I design a TIA with OPA356 and SFH250V(Photodiode):
Since maximum photocurrent of SFH250V is 100uA,
and I hope higher gain of photocurrent for my usage.
Thus, 100k Rfb is necessary after I experiment.
But max of voltage output would be 100k*100uA = 10V.
10V seems to over absolute maximum of signal input a lots
(My power is provided by USB-5V)
How do I select/design current/voltage limiter?
Your design is not particularly stable right now, I have the source C as 8pF from the diode datasheet,
You might want to increase the feedback C, here is 2.2pF,
To go further, really need your load defined,
Limiting? depends on how much you care about fast recovery = if you don't care, just put some clamp diodes on the inverting node, very low C ones preferred, Transimpedance from SFH250V with OPA356.TSC
Here is an example protection diode, might be too much for your needs, but 2- in a package, You might only need one polarity,
Did not seem to change the frequency response at all, not sure if the C is in the model, in TINA the model is locked and you cannot see the netlist,
Hi Dewei,
also, when the output of OPAmp clipps, the -input of OPAmp becomes negative (!) and you may run into a violation of common mode input voltage range of OPA356 which can make the OPAmp latch-up or lock-up:
Kai
Hi: @Michael Steffes
Actually, I've read tidu535 before design this circuit.
https://www.ti.com/lit/ug/tidu535/tidu535.pdf
Yes, I care about fast transient.
My purpose is detect a pulse which width about 100ns.
For the tidu535 with a target -3dB frequency of 1MHz, I tried to modify tidu535 to reach 10MHz bandwidth.
I think modify capacitor seems to be a good idea.
My object is detect a pulse which is small width (~100ns), so if system has a little overshoot, it's fine.
0.1pF of Cfb(where Rfb=100k) for OPA355 seems to has a oscillation after I do transient simulation
0.5pF is better
I know 0.5pF of Cfb, I have to take care about layout.
Because little parasitic capacitance would impact Cfb.
Hi Dewei,
the main issue here is the big detecttor capacitance which makes a rather big feedback capacitance necessary to restore the phase margin. And in order to achieve a bandwidth of >10MHz the only way is to decrease the feedback resistance:
A good remedy was to bias the SFH250V with a higher reverse voltage: A reverse voltage of 10V would decrease the detector capacitance from about 8pF to 2.5pF which would allow you to run the TIA with a higher feedback resistance and a smaller feedback capacitance.
Kai
Hi Dewei,
then you should urgently add the two BAV99 protection diodes, Michael already mentioned:
R4 = 100R additionally helps to limit the current into the OPA356.
To keep the phase margin sufficiently high, the feedback capacitance has to be increased to 1.2pF:
Take care, further increasing R4 can destabilize the circuit by ruining the phase margin. In this case the feedback capacitor would have to be furtherly increased. It's better to use R4 in combination with Michael's BAV99 protection diodes. Then R4 can be kept small enough.
Kai
