminal. The LED driver 20m selects the smallest voltage among the voltage input to its own MINSELV terminal from the FBV terminal of the LED driver 20s1 and the cathode voltages of the LED arrays A1 to A24, and uses the selected smallest voltage for the DC / DC function.

[0027] Therefore, the output voltage Vout is controlled so that the minimum voltage among the cathode voltages of all the LED arrays (24 channels×3=72 channels in the case of FIG. 2) connected to the plurality of connected LED drivers 20 becomes the desired value.

[0028] The DC / DC function in the LED driver 20 is not limited to the above-mentioned hysteresis control, but may be, for example, PWM control, etc. Also, the LED driver 20 does not necessarily need to have a DC / DC function.

[0029] Continuing with the explanation of the configuration shown in FIG. 1, the UVLO / TSD unit 2 monitors the input voltage Vin to provide low voltage protection, and monitors the junction temperature of the LED driver 20 to provide overheat protection.

[0030] The input voltage Vin is generated based on the battery power supply B and applied to the VIN terminal. The bandgap reference 3 is a reference voltage source that generates a stable reference voltage Vbg based on the input voltage Vin applied to the VIN terminal. The internal voltage generator 4 generates a 5V reference voltage Vdrv5 based on the input voltage Vin. The output terminal of the internal voltage generator 4 is connected to a capacitor via the VREG5 terminal. The internal voltage generator 5 generates a 3.3V reference voltage Vref33 based on the reference voltage Vdrv5. The output terminal of the internal voltage generator 5 is connected to a capacitor via the VREG3 terminal.

[0031] The MCU (Micro Controller Unit) 35 (external microcomputer) and the CAN (Controller Area Network) transceiver 30 are disposed outside the LED driver 20.

[0032] The NMOS transistor 7 is pulled up by a resistor to a reference voltage Vref33 generated at the VREG3 terminal. The abnormality notification unit 6 turns on the NMOS transistor 7 based on a command from the control logic unit 10, and notifies the MCU 35 of a low abnormality signal fault indicating an abnormality.

[0033] The MCU 35 sends an enable signal “enable” to the control logic unit 10 via the EN terminal and the I / O port 8 .

[0034] The CAN transceiver 30 receives data from the MCU 35 via the CAN bus CB and transmits it as received data Rxd to the RX terminal. The control logic unit 10 receives the received data Rxd via the I / O port 8. The control logic unit 10 transmits transmitted data Txd to the TX terminal via the I / O port 8. The CAN transceiver 30 transmits the transmitted data Txd received from the TX terminal to the MCU 35 via the CAN bus CB. The I / O port 8 is configured as a UART (Universal Asynchronous Receiver / Transmitter) and converts between serial and parallel signals.

[0035] The CS0 to CS3 terminals are each pulled up to the power supply voltage by a resistor. A unique number (ID) for identifying the LED driver 20 is set in the control logic unit 10 by a combination of High and Low being set in the CS0 to CS3 terminals.

[0036] The ring oscillator 9 is an oscillator that generates a clock signal, and a PWM signal is generated based on the clock signal to perform PWM dimming.

[0037] The PWMIN terminal, the PWMOUT terminal, and the selector 101 are used when a plurality of LED drivers 20 are connected as described below, and the frequencies of the clock signals generated by the ring oscillators 9 in the individual LED drivers 20 are synchronized.

[0038] A current driver 11 is provided corresponding to each of the LED1 terminal to LED24 terminal, and supplies a constant current to each of the LED arrays A1 to A24. The on / off of the current driver 11 is controlled based on a PWM signal, thereby performing PWM dimming of the LED arrays A1 to A24. Furthermore, DC dimming is also possible by varying the set value of the constant current while the current driver 11 is turned on.

[0039] The short circuit detection units 12 are provided corresponding to the LED1 to LED24 terminals, respectively, and detect short circuits (short circuits between the cathodes of the LEDs and the output voltage Vout) of the LED arrays A1 to A24 based on the voltages of the terminals, and perform LED short circuit protection. In the LED short circuit protection, the current driver 11 corresponding to the LED array of the channel in which a short circuit is detected is turned off.

[0040] The open detectors 13 are provided corresponding to the LED1 terminal to LED24 terminal, respectively, and detect an open circuit in the LED arrays A1 to A24 based on the voltage of the terminal, thereby performing LED open protection.

