Short circuit detection circuit

Abstract

A short circuit detection circuit (100) includes a first transistor (102), a switched load circuit (110), a second transistor (104), a switched capacitor circuit (120), and a comparator (130). The first transistor (102) is configured to conduct a load current. The switched load circuit (110) is coupled to the first transistor (102). The switched load circuit (110) is configured to switchably draw a test current. The second transistor (104) is coupled to the first transistor (102). The second transistor (104) is configured to conduct a sense current. The sense current includes a first portion and a second portion representative of the load current and the test current, respectively. The switched capacitor circuit (120) is coupled to the second transistor (104). The switched capacitor circuit (120) is configured to generate a short circuit detection voltage representative of the second portion. The comparator (130) has a first comparator input coupled to the switched capacitor circuit (120). The comparator (130) is configured to compare the short-circuit detection voltage to a short-circuit threshold voltage.

Description

Background Art

[0001] Circuit protection devices, such as fuses or circuit breakers, protect circuits from damage caused by overcurrent or short-circuit conditions. An overcurrent condition occurs when the current flowing in a circuit (e.g., due to the demand of the load) exceeds the design rating of the circuit. A short-circuit condition occurs when the conductive elements of a circuit make contact, causing current to bypass the electrical load of the circuit, possibly resulting in very high currents. Overcurrent and short-circuit conditions can damage conductors and other components of the circuit due to overheating of the wires and cause the wire insulation to burn. Circuit protection devices detect the occurrence of overcurrent or short-circuit conditions and open an electrical switch or otherwise reduce the current flowing to the protected circuit to prevent damage to the circuit.

[0002] Fuses, positive temperature coefficient resistors, and active circuit protection are several types of circuit protection devices available. Fuses are often used to isolate an overload or short circuit fault from the main system. However, the fault current often needs to be much higher than the fuse rating, and the response time can range from milliseconds to seconds, making it difficult to predict the exact overcurrent level at which a fuse will open. Once a fuse opens, it must be physically replaced, which increases system downtime and maintenance costs. Positive temperature coefficient resistors provide resettable overcurrent protection and, unlike fuses, do not require replacement. The reaction time of a positive temperature coefficient resistor is in the range of milliseconds, and the resistance increases with each activation.

[0003] Active circuit protection devices measure the current flowing through a field effect transistor (FET) and control the resistance of the FET to limit the current flowing to the load when a fault condition is detected. Active current protection devices can respond faster than passive solutions and provide more accurate fault detection. Summary of the invention

[0004] A circuit system for detecting a short circuit in or across a transmission transistor is described herein. In one example, a short circuit detection circuit includes a first transistor, a first resistor, a second transistor, a current source, a second resistor, a switched capacitor circuit, and a comparator. The first transistor has a first current terminal, a second current terminal, and a first control terminal. The first resistor is coupled between the second current terminal and a ground terminal. The second transistor has a third current terminal, a fourth current terminal, and a second control terminal. The third current terminal is coupled to the first current terminal. The second control terminal is coupled to the first control terminal. The current source has a current output and a current input. The current input is coupled to the fourth current terminal. The second resistor is coupled between the current output and the ground terminal. The switched capacitor circuit is coupled between the current output and the ground terminal. The comparator has a comparator output, a first comparator input, and a second comparator input. The first comparator input is coupled to the switched capacitor circuit. The second comparator input is coupled to a reference voltage terminal.

[0005] In another example, a short circuit detection circuit includes a first transistor, a switch load circuit, a second transistor, a switch capacitor circuit, and a comparator. The first transistor is configured to conduct a load current. The switch load circuit is coupled to the first transistor. The switch load circuit is configured to switchably draw a test current. The second transistor is coupled to the first transistor. The second transistor is configured to conduct a sensing current. The sensing current includes a first portion and a second portion. The first portion represents the load current, and the second portion represents the test current. The switch capacitor circuit is coupled to the second transistor. The switch capacitor circuit is configured to generate a short circuit detection voltage representing the second portion. The comparator has an output, a first comparator input, and a second comparator input. The first comparator input is coupled to the switch capacitor circuit. The comparator is configured to compare the short circuit detection voltage with a short circuit threshold voltage.

[0006] In another example, a system includes a power supply terminal, a load terminal and an electronic fuse (EFUSE) circuit. The EFUSE circuit includes a first transistor, a switch load circuit, a second transistor, a switch capacitor circuit and a comparator. The first transistor is configured to conduct a load current from the power supply terminal to the load terminal. The switch load circuit is coupled to the first transistor. The switch load circuit is configured to switchably absorb a test current. The second transistor is coupled to the first transistor. The second transistor is configured to conduct a sense current. The sense current includes a first part and a second part. The first part represents the load current, and the second part represents the test current. The switch capacitor circuit is coupled to the second transistor. The switch capacitor circuit is configured to generate a short circuit detection voltage representing the second part. The comparator has an output, a first comparator input and a second comparator input. The first comparator input is coupled to the switch capacitor circuit. The comparator is configured to compare the short circuit detection voltage with a short circuit threshold voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 is a schematic level diagram of an example short circuit detection circuit.

