LTC4015_15 Datasheet, PDF (30/76 Pages) Linear Technology – Multichemistry Buck Battery Charger Controller with Digital Telemetry System

LTC4015
Operation
Battery Detection
The LTC4015 begins a charging cycle by performing a
two to four second battery detection test, during which
a 1mA load is drawn from the battery. If the battery volt-
age remains stable during the battery detection test, the
LTC4015 proceeds with battery charger soft-start. If the
battery voltage does not remain stable, the LTC4015
proceeds with a battery open/short test. The battery is
charged at minimum charge current for one to two seconds.
If the battery voltage as a result of this brief charging is
within a reasonable range the LTC4015 will proceed with
a battery charger soft-start. A battery open fault will also
occur if the NTC resistor is open or has a very high value.
A programmable interrupt can be set to alert the system
if a battery detection fault has occurred.
Battery Charger Soft-Start
The LTC4015 soft starts by ramping ICHARGE_DAC from
0 to ICHARGE_TARGET at a nominal rate of 400µs per
ICHARGE_TARGET LSB. This results in a maximum soft-
start time of 31 • 400µs = 12.4ms.
Maximum Charge Time
The LTC4015 for Li-Ion battery charging provides a
maximum charge time safety timer. The MAX_CHARGE_
TIMER starts with the battery charger soft-start after
battery detection. If the total time charging the battery
exceeds MAX_CHARGE_TIME, the charger will enter the
MAX_CHARGE_TIME FAULT state and cease charging.
This fault state can only be exited in normal operation if
the battery voltage is less than 35% of V_CHARGE, where
upon a new charge cycle begins and the timer reset.
The timer is reset upon timer or C/x termination. The
MAX_CHARGE_TIME fault state can also be exited as a
result of the input voltage V_IN falling to within 100mV of
the BATSENS pin voltage, SUSPEND_CHARGER is written
to a 1 via the serial port or a system fault occurs.
Low Battery/Pre-Charge; Li-Ion
When a Li-Ion battery charge cycle begins, the LTC4015
first determines if the battery is deeply discharged. If
the battery voltage is below 2.85V per cell (VBAT_FILT
below 14822) and BATSENS pin is above 2.6V then the
LTC4015 begins charging by applying a preconditioning
charge equal to ICHARGE_TARGET/10 (rounded down
to the next LSB), and reporting precharge = 1. When the
battery voltage exceeds 2.9V per cell (VBAT_FILT above
15082), the LTC4015 proceeds to the constant-current/
constant-voltage charging phase (cc_cv_charge = 1).
Should the BATSENS pin voltage be lower than 2.4V, the
switching charger operates in constant peak current mode,
where the peak current is 7mV/R_SNSB. Exact average cur-
rent value depends on a number of factors including input
voltage, battery voltage and inductance value. When the
BATSENS pin voltage is higher than 2.6V, normal charg-
ing proceeds.
Low Battery; LiFePO₄
Low battery for LiFePO₄ chemistry is the same as
Li-Ion with the exception that there is no precon-
ditioning charge phase; charge current is set by
ICHARGE_TARGET.
However, if the BATSENS pin voltage is lower than 2.4V,
the switching charger operates in constant peak current
mode, where the peak current is 7mV/R_SNSB. Exact average
current value depends on a number of factors including
input voltage, battery voltage and inductance value. When
the BATSENS pin voltage is higher than 2.6V, normal
charging proceeds.
LiFePO₄ Absorb Charge
The LTC4015 can optionally perform an accelerated absorb
charge cycle on LiFePO₄ batteries. If VABSORB_DELTA
is greater than zero, the LTC4015 begins charging with
an absorb charge phase, and reports absorb_charge = 1
4015f
30
For more information www.linear.com/LTC4015