[0041] <2. Connecting multiple LED drivers> In this embodiment, it is possible to connect multiple LED driving devices 20 to accommodate applications requiring a large number of LEDs. FIG. 3 shows an example of a system configuration in which the LED driving device 20 is applied to a rear lamp of a vehicle as an example of an application. For convenience, in FIG. 3, the individual LED driving devices 20 are denoted by reference numerals 20A to 20H, respectively. Also, CAN transceivers 30A to 30C in FIG. 3 correspond to the CAN transceiver 30 shown in FIG. 1.

[0042] As shown in Figure 3, LED driving devices 20A, 20B and CAN transceiver 30A are applied to a rear lamp on the left rear of a vehicle. LED driving devices 20A, 20B and CAN transceiver 30A are mounted on a printed circuit board P1. LED driving devices 20A and 20B are connected to form an LED driving system 200A.

[0043] In the rear lamp on the left rear part of the vehicle, an LED array of 24 channels x 2 = 48 channels is driven by LED driver devices 20A and 20B. The PWMOUT terminal of LED driver device 20A on the front stage is connected to the PWMIN terminal of LED driver device 20B on the rear stage. This makes it possible to synchronize the frequency of the clock signal generated by ring oscillator 9B of LED driver 20B with the frequency of the clock signal generated by ring oscillator 9A of LED driver 20A, with LED driver 20A acting as the master and LED driver 20B acting as the slave.

[0044] 3, LED driving devices 20C to 20F and CAN transceiver 30B are applied to a rear lamp at the center of the rear of the vehicle. LED driving devices 20C to 20F and CAN transceiver 30B are mounted on a printed circuit board P2. LED driving system 200B is configured by connecting LED driving devices 20C to 20F.

[0045] In the rear lamp at the center of the rear of the vehicle, an LED array of 24 channels x 4 = 96 channels is driven by LED driving devices 20C to 20F. The PWMOUT terminal of LED driving device 20C on the front stage is connected to the PWMIN terminal of LED driving device 20D on the rear stage. The PWMOUT terminal of LED driving device 20D on the front stage is connected to the PWMIN terminal of LED driving device 20E on the rear stage. The PWMOUT terminal of LED driving device 20E on the front stage is connected to the PWMIN terminal of LED driving device 20F on the rear stage. This makes it possible to synchronize the frequency of the clock signal generated by ring oscillator 9C of LED driving device 20C with the frequency of the clock signal generated by ring oscillator 9D to 9F of LED driving devices 20D to 20F, with LED driving device 20C as the master and LED driving devices 20D to 20F as slaves.

[0046] As shown in Figure 3, LED driving devices 20G, 20H and CAN transceiver 30C are applied to a rear lamp on the right rear of a vehicle. LED driving devices 20G, 20H and CAN transceiver 30C are mounted on printed circuit board P3. LED driving devices 20G and 20H are connected to form LED driving system 200C.

[0047] In the rear lamp on the right rear part of the vehicle, an LED array of 24 channels x 2 = 48 channels is driven by LED driver devices 20G and 20H. The PWMOUT terminal of LED driver device 20G on the front stage side is connected to the PWMIN terminal of LED driver device 20H on the rear stage side. This makes it possible to synchronize the frequency of the clock signal generated by ring oscillator 9H of LED driver device 20H with the frequency of the clock signal generated by ring oscillator 9G of LED driver 20G, with LED driver device 20H as the slave.

[0048] Data can be transmitted and received between LED drivers 20A and 20B and CAN transceiver 30A. Data can be transmitted and received between LED drivers 20C to 20F and CAN transceiver 30B. Data can be transmitted and received between LED drivers 20G and 20H and CAN transceiver 30C.

[0049] The CAN transceivers 30A to 30C can transmit and receive data to and from the MCU 35 mounted on the printed circuit board P4 via a wire harness 40. The CAN bus CB (FIG. 1) is included in the wire harness 40. The MCU 35 can command the LED drivers 20A to 20H to set the PWM dimming duty via the CAN transceivers 30A to 30C. In addition to the PWM dimming duty, the MCU 35 can also set various other settings, such as DC dimming settings, for the LED drivers. The set values ​​can be written to a register 10A (FIG. 1) included in the control logic unit 10.

[0050] Furthermore, the MCU 35 can transmit an enable signal “enable” to the LED driving devices 20A to 20H via the wire harness 40, and can receive an abnormality signal “fault” from the LED driving devices 20A to 20H via the wire harness 40. The enable signal “enable” may be transmitted from a source other than the MCU 35.

[0051] <3. Dimming control unit> Next, a configuration for controlling the dimming of LEDs will be described with reference to Fig. 4. As shown in Fig. 4, the LED driving device 20 has a dimming control section 15. The dimming control section 15 is configured to be able to dim the LED arrays A1 to A24 of each channel. However, for convenience, Fig. 4 only shows the current driver 11 corresponding to the LED array of one channel.