[0008] Figure 2 Is applicable to Figure 1 Schematic diagram of an example current source of a short circuit detection circuit.

[0009] Figure 3A and 3B is Figure 1 Figure 2 is a graph of example signals generated in the short-circuit detection circuit of FIG.

[0010] Figure 4 is a flow chart of an example method for determining whether a short circuit exists based on multiple short circuit detection tests.

[0011] Figure 5 is based on Figure 4 The method in Figure 1 Graph of an example short circuit fault signal generated in a short circuit detection circuit.

[0012] Figure 6 and 7 is a block diagram of an example system including an electronic fuse circuit with short circuit detection. DETAILED DESCRIPTION

[0013] Many electrical systems contain active circuit protection devices, such as electronic fuses (EFUSEs), to limit power to the system or a portion of the system in the event of a fault. However, if the fault is a failure of the pass transistor of the EFUSE, the EFUSE cannot limit the power supplied to the system. Faults associated with the pass transistor of the EFUSE include external short circuits caused by faulty wiring or accidental soldering connections, as well as failures of the pass transistor itself. Some systems attempt to prevent such short circuits by using two EFUSEs in series, so that if one EFUSE fails, the other can limit the power to the system. However, using multiple EFUSEs increases system size (circuit area) and cost.

[0014] The short circuit detection circuit described herein can be used in an EFUSE or other electronic system to detect an internal or external short circuit of a transmission transistor. The short circuit detection switchably connects a current source to the output of the transmission transistor. The current flowing through the transmission transistor is represented by a sense current flowing through the sensing transistor. If the sense current generated by the current source is less than a threshold value, a short circuit is considered to exist. The sense current caused by the current source is detected by a switched capacitor circuit, which generates a voltage representing the difference in the sense current flowing when the current source is connected to the transmission transistor and when it is not connected to the transmission transistor.

[0015] Figure 1 1 is a schematic level diagram of an example short circuit detection circuit 100. The short circuit detection circuit 100 includes a pass transistor 102, a sense transistor 104, an amplifier 106, a transistor 108, a switch current source 110, a switch capacitor circuit 120, a comparator 130, a current source 132, a resistor 134, and a control circuit 136. The short circuit detection circuit 100 is coupled between a voltage source 140 (e.g., a power supply terminal) and a load 142 (e.g., a load terminal) to transfer power from the voltage source 140 to the load 142 through the pass transistor 102. The voltage source 140 can be a battery, a power supply circuit, or other voltage generating device. The load 142 can be an electrical or electronic circuit.

[0016] Pass transistor 102, sense transistor 104, and transistor 108 may be n-channel field effect transistors (NFETs). Sense transistor 104 is coupled in parallel with pass transistor 102. A first current terminal (e.g., drain) of pass transistor 102 is coupled to a first current terminal (e.g., drain) of sense transistor 104, and a control terminal (e.g., gate) of pass transistor 102 is coupled to a control terminal (e.g., gate) of sense transistor 104. A sense current (ISENSE) flowing through sense transistor 104 represents a current flowing through pass transistor 102 to load 142.

[0017] exist Figure 1, resistor Rext represents the external resistance across pass transistor 102, resistor Rfet represents the resistance of pass transistor 102, and resistor Rsns represents the resistance of sense transistor 104. If there is an external short across pass transistor 102, the resistance of Rext will be small (e.g., less than 40 milliohms). Similarly, if the pass transistor is faulty, the resistance of Rfet may be lower than a selected value (<30 milliohms). Sense transistor 104 may be a scaled replica of pass transistor 102. For example, the channel width of pass transistor 102 may be N times larger than the channel width of sense transistor 104, so that the current flowing through pass transistor 102 is N times larger than the sense current flowing through sense transistor 104.

[0018] An amplifier 106 and a transistor 108 are coupled to the sense transistor 104 to maintain a second current terminal of the sense transistor 104 at the same potential as the second current terminal of the pass transistor 102. A first input of the amplifier 106 is coupled to the second current terminal of the pass transistor 102, and a second input of the amplifier 106 is coupled to the second current terminal of the sense transistor 104. A first current terminal (e.g., drain) of the transistor 108 is coupled to the second input of the amplifier 106, and a second current terminal (e.g., source) of the transistor 108 is coupled to a ground terminal. A control terminal (e.g., gate) of the transistor 108 is coupled to the output of the amplifier 106. The transistor 108 sinks ISENSE, and the amplifier 106 controls the voltage of the control terminal of the transistor 108 so that the voltage of the second current terminal of the sense transistor 104 is equal to the voltage of the second current terminal of the pass transistor 102.

