LMZ31710EVM-001: Getting out of pulse-skip mode for input supply range

Ahmed Saeed1

Part Number: LMZ31710EVM-001
Other Parts Discussed in Thread: LMZ31704, LMZ31707

I have probed the switching node (PH node) to ground on the EVM. It skips pulses at 6Vin and switches continuously starting from 7Vin. Is there any way to avoid getting out of pulse-skip mode at no load as this increases the quiescent current and consumes the battery charge? Can LMZ31707 or LMZ31704 offer a mitigation for this problem?

over 4 years ago

0 Gerold Dhanabalan - Online Design Tools over 4 years ago

TI__Genius 14455 points

Hi Ahmed,

The purpose of pulse-skip mode is to save energy because you are not continuously switching as in case of CCM mode. Why are you concerned that pulse skip model will increase current consumption?

Regards,

Gerold

0 Ahmed Saeed1 over 4 years ago in reply to Gerold Dhanabalan - Online Design Tools

Prodigy 30 points

Hi Gerold, No, I want to avoid getting out of pulse skip mode at no-load condition. Unfortunately, this is not the case for LMZ 31710, the chip get of our pulse skip (low current) mode and enters the continuous switching(high current) mode at no-load for certain input supply range !! I don’t know the reason why this happens and I think this is a real design issue.

0 Kris F over 4 years ago in reply to Ahmed Saeed1

TI__Genius 17905 points

Hi Ahmed, just wanted to let you know that we are looking into your concerns. From speaking with a colleague, I believe this is expected but will prepare some measurements to help explain. Please give me a couple of days to get back to you.

0 Kris F over 4 years ago in reply to Kris F

TI__Genius 17905 points

Hi Ahmed,

I tried to explain the behavior you are seeing in the attached document. I hope that helps clarify how the device is operating.

You can try lowering the switching frequency to 750kHz on the EVM or even 500kHz to see if the increased inductor ripple at lower frequency helps keep the device in one operating mode (Eco-mode) over your input voltage range.

/cfs-file/__key/communityserver-discussions-components-files/196/LMZ31710-input-current-surge.docx

Regards,
Kris

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LMZ31710EVM-001: Getting out of pulse-skip mode for input supply range