Hi,
The customer reviews the OPA317 to measure the IGBT current.
However, the offset voltage is high compared to the competitor, so the customer does not want to use OPA317.
With the IGBT not turned on and 0A, OPA317 measures up to 1 mV.
OPA317 : Max 1mV
Competitor : Max 0.2mV
We are applying the same circuit, and please review the circuit to improve the offset voltage of OPA317 and advise us on how to improve it.
The customer circuit is stable with very little overshoot - see below.
I am not convinced that the issue customer sees is caused by the offset voltage. As far as OPA317 maximum offset goes, it is specified as +/-90uV and customer may use TLV333 with max Vos of +/-15uV. More likely the problem is that customer operates the op amp outside its output linear range.
The OPA317 linear output range is specified in AOL conditions to be 100mV from either rail (see below) so for 5V single supply this means 0.1V<Vout<4.9V
This means the the valid IG1 current range is from 0.4A to 19.6A (100mV<Vout<4.9V) - see below.
If they need to measure IG1 current down to 0A, they need to reference the output to 100mV with Vref as shown below.
The simplest way is to derive the Vref is by using a resistive divider - no need for another supply. However, it must be buffered with U2 as shown below.
Other than that, you could also use LM7705 (a negative charge pump) to drive the Vref pin.