[0019] The short circuit detection circuit 100 has no control over the load 142, so the short circuit detection circuit 100 cannot identify a short circuit based on the current flowing to the load 142. The short circuit detection circuit 100 includes a switching current source 110 to receive (sink) a predetermined test current for determining whether a short circuit (internal or external) exists across the pass transistor 102. The switching current source 110 includes an amplifier 112, a resistor 114, a transistor 116, and a switch 118. A first current terminal (e.g., a drain) of the transistor 116 is coupled to a second current terminal of the pass transistor 102 through the switch 118. A second current terminal (e.g., a source) of the transistor 116 is coupled to a first input (e.g., an inverting amplifier input) of the amplifier 112. A control terminal (e.g., a gate) of the transistor 116 is coupled to an output of the amplifier 112. A second input (e.g., a non-inverting amplifier input) is coupled to a reference terminal of a bandgap voltage circuit 117. The resistor 114 is coupled between the second current terminal of the transistor 116 and a ground terminal. Resistor 114 includes a first resistor terminal coupled to amplifier 112 and a second resistor terminal coupled to a ground terminal. Switch 118 includes a first terminal coupled to a second current terminal of pass transistor 102, a second terminal coupled to a first current terminal of transistor 116, and a control terminal coupled to control circuit 136. A signal provided at the amplifier output controls transistor 116 to make the voltage at the first input of amplifier 112 equal to the bandgap voltage provided at the second input of amplifier 112 and to set a current flowing through switch 118, transistor 116, and resistor 114 when switch 118 is closed. Control circuit 136 closes switch 118 to test for a short circuit across pass transistor 102.

[0020] The current source 132 generates a current equal to or representing the ISENSE flowing through the sense transistor 104. The current source 132 can be implemented as a current mirror circuit, whose current output is coupled to the resistor 134. The resistor 134 is coupled between the current source 132 and the ground terminal. The current 148 generated by the current source 132 flows through the resistor 134 to generate a sense voltage representing the current flowing through the pass transistor 102. The first terminal of the resistor 134 is coupled to the current source 132, and the second terminal of the resistor 134 is coupled to the ground terminal. The resistor 134 and the resistor 114 can be the same type of resistor (produced using the same manufacturing process) to offset each other's deviations and provide improved accuracy. The resistor 134 and the resistor 114 can be high sheet resistance resistors. The resistor 134 can have a resistance of about 5 kilo-ohms, and the resistor 114 can have a resistance of about 53 ohms.

[0021] The switched capacitor circuit 120 includes a capacitor 122, a switch 124, a switch 126, and a switch 128. The capacitor 122 includes a top plate and a bottom plate. The top plate is coupled to a first terminal of a resistor 134 through the switch 126. The switch 126 includes a first terminal coupled to the first terminal of the resistor 134, a second terminal coupled to the top plate of the capacitor 122, and a control terminal coupled to the control circuit 136. The switch 124 is coupled between the bottom plate of the capacitor 122 and a ground terminal. The switch 124 includes a first terminal coupled to the bottom plate of the capacitor 122, a second terminal coupled to the ground terminal, and a control terminal coupled to the control circuit 136. The switch 128 is coupled between the bottom plate of the capacitor 122 and a first input (e.g., a non-inverting comparator input) of the comparator 130. The switch 128 includes a first terminal coupled to the bottom plate of the capacitor 122, a second terminal coupled to the first input of the comparator 130, and a control terminal coupled to the control circuit 136. A second input (e.g., an inverting comparator input) of comparator 130 is coupled to a reference voltage terminal of reference voltage circuit 144. Reference voltage circuit 144 generates a short circuit threshold voltage that comparator 130 compares to the voltage at the bottom plate of capacitor 122 to identify a short circuit across pass transistor 102.

