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TPS65251 - Difference between High and Low threshold of Low power pin!!!

Hoang Truyen
Prodigy 10 points
Other Parts Discussed in Thread: TPS65251

Dear,

I am using TPS65251 in my application board. Buck1 o/p = 6V/2A, Buck2 o/p = 4.5V/1A, Buck3 o/p = 9V/1A, the power supply is 14V common to all. Frequency of operation is

500KHz (R on PIN6 = 383K). RLIM1 = 100K, RLIM2 = 120K, RLIM3 = 120K.

When Low_power pin is connected to V3V, all outputs are correct and they can be driven up to 150mA. But when I pull Low_power pin down, all outputs are floating.

They can not be driven at light load.

I also tried to turn on bucks step by step by changing capacitor at EN pins ( 4.7nF @ EN1, 10nF@En2, 47nF@EN3, respectively) but all outputs can not regulated.

I don't know why difference between High and Low threshold of Low power pin.

Please kindly get my schematic attached file and help me review it.\

I am looking forward to hearing from you soon.

Best regards,

HOANG TRUYEN

VIETTEL GROUP

 

 

  • 0
    TI__Intellectual 2025 points

    Hi.

    TPS65251 has not automatic transfer LOW power(PFM) and high power(PWM). If pin 25 goes to low(gnd). the part operating PWM( high power  mode)but  if low_p goes high(3.3V), the part operating PFM, low power mode.

    PS). Low power mode shuold activated (Active - high) one of channel under 100mA load condition. If not, efficiency goes low compare with normal mode(PWM). Any questions, let mek now.

    Regards.