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TPS748A: minimum output capacitor requirements confusion

John Wehle
Prodigy 100 points
Part Number: TPS748A
Other Parts Discussed in Thread: TPS74801EVM-177,

Tool/software:

The TPS748A datasheet on the first page notes:

Stable with any output capacitor >= 10 uF

which is also reflected in table "6.3 Recommended Operating Conditions".

However the schematic for the TPS74801EVM-177 evaluation module shows the output capacitor as 4.7 uF.

Also the TPS748A-Q1 datasheet on the first page notes:

Stable with any output capacitor >= 2.2 uF

even though that same datasheet lists 10 uF as the minimum in table "6.3 Recommended Operating Conditions".

Does the TPS748A-Q1 differ from the TPS748A regarding the minimum output capacitor requirements?

Should 10 uF be considered the minimum required value for both even though the TI evaluation module is using 4.7 uF?

  • 0
    TI__Genius 13720 points

    Hi John,

    Please see the guidance in Table 5-1 where it says the min Cout for stability is 2.2 uF. The output capacitor we have used on the EVM is sufficient. 

    Regards

    Ishaan

  • 0 in reply to Ishaan Shetye
    Prodigy 100 points

    The datasheet for the TPS748 (i.e. the original) says on the front page:

      Stable with any output capacitor ≥ 2.2μF

    shows in Table 4-1 Pin Functions:

      OUT A small capacitor (total typical capacitance >= 2.2uF)

    and in 5.3 Recommended Operating Conditions says:

      Cout   Output Capacitor   Min 2.2uF

    Which is to say the datasheet for the TPS748 is consistent in saying everywhere that 2.2uF is the minimum. However the datasheet for the TPS748A only mentions 2.2uF in the table 5-1. On both the front page and 5.3 it states 10uF is the minimum. This suggests the 2.2uF listing is a mistake.

    I'd expect the TPS748A datasheet to be consistent one way or another.

    Likewise the TPS748A-Q1 isn't consistent, though the TPS748-Q1 datasheet is.

    BTW: I realized after the fact that the EVM listed on the TPS748A web page in fact uses the TPS748 rather than the newer TPS748A. I agree / understand that the TPS748 has a minimum of 2.2uF based on it's datasheet so 4.7uF used on the EVM make sense for that (older) chip. My concern is regarding the newer chip.

  • 0 in reply to John Wehle
    TI__Genius 13720 points

    Hi John,

    Thank you so much for your detailed explanation of the issue. Yes, this is an anomaly and I will make sure it is fixed in the TPS748A and TPS748A-Q1 datasheets.

    Regards

    Ishaan