[0022] When the control circuit 136 opens the switch 118, current flows through the pass transistor 102 and any short circuit across the pass transistor 102 to the load 142. The current generated by the current source 132 and the voltage across the resistor 134 represent the current flowing through the pass transistor 102 to the load 142. When the switch 118 is open, the switch 124 is closed to connect the bottom plate of the capacitor 122 to the ground terminal, and the switch 126 is closed to connect the top plate of the capacitor 122 to the resistor 134. When the switch 118 is open, the capacitor 122 is charged to the voltage generated across the resistor 134. When the control circuit 136 closes the switch 118 to sink the current 146 through the transistor 116 and the resistor 114, the switch 124 is opened to disconnect the bottom plate of the capacitor 122 from the ground terminal. The current flowing through the pass transistor 102 increases according to the current 146 flowing through the switching current source 110. If there is no short across pass transistor 102, all of the current flowing through switch current source 110 flows through pass transistor 102. If there is a short across pass transistor 102, only a portion of the current flowing through switch current source 110 flows through pass transistor 102. The voltage developed across resistor 134 corresponds to the current flowing through pass transistor 102.

[0023] When control circuit 136 closes switch 118, control circuit 136 closes switch 126, and the voltage across resistor 134 is present on the top plate of capacitor 122. The voltage on the bottom plate of capacitor 122 is equal to the difference between the voltage across resistor 134 when switch 118 is closed and the voltage across resistor 134 when switch 118 is open. Therefore, when switch 118 is closed, the voltage on the bottom plate of capacitor 122 represents the portion of current 146 that flows through pass transistor 102.

[0024] The control circuit 136 closes the switch 128 to connect the bottom plate of the capacitor 122 to the comparator 130. The comparator 130 compares the short circuit detection voltage (ΔVcopy) at the bottom plate of the capacitor 122 with the short circuit threshold voltage (ΔVcopy(lim)) generated by the reference voltage circuit 144. If the voltage at the bottom plate of the capacitor 122 is greater than ΔVcopy(lim), the current through the pass transistor 102 is high enough that it is considered that there is no short circuit across the pass transistor 102. If the voltage at the bottom plate of the capacitor 122 is less than ΔVcopy(lim), not all of the current flowing through the switching current source 110 flows through the pass transistor 102, and it is considered that there is a short circuit across the pass transistor 102. The output of the comparator 130 is coupled to the control circuit 136. Based on the output signal (FET GOOD) provided at the comparator output, the control circuit 136 sets the state of the fault signal 138 provided at the output of the control circuit 136. The fault signal 138 indicates whether a short circuit is detected across the pass transistor 102.

[0025] Switches 118 , 124 , 126 , and 128 may be implemented using one or more transistors (eg, NFETs and / or PFETs) arranged to pass a signal in response to a control signal.

[0026] Figure 2 1 is a schematic diagram of an example current source 132. 132 includes transistor 202, transistor 204, and transistor 206. 202 may be an NFET. 204 and 206 may be PFETs. A control terminal (e.g., gate) of 202 is coupled to the output of amplifier 106 and a control terminal of transistor 108. A first current terminal (e.g., source) of 202 is coupled to a ground terminal. A second current terminal of 202 is coupled to 204 and 206.

[0027] 204 and 206 are connected as a current mirror circuit. 204 is connected by a diode. A first current terminal (e.g., source) of 204 is coupled to a power supply terminal. A second current terminal (e.g., drain) of 204 is coupled to a second control terminal of 202. A control terminal (e.g., gate) of 204 is coupled to a second control terminal of 204. A first current terminal (e.g., source) of 206 is coupled to a first current terminal of 204. A control terminal of 206 is coupled to a control terminal of 204. A second current terminal (e.g., drain) of 206 is coupled to 134 and 126.

[0028] The current flowing through 202 and 204 is the same as (or a scaled copy of) the sense current (ISENSE) flowing through 108. The current 148 flowing through 206 is the same as (or a scaled copy of) the current flowing through 204 and 202.

[0029] Figure 3A is a graph of example signals generated in the short circuit detection circuit 100 . Figure 3A 14 shows a current 146 flowing through the switching current source 110, a current 148 flowing through the resistor 134, a voltage ΔVcopy at the bottom plate of the capacitor 122, and a FET GOOD output by the comparator 130. When the switch 118 is closed, the current 146 increases. In some embodiments of the switching current source 110, the current 146 flowing through the switching current source 110 is about 30 milliamps (ma). As the switching current source 110 sinks current, the current 148 increases, and the voltage ΔVcopy increases. In interval 302, there is no short circuit across the pass transistor 102, the voltage ΔVcopy exceeds ΔVcopy(lim), and FET GOOD is high during the test to indicate that there is no short circuit across the pass transistor 102. For example, when there is no short circuit, ΔVcopy may be about 30 millivolts (mv), and ΔVcopy(lim) may be about 19mv. In interval 304, there is an external short circuit across the pass transistor 102. Due to the short circuit, the increase in current 148 and the increase in ΔVcopy produced by current 146 are small (relative to the increase when the short circuit is not present). ΔVcopy is less than ΔVcopy(lim), and FET GOOD is low during the test to indicate that a short circuit exists across pass transistor 102. For example, when a short circuit exists, ΔVcopy may be approximately 10 millivolts (mv).

