Power switch circuit with current sensing

Abstract

The present invention discloses a power switch circuit with current sensing. The power switch circuit is coupled between an input voltage and an output terminal. The power switch circuit includes a power switch, a first sensing switch, an adjustment circuit, and a second sensing switch. The power switch is coupled to the input voltage. The first sensing switch is connected in series between the power switch and the output terminal. There is a first node between the first sensing switch and the power switch. The adjustment circuit is coupled to the first node. The second sensing switch is coupled between the adjustment circuit and the output terminal. The control terminal of the power switch is coupled to a first control voltage. The control terminals of the first sensing switch and the second sensing switch are coupled to a second control voltage. The second control voltage is different from the first control voltage. The current sensing function of the power switch circuit of the present invention is not affected by the current limiting mechanism, so as to improve the accuracy of its current sensing.

Description

Technical Field

[0001] The present invention relates to a power switch, and more particularly to a power switch circuit with current sensing. Background Art

[0002] As Figure 1 shown, the existing current sensing circuit 1 usually uses a sensing switch 125 that is common-gate and common-source with the power switch 115 to sense the output current ILOAD to obtain a sensing current IOUT, and uses a feedback circuit including an error amplifier 140 and a feedback switch 130 to correct the error of current sensing. The current limiting circuit 160 controls the gate voltage VG of the power switch 115 according to the current sensing result to achieve the effect of limiting the output current ILOAD.

[0003] The correction principle of the above current sensing circuit 1 is as follows: when the voltages of the gate, source, and drain of the power switch 115 and the sensing switch 125 are all equal, the current ratio flowing through the two is equal to the area ratio of the two. Since the power switch 115 and the sensing switch 125 are common-gate and common-source, an error amplification signal can be generated as the control voltage VG of the feedback switch 130 according to the voltage difference at the input terminals of the error amplifier 140 to change its on-resistance.

[0004] Since the on-resistance of the feedback switch 130 and the on-resistance of the sensing switch 125 form a resistive voltage division circuit, the node voltage between the sensing switch 125 and the feedback switch 130 can be adjusted so that the voltages at the two input terminals of the error amplifier 140 can be maintained equal to ensure that the drain voltages of the power switch 115 and the sensing switch 125 are equal, so that a stable ratio can be maintained between the output current ILOAD and the sensing current IOUT.

[0005] However, the above current sensing circuit 1 still has the following problems in actual operation: when the output voltage at the load 120 is zero, there is at least a bias voltage (such as the on-voltage of a transistor element, 0.7 volts, but not limited thereto) caused by the feedback switch 130 between the two input terminals of the error amplifier 140 and it is not zero, resulting in poor correction effect, and this problem needs to be improved. Summary of the Invention

[0006] In view of this, the present invention provides a power switch circuit with current sensing to effectively solve the above problems encountered in the prior art.

[0007] A specific embodiment according to the present invention is a power switch circuit with current sensing. In this embodiment, the power switch circuit is coupled between an input voltage and an output terminal. The power switch circuit includes a power switch, a first sensing switch, an adjustment circuit, and a second sensing switch. The power switch is coupled to the input voltage. The first sensing switch is connected in series between the power switch and the output terminal, and there is a first node between the first sensing switch and the power switch. The adjustment circuit is coupled to the first node. The second sensing switch is coupled between the adjustment circuit and the output terminal. The control terminal of the power switch is coupled to a first control voltage. The control terminals of the first sensing switch and the second sensing switch are coupled to a second control voltage. The second control voltage is different from the first control voltage.

[0008] In one embodiment, the power switch circuit further includes a voltage supply circuit, which is respectively coupled to the control terminal of the power switch and the control terminal of the first sensing switch, and generates the first control voltage and the second control voltage according to the input voltage.

[0009] In one embodiment, the power switch circuit further includes a current source, which is coupled between the voltage supply circuit and the control terminal of the power switch, receives the first control voltage and provides current to the power switch.

