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TPS62150: Transition between PWM/PSM

Roy Hsu
Genius 9350 points
Part Number: TPS62150

Hi there,

My customer uses TPS62150 to convert 5.7 V to 5 V. They found that when there's no load, the transition between PWM/PSM varies with different switching frequencies.

I have the test results (with TPS62150EVM-505) summarized below.

1. Vin = 5.7V, Vout = 3.3V, No load, fsw = 1.25 MHz -> Device operates in PSM mode

2. Vin = 5.7V, Vout = 3.3V, No load, fsw = 2.5 MHz -> Device operates in PSM mode

3. Vin = 5.7V, Vout = 5V, No load, fsw = 1.25 MHz -> Device operates in PSM mode

4. Vin = 5.7V, Vout = 5V, No load, fsw = 2.5 MHz -> Device operates in PWM mode

Since there are no load currents in all 4 test scenarios, the device is supposed to operate in PSM mode.

Even the Vin in test 4 is about 15% higher than Vout, the device still operates in PSM mode when fsw is 1.25 MHz. 

I'd like to know what contributes to the difference between test 3 and 4. Besides, from test 1 &2, the behavior of the device seems also related to Vout.

Could you please explain about this?

Thanks!

Best regards,

Roy Hsu