current follower saturates on power up

[col_implant]

Hi,

I have a simple current to voltage converter amplifier circuit with a feedback gain fo 10K with a parallel 100pF for stability / bandwidth reduction.

For some reason the amplifiers output saturates when powered up and i cant bring it back down, despite driving the input current negative. This didnt not happen for lower gains

I have the supplies well decoupled with an RC (50OHM/10uF) filter, and another 100nF at the pins.

Anyone got any ideas?

Thanks

C

 

[ericgibbs]

Hi,

I have a simple current to voltage converter amplifier circuit with a feedback gain fo 10K with a parallel 100pF for stability / bandwidth reduction.

For some reason the amplifiers output saturates when powered up and i cant bring it back down, despite driving the input current negative. This didnt not happen for lower gains

I have the supplies well decoupled with an RC (50OHM/10uF) filter, and another 100nF at the pins.

Anyone got any ideas?

Thanks
C

hi,
Under certain input conditions a circuit can 'latch up' and not recover when the over input level is reduced.

Can you post a drawing.?

 

[col_implant]

Picture attached, as I mentioned i have 10K in place of the 100K.

Things that I have already tried

1) Shorting inputs together, and to AGND
2) Applying negative bias current (i.e. change to unity gain inverting amp)
3) Lowering the gain, seems to work for a gain around 300 OHM

Maybe its also worth mentioning that the amplifier is in a quad QFN package. Analog devices AD8643

Cheers

 

[crutschow]

Shorting the inputs won't work since that generates an open loop situation and the offset voltage can still saturate the output.

If the output is high then you want a postive current applied at the inverting input, not a negative current to reduce the output. The circuit is an inverter.

What is the input when the output saturates?