LTC1732-4 LINER [Linear Technology], LTC1732-4 Datasheet - Page 10

• Manufacturer Part Number: LTC1732-4
• Description: Lithium-Ion Linear Battery Charger Controller
• Manufacturer: LINER [Linear Technology]

LTC1732-4/LTC1732-4.2
APPLICATIONS
Gate Drive
Typically the LTC1732 controls an external P-channel
MOSFET to supply current to the battery. An external PNP
transistor can also be used as the pass transistor instead
of the P-channel MOSFET. Due to the low transconductance
of the current amplifier (CA), a high gain Darlington PNP
transistor is required to avoid excessive charge current
error. The transconductance of the current amplifier is
around 0.6 A/mV. For every 1 A of base current, a 1.6mV
of gain error shows up at the inputs of CA. With R
19.6k (100mV across R
error in charge current.
Constant-Current Only Mode
The LTC1732 can be used as a programmable current
source by connecting the TIMER pin to V
particularly useful for charging NiMH or NiCd batteries. In
the constant-current only mode, the timer and voltage
amplifier are both disabled. An external termination method
10
TYPICAL APPLICATIO S
U
SENSE
INFORMATION
U
). This represents a 1.6%
C
TIMER
0.1 F
R1
1k
U
W
R2
1k
Li-Ion Linear Charger Using a PNP Transistor
10
3
4
CHRG
ACPR
TIMER
SEL
LTC1732-4
CC
2
V
U
CC
. This is
8
SENSE
PROG
GND
PROG
DRV
BAT
5
9
7
1
6
=
R
19.6k
PROG
C1
1nF
is required to properly terminate the charging by floating
the PROG pin.
Stability
The charger is stable without any compensation when a
P-channel MOSFET is used as the pass transistor and
the battery is present. A 10 F tantalum capacitor is
recommended at the BAT pin to keep the ripple voltage
low when the battery is disconnected. A ceramic output
capacitor may also be used, but because of the very low
ESR and high Q characteristics of multilayer ceramic
capacitors, it may be necessary to add a 1 resistor in
series with the ceramic capacitor to improve voltage
mode stability.
If a PNP transistor is used for the pass transistor, a 1000pF
capacitor is required from the DRV pin to V
stablize the voltage loop a 10 F tantalum capacitor at the
BAT pin is also recommended when a battery is not
present.
Q1
2N5087
R3
10k
V
IN
= 6V
Q2
ZTX749
R
0.2
I
SENSE
MBRM120T3
BAT
C2
10 F
= 500mA
+
1732 TA02
C3
1 F
4.1V
Li-Ion
CELL
CC
. To help