[0052] As shown in FIG. 4, the current driver 11 has an NMOS transistor 11A, a resistor 11B, an error amplifier 11C, and a switch 11D. The drain of the NMOS transistor 11A is connected to one of the terminals LED1 to LED24. The source of the NMOS transistor 11A is connected to one end of the resistor 11B. The other end of the resistor 11B is connected to a terminal to which a ground potential is applied. A node N11, at which the source of the NMOS transistor 11A and the resistor 11B are connected, is connected to an inverting input terminal (-) of the error amplifier 11C. A reference voltage Vref (described later) is applied to a non-inverting input terminal (+) of the error amplifier 11C. The switch 11D is arranged between the output terminal of the error amplifier 11C and the gate of the NMOS transistor 11A.

[0053] The dimming control unit 15 has an LED current setting unit 14 (FIG. 1) and a control logic unit 10. A setting resistor Rextiset1 (first setting resistor) can be externally connected to an EXTISET1 terminal (first external terminal) which is an external terminal. A setting resistor Rextiset2 (second setting resistor) can be externally connected to an EXTISET2 terminal (second external terminal) which is an external terminal.

[0054] The LED current setting unit 14 includes an external current setting unit 14A, an internal current setting unit 14B, a DC dimming circuit 14C, a switch 14D, and an adder 14E. The external current setting unit 14A sets the external current setting value Iext according to the resistance value of a setting resistor Rset1 connected to the EXTISET1 terminal or the resistance value of a setting resistor Rset2 connected to the EXTISET2 terminal. The external current setting value Iext is expressed by the following equation (1): Iext=(Vextiset / Rextiset)×A (1) Where Vextiset is the voltage of the EXTISET1 and 2 terminals, Rextiset is the resistance value of Rextiset1 and 2, and A is a constant. The internal current setting unit 14B sets a predetermined internal current setting value Iint. The internal current setting value Iint is input to the adder 14E, and the external current setting value Iext is also input to the adder 14E via the switch 14D. The adder 14E outputs a terminal current setting value Its as the addition result.

[0055] If the EXTISET1 and EXTISET2 terminals are not used, the control logic unit 10 turns off the switch 14D. As a result, the internal current setting value Iint (=terminal current setting value Its) is output from the adder 14E and input to the DC dimming circuit 14C. In this case, the DC dimming circuit 14C sets the LED current setting value Iset, expressed by the following equation (2), based on the internal current setting value Iint and the DC dimming setting value [%] commanded by the control logic unit 10. Iset[mA]=Iint×DC dimming setting value[%] (2)

[0056] On the other hand, when the EXTISET1 terminal or the EXTISET2 terminal is set to be used, the control logic unit 10 turns on the switch 14D. As a result, the result of adding the internal current setting value Iint and the external current setting value Iext (=terminal current setting value Its) is output from the adder 14E and input to the DC dimming circuit 14C. In this case, the DC dimming circuit 14C sets the LED current setting value Iset, expressed by the following equation (3), based on the output from the adder 14E and the DC dimming setting value (%) commanded by the control logic unit 10. Iset[mA]=(Iint+Iext)×DC dimming setting value[%] (3)

[0057] The DC dimming circuit 14C outputs the reference voltage Vref according to the LED current set value Iset set as described above to the error amplifier 11C.

[0058] When the switch 11D is in the on state and the current driver 11 is in the on state, the voltage at the node N11 is controlled to match the reference voltage Vref, and an LED current ILED generated by the reference voltage Vref and the resistance value of the resistor 11B flows through the LED terminal (one of the LED1 terminal to the LED24 terminal). Therefore, an LED current ILED having a current value equal to the LED current set value Iset can be generated. DC dimming can be performed by varying the LED current set value Iset while maintaining the switch 11D in the on state using the dimming control unit 15 (control logic unit 10).

[0059] Furthermore, the control logic unit 10 generates a PWM signal pwms according to the PWM dimming on-duty setting value set in the register 10A. During the on-duty period in one cycle of the PWM signal pwms, the switch 11D is turned on, thereby turning the current driver 11 on, and during the off-duty period, the switch 11D is turned off, thereby turning the current driver 11 off. This allows PWM dimming according to the PWM signal pwms to be performed.

[0060] The LED current ILED (average LED current) during PWM dimming is expressed by the following equation (4). ILED [mA] = LED current setting Iset [mA] × PWM dimming on-duty setting [%] (4)

[0061] During DC dimming, the logic control unit 10 controls the switch 11D with the PWM dimming on-duty set to 100%.

