Current sense amplifier

Abstract

To enable a current-sense amplifier to be adapted to a wide range of DC voltages at input.SOLUTION: A current-sense amplifier 100 receives as input the upper-side voltage and the lower-side voltage of a current detection resistor 1, and obtains an output corresponding to the difference between the upper-side voltage and the lower-side voltage. A common voltage suppressor 12 includes: voltage dividing resistors R6a, R6b which are supplied with the upper-side voltage and the lower-side voltage at both ends and obtain a divided voltage; a first transistor M1 to one end of which the upper-side voltage is input, and the other end of which is connected to a prescribed power source; and a second transistor M2 to the one end of which the lower-side voltage is input, and the other end of which is connected to a prescribed power source. The control end of the first transistor M1 and the control end of the second transistor M2 are connected in common, and the divided voltage is input to a portion connected in common.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a current sense amplifier that detects a current flowing through a current detection resistor.

Background Art

[0002] In a drive circuit that drives a load such as a motor, a drive transistor for controlling a drive current is used. In order to control the drive current of the motor, it is necessary to detect the current flowing through the drive transistor, and a current sense amplifier is used to detect the drive current of the motor. In order to achieve excellent motor control, the current sense amplifier requires high speed, high accuracy, and low temperature drift.

[0003] Here, as the drive transistor, a power MOSFET is often used. However, since this power MOSFET conducts a large current, it is relatively large, and it is often used externally on a semiconductor substrate constituting the drive circuit. [[ID=1S]]

[0004] In such a case, a current detection resistor is connected in series with the power MOSFET, and the drive current of the motor can be detected by detecting the voltage drop across the current detection resistor with a current sense amplifier.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The current sense amplifier is used either on the upstream side (high side) or the downstream side (low side) of the load depending on the application. Therefore, it is desirable that the current sense amplifier can handle a wide range of DC voltage inputs.

[0007] In particular, current-sense amplifiers used on the high side must operate at an input voltage much higher than the amplifier's own power supply voltage.

[0008] Therefore, it is desirable that the current sense amplifier allows for gain setting and output offset voltage setting, provided that it can handle a wide range of DC voltages at the input. [Means for solving the problem]

[0009] The current sense amplifier relating to this disclosure has upper and lower voltages of a current sensing resistor. Having a supply input terminal , output corresponding to the difference between the upper voltage and the lower voltage It is configured to provide A current sense amplifier, comprising a common voltage suppressor that suppresses common-mode voltages in the upper voltage and the lower voltage, wherein the common voltage suppressor has the upper voltage at one end. It is supplied to the other end. The aforementioned lower voltage is supplied , divided voltage It is configured to provide A voltage divider resistor and the upper voltage at one end supplied , a first transistor whose other end is connected to a predetermined power supply, and the lower voltage at one end supplied The first transistor includes a second transistor, the other end of which is connected to a predetermined power supply, and Gate and The second transistor The gate Connected , at the connection point of these gates The divided voltage is input. [Effects of the Invention]

[0010] A common-mode voltage suppressor can suppress common-mode voltages in the input voltage, allowing it to handle a wide range of DC voltages at the input and enabling gain setting and output offset voltage setting. [Brief explanation of the drawing]

[0011] [Figure 1] This is a circuit diagram showing the configuration of a current sense amplifier according to an embodiment. [Figure 2]It is a circuit diagram showing the configuration of Modification 1. [Figure 3] It is a circuit diagram showing the configuration of Modification 2. [Figure 4] It is a circuit diagram showing the configuration of Modification 3.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present disclosure will be described below with reference to the drawings. Note that the following embodiments do not limit the present disclosure, and configurations formed by selectively combining a plurality of examples are also included in the present disclosure.

[0013] 「Overall Configuration」 FIG. 1 is a circuit diagram showing the configuration of a current sense amplifier according to an embodiment. The current sense amplifier 100 is a high-side current sense amplifier that detects the current flowing through the current detection resistor 2 disposed on the upstream side of the load 1. Here, the load 1 is, for example, a motor, and the current flowing through the load 1 is controlled by a drive transistor (not shown) connected in series with the load 1 and the current detection resistor 2. For example, PWM control is used for this current control. Further, as the transistor, for example, a MOSFET (metal oxide semiconductor field effect transistor) is used.

[0014] The current sense amplifier 100 includes four blocks: a preamplifier 10, a common voltage suppressor 12, a postamplifier 14, and an offset voltage switch 16. The current sense amplifier 100 is usually formed on a semiconductor substrate as a semiconductor integrated circuit.

[0015] The preamplifier 10 receives the voltages at both ends of the current detection resistor 2 (upper voltage Vip and lower voltage Vin), and outputs a pair of positive and negative voltages Vc and Vb corresponding to the difference between these inputs. The upper voltage Vip is input to the negative input terminal (-) of the operational amplifier OPA1 via the resistor R1a. The lower voltage Vin is input to the positive input terminal (+) of the operational amplifier OPA1 via the resistor R1b.

