LP87524J-Q1: Disabling FB_B0

Claudio ANUCHNIK

Part Number: LP87524J-Q1
Other Parts Discussed in Thread: AWR1843

Hi all,

I am using the LP87524J-Q1 as a power supply for my AWR1843 Board.

We try to operate the system using a Li-Ion Battery (3.2V < VIN_Bx < 4.2V), connected through some protection switch, directly to the VIN_Bx inputs and VANA.

For the System 3.3V we use an independent LDO connected the same way as above (LDO Vin parallel to VIN_Bx).

For such configuration, we don't need the FB_B0 output, in spite of we assembled all its components Lo_0(0.47uHy), Cout_0(22uF), C0(220pF) and R0(3.9 ohm). and VIN_B0 is tied to input voltage (Li-Ion Battery)

My questions are:

1.- Can I remove the above components without affecting the system performance?

2. Can I tie the VIN_B0 to Ground?

3. Can the FB_B0 work unloaded or there is a minimum load I should connect to it? Right now not load at all.

Thanks,

Claudio

over 4 years ago

0 Layne J over 4 years ago

TI__Genius 12735 points

Hi Claudio,

The expert for this device is located in the EU and will provide a response tomorrow.

Best regards,

Layne J

0 Tomi Koskela over 4 years ago

TI__Genius 11020 points

Hello Claudio,

Unless you disable the buck0 through I2C command the buck0 must be populated with the correct components and powered normally. The fault detection would trigger otherwise and keep the PGOOD signal low.

There is no minimum load requirements for the buck, so it can work with no load.

Thanks.

Regards,

Tomi Koskela

0 Claudio ANUCHNIK over 4 years ago in reply to Tomi Koskela

Expert 1100 points

Thank you Tomi,

Claudio

0 Claudio ANUCHNIK over 4 years ago in reply to Claudio ANUCHNIK

Expert 1100 points

Hi Tomi,

What happens to the the whole system LP87524J-Q1 if VIN_Bx is supplied by a Li-Ion Battery with a nominal voltage of 3.7V but when loaded, voltage can drop to less than 3.3V
Is there any minimum input voltage I should supply to the LP87524J-Q1 in order to assure the correct functioning even I don't use the FB_B0 output?
Which minimum input voltage will trigger the PGOOD low?

Thank you,

Claudio

0 Tomi Koskela over 4 years ago in reply to Claudio ANUCHNIK

TI__Genius 11020 points

HI Claudio,

That can actually cause problems. The minimum difference between VIN/VOUT should be 0.5V. So for 3.3V output voltage, the input voltage should be minimum 3.8V to make sure the buck stays in regulation all the time. It is not so critical in this case since the buck is not loaded, but if the input voltage drops below 3.3V the buck cannot regulate the voltage anymore and PGOOD fault is generated. PGOOD window is +50/-40mV.

Is it possible to consider for example LP87524P for this application instead? Please see the TRM for more details:

https://www.ti.com/lit/ug/snvu663/snvu663.pdf

Thanks.

Regards,

Tomi Koskela

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LP87524J-Q1: Disabling FB_B0