[0062] In addition, in the normal mode described below, the external current setting value Iext uses a value corresponding to the resistance value of the setting resistor Rextiset1 connected to the EXTISET1 terminal, but in the limp home mode described below, a value corresponding to the resistance value of the setting resistor Rextiset2 connected to the EXTISET2 terminal can be used.

[0063] <4. State transition> Next, the mode transition of the LED driver 20 will be described with reference to the state transition diagram in Fig. 5. As shown in Fig. 5, when the control logic unit 10 is released from a state in which it has been reset by the UVLO / TSD unit 2 or by a power-on reset, the control logic unit 10 transitions to idle mode (IDLE). Note that the release of the reset by a power-on reset is performed by an enable signal "enable" that rises together with the rise of the input voltage Vin.

[0064] The idle mode is a state in which the control logic unit 10 is able to receive a communication signal from the MCU 35 but is not receiving the communication signal via the CAN transceiver 30 and the I / O port 8. If the control logic unit 10 receives the communication signal (in the case of UART access) within a predetermined period (here, 1 second) after entering the idle mode, the control logic unit 10 enters the standby mode.

[0065] In standby mode, various settings are written to register 10A by the above communication signals from MCU 35. The LED is turned off in standby mode. The above various settings include the DC dimming setting value and the PWM dimming on-duty setting value.

[0066] When the setting in the register 10A is completed in the standby mode and the dimming start flag DIMSTART=1 is written to the register 10A by the communication signal from the MCU 35, the control logic unit 10 transitions to the normal mode (NORMAL).

[0067] <<4-1. Normal Mode>> When the mode shifts to normal mode, the dimming control unit 15 starts controlling the light emission of the LEDs by DC dimming or PWM dimming. Fig. 6 is a table showing the PWM dimming setting, DC dimming setting, external terminal usage setting, presence or absence of soft start, and active protection functions for normal mode (NORMAL) and limp home 1 and 2 modes (LIMP HOME1 and 2) described later.

[0068] 6, in normal mode, the DC dimming setting and PWM dimming setting used differ depending on the dimming mode flag DIMMODE set in register 10A. In DC dimming mode where the dimming mode flag DIMMODE=1, the dimming setting value DIMSETn set in register 10A is used as the DC dimming setting value [%], and 100% is used as the PWM dimming on-duty setting value [%]. Note that "n" in DIMSETn indicates each channel of the LED arrays A1 to A24 (LED1 terminals to LED24 terminals), and the same applies to the other setting values.

[0069] On the other hand, in the PWM dimming mode where the dimming mode flag DIMMODE=0, the DC setting value DCDIMn set in register 10A is used as the DC dimming setting value [%], and the dimming setting value DIMSETn is used as the PWM dimming on-duty setting value [%].

[0070] 6, in normal mode, whether or not the EXTISET1 terminal is used is set according to the current setting selection flag ISETSEL set in register 10 A. When ISETSEL=0, the EXTISET1 terminal is not used, and the LED current setting value Iset is set by the above equation (2) based on the internal current setting value Iint.

[0071] On the other hand, when ISETSEL=1, the EXTISET1 terminal is used, and the LED current set value Iset is set by the above equations (1) and (3).

[0072] Therefore, in the normal mode, in the case of the DC dimming mode (DIMMODE=1), the dimming control section 15 controls the light emission for each channel with the LED current ILED expressed as follows: ILED = Terminal current setting value Its (internal or EXTISET1) × DIMSETn × 100%

[0073] On the other hand, in the PWM dimming mode where DIMMODE=0, the DC setting value DCDIMn set in the register 10A is used as the DC dimming setting value, and the dimming setting value DIMSETn is used as the PWM dimming on-duty setting value.

[0074] Therefore, in the normal mode, in the PWM dimming mode (DIMMODE=0), the dimming control section 15 controls light emission for each channel with the LED current ILED expressed as follows: ILED = Terminal current setting value Its (internal or EXTISET1) × DCDIMn × DIMSETn

[0075] 5, when the dimming start flag DIMSTART=0 (dimming stop command) is written to the register 10A in the normal mode, the control logic unit 10 transitions to the standby mode (STAND BY). At this time, the setting of the register 10A is maintained, and the LED is turned off.

[0076] <<4-2. Limp home at startup>> As shown in FIG. 5, if the above communication signal from the MCU 35 is not received (if there is no UART access) even after a predetermined period of time (here, 1 second) has elapsed since the transition to idle mode, the control logic unit 10 determines that there is an abnormality and transitions to limp home 1 mode (LIMP HOME1) (second limp home mode).

