LTC 4020


We have purchased the demo board DC2134A  for the LTC 4020 but it’s operation doesn’t make sense. 

While the battery status is in float mode (battery fully charged  - RED LED is ON and Green is OFF  )  and there is input power available to the charger we are noticing that the battery is STILL sourcing the load even though the charger is powered up. 

The demo board, DC2134A,  is spec’ed as having a MAX output of 8 AMPS  from 21 to 28 volts.   Our load is set to 8 Ohms ( about 3 amps)  which is nowhere near the max  current capability of the charger output.  Our questions is this,    Why then would the charger allow the battery to source the load (FET on ) if the load doesn’t require the battery?

 We have meters connected to the demo board showing the following :

Vin            23.88V

Iin             800mA

Vout       23.2V

Iout         3 Amps

Battery Voltage    23.49

Battery  Current ( supping the load through the FET )  2 Amps

Batteries are  8 AH  rating -  We have two 12 volt ones setup in series. 

Jumper is set to LEAD ACID

 Are we missing something here  or are we misinterpreting  the indented purpose of the DEMO board or chip design ?  Any help would be greatly appreciated.