LP2985-N: Battery and USB power circuit

user6170139

Prodigy 30 points

Part Number: LP2985-N

Hi to all,

I built a circuit to power a 3.3v power source using both battery and/or

USB cable.

The battery section of my circuit seems to work fine.

the USB section is using a LP2985-33 and I cannot get 3.3v at the output.

instead, I get like 1.7v

here is my schematic :

Any suggestions?

Is my design good to avoid leakage into the battery ?

thanks

over 4 years ago

0 user6170139 over 4 years ago

Prodigy 30 points

Update : the gnd was not properly connected ! Sorry

Any comments/suggestions on the design ?

0 Stephen Ziel over 4 years ago in reply to user6170139

TI__Mastermind 29140 points

Hello,

I would confirm that the ESR of the 2.2uF capacitor is not below figure 20 of the datasheet.

Otherwise, the schematic looks okay.

Thanks,

- Stephen

0 user6170139 over 4 years ago in reply to Stephen Ziel

Prodigy 30 points

I used the KEMET calculator but not sure what parameters I should use :

0 Stephen Ziel over 4 years ago in reply to user6170139

TI__Mastermind 29140 points

Hello,

You would want to use the blue line.
From that plot, at room temperature your ESR is about 13m ohms.
In the Controls and Parameters box, you can change the temperature to see how this performs at other environments.
You should also enter your nominal voltage on the capacitor within the "bias voltage" section, instead of leaving it at 0V.

Thanks,

- Stephen

Power management

Power management forum

LP2985-N: Battery and USB power circuit