CN-119628574-B - Current sense amplifier

Abstract

The invention is to improve temperature dependence in a current sense amplifier. The current sense amplifier measures a voltage drop in a drive transistor (LS) and measures a current flowing through the drive transistor (LS). The current sense amplifier includes a pre-amp for inputting a voltage across the driving transistor (LS) to obtain a positive output and a negative output corresponding to a voltage difference of the inputted voltage across the driving transistor, and a switch (sw) connected to an input terminal of a common mode voltage (vcm) serving as an operation reference of the pre-amp and the negative output. A change in the positive output caused by turning on/off the switch (sw) can be detected.

Inventors

• KENICHIRO MIYAGUWA

Assignees

• 上海韦尔半导体股份有限公司

Dates

Publication Date

20260512

Application Date

20231018

Priority Date

20230913

Claims (4)

1. 1. A current sense amplifier that measures a voltage drop in a drive transistor to measure a current flowing in the drive transistor, the current sense amplifier comprising: A pre-amplifier to which a voltage of both ends of the driving transistor is input, and which obtains a positive output and a negative output corresponding to a voltage difference of the voltage of both ends inputted by the driving transistor; A post-amplifier to which the positive output and the negative output of the pre-amplifier are input and which obtains an output corresponding to a difference of the positive output and the negative output of the pre-amplifier, and A switch connecting an input terminal of a common mode voltage, which is used as an operation reference of the preamplifier, with the negative output, wherein A change in the positive output caused by turning on/off the switch can be detected as a change in the output of the post-amplifier.
2. 2. The current sense amplifier according to claim 1, wherein an attenuator using a transistor having the same characteristics as the driving transistor is provided in a front stage of the preamplifier.
3. 3. The current sense amplifier according to claim 1, wherein the post-amplifier is supplied with a reference voltage serving as an operation reference of the post-amplifier, and a relation of the output of the post-amplifier to the reference voltage when the current flowing in the driving transistor is 0 is set by a combination of resistances placed between an input terminal of the reference voltage and an input terminal of the common mode voltage.
4. 4. The current sense amplifier according to claim 3, wherein the output of the post-amplifier is set to 1/2 of the reference voltage when the current flowing in the driving transistor is 0.

Description

Current sense amplifier Technical Field The present invention relates to a current sense amplifier that detects a current flowing in a driving transistor. Background In a driving circuit for driving a load such as a motor, a driving transistor for controlling a driving current is used. In addition, in order to control the driving current, it is necessary to detect the current flowing through the driving transistor, and a current sense amplifier is used to detect the current flowing through the driving transistor. To achieve excellent motor control, the current sense amplifier needs to meet high speed, high accuracy, low temperature drift. In addition, it is desirable that the current sense amplifier operate with low power consumption. Therefore, a configuration in which the current detection resistor is connected in series to the driving transistor is not suitable. It is desirable to detect the current by a voltage drop generated by the on-resistance (Rdson) of a power MOSFET (metal-oxide-semiconductor field-effect transistor, metal oxide semiconductor field effect transistor) used as a driving transistor. However, the on-resistance Rdson varies nonlinearly according to the flow and temperature of the current, and it is therefore difficult to detect the current with high accuracy using the on-resistance. Offset trimming in particular in current sense amplifiers is very important for temperature dependent compensation. The reason is that if offset trimming is not performed accurately, a temperature drift at the current 0A is caused, and then correction by the user application system is difficult. [ Prior Art literature ] [ Patent literature ] [ Patent document 1] Japanese patent laid-open No. 7-113826 Disclosure of Invention [ Problem to be solved by the invention ] In the case where offset trimming is performed correctly and the input offset is zero, the input bias current flows steadily, and therefore, the output current from the input section does not flow into the current-voltage converter of the subsequent circuit. On the other hand, if there is an offset, there is a possibility that the temperature drift may occur due to an error current remaining after the center voltage is adjusted to the target value. [ Means of solving the problems ] A current sense amplifier measures a voltage drop in a drive transistor and measures a current flowing through the drive transistor, and includes a preamplifier for inputting a voltage across the drive transistor and obtaining a positive output and a negative output corresponding to a voltage difference between the inputted voltage across the drive transistor, a switch for connecting an input terminal of a common mode voltage serving as a reference of operation of the preamplifier to the negative output, and detecting a change in the positive output and the negative output caused by turning on/off the switch. In addition, the current sense amplifier of the present invention may further include a post-amplifier for inputting a positive output and a negative output of the pre-amplifier to obtain an output corresponding to an input voltage difference, the current sense amplifier being capable of detecting a change in the positive output and the negative output caused by turning on/off the switch as an output change of the post-amplifier. [ Effect of the invention ] The offset of the preamplifier can be detected by the output change when the switch is turned on/off. Therefore, the offset voltage can be reduced by trimming the preamplifier. Therefore, the temperature dependence of the current sense amplifier can be reduced. Drawings Fig. 1 is a circuit diagram showing a configuration of a current sense amplifier according to an embodiment. Fig. 2 is a diagram showing an example of setting resistance values of respective resistors in the circuit of fig. 1. Fig. 3 is a diagram showing a change in the output vout caused by turning on the switch sw. Fig. 4 is a graph showing temperature characteristics of vout at various trimming settings. Fig. 5 shows an example of a preamplifier constituted by 2 single-ended amplifiers, i.e., the 1 st operational amplifier OPA1-1 and the 1 st operational amplifier OPA 1-2. Detailed Description Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following embodiments are not intended to limit the present invention, and a configuration in which a plurality of examples are selectively combined is also included in the present invention. Integral structure Fig. 1 is a circuit diagram showing a configuration of a current sense amplifier according to an embodiment. The driving transistor LS is a transistor for supplying a driving current to a load. In this example, the driving transistor LS is formed by an n-channel MOSFET (metal-oxide-semiconductor field-effect transistor) with a drain connected to the load and a source connected to the ground. Here, the current flowing through the driving transis