LM2734: Boost to SW voltage

Taketo Sato

Part Number: LM2734

Hello team,

My customer in using LM2734Y in their design(12Vin, 5Vout, 0.6A) and evaluated the device operation.

They found voltage between BOOST and SW is about 7V for 1ms during power-up and exceeds absolute max rating which is 6V. Please see below O'scope capture and its CSV data.

Yellow: BOOST, Green: SW, Red: Vin(12V), Blue: Vout(5V).

LM2734_start up_zoom2_print_24.csv

They use LMK105BJ105KV-F capacitor for Cboost between Boost and SW.

Could you let me know below questions?

Will the 1ms over voltage cause immediate damage to the device?
If device will get damaged due to the over voltage event, what failure mode can be?
How do we improve the boost-sw voltage?

Best regards,

over 3 years ago

0 Ruby Li over 3 years ago

TI__Expert 7430 points

Hi Sato

Our America team will give you feedback soon.

BR
Ruby

0 Amod Vaze over 3 years ago

TI__Mastermind 23110 points

Sato-san,

Can you please share your design schematic? There are many ways to generate the boost voltage so would like to review the schematic. Considering the abs max voltage level is 6V, the BOOT-SW voltage needs to be below that. Based on datasheet, boot cap of 10nF is recommended with at least 16V VDC rating. The boot cap you mentioned is a 1uF10V (LMK105BJ105KV-F) cap so would recommend changing to the datasheet recommendation.

Thanks,

Amod

0 Taketo Sato over 3 years ago in reply to Amod Vaze

TI__Genius 9745 points

Hello Amod-san,

Thank you for your comment.

I just sent you customer's schematic through email.

Is 1uF too large for the boot cap? Do we have recommended maximum boot cap value?

Best regards,

0 Lishuang Zhao over 3 years ago in reply to Taketo Sato

TI__Expert 7500 points

Hi Taketo,

Since you have connect Amod through email. I will close this thread.

Thanks,

Lishuang

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LM2734: Boost to SW voltage