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AMC3311: Stability of Output DC/DC and LDO - which capacitor values?

Jörg Bornwasser
Prodigy 30 points
Part Number: AMC3311
Other Parts Discussed in Thread: TLV431A, TLV431,

Hy,

i'm designing a circuit with the AMC3311DWER isolation amplifier.

Unfortunately Your datasheet is a little shy with stability information for the Highside DC/DC output and the LDO output.

LDO's often very easily swing when using to small or to large capacity values.

There is just one example circuit (fig. 8-1) but there is no diagram like a stability boundary condition diagram (e. g. given for TLV431A and for the most LDOs).

Thus, because i want to use higher capacity values as given in figure 8-1 for stabilizing my auxillary circuit, i need a range of allowed capacity.

Thanks in advance,

Jörg

  • 0
    TI__Expert 4995 points

    Hi Jörg,

    What capacitor do you want a range for? I would have to know what your auxiliary circuit/system looks like to better identify a capacitor recommendation. Please let me know, thank you. 

    Best regards,

    Eva

  • 0
    Prodigy 30 points

    Hi Eva,

    thanks for the further inquiry.

    I just want to know a capacity range, where the HLDO_OUT is stable.

    But for now i derived my design from your examples in figure 8-1 and 8-5 in the datasheet and i only added a reference shunt diode (TLV431AID) as a aux. circuit.

    For this reference shunt diode i use a 2µ2 X7R capacitor in parallel for stability reasons, suggested in the datasheet of TLV431, Fig. 18.

    This aux. circuit is coupled with a 820 Ohm resistor to HLDO_OUT and because of this, i think it's fine.

    But at the end i searched for a Stability Boundary Condition diagram for the LDO of AMC3311 secondary side like it is given for TLV431.

    Best regards

    Jörg

    ps: I don't see an easy way to include a screenshoot (direct upload, not over 3rd party hoster) of my circuit to the post, this ist why i described it in words...

  • 0 in reply to Jörg Bornwasser
    TI__Expert 4995 points

    Hi Jörg,

    Have you tried the decoupling capacitance recommendations from the example designs if you are following them similarly? If you only added a reference shunt diode, I think the recommendations are a good starting point. 

    Also, there shouldn't be a Stability Boundary Condition on this device. 

    Best regards,

    Eva