TSV992A turn off output for few ms

hardware_eng · ‎2023-06-26

Hello together,

We are using the TSV992A to measure a current across a 10mOhm shunt resistor. We use a non-inverting amplifier circuit with a gain of 17.6. With a voltage divider (10k-10k) we create an offset voltage at the In+ input.

The amplifier is connected to 5V and GND.

If no current is flowing through the shunt the output voltage of the OPAMP is 1.65V.

Very rarely there are moments when the output of the amplifier no longer follows the input signal, but only outputs 0V. This misbehavior lasts a few ms.

In the attachment is a measurement which shows this behavior and the schematic. We observed noise/spikes on the 5V powersupply and on both inputs.

The arrow shows where the failure starts, from this point on the output and the feedback at the negative input drops to zero(green =output, red = negative input). The positive input is still at a normal level of about 96mV.

In this measurement this behavior lasted 86ms.

What could be the cause for this behavior?
- negative spikes at the negative input ( Input Voltage is specified by (Vcc-) -0.2 to (Vcc+)+0.2) ?
- Spikes at the supply?

- Is the OPAMP going into saturation?

I am grateful for any advice / help.

PieterInHetBos · ‎2023-06-27

What is C729 doing between 5V and 3V3. Maybe becase of the spikes it shorts out between de 5V and 3V3.

Peter BENSCH · ‎2023-06-27

It is very questionable whether a micro-power opamp with such a high offset voltage is suitable for your application. In addition, the voltage divider R723+R730 has no real effect, since R730 is almost completely bypassed by R725 and the shunt.

Overall, however, this approach can be improved, among other things, with a more suitable opamp. I recommend a look at the STEVAL-ISQ013V1 using the TS507, where such a lowside stage is also discussed in detail.

Hope that helps?

Regards
/Peter

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Pierre SENNEQUIER · ‎2023-06-30

Hi,

At the beginning of the issue, there is a huge power supply variation (between 6V and 3V). I recommend you to better decouple the power supply.

But it would not explain why on the right of you scope capture IN-=0V , IN+=100V and OUT is in low state.

Could you please check your connections and another part ?

Thanks and regards,

Pierre

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