| SLA Status | Assignee | Support Status |
|---|---|---|
| ⚠ 2041 hours | Open | |
MAX77961B
Production
The MAX77960B/MAX77961B are high-performance wide-input 3A (MAX77960B)/6A (MAX77961B) buck-boost chargers with Smart Power Selectorâ„¢ and operate as a...
Datasheet
MAX77961B on Analog.com
I'm having problems with this chip in 3S configuration. It's resistor-configured to charge at 4A (11kΩ on ILIM, I2C is not used) and connected to 3 Li-ion cells.
When charger (LAB PSU) is connected, it does not charge normally, instead it's running in what I can call a hiccup mode: trying for a couple of ms, switching off and trying again. This clicking is actually audible from output caps, especially if I touch them with multimeter/scope probe.
It does charge normally when I slowly increase charger voltage: clicking at low voltages, then starts charging normally from ~4.7V (at 200mA or so), increases current gradually when voltage is being increased (status LED blinking = indicating normal charging), and starts to hicckup/click once charger current reaches exactly 2.0A (voltage is above 4.8V). While slowly increasing input voltage I've found that it is charging normally until exactly 2.0A is reached - then it starts to hiccup. Interestingly, it's still happening at 2.0A even if I change the 10mΩ shunt to 20mΩ (would expect the current to drop 2x). When in hiccup mode, it pulses INOKB output ("input OK" flag). INOKB output is very vaguelly documented in the datasheet. I believe my charger input is fine, so what may be the other issues?
Here's an image of INOKB output (CH1) and converter's output (SYS, CH2):
And here's INOKB vs. CHGIN input voltage:
Voltage dips by 300mV, INOKB flag is set and then the ramp is (I think) caused by the PSU overreacting (which should not be an issue here).
My PCB layout is very similar to one suggested in page 77 of the datasheet. I've tried to optimize by cutting traces and connecting everything with wires, but no change. I've also tried to add more caps on input and output of the converter, still nothing. I've spent weeks on this already, no idea what's happening.
Here's my layout:
Any ideas? Any insights from Analog staff what conditions does INOKB actually report?
EDIT: noticed a weird one. Tried to re-configure it for 500mA with an ILIM resistor, but it did not respect that setting, nothing changes. Any ideas what's happening?