[0010] In one embodiment, the second control voltage has a fixed voltage value, causing the first sensing switch and the second sensing switch to continuously operate in the linear region.

[0011] In one embodiment, there is a second node between the adjustment circuit and the second sensing switch. The adjustment circuit includes an error amplifier and a third sensing switch. Two input terminals of the error amplifier are respectively coupled to the first node and the second node. The control terminal of the third sensing switch is coupled to the output terminal of the error amplifier, and one end of the third sensing switch is coupled to the second node.

[0012] In one embodiment, the second sensing switch matches the first sensing switch and generates a sensing signal according to the output current of the output terminal.

[0013] In one embodiment, the power switch circuit further includes a current limiting circuit, which is coupled to the control terminal of the power switch and a reference voltage, and provides a current limiting signal to the control terminal of the power switch according to a sensing voltage related to the sensing signal and the reference voltage to limit the output current.

[0014] In one embodiment, the power switch circuit further includes a current replication circuit, which is respectively coupled to the second sensing switch and the voltage supply circuit, and provides a sensing current according to the sensing signal generated by the second sensing switch.

[0015] In one embodiment, the power switch circuit further includes a sensing resistor, which is coupled between the current replication circuit and the ground terminal, and converts it into a sensing voltage and provides it to the current limiting circuit.

[0016] Compared with the prior art, the power switch circuit with current sensing of the present invention overcomes the aforementioned problems through a first sensing switch, and limits the operating range of the sensing switch to the linear region by separately supplying the control voltages of the power switch and the sensing switch, so that the current sensing function thereof is not affected by the current limit mechanism, thus effectively improving the accuracy of its current sensing.

[0017] The advantages and spirit of the present invention can be further understood through the following detailed description of the invention and the accompanying drawings. Description of the Drawings

[0018] Figure 1 It is a schematic diagram of a conventional MOS type current sensing circuit.

[0019] Figure 2 It is a schematic diagram of a power switch circuit with current sensing according to a specific embodiment of the present invention.

[0020] Figure 3 It is Figure 2 the waveform timing diagram of each signal in

[0021] Main Component Symbol Description:

[0022] 1: Current sensing circuit

[0023] 110: Current sensor

[0024] 115: Power switch

[0025] 120: Load

[0026] 125: Sensing switch

[0027] 130: Feedback switch

[0028] 140: Error amplifier

[0029] 145: Resistance ladder

[0030] 150: Analog-to-digital converter

[0031] 160: Power gating circuit

[0032] VDD: Operating voltage

[0033] VG: Control voltage

[0034] ILOAD: Output current

[0035] I1: Sensing signal

[0036] I2, IOUT: Sensing current

[0037] 2: Power switch circuit

[0038] 20: Adjustment circuit

[0039] 22: Current limit circuit

[0040] 24: Voltage supply circuit

[0041] 26: Current replication circuit

[0042] MN1: Power switch

[0043] MN2: First sensing switch

[0044] MNS1: Second sensing switch

[0045] CS: Current source

[0046] RILIM: Sensing resistor

[0047] OUT: Output terminal

[0048] COUT: Output capacitor

[0049] IL: Output current

[0050] GND: Ground terminal

[0051] VIN: Input voltage

[0052] VOUT: Output voltage

[0053] VG1: First control voltage

[0054] VG2: Second control voltage

[0055] IST: Current

[0056] N1: First node

[0057] N2: Second node

[0058] N3: Third node

[0059] EA: Error amplifier

[0060] MN3: Third sensing switch

[0061] MP1: Switch

[0062] MP2: Switch

[0063] VREF: Reference voltage

[0064] VCL: Sensing voltage

[0065] CL: Current limit signal

[0066] RON1: First on-resistance

[0067] RON2: Second on-resistance

[0068] t1 to t2: Time Detailed implementation

[0069] Now, reference will be made in detail to exemplary embodiments of the present invention, and examples of the exemplary embodiments will be described in the accompanying drawings. Elements / components having the same or similar reference numerals in the drawings and the embodiments are used to represent the same or similar parts.

