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TPS65251 Design

Shareef
Expert 1985 points
Other Parts Discussed in Thread: TPS65251

Hi All,

I wanted to migrate my design from TPS65232 to TPS65251 as per TI's recommendation. I have a clarification with respect to TPS65251 device:

As per the datasheet the maximum load on BUCK1 is 3.5A and BUCK2/3 is 2.5A. In my design I want to generate the following 

BUCK1 - 1.5V@3.4A (Max limit)

BUCK2 - 3.3V@2A (Max)

BUCK3 - 1.0V@ 2A (Max)

The input is 12V and Fsw = 500kHz. Can TPS65251 be used to generate the above supplies and  can the package withstand the thermal dissipation? The graphs to do power dissipation estimation in the datasheet dont have curves for 1.0V.

Regards,

Shareef.

  • 0
    TI__Expert 4005 points

    As long as the continuous loading on Buck 1 is 3A or below, TPS65251 can be used to generate the listed supplies.

    Using the supplied graphs from the data sheet to over estimate thermal dissapation (1.8 instead of 1.5, 1.2 instead of 1) show that the package will be fine for ambient temps below 50C as long as your board at least matches:

    Based on JEDEC 51.5 HIGH K environment measured on a 76.2 x 114 x .6-mm board with the following layer arrangement:

    (a) Top layer: 2 Oz Cu, 6.7% coverage

    (b) Layer 2: 1 Oz Cu, 90% coverage

    (c) Layer 3: 1 Oz Cu, 90% coverage

    (d) Bottom layer: 2 Oz Cu, 20% coverage

  • 0 in reply to Gregory Watkins
    Expert 1985 points

    Hi Watkins,

    Thanks for your response. Just few more queries:

    1. BUCK1 can deliver peak currents of 3.5A Maximum right? Will this happen say when the BUCK2 and BUCK3 are in continuous loading condition of 2A?

    2. Also can TPS65251 be used to generate 1.0V Output from 12V operating at 600kHz? In this case, the minimum Ton = 138ns which is below 80ns specified in the datasheet. Please confirm.

    -Shareef

  • 0 in reply to Shareef
    TI__Expert 4005 points

    1. Yes you can deliver peak currents of 3.5 as long as you can dissipate the generated heat, and Buck 1 inductor ripple peak does not exceed 4A.

    2. Yes Ton for 12V to 1V @ 600kHz is 138ns, which is longer than the min on time of 120ns.