[0077] When the mode shifts to limp home 1, the dimming control unit 15 starts the following LED light emission control. As shown in FIG. 6, in limp home 1 mode, the EXTISET2 terminal is used. 100% is used as the DC dimming setting value. The limp home duty setting value LHDTYn set in register 10A is used as the PWM dimming on-duty setting value.

[0078] 7 shows an example of a register map of the limp home duty setting value LHDTYn in register 10 A. As shown in FIG. 7, LHDTYn is assigned to the lower 4 bits and the upper 4 bits of the same address, and since there are 12 addresses (A to L), LHDTYn for 24 channels is assigned.

[0079] Figure 8 shows an example of the correspondence between the data value of LHDTYn, which is 4-bit data, and the PWM dimming on-duty setting value. Here, in limp home 1 mode, the limp home duty setting value LHDTYn has not yet been set in register 10A by MCU 35 and is the initial value. The initial value of limp home duty setting value LHDTYn is "F," and from Figure 8, the PWM dimming on-duty setting value is 100%.

[0080] Therefore, in the limp home 1 mode, the dimming control unit 15 controls the light emission for each channel based on the above equations (1) and (3) using the LED current ILED expressed as follows: ILED=(Iint+Iext)(EXTISET2)×100%×LHDTYn(100%)

[0081] In other words, in Limp Home 1 mode, for all channels Light emission control is performed using ILED = (Iint + Iext) (EXTISET2) x 100% x 100%.

[0082] This allows the brightness of the LEDs in limp home 1 mode to be set for each LED driver 20 by externally connecting a resistor Rextiset2 for setting the desired resistance value for each LED driver 20. For example, the brightness of the LEDs in limp home 1 mode can be set for each application (e.g., left, right, and center rear lamps) in the same vehicle. This also allows for cases where the required LED current value differs due to the different types of LEDs used in different vehicle models (e.g., white LEDs, yellow LEDs, etc.).

[0083] Furthermore, when the EXTISET2 terminal is open, the DC dimming circuit 14C sets the terminal current setting value Its to 0 mA. Therefore, in this case, the LEDs of all channels can be turned off. This allows, for example, applications where you want to turn off the LEDs in limp home 1 mode (such as turn signals or brake lights).

[0084] As shown in Figure 5, if there is UART access while in limp home 1 mode, the device transitions to standby mode.

[0085] <<4-3. Limp home in normal mode>> As shown in Fig. 5, in normal mode (NORMAL), if the limp home enable flag LIMPHEN is set to 1 (enabled) and there is no UART access for a predetermined period (here, 1 second), the control logic unit 10 transitions to limp home 2 mode (LIMP HOME2) (first limp home mode). Note that the limp home enable flag LIMPHEN is assigned to the least significant bit of a predetermined address (M) in the register 10, for example, as shown in Fig. 7.

[0086] When the mode shifts to limp home 2 mode, the dimming control unit 15 starts the following LED light emission control. In limp home 2 mode, as shown in Fig. 6, whether or not to use the EXTISET2 terminal is selected according to the EXTISET2 terminal selection flag LEXTISET2SEL set in register 10A. Note that, as shown in Fig. 7, LEXTISET2SEL is assigned to the second least significant bit of a predetermined address (M) where the limp home enable flag LIMPHEN is set, for example.

[0087] Specifically, when LEXTISET2SEL=0 (not used), whether or not to use the EXTISET1 terminal is selected according to the current setting selection flag ISETSEL, as in the normal mode. On the other hand, when LEXTISET2SEL=1, the EXTISET2 terminal is set to be used.

[0088] In addition, in limp home 2 mode, the DC dimming set value is the same as in normal mode, as shown in Fig. 6. That is, when the dimming mode flag DIMMODE = 1 (DC dimming mode), the dimming set value DIMSETn is used as the DC dimming set value, and when the dimming mode flag DIMMODE = 0 (PWM dimming mode), the DC set value DCDIMn is used as the DC dimming set value. Therefore, in normal mode and limp home 2 mode, the DC dimming set value for each channel is the same.

[0089] Furthermore, as shown in Fig. 6, the limp home duty setting value LHDTYn is used as the PWM dimming on duty setting value. Here, LHDTYn set for each channel based on Fig. 8 is used.

