LTC4060 does not recharge the 4 cells battery @ 2V

Hello,

I don't see anything in your schematic that would cause this operation.

Double-check that your SEL1 & SEL0 pins are configured as they are here. Try disconnecting the load. What does the /CHRG pin indicate in this state (is it trying to charge or not)? And is the NTC in a valid range?

Regards,

Zack

For LTC3124, I did not see the output capacitors on the schematic. Two 100uF, 6.3V, 1812 caps should be placed close to output pins.

How did you measure the leakage current? Did you disconnect other circuits before and after the LTC3124's circuit?

SEL1 & SEL0 are both set high (only R202 &R203 are installed). The NTC is at 5.5V  (voltage supply is 9V) which is a valid range. The /CHRG pin is low (at 0V)

We measured current at output of the battery (we placed a current meter between the battery and the charger LTC4060). The LTC3124 has two 22uF caps placed at output (not shown in the previous schematic), 

The /CHRG pin is open-drain. Do you have a pull-up on it (off-page)? If so, and it is low, then the LTC4060 thinks it is charging.

When you measure for current, try using a higher range on your ammeter or a sense resistor. If the resistance of the meter is high enough, it can interfere with charging or event terminate.

Also, did you try disconnecting the load? If you are measuring the current out of the battery terminals, you are not measuring all of the current being sourced by the charger. The load may be pulling all of the current - hence none into your battery.

Regards,

Zack

The /CHRG pin is floating no pull-up on it (it has just a test point on it). 

Plugging a battery that has 4V (4 cells) or higher the charger works fine. When the voltage of the 4-cells around 2V does not charge even the /CHRG pin shows 0V.

All these experiments are done with no other circuits involved (load disconnected).

To review this issue; the battery is initially fully charged to 5.4V (4-cells) plugged into our units. start leaking when the units assembled and stored in our production facility and cannot be recharged when the units installed in the field. The LTC3124 is leaking even though the SD pin is pulled down causing the battery drain to 2V or below. The LTC4060 seeing a very low voltage of the 4-cells and can not recharge.

The /CHRG pin will always show 0V if there is no pull-up on it. Try pulling it up to Vcc with 10kOhms.

Does this happen on all units?

Zack,

The pull up resistor at /CHRG pin works but not all the time, some batteries the charger initiate charging and some cases doesn't. 

/CHRG is an output should have anything to do with low voltage batteries charge

we connected PWM with VCC butThe LTC3124 still draw about 400uA even SD is low and VCC always showing some volatage even SD=0, any input in how to fully shutdown the switching. 

The /CHRG pin is a status output, so it is a clue to what is happening. Keep the pull-up on the /CHRG pin for these tests.

I would expect a more repeatable answer as to whether the /CHRG output is high or low when the batteries are below 2V and do not charge.

Please try disconnecting the entire LTC3124 circuit from the battery node. You may need to cut a trace on the demo board. This will help determine if that circuit is stealing current from the battery when this happens. If that's the case, we can find a solution from there.