LP5907-Q1: Schematic review

Hi Nick

After discuss with customer , we have updated SCH

1.Please help check this SCH, THX

2.Cause this case need design power sequence , how could I design & calculate THX

Hi Kygo,

1. What is the load current and ambient temperature? The schematic looks good but I would like to verify that the LDO is not going to get too hot
2. In what order do the devices need to be powered? Do you need another device after the LP5907 to power up after LP5907 is powered or do you need another device to enable the LP5907 when the other device is powered?

Regards,

Nick

Hi Nick

The power sequence as below

Hi Kygo,

Are they asking us to provide power sequencing calculations for this whole power section? It looks like they have already added RC delays and used an NR/SS pin to set delays in the power sequencing. They have also not provided any timing requirements so it seems that what is important is the order of the power sequencing and not necessarily the timing of the sequencing. Is that correct?

I want to point out again that using an inductor at the output of the TPS7B86-Q1 is not a good idea. I would like to know the reason they want it there.

Can you please also provide the load current and ambient temperature as I previously asked?

Regards,

Nick

Hi Nick

Got it , I will ask customer why they using an inductor at the output of the TPS7B86-Q1 !

The load current of LP5907QMFX-3.3Q1 is about 10mA,THX

I'm calculating the startup time, can you help me confirm whether my calculation is correct?

LP5907-Q1   after get  Vcc5V will need 80uS to give VLDO3V3

Hi Kygo,

Yes, but note that the 80us is the typical value and was specified at 25C, so it may be slightly different at different temperatures. 

What is the load current of TPS7B86-Q1?

Regards,

Nick

Hi Nick

Thank you!

The load current of TPS7B86-Q1 is about 0.4A,THX

Hi Kygo,

400mA is enough current to cause concern with the inductor at its output. I await the explanation for its inclusion.

Regards,

Nick