BQ25071: TS input oscillating and disabling charger

Hi Jim,

Is there an alternative approach to disabling the TS sampling? If I tie the TS to the battery directly (through a resistor divider) voltage change as a result of load and charging might bring the TS out of range. TS thresholds are set by the LDO so this may not work if LDO is failing to regulate. I will get back to you on whether this is possible or other work-arounds. What are your TS voltage divider values? If you can provide the schematic here that would be best. 

This part is not intended for solar input as it lacks a DPM/MPPT function to keep input voltage from collapsing. BQ24650 may be better suited here.

Best,

Thank you Nick.  I believe, however, that the BQ24650 requires minimum 5v in.  This is problematic with the PV that we are using.  Any other choices?

Jim S.

Thank you Eric.  Great resource. However, the BQ25895 is looking for a higher voltage input (9-12v).  I have 5v OC available.  I will study the design...it is possible that the algorithm will allow for lower voltages. 

Jim

Hi Jim,

Can you post the schematic here? I was not able to replicate the issue with BQ25071 EVM. 

Thanks,

Nick, having difficulty uploading the pdf.  The issue centers around the output of the solar harvester SPV1040 (ST Micro).  It does not provide a well regulated voltage to the BQ25071.  When the input voltage to the BQ25071 drops below threshold, the LDO drops and with it the TS voltage, thereby disabling the output.

Please advise on how to upload the pdf.  Thanks.

Jim

Hi Jim,

Look for this icon after clicking reply:

Best,

As I thought.  But the image does not appears after uploading and inserting file.

Jim

Hi Jim,

I've sent you a friend request on e2e with contact info, you can email me the schematic if you're having issues uploading.

Best,

Hi Jim,

Your values for TS voltage divider look good, TS is set to constant 17% of LDO voltage which is between both thresholds. There should be no issue operating at Vin = 4V with a stable power supply. 

If the LDO is oscillating from unstable Vin there are a few things to try

1. Increase IN capacitance, try 5 uF
2. Increase LDO capacitance, add a 1uF
3. Try reducing the charging current

Best,

Thank you Nick.  All makes sense.  Will give it a try.  One question/observation.  As I am driving the input from a solar harvester, input voltage will vary depending upon solar energy available.  Often this can vary over seconds to minutes (clouds, shade from tree, etc.).  I find that the BQ25071 actually does well down to 3.3 volts (but LDO drops as well....following it down to 3.3 volts).  As the TS divider is based upon LDO voltage, the charger turns off.

I will add capacitance and give it a whirl.

Jim

Jim,

The device shuts off at 3.3V from Under-voltage lock-out. TS thresholds are independent of LDO voltage. See d/s 9.2

Best,