Supplying two ICs from the PocketBeagle powered by a Lipo battery

[arad...@uncc.edu]

Hello all,

I want to use the two following ICs connected to the PocketBeagle and supplied by (SYS_VDD1_3P3V) (P1.14 or P2.23 that are the output of the LDO TL5209) because it has a maximum output current of 500mA.

1) ADXL357 Accelerometer with supply voltage of 2.25V to 3.6V and typical current of 200uA in measurement mode 

2) ESP-WROOM-02 wifi-module with a supply voltage of 2.7V to 3.6V and a minimum current delivered by power supply of 500mA required and average operating current of 80mA. 

The Pocketbeagle will be supplied by a 3.7V Lipo battery. The output ranges from 4.2V when completely charged to 3.7V.

The problem is that I read in the "OSD335x-SM Power Application note" the following and in OSD335x-SM Family datasheet:

" Due to the dropout behavior of the LDO TL5209, its output voltage rail SYS_VDD1_3P3V should not be used when the OSD335x is being powered through VIN_BAT. Please refer to the TL5209 datasheet for details."

It's true that the mentioned LDO has a voltage dropout of 500mV at full load of 500mA. But, even with full load, the voltage on the output delivered by the LDO should be at least (3.7V - 500mV = 3.2V) which is inside the range for the two ICs mentioned above. 

Will that then work or am I overlooking something here?  

[An Ra]

I was not aware of the battery switch dropout voltage V_DO,BAT of the PMIC (p. 9) which has a typical value of 60mV (no max value stated). But, I still do not understand why I should not use SYS_VDD1_3P3V as I am still within the range of the required supply voltage (above 2.7 V for both ICs). Is there another reason why I should definitely avoid the use of the built-in LDO TL5209 when the PocketBeagle is powered by the single cell LiPo battery?

[An Ra]

Or do I have to look for an external LDO with a better dropout voltage? and why? I still do not see the reason. 

Thanks

On Monday, July 9, 2018 at 3:28:53 PM UTC-4, An Ra wrote: