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Original question:

OPA2365: Analog Pulse Width Modulation

OPA2365: Abnormal output voltage of OPA2365

Sophia Yao
Prodigy 701 points
Part Number: OPA2365
Other Parts Discussed in Thread: OPA192,

Hi team,

The customer used OPA2365 for PFC current sensing and the sensing resistor is 0.01Ω. Input voltage of the system is 200-264V and input current is 5.9A. The PFC and OPA192 schematic are as below. When unit did the 12ms cycle drop with full load(62.5A) at 264vac input, the PFC Mosfets Q103 or Q102 will damage. And OPA2365 output voltage was abnormal. Test waveform is as below. Do you have any idea why OPA2365 output voltage is abnormal under this situation?

Thanks very much.

best regards,

Sophia Yao

  • 0
    Guru 140200 points

    Hi Sophia,

    are you overriding the input of OPA2365? Keep in mind that the input voltage of OPA2365 must not exceed the supply rails. Why not using a diode clamp at the input?

    Kai

  • 0 in reply to kai klaas69
    TI__Prodigy 701 points

    Hi Kai,

    Thanks for your reply. From the first schematic, we can see that opa2365 was used as low side current sensing. So even the sensing current was 60A, the input voltage of opa2365 was 0.6V, which is less than supply voltage(3.3V). But from below test waveform, when sensing current was 0A, the Vout of  opa2365 was nearly 3V; when sensing current was 50A, the Vout of  opa2365 was 0V and then when sensing current was over 60A, the Vout of  opa2365 had a glitch. what do you think is the root cause of the abnormal output voltage of opa2365?

    Sophia

  • 0 in reply to Sophia Yao
    TI__Expert 3126 points

    is OPA2365 output linear and being generated as expected under normal working condition ?

    is the issue of abnormal output ( non linear output ) only occurring when your current in the PFC is at its minimum (0A) or maximum value (upwards of 50A)  ?

  • 0 in reply to Sophia Yao
    Guru 140200 points

    Hi Sophia,

    sometimes an imbalance of differential amplifier (IC21A) can cause weird results, especially at the edges of input signal. Confirm, that all the components of differential amplifier (including the input filter) have exactly the same values.

    Keep in mind, that also the common mode rejection of IC21A isn't ideal.

    There could also be signal ground issues. Is IC21A sitting close to the shunt?

    Kai