LTC4020 full charge current not as expected

Hi,

We have designed a battery charger by using LTC4020. It has 8 NiMh batteries and each has capacity 4500mAh and want to charge them at 2.3A max.

Design Parameters:

Input Voltage: 10-16V

Output Voltage: 8-14V

Max Charge Current: 2.3A

f0 = ~500Khz

Mode = CC (mode pin floating)

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When I test the charger, I set the LTC_RNG pin to have 10% of full charging current, I measured charge current around 240mA which is good.

I set RNG to have 50%, we get charge current as around 1.2A which is ok too.

But when I set RNG to have 100%, we are getting only 400mA charge current while the expected is around 2.3A. (At this time RNG pin has 3V by internal source)

Pins status during charging are same and observed as STAT1 = 0 and STAT=3.5V at any level.

Any advice is highly appreciated about potential problems. 

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