Changes to ISET, VSET, and CHM_TMR pin values on the fly.
The ISET pin is monitored while charging and changes to R-ISET during operation will immediately change the charge current.
The VSET and CHM_TMR pins are not continuously monitored during charge. Changes to these pins will not be acknowledged by the device until the input supply or /CE pin is toggled.
ISET, VSET, CHM_TMR pins short/open protection
A short/open circuit
condition detected on VSET or CHM_TMR results in a non-recoverable
fault. Toggle /CE or input power supply to reset device
A short circuit condition
detected on ISET results in a non-recoverable fault.
An open circuit condition
on ISET causes charger to start charging with 0 A charge current.
NiMH charging profile
Device does not support fast charging NiMH.
The duration of the time based charge is set by CHM_TMR and the current is set by ISET.
Device charges NiMH battery in constant current mode only, option for additional intermittent charges set by VSET pin.
Intermittent charging enables a shortened charge cycle 25% of the charge timer set by CHM_TMR to replenish natural self-discharge, but not overcharge the battery.
The intermittent charge is initiated when battery voltage falls below VRECHG (1.3 V).
Disable automatic recharge with charge enable (/CE) pin
Under standard operation device automatically restarts the charge cycle following a battery voltage drop below the recharge threshold (VRECHG).
Disable the charger by pulling the /CE pin high from a host device to prevent the automatic start of a charge cycle.
Ensure your system has a method to re-enable charging when desired as device will not monitor battery voltage when disabled.
ISET as an output current monitor
Voltage developed on the R-ISET resistor maps to output current at a 300 to 1 ratio and can be monitored by an external circuit.
Output current regulation at low battery voltage
For Li-Ion battery voltage less than VBAT_SHORT (2.2 V), and LiFePO4 battery voltage less than 1.2 V the output current is limited to IBAT_SHORT (16 mA). Device is in trickle charge phase.
For Li-Ion battery voltage between VBAT_SHORT and VBAT_LOWV (2.2 V and 2.8 V), and LiFePO4 battery voltage between 1.2 V and 2.0 V output current is limited to the precharge current set to 20% of ISET value.
Battery voltage must rise above VBAT_LOWV threshold within the 30 minute precharge timer. Otherwise the timer expiration ends the charge cycle and a toggle of the input supply or /CE pin is required to restart charging.
Operation at low charge current
ICHG can be set as low as 10 mA via ISET, for
ICHG below 50mA TI recommends adding a RC circuit in parallel with
R-ISET for greater signal stability. R = 2 kΩ and C = 4.7 nF
recommended. Refer to Figure 5-1 above for implementation of RC circuit.
Precharge and termination current accuracy may be lower at very low charge currents,
Operation at very low charge current
The recommended minimum fast charge current is 10 mA, but ISET can be set less than 10 mA.
Charge current accuracy can no longer be guaranteed at less than 10 mA, current may drop to 0 A.
There is no fault indication for charging at 0 A STAT1 and STAT2 outputs will continue to indicate charge in progress.
STAT1/STAT2 pins
Open drain outputs, combination of STAT1 and STAT2 indicate charge complete, charge in progress, recoverable fault, or non-recoverable fault.
Open battery operation
When no battery is present the device will cycle in and out of charging and provide an output voltage equal to the VSET regulation voltage.
Device does not perform a battery detection routine at startup.
Efficiency of charge, how to reduce power dissipation
The closer Vin is to Vout the better the efficiency and lower the power dissipation. Be aware Vin will need to be larger than Vout + VDO (dropout voltage) to account for voltage loss internal to the IC.
Required power dissipation in IC is greatest during fast charge with a low battery voltage and a high input voltage.
Input/output protection
Device has input overvoltage protection, but does not have IN-DPM (voltage fold back protection).
Device has output overcurrent and overvoltage protection. The overcurrent condition will require a toggle of /CE or power supply to resume charging.
During Vin OVP unit cannot operate
Max input voltage without damaging device is 40 V.
Unit will enter standby mode above VIN_OV (18 V) until the input voltage recovers below the overvoltage threshold.
Safety timer reset events
Cycle input power, safety timer resets.
Toggle the /CE pin, safety timer resets.
Battery voltage falls below VRECHG, safety timer resets.
Battery voltage crosses the VBAT_LOWV threshold, safety timer resets.
For NiMH with intermittent charge enabled, VBAT falls below recharge threshold, charge timer resets.
Safety timer expiration
Timer expiration for Li+ charging results in non-recoverable fault.
Timer expiration for NiMH charging is the expected termination. A fault occurs if VOUT < VRECHG at timer expiration.
Charge is not terminating before safety timer expiration
Confirm CHM_TMR is set for the appropriate safety timer length, confirm VSET and ISET match the battery manufacturer specs.
A system load in parallel with the battery drawing a large % of the available charge current may cause charging to be incomplete at safety timer expiration.
Safety timer extension scenarios
When the device is in thermal regulation the safety timer is extended and counts at half clock rate for the duration of thermal regulation,
When a recoverable fault occurs the safety timer is suspended until charge is automatically resumed.
If the charge cycle is restarted safety timer will reset.
TS pin in battery temperature application
Device is in normal operation when TS pin voltage is between Vcold and Vhot, typically corresponds to 0°C to 45°C.
TS pin voltage outside the acceptable range results in a recoverable fault. Device stops charging and enters standby state until battery temperature returns to operational range.
Hot and cold thresholds can be modified using series and parallel resistors Rs and Rp between the TS pin and the NTC thermistor.
Thermal Regulation and shutdown
Device monitors internal junction temperature independent of TS pin battery temperature monitor.
Thermal regulation limits charge current when IC temperature exceeds TREG (125°C).
Thermal shutdown turns off unit if IC temperature exceeds TSHUT (150°C). Device resumes charge when temperature falls below TSHUT falling threshold of 135°C