1

LT1620/LT1621

Rail-to-Rail Current

Sense Amplifier

S

FEATURE

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

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Level-Shifted Current Sense Output for Current Mode

PWM Controllers

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Can be Used for NiCd, NiMH, Lead-Acid and Lithium-

Ion Battery Charging

s

Greater than 96% Efficiency Possible in Charger

Applications

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High Output Currents Possible: > 10A

Easily Obtained

DESCRIPTIO

The LT

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.

APPLICATI

TYPICAL

, LTC and LT are registered trademarks of Linear Technology Corporation.

BATTERY CHARGE CURRENT (A)

0

90

95

100

4

1620/21 • TA02

85

80

75

1

2

3

5

Efficiency

Figure 1. Low Dropout, High Current Li-Ion Battery Charger

FB

LTC1435

SYNCHRONOUS

BUCK

REGULATOR

AVG

SENSE

LT1620MS8

GND

18

6

3

LT1620/21 • F01

PROG

45

27

SIMPLIFIED SCHEMATIC. SEE FIGURE 2 FOR COMPLETE SCHEMATIC

0.1

µF

15.75k

1%

3k

1%

0.1

µF

SW

27

µH

0.025

Ω

22

µF

35V

× 2

1.43M

0.1%

110k

0.1%

22

µF

35V

+

+

S

APPLICATI

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High Current Battery Chargers

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High Output Voltage DC/DC Converters

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Constant Current Sources

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Overcurrent Fault Protectors