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PMP7282: Explanation of compensation and functionality

Nesh Johny
Expert 1310 points

Part Number: PMP7282
Other Parts Discussed in Thread: LM5116, , LMV431A

Hi Sir,

Could you please explain how the type II compensation in PMP7282 is used in multi-phase buck converter, the 2nd LM5116 controller is given feedback from the COMP pin of 1st controller after inverting.

1.how this feedback functionality helps ?

2. Is there any particular reason in using the LMV431A op-amp and 1.24V Reference?

Thanks and Regards,

Nesh

  • 0
    TI__Expert 5130 points

    Nesh,  hello and thank you for your interest in Texas Instruments' reference designs.  Your inquiry has been received and forwarded to our Power Design Services team.  Your question has come in while we are on Thanksgiving holiday.  The team will be back in the office on Monday, December 2nd.  You should be hearing from us then.

    Best Regards,

    J. Fullilove

    Texas Instruments

  • 0
    TI__Intellectual 1235 points

    Hi Nesh,

    For current mode control, the inductor current is proportional to the control voltage, which is the error amplifier output at the COMP pin. Be forcing the COMP pin voltage of the 2nd controller to match the 1st, both power stages will deliver the same output current.

    Since the error amplifier on the LM5116 is a standard operational amplifier, the error amplifier outputs cannot be connected directly together or they will fight each other. In this case an external amplifier with a reference voltage equal to the LM5116 internal Vref is used. In order to cover the dynamic range of the COMP voltage, the external amplifier uses a factor of 2 to scale down then up for the 2nd controller.

    Best Regards,

    Bob Sheehan

    Power Design Services

  • 0 in reply to Bob Sheehan
    Expert 1310 points

    Hi Bob Sheehan,

    thanks for the reply, while using the external amplifier for making the outputs of the LM5116 internal operational amplifier same. Is this scaling down and down the best way to do this or any other options are available for LM5116.

    1. Is there any impedance matching of the op-amp to be taken care LM5116 master and slave?

    2. Is it possible to give same output divider voltage feedback to both (master and slave) LM5116?

    Thanks and Regards,

    Nesh

  • 0 in reply to Nesh Johny
    TI__Intellectual 1235 points

    Hi Nesh,

    The external amplifier must have some scale factor to meet the dynamic range of the COMP voltage, which is from about 1V to 3V. A factor of 1 is too low so I chose a factor of 2, which works quite well.

    1. There is no need for impedance matching, since the bias are so low.

    2. No, the master controls the output voltage from the divider, and the slave follows the master for current sharing.

    Regards,

    Bob