[0016] The operational amplifier OPA1 amplifies the difference between the inputs (upper voltage Vip and lower voltage Vin) with the common voltage Vcm as the center voltage. The negative input terminal and the negative output terminal of the operational amplifier OPA1 are connected by two resistors R20a and R21a connected in series. The positive input terminal and the positive output terminal are connected by two resistors R20b and R21b connected in series. Then, the connection point of the two resistors R20a and R21a and the connection point of the two resistors R20b and R21b are connected by a variable resistor R22.

[0017] In this way, the preamplifier 10 is a fully differential amplifier, and the gain is determined by the resistance values of the above-mentioned resistors R20a, R21a, R20b, R21b, and R22. However, by changing the resistance value of the variable resistor R22, the gain of the operational amplifier OPA1 can be changed. Therefore, the operational amplifier OPA1 can be operated with a programmable gain setting. Let the voltage at the negative input terminal of the operational amplifier OPA1 be Va, the voltage at the negative output terminal be Vc, and the voltage at the positive output terminal be Vb.

[0018] A common voltage suppressor 12 is connected to the positive and negative input terminals of the operational amplifier OPA1. The negative input terminal of the operational amplifier OPA1 is connected to the drain of an n-channel transistor M1. The positive input terminal of the operational amplifier OPA1 is connected to the drain of an n-channel transistor M2. The gates of the transistors M1 and M2 are connected. Between the drains of the transistors M1 and M2, they are connected by resistors R6a and R6b connected in series, and the connection point of the resistors R6a and R6b is connected to the gates of the transistors M1 and M2. Also, the sources of the transistors M1 and M2 are connected to the ground GND, which is a predetermined power supply.

[0019] In such a common voltage suppressor 12, it is advisable to use the same type of transistors for M1 and M2 and make the resistance values of the resistors R6a and R6b the same. In this case, the mutual conductance of the transistors M1 and M2 is both gm, and the common-phase impedance is 1 / gm. Also, the differential impedance is 2xR6 (R6a = R6b = R6).

[0020] Therefore, the voltage Va can be reduced to a low voltage by attenuation due to the difference in magnitude between resistors R1a and R1b and the common-mode impedance 1 / gm. In other words, even if the input DC voltage is 40V, the voltage Va can be set to be near the threshold voltage Vth of transistors M1 and M2.

[0021] In other words, even if the input DC component fluctuates within the range of -2V to +40V, the negative input voltage Va and common voltage Vcm of the preamplifier 10 can be maintained at or below 3V, which is the operating power supply voltage of the current sense amplifier 100.

[0022] Thus, the common-mode voltage suppressor 12 is connected to the preamplifier 10 and consumes the common-mode current flowing to the differential input of the preamplifier 10. Therefore, the preamplifier 10 only needs to handle differential signals from the input.

[0023] Post-amplifier 14 has an internal operational amplifier OPA2, to which the pair of outputs Vb and Vc of operational amplifier OPA1 are input. Outputs Vb and Vc are input to the negative input terminal (-) and positive input terminal (+) of operational amplifier OPA2 through resistors R3a and R3b, respectively.

[0024] The OPA2 operational amplifier is a single-ended operational amplifier with one output, providing a voltage output Vout. This Vout output becomes the output signal of the current sense amplifier 100. In this way, the OPA2 operational amplifier can provide an output signal suitable for an ADC (analog-to-digital converter).

[0025] Furthermore, the output terminal and negative input terminal of the operational amplifier OPA2 are connected by a feedback resistor, resistor R5. In addition, a bias voltage Vbias is supplied to the negative input terminal of the operational amplifier OPA2 via resistor R4a, and to the positive input terminal via resistor R4b. The voltage at the negative input terminal of the operational amplifier OPA2 is denoted as Vd.

[0026] With this configuration, the post-amplifier 14 outputs an output Vout corresponding to the difference between the outputs Vb and Vc of the pre-amplifier 10. Furthermore, the output Vout is offset according to the voltage Vbias.

[0027] Here, the voltage Vbias is supplied from the offset voltage switch 16. The offset voltage switch 16 can set the voltage Vbias to either the reference voltage Vref or ground GND. Therefore, the offset voltage switch 16 can switch between supplying two offset voltages to the output of the post-amplifier 14.

[0028] By making the common voltage Vcm of the preamplifier 10 proportional to the reference voltage Vref, and by keeping the ratio of resistors R4a and R4b placed in the voltage Vbias supply path to resistors R3a and R3b placed in the input path of the operational amplifier OPA2 constant, the output of the post-amplifier 14 can be set to a desired offset voltage using a simple offset voltage switch 16. For example, the offset voltage of the output Vout can be selectively set to one of two offset values, such as Vref / 2 and Vref / 8. Vref / 2 is suitable for bipolar operation, and Vref / 8 is suitable for unipolar operation. The setting of the offset voltage will be described later.

