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PMP8750: lowest adjustable output current in PMP8740 2kW charger

Fabio Soriano
Intellectual 2345 points
Part Number: PMP8750
Other Parts Discussed in Thread: PMP8740, UCC28950

Hi Team,

I received the following request, can you help?

######################################

What is the lowest adjustable output current in PMP8740 2kW charger Project?

Can I set output current down to 0.1A, when converter is operating in constant current mode?

######################################

Regards,

Fabio

  • 0
    TI__Intellectual 2610 points
    Hi Fabio,

    You will want to the converter to operate in discontinuous conduction mode at low load currents. If the inductor produces negative current then power will transfer from the output back to input and potentially very high spikes can occur on the synchronous rectifiers. That is why UCC28950 has DCM and TMIN pins.

    I will let the designer comment on where PMP8740 reaches the DCM threshold. But please note that PMP8740 can operate safely all the way down to 0A load current.

    Thanks,
    Ryan
  • 0 in reply to Ryan Manack
    TI__Expert 5265 points

    Ryan, Fabio,

    Thanks for taking care of this thread.

    In the firmware of the MSP430, the reference voltage, associated to output current control, is function of the timer that has 16000 ticks (in main part of firmware, the compare register is TACCR1, which is = 16000 - pwm_ref_current).

    Here the full-scale current is 62.5A, therefore the resolution is 62.5A / 16000 = 3.9 mA. That means, the converter is able to supply also output current limit @ minimum 3.9mA. Please consider though that at so small output current, any noise in the peak current limit of the converter will have more impact.

    Best regards,

    Roberto