Datasheet

LTC4088
7
4088fb
Typical perForMance characTerisTics
T
A
= 25°C, unless otherwise noted.
CHRG Pin Current vs Voltage
(Pull-Down State)
3.3V LDO Transient Response
(5mA to 15mA)
Suspend LDO Transient Response
(500µA to 1mA)
CHRG PIN VOLTAGE (V)
0
CHRG PIN CURRENT (mA)
60
80
100
4
4088 G19
40
20
0
1
2
3
5
V
BUS
= 5V
V
BAT
= 3.8V
I
LDO3V3
5mA/DIV
0mA
20µs/DIVV
BAT
= 3.8V
4088 G20
V
LDO3V3
20mV/DIV
AC COUPLED
I
OUT
500µA/DIV
0mA
500µs/DIV
4088 G21
V
OUT
20mV/DIV
AC-COUPLED
pin FuncTions
NTC (Pin 1): Input to the NTC Thermistor Monitoring
Circuits. The NTC pin connects to a negative temperature
coefficient thermistor which is typically co-packaged with
the battery pack to determine if the battery is too hot or
too cold to charge. If the battery’s temperature is out of
range, charging is paused until the battery temperature re-
enters the valid range. A low drift bias resistor is required
from V
BUS
to NTC and a thermistor is required from NTC
to ground. If the NTC function is not desired, the NTC pin
should be grounded.
CLPROG (Pin 2): USB Current Limit Program and Monitor
Pin. A 1% resistor from CLPROG to ground determines
the upper limit of the current drawn from the V
BUS
pin.
A precise fraction of the input current, h
CLPROG
, is sent
to the CLPROG pin when the high side switch is on. The
switching regulator delivers power until the CLPROG
pin reaches 1.188V. Therefore, the current drawn from
V
BUS
will be limited to an amount given by h
CLPROG
and
R
CLPROG
. There are several ratios for h
CLPROG
available,
two of which correspond to the 500mA and 100mA USB
specifications. A multilayer ceramic averaging capacitor
is also required at CLPROG for filtering.
LDO3V3 (Pin 3): LDO Output. The LDO3V3 pin provides
a regulated, always-on 3.3V supply voltage. This pin gets
its power from V
OUT
. It may be used for light loads such
as a real-time clock or housekeeping microprocessor. A
1µF capacitor is required from LDO3V3 to ground if it will
be called upon to deliver current. If the LDO3V3 output is
not used it should be disabled by connecting it to V
OUT
.
D2 (Pin 4): Mode Select Input Pin. D2, in combination
with the D0 pin and D1 pin, controls the current limit and
battery charger functions of the LTC4088 (see Table 1).
This pin is pulled low by a weak current sink.
C/X (Pin 5): End of Charge Indication Program Pin. This pin
is used to program the current level at which a completed
charge cycle is indicated by the CHRG pin.
PROG (Pin 6): Charge Current Program and Charge Cur-
rent Monitor Pin. Connecting a 1% resistor from PROG
to ground programs the charge current. If sufficient input
power is available in constant-current mode, this pin servos
to 1V. The voltage on this pin always represents
the actual
charge current by using the following formula:
I
BAT
=
V
PROG
R
PROG
• 1031