LT1620/LT1621
Rail-to-Rail Current
Sense Amplifier
FEATURES
s Accurate Output Current Programming
s Usable in Charging Applications Up to 32V Output
s Programmable Load Current Monitor for End-of-
Charging-Cycle Notification (16-Pin Version)
s Dual Function IC (LT1621) Allows Convenient
Integration of Load and Input Current Sensing
s Level-Shifted Current Sense Output for Current Mode
PWM Controllers
s Can be Used for NiCd, NiMH, Lead-Acid and Lithium-
Ion Battery Charging
s Greater than 96% Efficiency Possible in Charger
Applications
s High Output Currents Possible: > 10A
Easily Obtained
APPLICATI S
s High Current Battery Chargers
s High Output Voltage DC/DC Converters
s Constant Current Sources
s Overcurrent Fault Protectors
DESCRIPTIO
The LT ®1620 simplifies the design of high performance,
controlled current battery charging circuits when used in
conjunction with a current mode PWM controller IC.
The LT1620 regulates average output current independent
of input and output voltage variations. Output current can
be easily adjusted via a programming voltage applied to
the LT1620’s PROG pin.
Most current mode PWM controllers have limited output
voltage range because of common mode limitations on the
current sense inputs. The LT1620 overcomes this restric-
tion by providing a level-shifted current sense signal,
allowing a 0V to 32V output voltage range.
The 16-pin version of the LT1620 contains a program-
mable low charging current flag output. This output flag
can be used to signal when a Li-Ion battery charging cycle
is nearing completion.
The LT1621 incorporates two fully independent current
control circuits for dual loop applications.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATI
VIN
LTC1435
SYNCHRONOUS
BUCK
REGULATOR
(VBATT + 0.5V) TO 32V
+ 22µF
35V
×2
VIN
IBATT TO 4A
6 0.1µF
1
VCC
SENSE
AVG
8
2 IOUT
PROG 7
LT1620MS8
3
GND
4 IN–
IN+ 5
ITH SW
SENSE–
27µH 0.025Ω
INTVCC
FB
0.1µF
3k
1%
15.75k
1%
1.43M
0.1%
+
110k
0.1%
22µF
35V
SIMPLIFIED SCHEMATIC. SEE FIGURE 2 FOR COMPLETE SCHEMATIC
LT1620/21 • F01
Figure 1. Low Dropout, High Current Li-Ion Battery Charger
VBATT
100
VIN = 24V
95
90
85
Efficiency
VBATT = 16V
VBATT = 12V
VBATT = 6V
80
75
0
1 2 34
BATTERY CHARGE CURRENT (A)
5
1620/21 • TA02
1
