LT1620/LT1621
Rail-to-Rail Current
Sense Amplifier
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DESCRIPTIO
FEATURES
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Accurate Output Current Programming
Usable in Charging Applications Up to 32V Output
Programmable Load Current Monitor for End-ofCharging-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
Can be Used for NiCd, NiMH, Lead-Acid and LithiumIon Battery Charging
Greater than 96% Efficiency Possible in Charger
Applications
High Output Currents Possible: > 10A
Easily Obtained
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APPLICATI
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High Current Battery Chargers
High Output Voltage DC/DC Converters
Constant Current Sources
Overcurrent Fault Protectors
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 restriction 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 programmable 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.
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TYPICAL APPLICATI
(VBATT + 0.5V) TO 32V
VIN
LTC1435
SYNCHRONOUS
BUCK
REGULATOR
0.1µF
6
VCC
1
8
SENSE
AVG
2
7
IOUT
PROG
LT1620MS8
3
GND
4
5
IN –
IN +
Efficiency
100
VBATT
27µH
VIN = 24V
IBATT TO 4A
SW
SENSE –
INTVCC
VIN
22µF
35V
×2
0.025Ω
1.43M
0.1%
FB
0.1µF
110k
0.1%
3k
1%
VBATT = 16V
95
VBATT = 12V
+
22µF
35V
EFFICIENCY (%)
ITH
+
90
VBATT = 6V
85
80
15.75k
1%
75
LT1620/21 • F01
SIMPLIFIED SCHEMATIC. SEE FIGURE 2 FOR COMPLETE SCHEMATIC
Figure 1. Low Dropout, High Current Li-Ion Battery Charger
0
1
3
4
2
BATTERY CHARGE CURRENT (A)
5
1620/21 • TA02
1