Bad power supply design ?

Thread Starter

Matt74

Joined Jun 29, 2019
8
Hello,
After a successful Teensy-based proof-of-concept, I tried to go a step further by designing my own prototype. Because I am not an electronics engineer I thought I would test first the power management part. Good thing because it is not working... I have 0V at all test points except Tp7=20mV with 5V supplied via USB (I checked and there is indeed 5V there)
I followed the manufacturer's recommendations for the Li-Ion battery charger (LTC4063) and the load switch (SIP32510) but obviously I did something wrong. What am I missing ?
Thanks !
 

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sagor

Joined Mar 10, 2019
109
You won't get an output unless LDOEN is low. Never leave unused pins disconnected, they should be either held high or held low, depending on their functions.
Read the datasheet for pin definitions and how they should be connected.
 

Thread Starter

Matt74

Joined Jun 29, 2019
8
Thanks a lot ! I did read it but must have missed that...

I'll connect the other ones too then
 

Thread Starter

Matt74

Joined Jun 29, 2019
8
Actually the data sheet reads "A 2M pull-down resistor defaults the LDO to its enabled state", that's why I left it unconnected (bad practice I acknowledge that and shall correct it in the future design).

When I initially tested my design, I supplied 5V through Vcc (pin 10) and looked at Vout (pin 2) WITHOUT any battery connected to Bat (pin 1).
After a lot of fiddling, I eventually tested my board WITH a battery and tadaaa I got my regulated Vout=2.8V !

I probably misunderstood the way this chip was working. I thought the LDO would use EITHER the battery OR Vcc as a source of current:
"When the input supply (wall adapter or USB supply) is removed, the LDO regulates the output voltage without interruption. The battery charger and LDO regulator can be enabled individually."
However it seems that the LDO will not work regardless of Vcc if Bat is unconnected. Pulling down LDOEN does not make any change (I guess because it is already internally pulled down)

What's your understanding ?

Cheers
 

Thread Starter

Matt74

Joined Jun 29, 2019
8
Excellent, thanks Joël. It will take me some time to go through your schematics but I am hoping to learn a lot in the process !
 
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