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LT1620/LT1621

Rail-to-Rail Current

Sense Amplifier

■

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

■

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

ESCRIPTIO

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.

ITY

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

BATTERY CHARGE CURRENT (A)

EFFICIENCY (%)

100

1620/21 • TA02

= 24V

BATT

= 16V

BATT

= 12V

BATT

= 6V

Efficiency

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

LTC1435

SYNCHRONOUS

BUCK

REGULATOR

AVG



SENSE



LT1620MS8

GND

BATT

TO 4A

BATT

+ 0.5V) TO 32V

LT1620/21 • F01

–

OUT

PROG



SIMPLIFIED SCHEMATIC. SEE FIGURE 2 FOR COMPLETE SCHEMATIC

0.1µF

15.75k

3k

0.1µF

SENSE

–

INTV

27µH

0.025Ω

22µF

35V

× 2

1.43M

0.1%

110k

0.1%

22µF

35V

■

High Current Battery Chargers

■

High Output Voltage DC/DC Converters

■

Constant Current Sources

■

Overcurrent Fault Protectors

Summary of content (12 pages)

PAGE 1
LT1620/LT1621 Rail-to-Rail Current Sense Amplifier U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ ■ 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
PAGE 2
LT1620/LT1621 W W W AXI U U ABSOLUTE RATI GS (Referenced to Ground) (Note 1) Power Supply Voltage: VCC ..........................– 0.3V to 7V Programming Voltage: PROG, PROG2 ............ – 0.3V to VCC + 0.3V (7V Max) IOUT, SENSE, AVG, AVG2, MODE Voltage ................ – 0.3V to VCC + 0.3V (7V Max) Sense Amplifier Input Common Mode .......– 0.3V to 36V Operating Ambient Temperature Range Commercial ............................................ 0°C to 70°C Industrial .................................
PAGE 3
LT1620/LT1621 ELECTRICAL CHARACTERISTICS IN+ = 16.8V, VCC = 5V, VIOUT = 2V, TA = 25°C unless otherwise noted.
PAGE 4
LT1620/LT1621 U U U PI FU CTIO S input (across external sense resistor) equal to (VCC – VPROG)/10. Input voltage range is VCC to (VCC – 1.25V). equals (VCC – VPROG2)/20. Input voltage range is (VCC – 0.15V) to (VCC – 2.5V). AVG2: Sense Amplifier AV = – 20 Output and Comparator Positive Input. Used as integration node for end-of-cycle determination flag. Integration time constant is calculated using 5kΩ typical output impedance. GND: Ground Reference. PROG2: Comparator Negative Input.
PAGE 5
LT1620/LT1621 U OPERATION (Refer to the Functional Block Diagram) used as integration nodes to facilitate averaging of the current sense amplifier signal. (Note: filter capacitors on these pins should bypass to the VCC supply.) Integration of these signals enables direct sensing and control of DC load current, eliminating the inclusion of ripple current in load determination.
PAGE 6
LT1620/LT1621 U U W U APPLICATIONS INFORMATION + R2 1.5M C4 0.1µF RUN C11, 56pF C13 0.033µF X7R C12, 0.1µF COSC TG RUN/SS BOOST R1 1k SFB C9, 100pF 5 6 C18 0.1µF 7 8 RP1 3k 1% C16 0.1µF IN+ IN– VCC GND LT1620MS8 IOUT PROG AVG SENSE 4 C2 22µF 35V VIN 17.3V TO 28V RSENSE 0.025Ω VBATT 16.8V SW LTC1435 SGND C17, 0.01µF + Si4412DY L1 27µH D1* ITH C14 1nF C5, 0.1µF C1 22µF 35V VIN + D2* C6 0.
PAGE 7
LT1620/LT1621 U W U U APPLICATIONS INFORMATION between the IN+ and IN– inputs. Effective decoupling of supply rails is also imperative in these types of circuits, as large current transients are the norm. Power supply decoupling should be placed as close as possible to the ICs, and each IC should have a dedicated capacitor.
PAGE 8
LT1620/LT1621 U W U U APPLICATIONS INFORMATION reduces battery charging current until the external load subsides. In Figure 4 the LT1620 is coupled with an LT1513 SEPIC battery charger IC to create an input overcurrent protected charger circuit. The programming voltage (VCC – VPROG) is set to 1.0V through a resistor divider (RP1 and RP2) from the 5V input supply to ground.
PAGE 9
LT1620/LT1621 U W U U APPLICATIONS INFORMATION 40 20 VCC = 5V VID = 80mV VCM = 16.8V 20 VCC = 5V VCM = 16.8V IOUT = 130µA 10 VPROG OFFSET (mV) VPROG OFFSET (mV) 30 10 0 –10 0 –10 –20 –20 –30 –30 –40 50 0 100 200 150 IOUT SINK CURRENT (µA) –40 250 0 20 80 100 120 60 40 IN+ – IN– (VID) INPUT (mV) LT1620/21 • F05a LT1620/21 • F05b Figure 5a. Typical Setpoint Voltage (VPROG) Changes Slightly Depending Upon the Amount of Current Sinked by the IOUT Pin Figure 5b.
PAGE 10
LT1620/LT1621 U TYPICAL APPLICATIONS Programmable Constant Current Source D45VH10 6V TO 28V 0.1Ω IOUT 0A TO 1A 0.1µF 470Ω LT1121CS8-5 8 IN 0.1µF OUT SHDN 5 1 GND 3 SHUTDOWN + 0.1µF 1µF 18k 1 SENSE AVG 7 PROG LT1620MS8 3 6 VCC GND 2 VN2222LM 2N3904 22Ω 4 10k 1% 0.1µF 8 IOUT +IN –IN IPROG RPROG 5 IOUT = (IPROG)(10,000) RPROG = 40k FOR 1A OUTPUT LT1620/21 • TA01 High Efficiency Buck Constant Current Source 6V TO 15V 50µH CTX50-4 Si9405 + 22µF 25V TPS 0.05Ω + 4.
PAGE 11
LT1620/LT1621 U PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted. GN Package 16-Lead Plastic SSOP (Narrow 0.150) 0.189 – 0.196* (4.801 – 4.978) (LTC DWG # 05-08-1641) 16 15 14 13 12 11 10 9 0.015 ± 0.004 × 45° (0.38 ± 0.10) 0.0075 – 0.0098 (0.191 – 0.249) 0.229 – 0.244 (5.817 – 6.198) 0.053 – 0.069 (1.351 – 1.748) 0.150 – 0.157** (3.810 – 3.988) 0.004 – 0.009 (0.102 – 0.249) 0° – 8° TYP 0.016 – 0.050 (0.406 – 1.270) 0.025 (0.635) BSC 0.008 – 0.012 (0.203 – 0.
PAGE 12
LT1620/LT1621 U TYPICAL APPLICATION Electronic Circuit Breaker Si9434DY 0.033Ω 5V AT 1A PROTECTED 5V 0.1µF 1k FAULT CDELAY 100Ω 33k 2N3904 1 2 SENSE AVG 1N4148 8 7 PROG LT1620MS8 6 3 VCC GND 4 100k IOUT –IN +IN 4.7k 33k 5 TYPICAL DC TRIP AT 1.6A 3A FAULT TRIPS IN 2ms WITH CDELAY = 1.