Regarding LTC4011, when RTIMER is equal to 100kohm, the tmax=100k*30^(-6)=3h which is the fast charge time and the top-off charge time is tmax/3=1h.
But top-off charge time of NiMH battery (4cells) isn’t constant at the customer side. It takes about 1h as the first time of the top-off charge, but after discharge, it takes about 1h25m as the top-off charge. The time is sometimes 1h again repeating the charge and the discharge.
The customer says that the top-off charge time of NiMH battery (3cells) is always 1h and wants to know the reason why the top-off charge time of 4cells isn’t constant.
Could you have any idea of this phenomenon? LTC4011 works correctly?
Fig.1 The NiMH battery characteristics
Fig.2 Measurement data by the customer (Vertical:Voltage, Horizontal:Time)