[0070] According to a specific embodiment of the present invention, a power switch circuit with current sensing is provided. Please refer to Figure 2 , Figure 2 which is a schematic diagram of the power switch circuit with current sensing in this embodiment.

[0071] As Figure 2 shown, the power switch circuit 2 is coupled between the input voltage VIN and the output terminal OUT. The output terminal OUT is coupled to one end of the output capacitor COUT, and the other end of the output capacitor COUT is coupled to the ground terminal GND. The output terminal OUT has an output voltage VOUT, and the output current IL flows from the output terminal OUT to the ground terminal GND.

[0072] The power switch circuit 2 includes a power switch MN1, a first sensing switch MN2, a second sensing switch MNS1, an adjustment circuit 20, a current limiting circuit 22, a voltage supply circuit 24, a current replication circuit 26, a current source CS, and a sensing resistor RILIM.

[0073] The power switch MN1 and the first sensing switch MN2 are connected in series between the input voltage VIN and the output terminal OUT, and there is a first node N1 between the power switch MN1 and the first sensing switch MN2. The second sensing switch MNS1 is coupled between the adjustment circuit 20 and the output terminal OUT. The second sensing switch MNS1 matches the first sensing switch MN2, and the control terminals of the second sensing switch MNS1 and the first sensing switch MN2 are coupled to each other.

[0074] The adjustment circuit 20 is coupled between the second sensing switch MNS1 and the current replication circuit 26, and the adjustment circuit 20 is also coupled to the first node N1. There is a second node N2 between the adjustment circuit 20 and the second sensing switch MNS1.

[0075] In this embodiment, the adjustment circuit 20 includes an error amplifier EA and a third sensing switch MN3. The third sensing switch MN3 is coupled between the second sensing switch MNS1 and the current replication circuit 26, and the second node N2 is located between the third sensing switch MN3 and the second sensing switch MNS1. The input terminal + of the error amplifier EA is coupled to the first node N1 located between the power switch MN1 and the first sensing switch MN2. The input terminal - of the error amplifier EA is coupled to the second node N2 located between the third sensing switch MN3 and the second sensing switch MNS1. The output terminal of the error amplifier EA is coupled to the control terminal of the third sensing switch MN3.

[0076] The sensing resistor RILIM is coupled between the current replication circuit 26 and the ground terminal GND, and a third node N3 is provided between the current replication circuit 26 and the sensing resistor RILIM. The current limiting circuit 22 is respectively coupled to the reference voltage VREF, the third node N3 between the current replication circuit 26 and the sensing resistor RILIM, and the control terminal of the power switch MN1.

[0077] The voltage supply circuit 24 is respectively coupled to the input voltage VIN, the current replication circuit 26, the control terminal of the power switch MN1, the control terminal of the first sensing switch MN2, and the control terminal of the second sensing switch MNS1. The current source CS is coupled between the voltage supply circuit 24 and the control terminal of the power switch MN1.

[0078] The voltage supply circuit 24 receives the input voltage VIN and respectively generates different first control voltages VG1 and second control voltages VG2 to the control terminal of the power switch MN1 and the control terminal of the first sensing switch MN2 according to the input voltage VIN. In other words, the control terminal of the power switch MN1 and the control terminal of the first sensing switch MN2 are respectively coupled and controlled by different first control voltages VG1 and second control voltages VG2. The current source CS generates a current IST for the power switch MN1 according to the first control voltage VG1 to perform soft start of the power switch MN1.

[0079] In practical applications, the current source CS is adjustable. Its current value of the current IST provided (such as a current in the uA level) can be changed by coupling an external resistor (not shown in the figure) through a setting pin as required to change the soft start speed, but it is not limited thereto.

