TIDA-00978: when the voltage of D1-pin2 exceed 24V, the output voltage of OPA857-pin8 will be 0V, why?

Hello,

  Would you be able to share the diode you are using for these tests?

Thank you,
Sima

AD500-8, thanks!

Hello,

Thank you! That is strange, from the diode graphs the bias voltage should be fine above 24V. Can you measure the amount of output current at pin 1 from the APD from a bias voltage below 24V and a bias voltage above 24V? 

Thanks,

Sima

 I have found a problem, when I improve the voltage of VAPD, the DCvoltage of PIN15 will  also be changed,maybe very different from reference voltage, so the output will be strange. Is there something broken?

Hello,

Pin 15 should not be close to VAPD due to the diode in between the bias voltage and the input of the amplifier. Are you disabling test mode by setting Test_SD = GND and Test_In = +VS? Also would you be able to measure the current output out of the AD500-8 diode, and if so what is the gain resistor set at?

Thank you,

Sima