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TPS650864: Question about TPS6508640 design

na na78
Guru 16770 points
Part Number: TPS650864
Other Parts Discussed in Thread: TPS544C25, CSD85301Q2, CSD87331Q3D, CSD87381P, CSD87588N, CSD87350Q5D, TIDA-01393

Hi

The datasheet of TPS650864 shows some power map examples.

One of them looks like as below.

In this configuration, TPS544C25 is used to supply VCCINT to FPGA.
While we should connect VCCINT to BUCK2 output if these are same voltage level.

1. In this power map, TPS544C25 is used to supply 0.72V which is different voltage level with VCCBRAM.
The purpose of TPS544C25 implemented is just to supplying different voltage with BUCK2, isn't it?

2. Assumed VCCINT and VCCBRAM are same voltage, would the current into VCCINT and VCCBRAM which are same voltage depend on ext FET?  (Additional power regulator is not needed?)

BestRegards

  • 0
    TI__Mastermind 30260 points

    na na78 said:
    1. In this power map, TPS544C25 is used to supply 0.72V which is different voltage level with VCCBRAM.
    The purpose of TPS544C25 implemented is just to supplying different voltage with BUCK2, isn't it?

    Yes and no. TPS544C25 can be used to supply power to VCCINT when the speed grade of the Xilinx ZU+ device will allow 0.72V operation, but this is not the primary reason. The primary reason is for when VCCINT rail will consume current >25A. BUCK1 and BUCK2 controllers can be used with External FETs for current ranges from 1A to 25A, depending on the FET that is used. But when VCCINT current is very high, external DC-DC regulator like TPS544C25 or similar should be used. VCCINT, VCCINT_IO, and VCCBRAM may all be 0.85V or 0.9V, but the high current for VCCINT is delivered by the TPS544C25 instead of the PMIC.

    na na78 said:
    2. Assumed VCCINT and VCCBRAM are same voltage, would the current into VCCINT and VCCBRAM which are same voltage depend on ext FET?  (Additional power regulator is not needed?)

    If VCCINT,VCCINT_IO, and VCCBRAM will all operate at the same voltage, the maximum current that will be delivered by the PMIC through external FETs is approximately 25A.

    • TI's CSD85301Q2, CSD87331Q3D, CSD87381P, CSD87588N, and CSD87350Q5D devices are recommended for the controllers, depending on the required maximum current
      • The default FETs used for the TIDA-01393 design are the CSD87381P
      • CSD87350Q5D is suitable up to approximately 30 A
      • CSD87588N is suitable up to approximately 20 A
      • CSD87381P is suitable up to approximately 15 A
      • CSD87331Q3D is suitable up to approximately 15 A
      • CSD85301Q2 is suitable up to approximately 7 A

    If CSD87350Q5D is used, efficiency and thermal performance will decrease at loads greater than 25A.

  • 0 in reply to Brian Berner
    Guru 16770 points

    Hi Brian

    Thank you for your reply.

    >If VCCINT,VCCINT_IO, and VCCBRAM will all operate at the same voltage, the maximum current that will be delivered by the PMIC through external FETs is approximately 25A.

    Does it mean that you recommend to use external regulator if over 25A current required?
    If so, could you tell me more detail why PMIC through external FETs should not provide over 25A?

    BestRegards

  • 0 in reply to na na78
    TI__Mastermind 30260 points

    na na78 said:
    Does it mean that you recommend to use external regulator if over 25A current required?

    Yes

    na na78 said:
    If so, could you tell me more detail why PMIC through external FETs should not provide over 25A?

    It is based on the datasheet of the FET. CSD87350Q5D datasheet says "90% system Efficiency at 25 A". If efficiency start to drop, FETs start to get hot. Additionally, the gate drivers of the PMIC are not strong enough to drive the FETs at these very high currents and the efficiency is actually worse than expected, so the FETs get hotter.

    Unless the FETs are under a heatsink, which is difficult because of the tall inductors right next to the FETs, 25A is the limit I recommend.

  • 0 in reply to Brian Berner
    Guru 16770 points

    Hi Brian 

    Thank you for your reply.

    I'll consider your advice.

    BestRegards