[0080] The second sensing switch MNS1 generates sensing signals I1 related to the output current IL at the output terminal OUT to the adjustment circuit 20. In an embodiment, assuming that the first sensing switch MN2 is the same as the second sensing switch MNS1 and the area ratio of the power switch MN1 to the first sensing switch MN2 / second sensing switch MNS1 is 1:MOC, the sensing signal I1 will be equal to (IL / MOC), but not limited thereto.

[0081] In an embodiment, the current replication circuit 26 is a current mirror with a magnification constant K and includes switches MP1 and MP2 with their control terminals butted against each other. The switch MP1 is respectively coupled to the voltage supply circuit 24 and the adjustment circuit 20. The switch MP2 is respectively coupled to the voltage supply circuit 24 and the third node N3. When the current replication circuit 26 receives the sensing signal I1 from the adjustment circuit 20, the current replication circuit 26 generates a sensing current I2 to the sensing resistor RILIM according to the sensing signal I1 and the magnification constant K, and the sensing resistor RILIM converts the sensing current I2 into a sensing voltage VCL on the third node N3 to be provided to the current limiting circuit 22.

[0082] Continuing from the above, when the sensing signal I1 is equal to (IL / MOC), the sensing current I2 provided by the current replication circuit 26 according to the sensing signal I1 will be equal to [IL / (MOC*K)] and the sensing voltage VCL will be equal to [(IL*RILIM) / (MOC*K)], so the magnification of the sensing current I2 can be adjusted according to the design requirements, but not limited thereto. In fact, the sensing resistor RILIM is an external resistor, and the user can select an appropriate resistor according to the requirements to generate the sensing voltage VCL, but not limited thereto.

[0083] In other words, the sensing voltage VCL received by the current limiting circuit 22 is related to the sensing signal I1, that is, the sensing voltage VCL is related to the output current IL. When the current limiting circuit 22 receives the reference voltage VREF and the sensing voltage VCL related to the output current IL, the current limiting circuit 22 provides a current limiting signal CL to the control terminal of the power switch MN1 according to the reference voltage VREF and the sensing voltage VCL to adjust the first control voltage VG1, so as to change the first on-resistance RON1 of the power switch MN1 to achieve the effect of limiting the output current IL.

[0084] It should be noted that since the second sensing switch MNS1 is matched with the first sensing switch MN2, and the control terminals of both are controlled by the second control voltage VG2, and one end (e.g., the drain) of both is coupled to the output terminal OUT, while the control terminal of the power switch MN1 is controlled by the first control voltage VG1 different from the second control voltage VG2. Therefore, when the power switch MN1 receives the current limit signal CL of the current limit circuit 22 and operates in the saturation region, the second control voltage VG2 with a fixed voltage value will cause the first sensing switch MN2 and the second sensing switch MNS1 with current sensing functions to continuously operate in the linear region and will not be affected by the current limit signal CL.

[0085] Please refer to Figure 2 and Figure 3 , in an embodiment, at t0, the circuit starts. The current source CS receives the voltage provided by the voltage supply circuit 24 and generates a current IST of several μA to the control terminal of the power switch MN1 to enable the soft start of the power switch MN1; at time t1, the power switch MN1 conducts. During the period from time t1 to time t2, the current source CS provides a fixed value of current IST to make the system work normally. The output voltage VOUT is maintained at 5 volts, the first control voltage VG1 and the second control voltage VG2 are both maintained at 10 volts, and the load draws a load such that the output current IL continuously climbs. The first on-resistance RON1 of the power switch MN1 and the second on-resistance RON2 of the first sensing switch MN2 are both maintained in the linear region;

