I am having a little trouble with a circuit design.

I am running a Lithium flat pack battery.

I have a charge circuit with MCP73831, then a Buck circuit with a 3.3v out using a TPS64203, then a Boost circuit using the TPS61222.
Circuit requirements are
<4uA when turned off
3.3V@400mA Max and 150mA Min
5.0V@20mA Max and 2mA min
Input from 1 3.7V battery (max charge of 4.2V, and min of 3.0V)
The ground for 3.3V and 5.0V circuits need to be the same as there is ttl communication between them.


The charge and 3.3v segments are working correctly the 5V output is working but only at very low current ratings.... once it goes above about 10mA it loses voltage.

the 3.3V line provides plenty of current 800mA no issues but even with no draw on the 3.3v line the 5V boost circuit does not provide enough current at the 5V output ...

I don't see much ripple in the 3.3V line on the oscilloscope. Am I doing something wrong by connecting the output of a 3.3V to the input of the 5.0V ?

 

Charge

3.3V

5.0V

 

see the TPS61222 input and output requirements/relation . . . sometimes for the lower input voltages the output current is less than otherwise

 

see the TPS61222 input and output requirements/relation . . . sometimes for the lower input voltages the output current is less than otherwise

I am not seeing what you mean my input should never be below 3.0V min ... and typically would be at 3.2V
AT 3.2V I see output current of > 100mA (I only need about 20-> 50mA)


I also see


at 3.2V I don't start loosing voltage until about the 70mA or 80mA mark (according to data sheet)

 

? wrong saturating inductor (i don't know) . . . switch fails at high current (?current limit to inductor thermal limit -- i guess you can continue this list and yourself)

 

? wrong saturating inductor (i don't know) . . . switch fails at high current (?current limit to inductor thermal limit -- i guess you can continue this list and yourself)

was just looking for what I missed thanks for the response just didn't see where you were looking. If you have something that I missed in the data sheet please let me know. Yes I am checking another inductor, I had found one similar to what what specified in the data sheet but was not magnetically shielded. I will try one with magnetic shielding and see where I get from there.

 

Why not simply boost the batteries to get the 5V source and add a 3.3V linear regulator to get the other source?

 

Why not simply boost the batteries to get the 5V source and add a 3.3V linear regulator to get the other source?

The linear regulator is inefficient compared to switching regulators. on the 3.3V line average use is 150mA with a max of >400mA while the 5V line is 2mA average and about 20mA max. Boosting all current to the 5V level in order to use only 4-20mA then use and inefficient linear regulator for most of the current would drop my battery life too much for the system requirements.

 

perhaps . . . just perhaps ... with single flyback transformer with two output sections you can do this ← the requirement here is that the "5v" coil would have sufficient voltage for "20mA + some more" at max power on 3.3v coil

Input from 1 3.7V battery (max charge of 4.2V, and min of 3.0V)
The ground for 3.3V and 5.0V circuits need to be the same as there is ttl communication between them.

( just an attempt to fast fetch SOC versus V and r ) . . .
https://www.batterystandards.info/s...st_methods_for_battery_understanding_v3_0.pdf
https://www.mdpi.com/1996-1073/12/15/3023/htm
( https://www.e3s-conferences.org/articles/e3sconf/pdf/2018/19/e3sconf_eko-dok2018_00074.pdf )
2.5V to 3.6V 10mΩ to 30mΩ
worst case 2.5V 30mΩ ??? 83A . . . more likely 2A continuous drain models ::
https://ecksteinimg.de/Datasheet/703759-2000mAh.pdf ~ 400mA(2A) 150mΩ(? 230mΩ end of cycle @ 2.75V ?) 3.7÷2.75 2.0Ah ***
http://www.batteryonestop.com/baotongusa/products/datasheets/li-ion/sanyo-ur18650f-26a.pdf ~ 520mA(5A) 100mΩ(? 150mΩ @ 3V ?) 3.7÷3.0 2.6Ah

3.0V 200mΩ 45W , 22.5W to equivalent load , (2A → 1.3Ω max. external continuous load)=> 6W RMS lossless safe output of what 5.2W on RMS 1.3Ω ***
3.3V 400mA 1.32W
5.0V 20mA 100mW -- Total useful output 1.42W ( if your battery is ok there's you can go with 27% efficiency = you have some mystery bug)

 

i simulated 3.3V 400 (not your controller but a simple logical) the input draw was roughly 1.5W and . . . inputr woltage does not much drop - however it's inverter topology with an extra supply cut-off switch . . . just to verify the prev post