[0030] Figure 3B is a graph of signals in the short-circuit detection circuit 100 . Figure 3B 1 and 12 are signals θ1, θ2, θ3 generated by the control circuit 136 for controlling the switches 118, 124, and 128, respectively. θ2. Figure 3BAlso shown are current 146, Vcopy, and ΔVcopy. Control circuit 136 activates θ1 to close switch 118 and increase current 146. At approximately 2.1 milliseconds, a short circuit is formed across pass transistor 102. Before the short circuit is formed, ΔVcopy increases by a relatively large amount in response to current 146. After the short circuit is formed, ΔVcopy increases by a relatively small amount in response to current 146, enabling comparator 130 to detect the short circuit.

[0031] Because the load 142 is not controlled by the short circuit detection circuit 100, the current drawn by the load 142 and the current flowing through the pass transistor 102 and any short circuit across the pass transistor 102 may change at any time, resulting in a change in ΔVcopy, which may cause errors in short circuit detection. For example, the current drawn by the load 142 may change during the short circuit detection cycle (when the switch 118 is closed). In order to improve the accuracy of short circuit detection, the control circuit 136 performs a plurality of randomly spaced short circuit detection cycles and determines whether a short circuit exists based on the results provided by most of the short circuit detection cycles. For example, the control circuit 136 can perform 5 randomly spaced 600 microsecond short circuit detection cycles (the time during which the switch 118 is closed) within an interval of 200 milliseconds. The control circuit 136 identifies whether a short circuit exists based on the short circuit state indicated by three of the five cycles.

[0032] Figure 4 400 is a flow chart of an example method for determining whether a short circuit exists based on multiple short circuit detection tests. Although described in order for convenience, at least some of the actions shown can be performed in a different order and / or in parallel. In addition, some embodiments may only perform some of the actions shown. The operations of method 400 can be performed by control circuit 136.

[0033] At block 402, the control circuit 136 performs a short circuit detection test. The short circuit detection test includes charging the capacitor 122 to a voltage across the resistor 134 with the switch 118 open and the switch 124 closed, then closing the switch 118 and opening the switch 124, and comparing the voltage on the bottom plate of the capacitor 122 to ΔVcopy(lim). If the voltage on the bottom plate of the capacitor 122 is greater than ΔVcopy(lim), the test is considered passed, and if the voltage on the bottom plate of the capacitor 122 is less than ΔVcopy(lim), the test is considered failed.

[0034] At block 404, control circuit 136 evaluates the results of the last N short circuit detection tests performed at block 402. If M of the last N short circuit detection tests fail, then a short across pass transistor 102 is deemed detected at block 406. For example, if the bottom plate of capacitor 122 is less than ΔVcopy(lim) in three of the last five short circuit detection tests, then control circuit 136 determines that a short has been detected across pass transistor 102. Control circuit 136 may set fault signal 138 to indicate that a short has been detected.

[0035] If at block 404 , M of the last N short circuit detection tests have not failed, then short circuit testing continues at block 402 .

[0036] Figure 5 is a diagram of an example short circuit fault signal generated in the short circuit detection circuit 100 based on the method 400. Figure 5 , ΔVcopy in eight short circuit detection tests is shown. During short circuit detection tests 506, 508, and 510, a short circuit exists across the pass transistor 102, so ΔVcopy is much lower than short circuit detection tests 502, 504, 512, 514, 516, and 518. Figure 5 , the control circuit 136 determines whether a short circuit exists based on the last 5 tests performed. If 3 of the last 5 tests fail, it is considered that a short circuit exists. If 3 of the last 5 tests do not fail, it is considered that there is no short circuit. In the case of performing the short circuit detection test 510, the short circuit detection tests 506, 508, and 510 have failed, so the control circuit 136 determines that there is a short circuit. As the test continues, and the short circuit detection tests 512, 514, and 516 pass, 3 of the last 5 tests have passed, and the control circuit 136 determines that there is no short circuit in response to the short circuit detection test 516.

[0037] Figure 6 6 is a block diagram of an example system 600 including an EFUSE circuit 604 with short circuit detection. System 600 includes a power supply 602, an EFUSE circuit 604, a load circuit 606, and a switch 610. Power supply 602 can be a battery, a DC-DC converter, an AC-DC converter, or other power supply. EFUSE circuit 604 includes a short circuit detection circuit 608. Short circuit detection circuit 608 is an implementation of short circuit detection circuit 100. System 600 also includes a switch 610 coupled between power supply 602 and EFUSE circuit 604. Switch 610 can be implemented using a transistor (e.g., a PFET) coupled between power supply 602 and EFUSE circuit 604. Switch 610 includes a control terminal coupled to a fault output of EFUSE circuit 604.

