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TPS745: Is the device ok with surge from photodiode

David Huang
Intellectual 2285 points
Part Number: TPS745
Other Parts Discussed in Thread: LP3988, , TPS7A25, TPS7A20, TPS7A90

Hi Team

I have a customer asking me if we have any solution that supports the photodiode application with the following electrical requirements.

3.3V-2.8V, 115mA(LDO) with PG pin

I have found that the LP3988, TPS7A25 and TPS745 meets such requirements while having excellent cost/performance.

The problem is, however, as the customer is planning on using the LDO on the photodiode sensor, he mentioned that there would possibly be a surge generates by the photodiode as the CMOS sensor turns off, and he would prefer an LDO solution that's able to withstand such situation without needing to be turned off.

I don't have any information regarding how large the surge is but does TPS745(or LP3988, TPS7A25) look good for this kind of application? If not, some device suggestions would be much appreciated.

Regards

David

  • 0
    TI__Intellectual 2285 points

    Hi Team

    Sorry for keeping the post separated but I just received some new information regarding this case.

    The customer mentioned that the surge could be -2V maximum under some cases.

    Also I was asked that if we have some solutions regarding the CMOS sensor applications that offers high PSRR (the surge problem aside), are the any device recommendations?

    Appreciate the help.

    Regards

    David

  • 0 in reply to David Huang
    TI__Genius 13265 points

    Hey David, 

    A couple of questions since I'm not familiar with the needs of a photodiode application.

    Where is the surge happening, on Vout or Vin? 

    When you mention that the surge could be -2V, is that a 2V dip below the normal operating voltage or does the surge go to -2V referenced to GND? 

    Regarding solutions for CMOS sensor we have many high PSRR + low noise LDOs so it would depend on the needs. For low current applications I'd suggest TPS7A20 (300mA) and for higher current applications I'd suggest the TPS7A90/1/2 (500mA, 1A, 2A) families.

  • 0 in reply to Kyle Van Renterghem
    TI__Intellectual 2285 points

    Hi Kyle

    Thanks for the swift response!

    The surge happens on Vout and -2V is reference to GND voltage.

    The TPS7A20 looks perfectly fine, I will share this info with the customer.

    Regards

    David

  • +1 in reply to David Huang
    TI__Genius 13265 points

    Hey David, 

    -2V is certainly a risk since the abs max voltage for most positive voltage LDOs is typically -0.3V. They should consider adding a protection diode or something to limit this surge in order to ensure reliable operation.