Questions about initial register setting of LTM4676A & LTM4677


My customer decides to use LTM4676A and LTM4677 in their system.

At their system, the operating condition of LTM4676A and LTM4677.

              A. Vin : 5V

              B. Vout : 1V

But when they test with ADI EVM, the initial value of VIN_ON isn't support 5V Vin because the default value of VIN_ON would be 5.5V.

So they need to change the value of VIN_ON register to 4.2V.

For this reason, they should change the value of VIN_ON register to 4.2V.

But unfortunately, before turning on power ( supplying 1V), they can't use PMBUS or MCU.

So they need your help about changing initial value of VIN_ON register .

Please refer below questions and let me know your advices.

Q1) For supporting their condition (Vin: 5V, Vout 1V) , should they change the value of VIN_ON register from 5.5V to 4.2V?

Q2) Could you provide LTM4676A & LTM4677 with changing the value of VIN_ON register from 5.5V to 4.2V?

Q3) Do you have any other methods to support Vin 5V and Vout 1 V condition at LTM4676A and LTM4677 without using PMBUS ?

If you have any opinions, please advise me.



Parents Reply
  • +1
    •  Analog Employees 
    on Oct 12, 2020 3:54 AM 4 months ago in reply to Se-woong

    Hi Se-woong,

    Sorry for delay. If you have local ADI FAE support, please go through them as you may get answers faster than in E-zone.

    I am not expert of these products but these are what I got after LTM4676A datasheet study:

    1. Minimum input voltage is 4.5V that you should consider for setting VIN_ON not 4.2V
    2. Changing default VIN_ON should be done through LTpowerPlay
    3. I don’t think there is other way to change VIN_ON than only PMBus