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LTC4155 Charging Status Issue


We are using LTC4155 and have tested the behavior of LTC4155 under charging condition. Charging status, constant current(0X40) and constant voltage (Vprog>Vc/x = 0X60) is OK but facing issue to get (Vprog<Vc/x = 0X80) and charger off condition (0X00).


We have evaluated charger with different C/x modes but not getting expected results as per datasheet. 


As per datasheet the PROG pin always represents the actual charge current flowing, even in the constant-voltage phase of charging, LTC continuously monitors Vprog and automatically reduces it. The charge current mode reduces from 100% to 12.5% in 6.25% steps and Vprog also reduces from 1.2V to 150mV respectively in 75mV steps.


Here our assumption is that charge current mode also should go from 12.5% to 6.25% and then 0 % if it reduces in 6.25% steps and Vprog will be 75mV for 6.25% Charging current mode.


We have tested LTC4155 for our battery specs 3.7/1400mA with USB input.


1) We have settled below parameters to test C/10 mode:

  •  Vflot = 4.2V (I2C)
  •  Safety timer = 8Hr or C/x indication (I2C)
  •  I Charge = 760mA (hardware resistor on Prog pin)
  •  I Charge limit = 100% CCM (I2C)
  •  Full Capacity Charge Indication Threshold = C/10 Mode (ICHARGE = 10%FS) (I2C)


I2C register setting for above parameters are:

  • Register 0X01 = 0X3F (Safety timer 8Hr or C/x)
  • Register 0X02 = 0XFC (C/10 mode , Vflot =4.2V, 100% CCM)


For 12.5% Charge mode Vprog will be 150 mV and for 6.25% charge mode Vprog will be 75mV if CCM reduces in 6.25% steps and Vprog reduces in 75mV steps.


Now, for the above settings of (C/10) mode, the typical value of V(C/x) is 120 mV and during charging Vprog value will reduce to 75 mV for (6.25% charge mode). if so then (Vprog < VC/x ) condition will be ok and should provide 0X80 or 0X00 value because as per datasheet  the eight hour timer termination setting will also terminate the charge cycle before the expiration of the eight hour timer when the battery charge current falls to the programmed full capacity (C/x) charge indication threshold.   


But we are not getting 0X80 or 0X00 value even if Vprog value is < 75mV.


Here we have described only a single C/10 mode issue but the same issue is also observed with all C/X modes.


Please, we need your help to understand/ solve this issue ASAP.