[0038] Short circuit detection circuit 608 tests for a short circuit (internal or external) across EFUSE circuit 604 as described with respect to short circuit detection circuit 100. If a short circuit is detected, EFUSE circuit 604 opens switch 610 via fault signal 138 to interrupt current flow from power source 602 to EFUSE circuit 604 and load circuit 606.

[0039] Figure 7 6 is a block diagram of an example system 700 including an EFUSE circuit 604 with short circuit detection. System 700 includes a power supply 702, an EFUSE circuit 604, and a load circuit 606. Power supply 702 can be a linear regulator, a DC-DC converter, an AC-DC converter, or other power supply. EFUSE circuit 604 includes a short circuit detection circuit 608. Short circuit detection circuit 608 is an implementation of short circuit detection circuit 100. Power supply 702 includes an input terminal coupled to a fault output of EFUSE circuit 604.

[0040] The short circuit detection circuit 608 tests for a short circuit (internal short circuit or external short circuit) across the EFUSE circuit 604, as described with respect to the short circuit detection circuit 100. If a short circuit is detected, the EFUSE circuit 604 changes the state of the fault signal 138 to indicate that a fault (short circuit) has been detected. In response to the fault signal 138, the power supply 702 interrupts the supply of current to the EFUSE circuit 604 and the load circuit 606.

[0041] System 600 or system 700 may be a household appliance, such as a refrigerator, a washing machine, a dryer, an oven, a stove, or other household appliance, or an electrical part of an electronic device.

[0042] In this specification, the term "coupled" may encompass connections, communications, or signal paths that support a functional relationship consistent with this specification. For example, if device A generates a signal to control device B to perform an action, then: (a) in a first instance, device A is coupled to device B through a direct connection; or (b) in a second instance, device A is coupled to device B through an intermediate component C, but the intermediate component C does not change the functional relationship between device A and device B, so that device B is controlled by device A via the control signal generated by device A.

[0043] Also, in this specification, the recitation “based on” means “based, at least in part, on.” Thus, if X is based on Y, then X may vary with Y and any number of other factors.

[0044] A device "configured to" perform a task or function may be configured (e.g., programmed and / or hardwired) at the time of manufacture by the manufacturer to perform the function, and / or may be configured (or reconfigured) by a user after manufacture to perform the function and / or other additional or alternative functions. Configuration may be performed through firmware and / or software programming of the device, through construction and / or arrangement of hardware components and interconnection of the device, or through a combination of these operations.

[0045] As used herein, the terms "terminal", "node", "interconnect", "pin" and "lead" are used interchangeably. Unless explicitly stated to the contrary, these terms are generally used to refer to the interconnection between device elements, circuit elements, integrated circuits, devices or other electronic devices or semiconductor components or their terminations.

[0046] A circuit or device described herein as including specific components may actually be adapted to be coupled to these components to form the described circuit system or device. For example, a structure described as including one or more semiconductor elements (e.g., transistors), one or more passive elements (e.g., resistors, capacitors, and / or inductors), and / or one or more sources (e.g., voltage and / or current sources) may actually include only semiconductor elements within a single physical device (e.g., a semiconductor die and / or an integrated circuit (IC) package), and may be adapted to be coupled to at least some of the passive elements and / or sources to form the described structure, either at the time of manufacture or after manufacture, for example, by an end user and / or a third party.

[0047] Although the use of specific transistors is described herein, other transistors (or equivalent devices) may be used with little or no change to the remaining circuitry. For example, field effect transistors ("FETs") (e.g., n-channel FETs (NFETs) or p-channel FETs (PFETs)), bipolar junction transistors (BJTs, such as NPN transistors or PNP transistors), insulated gate bipolar transistors (IGBTs), and / or junction field effect transistors (JFETs) may be used in place of or in conjunction with the devices described herein. The transistors may be depletion-mode devices, drain-extended devices, enhancement-mode devices, native transistors, or other types of device structure transistors. Furthermore, the devices may be implemented in / on silicon substrates (Si), silicon carbide substrates (SiC), gallium nitride substrates (GaN), or gallium arsenide substrates (GaAs).

[0048] In the claims reference may be made to the control input of a transistor and its current terminals. In the context of a FET, the control input is the gate, and the current terminals are the drain and source. In the context of a BJT, the control input is the base, and the current terminals are the collector and emitter.

[0049] When a FET is "on" in this article, it means that the conduction channel of the FET exists and drain current can flow through the FET. When a FET is "off" in this article, it means that the conduction channel does not exist and drain current will not flow through the FET. However, an "off" FET may have current flowing through the body diode of the transistor.