[0029] "About the functions of preamplifiers and postamplifiers" <Gain of preamplifier 10> Let me explain the gain of preamplifier 10. If Vpreo is the difference in output from preamplifier 10, Vpreo=Vc-Vb That is the case.

[0030] In this example, let R1a=R1b=R1, R20a=R20b=R20, and R21a=R21b=R21.

[0031] Here, assuming the common voltage is 0V (Vcm=0), Vip + Vin = 0.

[0032] Therefore, Vip=-Vin, Vc=-Vb, Va=0 Therefore, the gain Gpre of the preamplifier 10 is expressed as follows: Gpre=Vpreo / (Vip-Vin)=Vc / Vip

[0033] Next, we will explain how to adjust the gain using the variable resistor R22. If Vip / R1 = i, and the negative current is ia and the positive current is ib, R20*i ​​= R22*ia / 2, ia = i*2*R20 / R22 R21*(i+ia)+R20*i=Vc R21*(i+2*i*R20 / R22)+R20*i=Vc i*[R20+R21*(1+2*R20 / R22)]=Vc Vip / R1*[R20+R21*(1+2*R20 / R22)]=Vc This is the result.

[0034] Therefore, the gain Gpre of the preamplifier 10 can be expressed as follows: Gpre=[R20+R21*(1+2*R20 / R22)] / R1

[0035] Therefore, the gain of the preamplifier 10 can be adjusted by adjusting the resistance value of the variable resistor R22.

[0036] If R22 = ∞, that is, if no variable resistor R22 is provided, the feedback resistance is R20 + R21, and the normal gain is as follows.

[0037] Gpre = (R20 + R21) / R1

[0038] <Post-amp gain> This section explains the gain Gpost of post-amplifier 14. Note that R3a=R3b=R3 and R4a=R4b=R4.

[0039] The gain of post-amp 14, Gpost, is Gpost=Vout / (Vc-Vb) That is the case.

[0040] The outputs Vb and Vc of preamplifier 10 are expressed as follows: Vb=-Vpreo / 2+Vcm,Vc=Vpreo / 2+Vcm

[0041] Here, assuming Vbias=0, the result is as follows: Vd = Vc * R4 / (R3 + R4) (Vout-Vd) / R5=Vd / R4+(Vd-Vb) / R3 Vout-Vd=Vd*(R5 / R4+R5 / R3)-Vb*R5 / R3 Vout=Vd*[1+R5*(R3+R4) / (R3*R4)]-Vb*R5 / R3 =Vc*R4*[1 / (R3+R4)+R5 / (R3*R4)]-Vb*R5 / R3 =(Vpreo / 2+Vcm)*[R4 / (R3+R4)+R5 / R3] +(Vpreo / 2-Vcm)*R5 / R3 =(Vpreo / 2)*[R4 / (R3+R4)+2*R5 / R3] +Vcm*R4 / (R3+R4) =Vpreo*[(R4 / 2) / (R3+R4)+R5 / R3] +Vcm*R4 / (R3+R4)

[0042] The gain of post-amp 14 is, Gpost=ΔVout / ΔVpreo And, Gpost=(R4 / 2) / (R3+R4)+R5 / R3 Therefore, the gain can be set by the resistance values ​​of resistors R3, R4, and R5.

[0043] <Regarding the offset voltage of the output Vout> When Vbias=0, the output Vout is represented as follows in relation to the inputs Vip and Vin. Vout = Gpost * Gpre * (Vip - Vin) +Vcm*R4 / (R3+R4)

[0044] Here, Vip = Vin. Therefore, the output Vout can be expressed as follows: Vout=Vd=Vcm*R4 / (R3+R4)+Vbias*R3 / (R3+R4)

[0045] Let's consider the case where, when Vref is selected by the offset voltage switch 16, the offset voltage at Vout is set to Vref / 2. When Vbias=Vref, Vout=Vref / 2 In this case, Vref / 2=Vcm*R4 / (R3+R4)+Vref*R3 / (R3+R4) This holds true.

[0046] Next, consider the following case where, when GND is selected by the offset voltage switch 16, the offset voltage at Vout is set to Vref / 8. When Vbias=0 and Vout=Vref / 8, Vref / 8 = Vcm * R4 / (R3 + R4) This holds true.

[0047] If both of the above two cases are to be true, Vref / 2 = Vref / 8 + Vref*R3 / (R3+R4) 4 = 1 + 8 * r³ / (r³ + r⁴) 3 / 8 = R3 / (R3+R4) R3:R4=3:5 This is the result.

