LMZ31503: INH/UVLO pin: internal pullup and adjustment sequence

Satoshi

Guru 19655 points

Part Number: LMZ31503
Other Parts Discussed in Thread: TPS54320

Please let me know about two points below for LMZ31503's INH/UVLO pin function;

・About internal pullup, below thread is described "The INH/UVLO has an internal pull-up to Vin".

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1070218/lmz31503-pwrgd-behavior

　But the other thread is described "the internal INH pull-up current source goes to an internally generated 3V, not Vin" .

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/905974/lmz31503-mosfet-for-inhibit-pin

　Which is correct?

・On the sequence setting, when INH/UVLO connect directory the other PGOOD pin and startup VIN / PVIN earlier then the other DC/DC, LMZ31503 startup is ahead of sequence setting.

　I considering to add below circuit based on datasheet Figure-29.

　If there the other recommend circuit or idea, please let me know.

Best regards,

Satoshi

over 3 years ago

0 Miranda Gu over 3 years ago

TI__Genius 16632 points

Hi Satoshi,

Our US team will check it and reply you soon.

0 Caleb Perez over 3 years ago

TI__Genius 11935 points

Hello,

As the datasheet states in section 9.11, the pin is puled up to VIN potential.

Thanks,
Caleb

0 Nancy Zhang over 3 years ago in reply to Caleb Perez

TI__Mastermind 49470 points

Hi Satoshi,

The internal INH pull-up current source goes to an internally generated 3V, not Vin as confirmed by waveforms. Sorry for confusing. Your circuit looks good to me.

Thanks,

Nancy

0 Satoshi over 3 years ago in reply to Nancy Zhang

Guru 19655 points

Hi Caleb, Nancy

Thank you for reply,

When INH pullup is not VIN, please let me know additional question below;

・Datasheet Figure 28 is VINH: 3V, but Figure 37 is VINH: 2V and Figure 39 is VINH: about 1.5V.

　What method is VINH voltage deciding?

　And, is VINH voltage depend on VIN?

I guess that INH pullup to current source because of Figure 28 is VIN: 5V and VINH: 3V, these are differing.

Best regards,

Satoshi

0 Nancy Zhang over 3 years ago in reply to Satoshi

TI__Mastermind 49470 points

Hi Satoshi,

I check TPS31503 EVM user's guide. All the waveforms in the datasheet should be from EVM testing. VINH voltage level is from external resistor setting. The Figure 28/30/31 VINH voltage level is 3.156V(12*24.3/(68.1+24.3)=3.156V). Figure 37 VINH voltage is 1.81V (12*12.1/(68.1+12.1)=1.8V). Figure 39 the scale of VINH should be 2v/div which is 3.156V. Pease refer to datasheet of TPS54320 which is IC inside LMZ31503 module.

Hope this helps,

Thanks,

Nancy

0 Satoshi over 3 years ago in reply to Nancy Zhang

Guru 19655 points

Hi Nancy,

Thank you for reply,

Internal INH/UVLO is cleared.

Sorry for additional question, is INH/UVLO input add external pullup resister, no problem?

Best regards,

Satoshi

+1 Nancy Zhang over 3 years ago in reply to Satoshi

TI__Mastermind 49470 points

Hi Satoshi,

No problem. You can refer to EVM user's guide schematic.

Thanks,

Nancy

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LMZ31503: INH/UVLO pin: internal pullup and adjustment sequence