[0090] Therefore, in the limp home 2 mode, the dimming control section 15 controls the light emission for each channel with the LED current ILED expressed as follows: ILED = Terminal current setting value Its (internal or EXTISET1 or EXTISET2) × DC dimming setting value (DCDIMn or DIMSETn) × LHDTYn

[0091] In this way, in Limp Home 2 mode, which is entered from normal mode, the LED brightness can be set for each channel, allowing for highly flexible dimming. For example, this makes it possible to change the LED current between channels, turn off LEDs on certain channels, or use different types of LEDs (white LEDs, yellow LEDs, etc.) between channels.

[0092] In addition, even if there is no UART access for a predetermined period of time in normal mode, if the limp home enable flag LIMPHEN=0 (disabled), the mode will not transition to limp home 2 mode.

[0093] Also, as shown in FIG. 5, when the device transitions from normal mode to limp home 2 mode, if there is UART access, the device returns to normal mode.

[0094] 5, when in standby mode, if the limp home enable flag LIMPHEN=1 (enabled) and there is no UART access for a predetermined period (here, 1 sec), the device will also transition to limp home 2 mode. Furthermore, in this case, if there is UART access while in limp home 2 mode, the device will return to standby mode.

[0095] <<4-4. LED current setting example>> Here, we will explain examples of LED current settings for each mode.

[0096] <Case 1> Limp Home 1 Mode: Terminal current setting value Its(EXTISET2)(60mA)×100%×LHDTYn(all channels 100%) Normal mode: Terminal current setting value Its(EXTISET1)(125mA)×DCDIMn(all channels 100%)×DIMSETn Limp Home 2 Mode: Terminal current setting value Its(EXTISET2)(60mA) × DCDIMn(all channels 100%) × LHDTYn

[0097] In the above case 1, a setting resistor Rextiset2 is connected to the EXTISET2 terminal, and the EXTISET2 terminal is not left open, and in the limp home 2 mode, LEXTISET2SEL=1 is set to select use of the EXTISET2 terminal.

[0098] <Case 2> Limp Home 1 Mode: Terminal current setting value Its(EXTISET2)(0mA)×100%×LHDTYn(all channels 100%) Normal mode: Terminal current setting value Its(EXTISET1)(125mA)×DCDIMn(all channels 100%)×DIMSETn Limp Home 2 Mode: Terminal current setting value Its(EXTISET2)(0mA) × DCDIMn(all channels 100%) × LHDTYn

[0099] In the above case 2, the EXTISET2 terminal is left open, and in limp home 2 mode, the use of the EXTISET2 terminal is selected by setting LEXTISET2SEL=1. As a result, the LEDs of all channels are turned off in both limp home 1 mode and limp home 2 mode.

[0100] <Case 3> Limp Home 1 Mode: Terminal current setting value Its(EXTISET2)(0mA)×100%×LHDTYn(all channels 100%) Normal mode: Terminal current setting value Its(EXTISET1)(125mA)×DCDIMn(all channels 50%)×DIMSETn Limp Home 2 Mode: Terminal current setting value Its(EXTISET1)(125mA) × DCDIMn(all channels 50%) × LHDTYn

[0101] In the above case 3, the EXTISET2 terminal is left open, and in limp home 2 mode, the use of the EXTISET1 terminal is selected with LEXTISET2SEL = 0 and ISETSEL = 1. As a result, in limp home 1 mode the LEDs for all channels are turned off, but in limp home 2 mode the LED brightness can be set for each channel.

[0102] <<4-5.Others>> As for the update timing of LHDTYn, as soon as LHDTYn is written to the register 10A, it is reflected in the operation of the PWM generating unit (included in the logic control unit 10) that generates the PWM signal pwms.

[0103] Furthermore, when transitioning to normal mode, limp home 1 mode, or limp home 2 mode, the control logic unit 10 commands the DC / DC control unit 1 to start up the output voltage Vout. At this time, as shown in Fig. 6, the DC / DC control unit 1 performs a soft start to suppress overshoot of the output voltage Vout.

[0104] 6, all protection functions are enabled in normal mode, but in limp home 1 mode and limp home 2 mode, only specific protection functions shown in FIG. 6 are enabled. The specific protection functions are undervoltage protection (UVLO), thermal protection (TSD), external terminal short protection (ISET short), and LED open protection (LED OPEN). Note that external terminal short protection is a function in which, when it detects that the EXTISET2 terminal is shorted to ground potential, dimming control unit 15 switches the terminal current setting value Its to a predetermined internal setting value (e.g., 60 mA) in limp home 1 mode, and to a predetermined setting value in register 10A in limp home 2 mode.

