LM5122: Why is forced PWM mode recommended for bypass operation?

Tim Laux1

Prodigy 90 points

Part Number: LM5122

Hello,

For LM5122, in the datasheet, under 7.3.9 Bypass Operation (VOUT = VIN), it says the following:

"Forced-PWM mode is the recommended PWM configuration when bypass operation is required"

Can you explain why it is preferred? Why is it preferred to allow the input to sink current in bypass operation?

Thank you,

Tim

over 4 years ago

0 Yinsong Cai1 over 4 years ago

TI__Expert 7450 points

Hi Tim,

Thank you for your interest in LM5122.

The high-side driver doesn’t turn on 100% if it is not PFWM mode.

Thanks,

Yinsong

0 Tim Laux1 over 4 years ago in reply to Yinsong Cai1

Prodigy 90 points

Thank you. So, if in diode-emulation mode, the high-side driver will have something like ~95% duty cycle, even when in bypass operation? I don't see any mention of minimum off-time for HO driver.

Thank you,

Tim

0 Yinsong Cai1 over 4 years ago in reply to Tim Laux1

TI__Expert 7450 points

Hi Tim,

The bypass mode means the high-side driver is 100% on. However, the zero crossing could still be triggered and that can cause a conflict.

Thanks,

Yinsong

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LM5122: Why is forced PWM mode recommended for bypass operation?