LTC4010 for NiMH battery charger application. There are some field failures: CHRG indicators ON, FAULT off, no PWW, no charger current. VTEM 10k to GND.
This is not enough information to tell if the circuit is damaged or if something else is wrong. I recommend that you check the requirements for charging (battery voltage, for example) and refer to the abs max limits in the datasheet. If you think the circuit may be damaged, perhaps try probing around and replacing parts that don't seem to be working.
Please refer to the circuit. The charger voltage is 12V, battery pack is 5xAA NiMH. The components around IC are confirmed without issue. We saw quite some failures in field. Question is: What can cause the damage of PWM output?
Does that mean if you replace the LTC4010 then the circuit works as usual?
I don't see any problems with the circuit. Are the batteries ever replaced in the field? Or is power ever shut off and re-applied?
I notice you are using ferrite beads on the input. If input voltage is applied quickly, they could cause a voltage transient that may violate an abs max of the charger, damaging something required for the PWM to switch. Same with connecting the battery if there are any sort of leads (with parasitic inductance) between the battery and the charger circuit.
It would be good to test and look for this during connection of either supply.
The battery has not been replaced. The charger is a wall-plug 12V switching power supply, it is only plugged in for charging battery. The PWM output is not directly exposed to external circuit, what could cause it damaged? can you find some hints from the internal circuit?
Can we first verify that the damage is with the LTC4010 IC? If you replace the IC, does the circuit work as expected?
I did, the IC was damaged. After I replaced with a known good one. the issue is gone.
Ok, great. When the circuit is running, is the battery always installed?
I recommend you start with some hot-plug testing. Plug your power supply into the wall first and then plug it into the circuit. Try this with no battery installed first and monitor the voltage on VCC with a scope. You should trigger on maybe 12.5V rising. Does it hit the trigger (if not, try 11.5V to make sure you see it)? And if so, how high does the voltage go?
Try the same thing on the battery side: with no power supply connected, and the circuit discharged, connect the battery and monitor the voltage on VCC. If you trigger a scope at the battery voltage, how high does the voltage peak to?
The peaks could be in the microsecond range, so make sure you zoom appropriately. You should try these tests repetitively, at least 10 times each. And after this testing, try to charge the battery again. Does the circuit still work?
Without battery, plug in 12V charge, Vcc(peak)=15.9
Without charge, plug in battery(V=7.04), Vcc(peak) =7.4V
After I did much more than 10 times, the charge circuit is still functioning.
Thanks for running the test. Looks like there are some transients but those voltages should not damage the part. Why don't you contact me privately at email@example.com so we can put you in touch with your local FAE support and get some of these damaged parts to failure analysis for a better diagnosis.
You have a fairly high sense resistor, which is fine, but that increases the voltage differential across your BAT/SENSE pins for which there is an abs max of +/- 0.3V. During a hot-plug of your battery, a 1.67A current spike across the sense resistor (through R21, L4, and Q1 body diode then into the caps on VCC) would violate this abs max temporarily.
If you have a current probe (or differential voltage probes across the sense resistor) you can measure what this voltage gets to instantaneously during a hot-plug event of the battery just like in the previous test. Again, make sure the VCC caps are completely discharged. Failure analysis of your units will also help to determine if this is the cause of the damage.
I could not see current inrush through the sense resistor. Without the battery, plug-in charger would not cause current flow through the sense resistor. What I did is connecting the battery first, then plug in the charger, and I did not the high inrush current.
I really appreciate your help. My email is firstname.lastname@example.org
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