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TPS65400: Schematic review

chu anh
Prodigy 30 points
Part Number: TPS65400

Hi TI,

We have designed a power supply to be used with a custom network processor.

Our noise requirement is less than 40mv peak to peak.

Please review the schematic and give suggestions if any modification is required in schematic like inductor value, C_Roll, Rc, Cc, Rfb1 Rfb2 and C1 base on the datasheet figure 17. 

2330.pmu.pdf

Thanks,

  • 0
    TI__Genius 9550 points

    Hi,

    Will check for you on Monday.

  • 0
    TI__Genius 15135 points

    Hi, chu 

    Some comments: 

    1. "noise requirement is less than 40mv peak to peak" 

    You mean Vout peak to peak ripple is less than 40mV, right?  

    2. What is the voltage of "PWR_main"? it is 12V? and what is the range of it? 

  • 0 in reply to Zhao Ma
    Prodigy 30 points

    Hello Zhao, 

     1. Indeed, the Vout peak to peak is 40mV

     2. The "PWR_main" range is 12 to 16V

    Best regards

  • 0 in reply to chu anh
    TI__Genius 15135 points

    Hi, Chu 

    Based on your information, some comments: 

    For U9000, 

    1. When Vin is 16V, for 0.88V output, due to the minimum on time limitation, you have to set operating frequency to ~380kHz, so suggest to change R9042 to ~500kohm. 

    2. suggestions for inductor: 

    Set L9000 = L9001 = L9002 = L9003 = 4.7uH. 

    And add another 47uF for 2.5Vout. 

    3. Compensation circuit: 

    Change R9000 = R9001 = R9002 = R9003 = 15kohm. 

    For U9001, 

    1. The operating frequency can keep 500kHz, R9048=374kohm. 

    2. suggestions for inductor: 

    Set L9004 = L9005 = 4.7uH. 

    Set L9006 = L9007 = 10uH. 

    3. Compensation circuit: 

    Change R9018 = R9021 = 15kohm. 

    Change R9019 = R9020 = 10kohm. 

  • 0 in reply to Zhao Ma
    Prodigy 30 points

    Hi Zhao, 

     Thank for the advice. For my understanding, did you use Type 2 or Type 3 to calculate the value?

     Where could I find the minimum on-time limitation?

     As in the Vout_ripple calculation, Could I increase the switching frequency or Cout to reduce the  Vout_ripple calculation? 

     

    For U9000.

    1. I could use the clock divider for the 0.88V output and set it to 250kHz. 

    2. I prefer to use 2.2uH because of the limited space. 

    3. I will test with 15k.

    For U9001.

    2. I prefer to use 2.2uH because of the limited space. 

    3. I will test with 15k.

    Please check my calculation below:

    1070.PMU calculation.xlsx

    Thanks

    Best regards

  • 0 in reply to chu anh
    TI__Genius 15135 points

    Hi, Chu 

    1. Usually we use Type 3 to calculate the value. 

    Actually the values i gave is based on EVM reference design. 

    2. In EC table, you can see the minimum on time tON_min, typ=80nS, max=150nS. 

    In application, we should make sure the ON time of every buck converter >=150nS, otherwise, Voutx would trigger OVP. 

    3. Sure, you can increase Fsw or enlarge Cout to reduce output ripple. 

    you can leave some Cout unmounted in case output ripple is bigger. 

    4. It is a good idea to clock divider for the 0.88V. 

    5. You can reduce the inductor value, but you should make sure the inductor ripple current is no more than 50% of the max buck output current (buck1/2 is 4A, buck3/4 is 2A.)

    6. For the 5Vout, the inductor ripple current is too big when Fsw is low, suggest to use big inductance.