[0086] At time t2, the output current IL climbs to the protection value (e.g., 3 amperes) and triggers the current limit circuit 22 to issue a current limit signal CL, causing the power switch MN1 to enter the saturation region. In this example, the current limit signal CL is a negative current, which reduces the first control voltage VG1 received by the control terminal of the power switch MN1 by reducing the current IST. Therefore, during the period from time t2 to t3, the first on-resistance RON1 of the power switch MN1 will continuously climb, while the output current IL maintains the protection value, causing the output voltage VOUT to continuously drop;

[0087] At time t3, the output voltage VOUT drops to 0 volts. After time t3, since the second control voltage VG2 still maintains a fixed value (e.g., 10 volts), the first sensing switch MN2 continues to operate in the linear region, and its second on-resistance RON2 also remains at a fixed value, so that there is no sensing error during the current limit, and the output current IL current limit can still be maintained at the protection value (e.g., 3 amperes) without dropping.

[0088] In other words, during current limiting, the power switch MN1 is affected by the current limiting mechanism to perform the function of limiting the output current IL, but the first sensing switch MN2 is not. On the contrary, the first sensing switch MN2 with current sensing function still operates in the linear region during current limiting and the sensing result is not affected by the current limiting mechanism.

[0089] Compared with the prior art, the power switch circuit with current sensing of the present invention uses the first sensing switch to overcome the problem of sensing error generated at low output voltage, and limits the operating range of the sensing switch to the linear region by separately supplying the control voltages of the power switch and the sensing switch, so that the current sensing function is not affected by the current limiting mechanism, thus effectively improving the accuracy of its current sensing.

Claims

1. A power switch circuit with current sensing, coupled between an input voltage and an output terminal, characterized in that, The above power switch circuit includes: A power switch, coupled to the above input voltage; A first sensing switch, connected in series between the above power switch and the above output terminal, and there is a first node between the above first sensing switch and the above power switch; A voltage supply circuit, coupled to the control terminal of the above power switch and the control terminal of the above first sensing switch respectively, and generating a first control voltage and a second control voltage according to the above input voltage; A current source, coupled between the above voltage supply circuit and the control terminal of the above power switch, receiving the above first control voltage and providing a current to the above control terminal of the above power switch; An adjustment circuit, coupled to the above first node; and A second sensing switch, coupled between the above adjustment circuit and the above output terminal, wherein, the control terminal of the above power switch is coupled to the above first control voltage, the control terminals of the above first sensing switch and the above second sensing switch are coupled to the above second control voltage, and the above second control voltage is different from the above first control voltage, wherein, when the output voltage of the above output terminal drops to zero, the above second control voltage has a fixed voltage value and the on-resistance of the above first sensing switch operating in the linear region remains at a fixed value, so that the output current of the above output terminal remains at the protection value and does not decrease.

2. The power switch circuit according to claim 1, wherein There is a second node between the above adjustment circuit and the above second sensing switch, and the above adjustment circuit includes: An error amplifier, whose two input terminals are respectively coupled to the above first node and the above second node; and A third sensing switch, whose control terminal is coupled to the output terminal of the above error amplifier, and one end of it is coupled to the above second node.

3. The power switch circuit according to claim 1, characterized in that, The above second sensing switch matches the above first sensing switch, and the above second sensing switch generates a sensing signal according to an output current of the above output terminal.

4. The power switch circuit according to claim 3, wherein The above power switch circuit further includes; A current limiting circuit, coupled to the control terminal of the above power switch and a reference voltage, and providing a current limiting signal to the control terminal of the above power switch according to a sensing voltage related to the above sensing signal and the above reference voltage to limit the above output current.

5. The power switch circuit according to claim 1, wherein, The above power switch circuit further includes: A current replication circuit, coupled to the above second sensing switch, and providing a sensing current according to a sensing signal generated by the above second sensing switch.

6. The power switch circuit according to claim 5, characterized in that, The above power switch circuit further includes: A sensing resistor, coupled between the above current replication circuit and a ground terminal, and converting the above sensing current into a sensing voltage to provide it to a current limiting circuit.

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