TLV61046A: Why the tlv61046A PWM Mode and PFM Mode FB reference is different? It will cause the different output.

Kevin Zeng

Part Number: TLV61046A

This picture show that PWM mode Vout_nom and PFM mode Vout_nom is differerent. The PFM Mode FB reference is higher than PWM's.

And I use webeach power design simulate the Load Transient.

And when tlv61040a worked in PFM mode, the output voltage will reach 12.3V; And when tvl91046a worked in PWM mode, the output voltage will reach 12V.

SO Why the tlv61046A PWM Mode and PFM Mode FB reference is different? It will cause the different output.

over 3 years ago

0 Bryce Xun over 3 years ago

TI__Mastermind 27910 points

Hi Kevin,

The output voltage in PFM is controlled by comparison of FB and PFM reference voltage, when FB rises over PFM reference voltage(1.01*FB), the device ought to stop switching, so output voltage can be regulated at target value.

But due to the delay of internal comparators, the device will continue switching for several cycles. So that the output voltage will be higher than target value.

Regards,

Bryce

0 Kevin Zeng over 3 years ago in reply to Bryce Xun

TI__Intellectual 2160 points

Thank you Bryce kindly answer.

I just not real know that why PFM and PWM FB reference voltage is different?

0 Bryce Xun over 3 years ago in reply to Kevin Zeng

TI__Mastermind 27910 points

Hi Kevin,

It was because of their different regulation strategies.

In PFM, hysteresis voltage control is used. But in FPWM, error amplifier is used to eliminate static errors between FB and reference voltage.

Regards,

Bryce

0 Kevin Zeng over 3 years ago in reply to Bryce Xun

TI__Intellectual 2160 points

Hi Bryce，

Thank you kindly answer, and I have another question.

Why PFM and PWM regulation strategies is different?

+1 Bryce Xun over 3 years ago in reply to Kevin Zeng

TI__Mastermind 27910 points

Hi Kevin,

PFM is designed to increase the efficiency as switching will be stopped when FB is higher than PFM reference voltage at light load.

FPWM is designed to get the smaller output voltage ripple as the switching frequency is fixed at all loads.

Regards,

Bryce

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TLV61046A: Why the tlv61046A PWM Mode and PFM Mode FB reference is different? It will cause the different output.