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TPS546D24A: PMBus connection and NVM programming in multi-phase configuration

fls20
Prodigy 60 points
Part Number: TPS546D24A

Hello TI!

A couple of questions about TPS546D24A in a multi-phase configuration:

A) Datasheet section 7.3.20 (Back-Channel communication) mentions this: "During operation, the master device receives and responds to all PMBus communication, and slave devices do
not need to be connected to the PMBus."

So (while BCX_* pins are interconnected) according to datasheet only master device must expose its PMBus connection to the outside world. However, in SLUUC47 (Stacking TPS546D24A Two-Phase Evaluation Module) both devices are connected to PMBus via R23_P1 / R25_P1 and  R23_P2 / R25_P2 jumper resistors. There are no mention about R23_P2 / R25_P2 may be not stuffed.

1. Is it safe to connect the PMBus only to the master device and leave PMBus pins of slave phases floating?

2. Are there drawbacks of doing so?

3. Also, are there any drawbacks of connecting PMBus to all devices in a multiphase stack (as in SLUUC47)?

B) Datasheet 7.5.2 Pin Strapping says its better to program device's NVM and override pin strap settings.

4. How to program all settings to slave devices as well to make sure they'll rely to NVM and not to pin straps after programming? Is direct PMBus connection to slave devices required for that?

5. Is it possible to drop (leave to default AGND-short or floating) all resistors from all the pin straps for master and slave devices (except for GOSNS/SLAVE on slave devices) and fully rely on NVM programming (including all required settings on slave devices) to save board space and simplify routing?

6. Is it safe to tie GOSNS/SLAVE directly to BP1V5 without any external resistor? SLUUC47 use 10k resistor and I'd like to drop it too.

Thank you!

  • +1
    TI__Expert 5310 points

    Hello,

    To answer your questions:

    1. Yes, it is safe to only use the PMBus interface on the primary (master) device and leave the other devices floating. The primary device will interface according with the remaining devices via the SYNC/VSHARE/ISAHRE interfaces.

    2. There are no drawbacks to using only the primary device for PMBus communication.

    3.Yes, connecting all of the devices adds complexity and may increase the chance of an address conflict/NACK on the communications bus.

    4. For the slave devices, please program the MSEL2 pin with the appropriate pinstrap resistors to ensure proper operation in terms of overcurrent warning/protection and device configuration.

    5. The pinstrap pins on the slave devices can be left floating with the exception of MSEL2. MSEL2 must be configured properly.

    6. I believe it should be safe to tie GOSNS/SLAVE directly to BP1V5 on the secondary devices due the internal resistances of the part.

    Regards,

    Alec Biesterfeld