Rainbow Electronics MAX8922L - Manual (Page 7)

Detailed Description
The MAX8922L is designed to charge a single-cell Li+
battery from a DC source voltage between 4.45V and
7V, while V
IN can withstand up to 30V. The fast-charge
current and top-off current thresholds are programma-
ble with EN/SET, SETI, and MIN.
Charger-Enable and Program Input
(
EN/SET)
EN/SET is an active-low logic input that enables the
charger. Drive EN/SET high longer than 4ms to disable
the charger-control circuitry. If EN/SET is left uncon-
nected, an internal 2M
Ω pulldown resistor enables
400mA fast-charge current by default. The pulse pro-
gramming scheme shown in Table 1 and Figure 3 is
used to program the charge current and GSM test
mode. There are four different fast-charge current
states. Default fast-charge current state is 400mA
mode. More than three pulses are interpreted to 90mA
mode. After programming is locked, the MAX8922L
ignores pulses until the IC is disabled/enabled or input
power is cycled. Each fast-charge state is locked after
a 4ms logic-low is asserted on EN/SET, followed by
programming pulses. However, during default mode, if
EN/SET does not receive any pulses, the charger stays
in default mode unlocked indefinitely.
Debounce Timer
To prevent the MAX8922L from charging the battery
momentarily upon IN power-up with EN/SET held low, a
2ms (typ) debounce timer delays the charging loop
upon power-up. If EN/SET is logic-low or unconnected
(pulled down by an internal pulldown resistor) during IN
power-up, the charger starts charging the battery 2ms
after V
UVLO < V IN < V OVP and V BAT + 250mV < V IN . If
EN/SET is logic-high during IN power-up, the charger
does not charge the battery.
Soft-Start
To prevent input transients, the rate of change of the
charge current is limited when the charger is turned on
or changes its current compliance. It takes approxi-
mately 250µs (typ) (t
SOFTSTART ) for the charger to go
from 0mA to the maximum fast-charge current.
Thermal-Limit Control
The MAX8922L features a thermal limit that reduces the
charge current when the die temperature exceeds
+105°C. As the temperature increases above +105°C,
the IC decreases the charge current by 28mA/°C.
Charge-Indicator Output (
CHG)
CHG is an open-drain output that indicates charger sta-
tus. CHG goes low during charging in prequalification
or fast-charge mode. The CHG internal open-drain
MOSFET turns off when the charge current reaches the
top-off threshold. The CHG status is latched after the
top-off threshold is reached. The latch can be reset as
follows:
• Disable and re-enable the MAX8922L.
• Input power is cycled.
• Battery-charge current increases greater than the
top-off threshold + hysteresis.
When the MAX8922L is used in conjunction with a
microprocessor, connect a pullup resistor between
CHG and the logic I/O voltage to indicate charge status
to the µP. Alternatively, CHG can sink 5mA or more for
an LED charge indicator.
MAX8922L
30V Li+ Linear Battery Charger
with GSM Test Mode in 3mm x 2mm TDFN
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CHARGE CURRENT DEFAULT
NUMBER OF PULSES + > 4ms
LOGIG-LOW
FAST-CHARGE CURRENT SETTING
One SETI, resistor programmable
Two 90mA
Three 2.3A (GSM test)
I BAT (mA) 400mA
Four and more 90mA
Table 1. Charge-Current Pulse Settings