[0050] The circuits described herein are reconfigurable to include additional or different components, thereby providing functionality that is at least partially similar to functionality available prior to component replacement. Unless otherwise specified, components shown as resistors generally represent any one or more elements coupled in series and / or in parallel to provide the impedance amount represented by the resistor shown. For example, a resistor or capacitor shown and described herein as a single component may alternatively be a plurality of resistors or capacitors coupled in parallel between the same nodes, respectively. For example, a resistor or capacitor shown and described herein as a single component may alternatively be a plurality of resistors or capacitors coupled in series between the same two nodes as the single resistor or capacitor, respectively.

[0051] Although certain elements of the described examples are included in the integrated circuit and other elements are external to the integrated circuit, in other examples, additional or fewer features may be incorporated into the integrated circuit. In addition, some or all of the features shown as external to the integrated circuit may be included in the integrated circuit, and / or some features shown as internal to the integrated circuit may be incorporated outside the integrated circuit. As used herein, the term "integrated circuit" refers to one or more circuits that are: (i) integrated in / on a semiconductor substrate; (ii) incorporated in a single semiconductor package; (iii) incorporated in the same module; and / or (iv) incorporated in / on the same printed circuit board.

[0052] The use of the phrase "ground" in the foregoing description includes chassis ground, earth, floating ground, virtual ground, digital ground, common ground and / or any other form of ground connection applicable or suitable for the teachings of this specification. In this specification, unless otherwise specified, "about", "approximately" or "substantially" in front of a parameter means that the difference is within + / -10% of the parameter.

[0053] The described examples can be modified and other examples are possible within the scope of the claims.

Claims

1. A short circuit detection circuit, comprising: a first transistor having a first current terminal, a second current terminal and a first control terminal; a first resistor coupled between the second current terminal and a ground terminal; a second transistor having a third current terminal, a fourth current terminal, and a second control terminal, wherein: The third current terminal is coupled to the first current terminal; and the second control terminal is coupled to the first control terminal; a current source having a current output and a current input, wherein the current input is coupled to the fourth current terminal; a second resistor coupled between the current output and the ground terminal; a switched capacitor circuit coupled between the current output and the ground terminal; and A comparator having a comparator output, a first comparator input and a second comparator input, wherein: the first comparator input is coupled to the switched capacitor circuit; and The second comparator input is coupled to a reference voltage terminal. 2 . The short circuit detection circuit of claim 1 , further comprising a switch coupled between the second current terminal and the first terminal of the first resistor.

3. The short circuit detection circuit according to claim 2, further comprising: a third transistor having a fifth current terminal, a sixth current terminal, and a third control terminal, wherein the sixth current terminal is coupled to the first terminal of the first resistor; as well as An amplifier having an amplifier output, a first amplifier input, and a second amplifier input, wherein: the first amplifier input coupled to the first terminal of the first resistor; The second amplifier input is coupled to a bandgap voltage circuit; and The amplifier output is coupled to the third control terminal; Wherein the switch is coupled between the sixth current terminal and the second current terminal.

4. The short circuit detection circuit of claim 1 , wherein the switched capacitor circuit comprises: a capacitor having a top plate and a bottom plate; and A switch is coupled between the top plate and the current output.

5. The short circuit detection circuit according to claim 4, wherein: The switch is a first switch; and The switched capacitor circuit comprises: a second switch coupled between the base plate and the ground terminal; and A third switch is coupled between the base plate and the first comparator input.

6. The short circuit detection circuit according to claim 1, wherein: The first current terminal is coupled to a power supply terminal; and The second current terminal is coupled to a load terminal. 7 . The short circuit detection circuit of claim 1 , wherein the current source comprises a current mirror circuit configured to generate a first current conducted by the second resistor based on a second current conducted by the second transistor.

8. A short circuit detection circuit, comprising: a first transistor configured to conduct a load current; a switched load circuit coupled to the first transistor, the switched load circuit being configured to switchably draw a test current; a second transistor coupled to the first transistor, the second transistor configured to conduct a sense current, wherein the sense current comprises a first portion and a second portion, the first portion representing the load current and the second portion representing the test current; a switched capacitor circuit coupled to the second transistor, the switched capacitor circuit configured to generate a short circuit detection voltage representative of the second portion; as well as A comparator having an output, a first comparator input, and a second comparator input, wherein the first comparator input is coupled to the switched capacitor circuit, and the comparator is configured to compare the short circuit detection voltage to a short circuit threshold voltage.

