LT1769 Datasheet, PDF (1/16 Pages) Linear Technology – Constant-Current/ Constant-Voltage 2A Battery Charger with Input Current Limiting

LT1769
Constant-Current/
Constant-Voltage 2A Battery
Charger with Input Current Limiting
FEATURES
s _{Simple Solution to Charge NiCd, NiMH and Lithium}
Rechargeable Batteries—Charging Current
Programmed by Resistors or DAC
s _{Adapter Current Limit Allows Maximum Possible}
Charging Current During System Use*
s _{Precision 0.5% Accuracy for Voltage Mode Charging}
s _{High Efficiency Current Mode PWM with 3A Internal}
Switch
s _{5% Charge Current Accuracy}
s _{Adjustable Undervoltage Lockout}
s _{Automatic Shutdown When AC Adapter is Removed}
s _{Low Reverse Battery Drain Current: 3µA}
s _{Current Sensing Can Be at Either Terminal of the Battery}
s _{Charging Current Soft Start}
s _{Shutdown Control}
s _{Available in 28-Lead Narrow SSOP Package}
U
APPLICATIO S
s _{Chargers for NiCd, NiMH, Lead-Acid, Lithium}
Rechargeable Batteries
s _{Switching Regulators with Precision Current Limit}
, LTC and LT are registered trademarks of Linear Technology Corporation.
*US patent number 5,723,970
**See LT1510 for 1.5A charger; see LT1511 for 3A charger
DESCRIPTIO
The LT^®1769 current mode PWM battery charger is a
simple, efficient solution to fast charge modern recharge-
able batteries including lithium-ion (Li-Ion), nickel-metal-
hydride (NiMH) and nickel-cadmium (NiCd) that require
constant-current and/or constant-voltage charging. The
internal switch is capable of delivering 2A** DC current
(3A peak current). Charge current can be programmed by
resistors or a DAC to within 5%. With 0.5% reference voltage
accuracy, the LT1769 meets the critical constant-voltage
charging requirement for Li-Ion cells.
A third control loop is provided to regulate the current
drawn from the input AC adapter. This allows simulta-
neous operation of the equipment and battery charging
without overloading the adapter. Charge current is reduced
to keep the adapter current below specified levels.
The LT1769 can charge batteries ranging from 1V to 20V.
Ground sensing of current is not required and the battery’s
negative terminal can be tied directly to ground. A saturat-
ing switch running at 200kHz gives high charging effi-
ciency and small inductor size. A blocking diode is not
required between the chip and the battery because the
chip goes into sleep mode and drains only 3µA when the
wall adapter is unplugged.
TYPICAL APPLICATIO
D1^††
SS24
L1**
22µH
D2
1N4148
C2
0.47µF
2nF
10k
NOTE: COMPLETE LITHIUM-ION CHARGER,
NO TERMINATION REQUIRED. R_S4, R7
AND C1 ARE OPTIONAL FOR I_IN LIMITING
*TOKIN OR UNITED CHEMI-CON/MARCON
CERAMIC SURFACE MOUNT
**22µH SUMIDA CDRH125
†_{SEE APPLICATIONS INFORMATION FOR}
INPUT CURRENT LIMIT AND UNDERVOLTAGE LOCKOUT
††_{GENERAL SEMICONDUCTOR. FOR TJ LESS THEN 100°C}
MBRS130LT3 CAN BE USED
GND
CLP
SW
CLN
V_CC
BOOST
LT1769
COMP1
UV
SPIN
PROG
V_C
OVP SENSE BAT
R_S3
200Ω
1%
R_S2
200Ω
1%
R_S1
0.05Ω
BATTERY CURRENT
SENSE
C_IN*
15µF
R7^†
500Ω
C1
1µF
0.33µF
300Ω
C_PROG
1µF
R3
+
390k
0.25%
BATTERY
VOLTAGE SENSE
R4
162k
0.25%
C_OUT
22µF
TANT
D3^††
SS24
R_S4^†
ADAPTER
CURRENT SENSE
V_IN (ADAPTER INPUT)
11V TO 28V
TO MAIN
R5^{† SYSTEM LOAD}
UNDERVOLTAGE
LOCKOUT
R6
5k
R_PROG
4.93k
1%
8.4V
Li-Ion
V_BAT
1511 • F01
Figure 1. 2A Lithium-Ion Battery Charger
1