TIA LTC6268-10 input overdrive - this is bad?

Hi,

With a signal range of 40 nA to 15 mA and a feedback resistor of 402k, will surely saturate the amplifier at the maximum current (15 mA).  15 mA current flowing into 402k resistor will raise the inverting voltage to 15 mA * 402 kohms = 6.03 kV and will most like destroy the amplifier. At saturation, the output of the amplifier will not measure the input current and is therefore useless. Recovery from such overload takes time, which depends on the sensor capacitance and the feedback resistor, τ = RC. The amplifier remains some sort of "useless" mode during the overload recovery.

Since you said that the anticipated max current would be 15 mA, why not design the feedback resistor based on 15 mA? So let's assume a supply of 5V, choose RF = 5V/0.015 = 300 ohms. Although it sacrifices the sensitivity for your TIA, this is a workable solution.  RF=402kohm is not a realistic workable solution.

Regards,

Jino

Hi Mikalay,

Ref:Working with Avalanche photo diode - Beginner problems 

i am now not using a LTC6268-10 as i am facing the stability issues, i am trying to use a LTC6268 rather, even that also when saturates has the problem of positive overshoot pulse in output

after debugging further i found that the photo diode i am using is so responsive that it generates a current of 50mA

so an input current of 50mA makes it to saturate and behave abnormally, so i am using a diode at the input PMEG4002EJ which can bypass the extra current and solves the problem to an extent only, this is happening as because i am feeding toomuch current to the opamp

for now placing a diode in the input is the only workarround i have done

are you able to achieve the 40nA target ?? its seems like a night mare to me