[0105] The specific protection functions described above are necessary to avoid abnormal operation of the LED driver 20, even though they cannot notify the MCU 35 of the abnormal signal fault (FIG. 1) because the device is in limp home mode, which indicates an abnormal state of communication with the MCU 35. LED short circuit protection is not included in the specific protection functions described above, as it does not result in abnormal operation and therefore there is little need to protect against it.

[0106] Although exemplary embodiments of the present disclosure have been described above, the embodiments can be modified in various ways within the scope of the spirit of the present disclosure.

[0107] <5. Notes> As described above, the light emitting element driving device (20) disclosed in this specification: a current driver (11) that generates a current to be passed through each of the light emitting elements (A1 to A24) of the plurality of channels; a dimming control unit (15) for controlling the current driver; a control logic unit (10) including a register (10A); External terminals (EXTISET1, 2) to which setting resistors (Rextiset1, 2) can be externally connected; and In a normal mode in which the light-emission control unit controls the light emission of the light-emitting element, when there is no communication signal from an external microcomputer (35) for a period exceeding a first predetermined period, the control logic unit transitions from the normal mode to a first limp home mode (limp home 2 mode), In the first limp home mode, the dimming control unit: a terminal current setting value (Its) corresponding to the resistance value of the setting resistor and a light-emitting element current setting value (Iset) based on the DC dimming setting value for each channel set in the register; controlling the current driver to generate a current of the set light emitting element current setting value; The current driver is configured to be on / off controlled based on the PWM on-duty setting value for each channel set in the register (first configuration).

[0108] In addition, in the first configuration, a first external terminal (EXTISET1) to which a first setting resistor (Rextiset1) can be externally connected is provided, In the normal mode, the dimming control unit sets a light emitting element current setting value based on a terminal current setting value and a DC dimming setting value corresponding to the resistance value of the first setting resistor, and controls the current driver to generate a current of the light emitting element current setting value that has been set; the external terminal is the same as the first external terminal, The setting resistor may be the same as the first setting resistor (second configuration).

[0109] In the second configuration, a predetermined internal value may be selectable as the terminal current setting value in the normal mode and the first limp home mode (third configuration).

[0110] In the second or third configuration, the DC dimming setting value for each channel may be the same in the normal mode and the first limp home mode (fourth configuration).

[0111] In addition, in any one of the first to fourth configurations, a second external terminal (EXTISET2) to which a second setting resistor (Rextiset2) can be externally connected is provided, When there is no communication signal from the external microcomputer even after a second predetermined period has elapsed since the reset is released and the device has transitioned to the idle mode, the control logic unit transitions from the idle mode to a second limp home mode (limp home 1 mode), In the second limp home mode, the dimming control unit sets a light emitting element current setting value based on a terminal current setting value corresponding to the resistance value of the second setting resistor and a DC dimming setting value common to all of the channels, controls the current driver to generate a current of the set light emitting element current setting value, and performs on / off control of the current driver based on the PWM on-duty setting value common to all of the channels; The external terminal is different from the second external terminal, The setting resistor may have a different configuration from the second setting resistor (fifth configuration).

[0112] In the fifth configuration, when the second external terminal is open, the dimming control unit may set the terminal current setting value to 0 (sixth configuration).

[0113] In addition, in the fifth or sixth configuration, in the first limp home mode, a value corresponding to the resistance value of the second setting resistor may be selected as the terminal current setting value (seventh configuration).

[0114] In addition, in any of the above first to seventh configurations, in the standby mode, which is transitioned from the normal mode when a dimming stop command is received in the normal mode, if there is no communication signal from the external microcomputer for more than a third predetermined period, the control logic unit may be configured to transition from the standby mode to the first limp home mode (eighth configuration).

[0115] Furthermore, in the eighth configuration, a DC / DC control unit (1) may be provided for generating an output voltage to be applied to the light-emitting element, and when transitioning to the first limp home mode, the DC / DC control unit may be configured to perform a soft start (ninth configuration).

[0116] In addition, in any of the above first to ninth configurations, the dimming control unit may be configured to have an external terminal short-circuit protection function that uses a predetermined setting value as the terminal current setting value when it detects that the external terminal is shorted to ground potential (tenth configuration).

[0117] In addition, in the above-mentioned tenth configuration, in the first limp home mode, the protection functions may be limited to specific protection functions including the external terminal short protection function and enabled (eleventh configuration).

