LT1620/LT1621
Rail-to-Rail Current
Sense Amplifier
U
DESCRIPTIO
EATURE
S
F
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.
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Accurate Output Current Programming
Usable in Charging Applications Up to 32V Output
Programmable Load Current Monitor for End-of-
Charging-Cycle Notification (16-Pin Version)
Dual Function IC (LT1621) Allows Convenient
Integration of Load and Input Current Sensing
Level-Shifted Current Sense Output for Current Mode
PWM Controllers
TheLT1620regulatesaverageoutputcurrentindependent
of input and output voltage variations. Output current can
be easily adjusted via a programming voltage applied to
the LT1620’s PROG pin.
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Most current mode PWM controllers have limited output
voltagerangebecauseofcommonmodelimitationsonthe
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.
Can be Used for NiCd, NiMH, Lead-Acid and Lithium-
Ion Battery Charging
Greater than 96% Efficiency Possible in Charger
Applications
High Output Currents Possible: > 10A
Easily Obtained
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.
O U
PPLICATI
A
S
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High Current Battery Chargers
High Output Voltage DC/DC Converters
Constant Current Sources
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The LT1621 incorporates two fully independent current
control circuits for dual loop applications.
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Overcurrent Fault Protectors
, LTC and LT are registered trademarks of Linear Technology Corporation.
U
O
TYPICAL APPLICATI
(V
+ 0.5V) TO 32V
BATT
V
IN
V
IN
+
22µF
LTC1435
Efficiency
35V
SYNCHRONOUS
BUCK
100
95
× 2
V
= 24V
IN
I
TO 4A
V
= 16V
= 12V
BATT
BATT
REGULATOR
V
I
SW
BATT
TH
0.025Ω
–
1.43M
0.1%
27µH
SENSE
V
BATT
+
INTV
FB
CC
22µF
35V
90
V
= 6V
BATT
0.1µF
0.1µF
110k
0.1%
6
3k
1%
85
80
75
V
CC
1
2
8
SENSE
AVG
7
5
I
PROG
LT1620MS8
OUT
15.75k
1%
3
4
GND
–
+
IN
IN
0
1
2
3
4
5
LT1620/21 • F01
BATTERY CHARGE CURRENT (A)
SIMPLIFIED SCHEMATIC. SEE FIGURE 2 FOR COMPLETE SCHEMATIC
1620/21 • TA02
Figure 1. Low Dropout, High Current Li-Ion Battery Charger
1