LTC4110
20
4110fb
• The CAL_START bit in the BBuControl() register is set.
The LTC4110 enters the calibration state.
• The battery thermistor is registering RES_OR. The
LTC4110 enters the reset state.
LEAD ACID BATTERY CHARGE MODE
The charger is programmed for lead acid batteries by con-
necting the TYPE pin to a voltage derived from the V
REF
pin resistor divider of nominally 0.5 • V
REF
. During charge,
the LTC4110 operates as a high effi ciency, synchronous,
PWM fl yback battery charger with constant current and
constant fl oat voltage regions of operation. The constant-
charge current is programmed by the combination of a
resistor (R
CHG
) from the I
CHG
pin to ground, a battery
current sense resistor (R
SNS
) and CSP/CSN pin resistors.
The fl oat voltage is programmed to one of four values
(4.7V, 7.05V, 11.75V, 14.1V) depending on the number of
series cells (2, 3, 5 or 6) using the SELC pin and can be
adjusted ±0.15V/cell with the V
CHG
pin.
A new charge cycle begins with the charger in the bulk
charge current limited state. In this state, the charger is
a current source providing a constant charge rate and the
CHGb (GPIO1 pin) is forced low. No time limits are placed
upon lead acid battery charge. The charger monitors the
battery voltage and as it reaches the fl oat voltage the
charger begins its fl oat charge. While in fl oat, the charge
current diminishes as the battery accepts charge. Float
voltage temperature compensation and temperature fault
monitoring, if desired, are accomplished with an external
thermistor network.
Charge is active when the supply input is present as sensed
by the DCDIV pin and DCIN above UVLO, thermistor
temperature is ideal according to the thermistor monitor
circuit (see SafetySignal Decoder) and the charge register
bit CHARGE_INHIBIT is cleared. Soft-start ramps the charge
current at a rate set by the capacitor on the I
TH
pin. When
charge begins, the CHGb (GPIO1 pin) status output is
forced to GND. At any time charge can be forced to stop by
pulling the SHDN pin high or setting the CHARGE_INHIBIT
bit high through the SMBus.
If the battery voltage exceeds 107.5% (V
BOV
) of the pro-
grammed fl oat voltage during any stage of charge, the
charger pauses until the voltage drops below the hysteresis
(V
BOVH
). No fault is indicated.
An optional external NTC thermistor network can be used
to provide an adjustable negative TC for the fl oat voltage,
monitor battery temperature and to detect battery pres-
ence. If the thermistor value indicates a hot temperature,
voltage falling to V
HOT
on THB pin, charge current is halted,
CHG_FLTb (GPIO3 pin) is forced low and the CHG_FLT bit
will be set high. CHGb (GPIO1 pin) and CHG_STATE_0 and
CHG_STATE_1 register bits will not be affected. When the
thermistor value returns to ideal when the voltage exceeds
V
HOT
+V
HOTH
on THB pin, charge resumes CHG_FLTb
(GPIO3 pin) returns to high impedance and the CHG_FLT
bit will be reset low. An open thermistor indicates an
over-range which is considered absence of a battery.
Low temperature is not monitored. However, since bat-
tery removal detection looks at the thermistor for a high
resistance (V
REM
on THB pin), extremely cold temperatures
may result in an indication of battery absence. To defeat
the temperature monitoring register, replace the thermis-
tor with a resistor to indicate normal battery temperature.
When a thermistor is not used the resistor circuit must be
routed through the battery connector if battery presence
detection is required.
BATTERY CALIBRATION MODE
Figure 6 shows the LTC4110 in battery calibration mode and
the corresponding PowerPath enabled. During calibration,
the host CPU can calibrate a gas gauge or verify the battery’s
ability to support a load by use of a low heat producing
method. Calibration requires a host to communicate over
a SMBus. In the low heat method, a synchronous PWM
fl yback charger is used in reverse to discharge the battery
with a programmable constant-current into the system
load thereby saving space and eliminating heat generation
compared with resistive loads. Protection circuits prevent
accidental overdrive back into the power source if the
system load is insuffi cient. The constant-charge current
is programmed by the combination of a resistor (R
CAL
)
from the I
CAL
pin to ground, a battery current sense resis-
tor (R
SNS(BAT)
) and CSP/CSN pin resistors. Calibration is
initiated by setting the CAL_START bit in the BBuControl()
register. The CAL_ON bit in the BBuStatus() register will
OPERATION
