Supplying two ICs from the OSD3358-SM powered by a Lipo battery

[Lanwer]

Hi all,

I want to use the two following ICs connected to the OSD3358-SM and supplied by (SYS_VDD1_3P3V) (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 SiP will be supplied by a 3.7V Lipo battery. Its output ranges from 4.2V when completely charged to 3.7V. The battery will be charged with the USB input of the integrated linear charger.

The problem is that I read in the “OSD335x-SM Power Application note” 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?

[Neeraj Dantu]

Lanwer,

The input voltage for the LDO TL5209 is provided by the PMIC SYS_VOUT voltage rail, which has its own drop out voltage from the power inputs to the PMIC. We can only guarantee the performance of the device within the specification of the device in the datasheet. There are a number of LDOs with better drop-out characteristics you could explore using external to the OSD335x-SM SiP.

Best regards,

Neeraj

[Lanwer]

Thank you for your answer.

1) 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).  I don’t think this will have an impact thought 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?

1) Considering your tip, won’t I need then another whole circuit to take care of the battery charging? Or can I just take the SYS_VOUT on the balls K6, K7, L6, L7 and route it to another LDO with a better drop-out voltage, enable this new LDO by the TPS65217C LDO4 as it’s the case for the TL5209 and use this new LDO’s output voltage (3V3) to supply the two ICs mentioned earlier.

2)Any suggestions for an LDO that Octavo Systems is considering to replace the TL5209 in the future?

Thanks

[Neeraj Dantu]

Hey Lan,

Sorry for the delayed response. The specifications on our datasheet are based on our testing of the device. We do not guarantee performance outside these specifications, but you can try and see if it works for your case.

Our recommendation would be to use an external battery charger as in the Beaglebone Blue(https://github.com/beagleboard/beaglebone-blue/blob/master/BeagleBone_Blue_sch.pdf).

If the battery voltage falls below 3.6V(Look at battery curve here: https://learn.sparkfun.com/tutorials/battery-technologies/lithium-polymer), LDO4 for example will lose regulation because of the drop out voltage. This does not generate an action form the PMIC either. So, 2S LiPo with external charger as shown in Beaglebone Blue would be the best bet.

We do not plan to replace the LDO on OSD335x-SM.

Best regards,

Neeraj

[Author]

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