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LM5146-Q1: Implementation of CC Circuit

Sankalp Shembekar
Prodigy 20 points
Part Number: LM5146-Q1
Other Parts Discussed in Thread: LMP8646, LM5149-Q1, LM5117-Q1

Hi,

We are trying to have CC operation with LM5146-Q1. For this we are thinking of putting NPN transistor across SS pin and ground or COMP pin and ground. The base of this NPN transistor would be connected to output of opamp with type 2 compensation. The non-inverting pin is connected to reference voltage achieved at the current limit and inverting pin is connected to the voltage feedback of the current flowing.

Among the two mentioned options, which would be better?

Thanks & Regards,

Sankalp Shembekar

  • 0
    TI__Guru 63027 points

    Hi Sankalp,

    We typically recommend sensing the output current with a shunt and injecting a current into FB to adjust VOUT according to the required constant current. Take a look at the circuits/app note notes associated with the LMP8646:  https://www.ti.com/product/LMP8646. Also, see app note SNVA829.

    With an op-amp type error amp in a voltage-mode controller, it's not a good idea to force the COMP voltage (overdriving the error amp output) as tjhe COMP sink/source current capability is quite high.

    Note that it's much easier to implement CC in a current-mode controller - take a look at the LM5149-Q1 80V peak current-mode controller as an example. Alternatively, consider the LM5117-Q1 65V controller as it has a CM pin for easy CC/CV implementation.

    If you can send your spec (Vin range, Vout, Iout), we can recommend a suitable part.

    Regards,

    Tim