[0048] Therefore, by setting R3:R4=3:5, the offset voltage of Vout can be set to Vref / 2 by selecting Vref with the offset voltage switch 16, and the offset voltage of Vout can be set to Vref / 8 by selecting GND with the offset voltage switch 16.

[0049] Furthermore, with these settings, the common voltage Vcm of the preamplifier 10 is set to Vref / 5 as follows.

[0050] Vcm=Vref / 8*(R3+R4) / R4=Vref / 8*(3+5) / 5 =Vref / 5

[0051] Thus, in the current sense amplifier 100 shown in Figure 1, When Vbias=0, Vout=Gpost*Gpre*(Vip-Vin)+Vref / 8 And so, When Vbias = Vref, Vout=Gpost*Gpre*(Vip-Vin)+Vref / 2 This is the result.

[0052] Furthermore, the gains of the post-amplifier 14 and the pre-amplifier 10 are expressed as follows: Gpost=5 / (2*8)+R5 / R3=R5 / R3+5 / 16 Gpre=[R20+R21*(1+2*R20 / R22)] / R1

[0053] "Variation 1" Figure 2 is a circuit diagram showing the configuration of Modification 1. In this example, the variable resistor R22 of the preamplifier 10 in Figure 1 has been removed. Therefore, it is not necessary to divide the feedback path resistor into two, and the negative feedback and positive feedback resistors are each a single resistor R2a and R2b.

[0054] Here, if we set R2a = R2b = R2, the gain of the preamplifier 10 becomes Gpre = R2 / R1. Thus, Modification 1 is a single-gain amplifier in which the gain of the preamplifier 10 cannot be changed.

[0055] "Variation 2" Figure 3 is a circuit diagram showing the configuration of Modification 2. In this example, current sources I1 and I2 are added to the common voltage suppressor 12. That is, current sources I1 and I2 are connected to the drains of transistors M1 and M2, ensuring a constant current (bias current) for transistors M1 and M2.

[0056] Therefore, even if sufficient common-mode current is not supplied through inputs Vip and Vin, it is possible to prevent the common-mode voltage suppressor 12 from becoming unstable.

[0057] "Variation 3" Figure 4 is a circuit diagram showing the configuration of Modification 3. In this example, current sources I1 and I2 are added to the common voltage suppressor 12, similar to the configuration in Figure 3, and the feedback resistors of the preamplifier 10 are set to two, R2a and R2b, similar to the configuration in Figure 2.

[0058] Furthermore, resistor R5a is used as the negative feedback resistor for the operational amplifier OPA2, and the voltage Vcm is supplied to the positive input terminal via resistor R5b. Also, the offset voltage switch 16 and resistors R4a and R4b are removed. As a result, the gain of the post-amplifier 14 is determined by resistors R3a and R5a, and the offset voltage is determined by resistors R3b and R5b. [Explanation of Symbols]

[0059] 1 load, 2 current sense resistors, 10 preamplifier, 12 common voltage suppressor, 14 post-amplifier, 16 offset voltage switch, 100 current sense amplifier.

Claims

1. A current sense amplifier having input terminals to which the upper and lower voltages of a current sensing resistor are supplied, and configured to provide an output corresponding to the difference between the upper and lower voltages, Includes a common voltage suppressor that suppresses the in-phase voltage in the upper voltage and the lower voltage, The aforementioned common voltage suppressor is A voltage divider resistor is configured to provide a divided voltage, with the upper voltage supplied to one end and the lower voltage supplied to the other end. A first transistor having the upper voltage supplied to one end and the other end connected to a predetermined power supply, A second transistor, to which the lower voltage is supplied at one end and to which the other end is connected to a predetermined power supply, Includes, The gate of the first transistor and the gate of the second transistor are connected, and the divided voltage is input to the connection point of these gates. Current sense amplifier.

2. A current sense amplifier according to claim 1, The first and second transistors are n-channel MOSFETs. Current sense amplifier.

3. A current sense amplifier according to claim 1, A preamplifier having input terminals to which the upper voltage and the lower voltage are supplied, and which outputs a positive output and a negative output corresponding to the voltage difference between the upper voltage and the lower voltage, A post-amplifier having an input terminal to which the positive and negative outputs of the preamplifier are supplied, Further including, Current sense amplifier.

4. A current sense amplifier according to claim 3, The post-amplifier is supplied with a reference voltage, and the offset voltage of the post-amplifier's output is set by a combination of resistors placed between the input terminal of this reference voltage and the two outputs of the preamplifier. Current sense amplifier.

5. A current sense amplifier according to claim 4, There are two types of reference voltages, and they are switchable. Current sense amplifier.

6. A current sense amplifier according to claim 1, A first constant current source that supplies a constant current to one end of the first transistor, A second constant current source that supplies a constant current to one end of the second transistor, Further including, Current sense amplifier.

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