9. The short circuit detection circuit according to claim 8, wherein the switch load circuit comprises: a current source configured to receive the test current; and A switch is coupled between the first transistor and the current source, the switch being configured to switchably connect the current source to the first transistor.

10. The short circuit detection circuit according to claim 9, wherein the current source comprises: a third transistor having a control terminal; a resistor having a first resistor terminal and a second resistor terminal, wherein the first resistor terminal is coupled to the third transistor, the second resistor terminal is coupled to a ground terminal, and the third transistor is coupled between the first resistor terminal and the switch; as well as an amplifier having an amplifier output and a first amplifier input and a second amplifier input, wherein the first amplifier input is coupled to the first resistor terminal, the second amplifier input is coupled to a reference terminal, the amplifier output is coupled to the control terminal, the amplifier is configured to provide a control signal at the amplifier output in response to voltages at the first amplifier input and the second amplifier input, and the third transistor is configured to conduct the test current in response to the control signal.

11. The short circuit detection circuit according to claim 10, wherein: The resistor is a first resistor; The current source is a first current source; and The short circuit detection circuit comprises: a second current source coupled to the second transistor, the second current source configured to generate a current representative of the sense current; as well as A second resistor is coupled between the second current source and the ground terminal. 12 . The short circuit detection circuit of claim 11 , wherein the second current source comprises a current mirror circuit configured to generate the current representing the sensed current based on the sensed current.

13. The short circuit detection circuit of claim 11 , wherein the switched capacitor circuit comprises: a capacitor having a top plate and a bottom plate; and A first switch is coupled between the second resistor and the top plate, the first switch being configured to switchably connect the top plate to the second current source.

14. The short circuit detection circuit of claim 13, wherein the switched capacitor circuit comprises: a second switch coupled between the base plate and the ground terminal, the second switch configured to switchably connect the base plate to the ground terminal; and A third switch is coupled between the base plate and the first comparator input, the third switch being configured to switchably connect the base plate to the first comparator input.

15. The short circuit detection circuit of claim 8, wherein the second comparator input is coupled to a reference voltage circuit configured to generate the short circuit threshold voltage.

16. A system comprising: Power terminal; Load terminals; as well as An electronic fuse (EFUSE) circuit comprising: a first transistor configured to conduct a load current from the power terminal to the load terminal; a switched load circuit coupled to the first transistor, the switched load circuit being configured to switchably draw a test current; a second transistor coupled to the first transistor, the second transistor configured to conduct a sense current, wherein the sense current comprises a first portion and a second portion, the first portion representing the load current and the second portion representing the test current; a switched capacitor circuit coupled to the second transistor, the switched capacitor circuit configured to generate a short circuit detection voltage representative of the second portion; as well as A comparator having an output, a first comparator input, and a second comparator input, wherein the first comparator input is coupled to the switched capacitor circuit, and the comparator is configured to compare the short circuit detection voltage to a short circuit threshold voltage.

17. The system of claim 16, wherein the switch load circuit comprises: a current source configured to receive the test current; and A switch is coupled between the first transistor and the current source, the switch being configured to switchably connect the current source to the first transistor.

18. The system of claim 17, wherein the current source comprises: a third transistor having a control terminal; a resistor having a first resistor terminal and a second resistor terminal, wherein the first resistor terminal is coupled to the third transistor, the second resistor terminal is coupled to a ground terminal, and the third transistor is coupled between the first resistor terminal and the switch; as well as an amplifier having an amplifier output and a first amplifier input and a second amplifier input, wherein the first amplifier input is coupled to the first resistor terminal, the second amplifier input is coupled to a reference terminal, the amplifier output is coupled to the control terminal, the amplifier is configured to provide a control signal at the amplifier output in response to voltages at the first amplifier input and the second amplifier input, and the third transistor is configured to conduct the test current in response to the control signal.

19. The system of claim 18, wherein: The resistor is a first resistor; The current source is a first current source; and The system comprises: a second current source coupled to the second transistor, the second current source configured to generate a current representative of the sense current; as well as A second resistor is coupled between the second current source and the ground terminal.

20. The system of claim 19, wherein the switched capacitor circuit comprises: a capacitor having a top plate and a bottom plate; and A first switch is coupled between the second resistor and the top plate, the first switch being configured to switchably connect the top plate to the second resistor and the second current source.

21. The system of claim 20, wherein: The switched capacitor circuit comprises: a second switch coupled between the base plate and the ground terminal, the second switch configured to switchably connect the base plate to the ground terminal; as well as a third switch coupled between the base plate and the first input of the comparator; The third switch is configured to switchably connect the base plate to the first input of the comparator; and The comparator includes a second input coupled to a reference voltage circuit configured to generate the short circuit threshold voltage.

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