LM25141-Q1: Pull down for DEMB and OSC through PD register

Kazuki Kuramochi

Part Number: LM25141-Q1

Hello Expert,

My customer is designing circuit using LM25141-Q1.
In there circuit they will use VDDA as pull up power source for DEMB and OSC as same as EVM.
On the other hands, they are considering to do on-the-fly change at those pin's so want to add pull-down resistor through FET.

For this use case, could you please answer following questions?

How much pull down resistor can they use?
- At this moment, they plan to use 4.7kohm or 10kohm.
Could you tell me sink current of DEMB pin during high?
Could you tell me sink current of OSC pin during high?

Best regards,
Kazuki Kuramochi

8 months ago

0 Timothy Hegarty 8 months ago

TI__Guru 57222 points

Hi Kuramochi-san,

Thanks for the question. The sink current of these pins is minimal. 10kΩ may be somewhat low, as this would give 0.5mA current from VDD when each pin is pulled low (total 1mA). Maybe try 47-100kΩ.

Regards,

Tim

0 Kazuki Kuramochi 8 months ago in reply to Timothy Hegarty

TI__Genius 9130 points

Hi Tim,

"minimal" is little rough explanation against their expectation.
Would you provide little more detailed sink current?
EN has leakage current rating as typical, so it is helpful if we can say this spec will be similar as EN.

Best regards,
Kazuki Kuramochi

0 Timothy Hegarty 7 months ago in reply to Kazuki Kuramochi

TI__Guru 57222 points

Hi Kazuki-san,

My expectation is that it will be in the sub uA range. Let me check if we have data and get back to you by tomorrow.

Regards,

Tim

0 Kazuki Kuramochi 7 months ago in reply to Timothy Hegarty

TI__Genius 9130 points

Hi Timothy-san,

Thank you for your reply.
I understand that the expected leakage current for DEMB and OSC may be sub uA range as similar as EN pin.
If there is any data, please share it to us.
It is really helpful.

Best regards,
Kazuki Kuramochi

+1 Timothy Hegarty 7 months ago in reply to Kazuki Kuramochi

TI__Guru 57222 points

Hi Kazuki-san,

The state of OSC is latched at startup, so it is not suitable for change on the fly. However, you can adjust the effective RT resistance (as shown in the datasheet) to shift the Fsw from its nominal value. Typical applications would not require a change from 440kHz to 2.2MHz for example (by changing the OSC pin state from low to high).

The DEMB pin pullup can be 100kΩ to minimize input quiescent current consumption when DEMB is low for PFM mode operation at light loads.

Regards,

Tim

0 Kazuki Kuramochi 7 months ago in reply to Timothy Hegarty

TI__Genius 9130 points

Hi Timothy-san,

Thank you for your kindly explanation.
I understand.

Best regards,
Kazuki Kuramochi

0 Timothy Hegarty 7 months ago in reply to Kazuki Kuramochi

TI__Guru 57222 points

Thank you too.

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LM25141-Q1: Pull down for DEMB and OSC through PD register