[0118] In the eleventh configuration, the light emitting element short circuit protection function for detecting and protecting the light emitting element from a short circuit may be configured not to be included in the specific protection function (twelfth configuration). [Industrial Applicability]

[0119] The present disclosure can be used, for example, to drive LEDs mounted on vehicles. [Explanation of symbols]

[0120] 1 DC / DC control unit 1A Minimum voltage selection section 2 UVLO / TSD section 3 Bandgap Reference 4, 5 Internal voltage generator 6 Abnormality notification section 7 NMOS transistor 8 I / O ports 9 Ring Oscillator 10 Control logic section 10A resistor 11 Current Driver 11A NMOS transistor 11B resistance 11C Error Amplifier 11D Switch 12 Short circuit detection section 13 Open detection section 14 LED current setting section 14A external current setting section 14B Internal current setting section 14C DC Dimmer Circuit 14D Switch 14E Addition section 15 Dimming control unit 20 LED driver 25 output stage 30 CAN transceivers 35 MCU 40 Wire harness 101 Selector A1~A24 LED array B Battery power CB CAN bus Cb Boot capacitor Co Output Capacitor D1 Diode L1 inductor N1 switching element P1~P4 printed circuit board R1 Resistor Resistors for setting Rextiset1 and Rextiset2

Claims

1. a current driver that generates a current to be passed through each of the light emitting elements of the plurality of channels; a dimming control unit that controls the current driver; a control logic section including registers; an external terminal to which a setting resistor can be externally connected; and In a normal mode in which the light emission control unit controls the light emission of the light-emitting element, when there is no communication signal from an external microcomputer for a period exceeding a first predetermined period, the control logic unit transitions from the normal mode to a first limp home mode; In the first limp home mode, the dimming control unit: setting a terminal current setting value according to the resistance value of the setting resistor and a light-emitting element current setting value based on a DC dimming setting value for each channel set in the register; controlling the current driver to generate a current of the set light emitting element current setting value; The light emitting element driving device controls the on / off of the current driver based on the PWM on-duty setting value for each channel set in the register.

2. a first external terminal to which a first setting resistor can be externally connected; In the normal mode, the dimming control unit sets a light emitting element current setting value based on a terminal current setting value and a DC dimming setting value corresponding to the resistance value of the first setting resistor, and controls the current driver to generate a current of the light emitting element current setting value that has been set; the external terminal is the same as the first external terminal, 2. The light-emitting element driving device according to claim 1, wherein the setting resistor is the same as the first setting resistor.

3. 3. The light-emitting element driving device according to claim 2, wherein a predetermined internal value can be selected as the terminal current setting value in the normal mode and the first limp home mode.

4. 4. The light-emitting element driving device according to claim 2, wherein the DC dimming setting value for each channel is the same in the normal mode and the first limp-home mode.

5. a second external terminal to which a second setting resistor can be externally connected; when there is no communication signal from the external microcomputer even after a second predetermined period has elapsed since the reset is released and the mode is changed to the idle mode, the control logic unit changes from the idle mode to a second limp home mode, In the second limp home mode, the dimming control unit sets a light emitting element current setting value based on a terminal current setting value corresponding to the resistance value of the second setting resistor and a DC dimming setting value common to all the channels, controls the current driver to generate a current of the set light emitting element current setting value, and performs on / off control of the current driver based on the PWM on-duty setting value common to all the channels; The external terminal is different from the second external terminal, 5. The light-emitting element driving device according to claim 1, wherein the setting resistor is different from the second setting resistor.

6. The light-emitting element driving device according to claim 5 , wherein the dimming control unit sets the terminal current setting value to 0 when the second external terminal is open.

7. 7. The light-emitting element driving device according to claim 5, wherein in the first limp-home mode, a value corresponding to a resistance value of the second setting resistor can be selected as the terminal current setting value.

8. 8. The light-emitting element driving device according to claim 1, wherein, in a standby mode transitioned from the normal mode when a dimming stop command is received in the normal mode, if there is no communication signal from the external microcomputer for more than a third predetermined period, the control logic unit transitions from the standby mode to the first limp home mode.

9. a DC / DC control unit for generating an output voltage to be applied to the light-emitting element; The light emitting element driving device according to claim 8 , wherein the DC / DC control unit performs a soft start when transitioning to the first limp home mode.

10. 10. The light-emitting element driving device according to claim 1, wherein the dimming control unit has an external terminal short-circuit protection function that uses a predetermined setting value as the terminal current setting value when it detects that the external terminal is shorted to ground potential.

11. The light-emitting element driving device according to claim 10 , wherein in the first limp home mode, only specific protection functions including the external terminal short-circuit protection function are enabled.

12. The light-emitting element driving device according to claim 11 , wherein a light-emitting element short-circuit protection function for detecting a short circuit in the light-emitting element and protecting the light-emitting element is not included in the specific protection function.

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