High-side current sampling problem

zhuyu630

High-side current sampling problem [Copy link]

 

As the title says, is it correct to sample the current in this way under negative pressure?

maychang

There are no feedback resistors at the inverting and non-inverting inputs of the op amp, which is obviously incorrect.

呜呼哀哉

No, you marked INA180A, which is either a differential op amp or an instrumentation op amp. If it is an instrumentation op amp, it is definitely wrong. If it is a differential op amp, you need to look at the common-mode voltage input range under power supply conditions. Your common-mode voltage is basically -15V. Check the data sheet under your 5V single power supply conditions to see if this range is covered to determine whether it is usable.

1399866558

maychang posted on 2022-3-10 17:45 There are no feedback resistors at the inverting input and non-inverting input of the op amp, which is obviously incorrect.

This chip has an integrated feedback resistor, but it is not shown in the schematic diagram.

PowerAnts

PowerAnts

zhuyu630

1399866558 Published on 2022-3-10 21:30 This chip has an internal feedback resistor. It is not shown in the schematic diagram.

Yes, this chip is integrated

zhuyu630

PowerAnts posted on 2022-3-10 21:40

Thank you for your reply. Low-end sampling is not suitable for my circuit because there is another set of positive 15V that needs to be sampled, and GND is a common point.

zhuyu630

Alas, published on 2022-3-10 18:56 No, you marked INA180A, which is either a differential op amp or an instrumentation op amp. If it's an instrumentation op amp, it's definitely wrong. If it's a differential op amp, you need to...

This IC is a dedicated chip for current sampling. The power supply range of the chip manual is 0 to +5V

zhuyu630

1399866558 Published on 2022-3-10 21:30 This chip has an internal feedback resistor. It is not shown in the schematic diagram.

The application circuit of this IC

PowerAnts

This IV from TI is very clever, with a common mode voltage range as low as -0.2V, so it can directly detect negative currents.

PowerAnts

TI's IC is good, but too expensive. It has been mass-produced with 4 resistors plus an op amp unit. 0.01% resistors are 8 cents each, which halves the cost, has almost the same performance, and is more flexible.

zhuyu630

PowerAnts posted on 2022-3-11 09:27 TI's IC is good, but it's too expensive. It has been mass-produced with 4 resistors and an op amp unit. 0.01% resistors are 8 cents each, the cost is halved, and the performance is different...

Well, general-purpose op amps are more flexible.

1399866558

zhuyu630 posted on 2022-3-11 09:32 Yeah, general-purpose op amps are more flexible

High-side sampling has better performance than low-side sampling. Low-side sampling is a little cheaper.
The specific low-side or high-side sampling needs to be determined based on the actual application.

PowerAnts

1399866558 Published on 2022-3-11 10:58 High-side sampling has better performance than low-side sampling. Low-side sampling is a little cheaper. The specific low-side or high-side sampling needs to be determined according to the actual application...

For the same cost, low side sampling performs better than high side!!! The only advantage of high side sampling is that the load reacts to ground faults, while low side sampling will have problems in this case.

zhuyu630

PowerAnts posted on 2022-3-11 09:27 TI's IC is good, but it's too expensive. It has been mass-produced with 4 resistors and an op amp unit. 0.01% resistors are 8 cents each, the cost is halved, and the performance is different...

Excuse me, how to do high-side sampling with a general-purpose op amp? Can you send me a reference circuit?

PowerAnts

zhuyu630 posted on 2022-3-11 12:06 May I ask how to use a general-purpose op amp for high-side sampling? Can you send me a reference circuit?

Isn't it in the data sheet of the dedicated device?

maychang

1399866558 Published on 2022-3-10 21:30 This chip has an internal feedback resistor. It is not shown in the schematic diagram.

After checking the manual of this model chip, I found that the chip does have integrated resistors.

However, the chip manual states that the common mode range is -0.2~+26V, and the common mode voltage in the first picture is -15V, which is not usable.

maychang

zhuyu630 posted on 2022-3-11 09:08 The application circuit of this IC

The application circuit provided by the manufacturer has a common mode voltage range of -0.2~+26V. The common mode voltage in the first post is -15V, which is not applicable.

maychang

1399866558 Published on 2022-3-11 10:58 High-side sampling has better performance than low-side sampling. Low-side sampling is a little cheaper. The specific low-side or high-side sampling needs to be determined according to the actual application...

[High-side sampling has better performance than low-side sampling. Low-side sampling is a little cheaper. ]

As long as low-side sampling is allowed, its performance will definitely be higher than high-side sampling.