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LT1769

1769fa

Constant-Current/

Constant-Voltage 2A Battery

Charger with Input Current Limiting

■

Simple Solution to Charge NiCd, NiMH and Lithium

Rechargeable Batteries—Charging Current

Programmed by Resistors or DAC

■

Adapter Current Limit Allows Maximum Possible

Charging Current During System Use*

■

Precision 0.5% Accuracy for Voltage Mode Charging

■

Available in 20-Lead Exposed Pad TSSOP and

28-Lead Narrow SSOP Packages

■

High Efficiency Current Mode PWM with 3A Internal

Switch

■

5% Charge Current Accuracy

■

Adjustable Undervoltage Lockout

■

Automatic Shutdown When AC Adapter is Removed

■

Low Reverse Battery Drain Current: 3µA

■

Current Sensing Can Be at Either Terminal of the Battery

■

Charging Current Soft Start

■

Shutdown Control

The LT

1769 current mode PWM battery charger is a

simple, efficient solution to fast charge modern recharge-

able batteries including lithium-ion (Li-Ion), nickel-metal-

hydride (NiMH) and nickel-cadmium (NiCd) that require

constant-current and/or constant-voltage charging. The

internal switch is capable of delivering 2A** DC current

(3A peak current). Charge current can be programmed by

resistors or a DAC to within 5%. With 0.5% reference voltage

accuracy, the LT1769 meets the critical constant-voltage

charging requirement for Li-Ion cells.

A third control loop is provided to regulate the current

drawn from the input AC adapter. This allows simulta-

neous operation of the equipment and battery charging

without overloading the adapter. Charge current is reduced

to keep the adapter current below specified levels.

The LT1769 can charge batteries ranging from 1V to 20V.

Ground sensing of current is not required and the battery’s

negative terminal can be tied directly to ground. A saturat-

ing switch running at 200kHz gives high charging effi-

ciency and small inductor size. A blocking diode is not

required between the chip and the battery because the

chip goes into sleep mode and drains only 3µA when the

wall adapter is unplugged.

Figure 1. 2A Lithium-Ion Battery Charger

■

Chargers for NiCd, NiMH, Lead-Acid, Lithium

Rechargeable Batteries

■

Switching Regulators with Precision Current Limit

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

*US patent number 5,723,970

**See LT1510 for 1.5A charger; see LT1511 for 3A charger

FEATURES

DESCRIPTIO

APPLICATIO S

TYPICAL APPLICATIO

BOOST

COMP1

CLN

OVP SENSE BAT

1µF

†

ADAPTER

CURRENT SENSE

†

500Ω

†

UNDERVOLTAGE

LOCKOUT

(ADAPTER INPUT)

11V TO 28V

BAT

PROG

1µF

15µF

300Ω

PROG

4.93k

0.33µF

0.47µF

200Ω

L1**

22µH

1N4148

2nF

10k

0.05Ω

BATTERY CURRENT

SENSE

390k

0.25%

BATTERY

VOLTAGE SENSE

162k

0.25%

OUT

22µF

TANT

8.4V

Li-Ion

LT1769

NOTE: COMPLETE LITHIUM-ION CHARGER,

NO TERMINATION REQUIRED. R

, R7

AND C1 ARE OPTIONAL FOR I

LIMITING

*TOKIN OR UNITED CHEMI-CON/MARCON

CERAMIC SURFACE MOUNT

**22µH SUMIDA CDRH125

†

SEE APPLICATIONS INFORMATION FOR

INPUT CURRENT LIMIT AND UNDERVOLTAGE LOCKOUT

††

GENERAL SEMICONDUCTOR. FOR T

LESS THEN 100°C

MBRS130LT3 CAN BE USED

TO MAIN

SYSTEM LOAD

SPIN

††

SS24

GND

CLP

††

SS24

1511 • F01

PROG

Summary of content (16 pages)

PAGE 1
LT1769 Constant-Current/ Constant-Voltage 2A Battery Charger with Input Current Limiting DESCRIPTIO U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ The LT®1769 current mode PWM battery charger is a simple, efficient solution to fast charge modern rechargeable batteries including lithium-ion (Li-Ion), nickel-metalhydride (NiMH) and nickel-cadmium (NiCd) that require constant-current and/or constant-voltage charging. The internal switch is capable of delivering 2A** DC current (3A peak current).
PAGE 2
LT1769 U W W W ABSOLUTE MAXIMUM RATINGS (Note 1) Supply Voltage (VCC, CLP and CLN Pin Voltage) ......................... 30V BOOST Pin Voltage with Respect to VCC ................. 25V IBAT (Average)........................................................... 2A Operating Junction Temperature Range Commercial ........................................... 0°C to 125°C Industrial ......................................... – 40°C to 125°C Operating Ambient Temperature Commercial ..............................
PAGE 3
LT1769 ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 16V, VBAT = 8V, RS2 = RS3 = 200Ω (see Block Diagram), VCLN = VCC. No load on any outputs unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS 6 7 8 V µA Overall VCC Undervoltage Lockout (Switch OFF) Threshold Measured at UV Pin ● UV Pin Input Current 0.2V ≤ VUV ≤ 8V ● 0.
PAGE 4
LT1769 ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 16V, VBAT = 8V. No load on any outputs unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS Transconductance (Note 3) Output Current from 50µA to 500µA 0.25 0.6 1.3 mho Output Source Current VOVP = VREF + 10mV, VPROG = VREF + 10mV 1.1 OVP Input Bias Current VA Output Current at 0.5mA VA Output Current at 0.
PAGE 5
LT1769 U W TYPICAL PERFORMANCE CHARACTERISTICS IVA vs ∆VOVP (Voltage Amplifier) VREF Line Regulation 0.003 4 0.002 3 ALL TEMPERATURES ∆VOVP (mV) ∆VREF (V) 0.001 0 2 TJ = 125°C –0.001 1 –0.002 –0.003 TJ = 25°C 0 10 5 15 VCC (V) 20 25 0 30 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 IVA (mA) 1769 G04 1769 G05 Maximum Duty Cycle VC Pin Characteristics 98 –1.20 –1.08 97 –0.96 –0.84 –0.72 95 IVC (mA) DUTY CYCLE (%) 96 94 –0.60 –0.48 93 –0.36 92 –0.24 –0.
PAGE 6
LT1769 U U U PIN FUNCTIONS (GN/FE Pin Numbers) GND (Pins 1 to 3, 7, 8, 14, 15, 22, 26 to 28/Pins 4, 5, 14, 20): Ground Pins. Must be connected to expanded PC lands for proper heat sinking. See Applications Information section for details. SW (Pin 4/Pin 1): Switch Output. The Schottky catch diode must be placed with very short lead length in close proximity to SW pin and GND.
PAGE 7
LT1769 W BLOCK DIAGRAM – UV UVOUT + + 7V 200kHz OSCILLATOR + SHUTDOWN 0.7V + VCC – VSW S BOOST – VCC R R + + SLOPE COMPENSATION SW 1.5V VCC SPIN VBAT – PWM C1 – + B1 + GND QSW R R2 + SENSE RS3 – BAT RS2 CA1 IPROG R1 1k R3 0VP – VA CA2 + 75k RS1 BAT + VC IBAT gm = 0.64 VREF Ω – VREF 2.465V 100mV + CLP + CL1 – CLN COMP1 COMP2 PROG CPROG IPROG RPROG )(R ) (I IBAT = PROG S2 RS1 RS2 = 2.
PAGE 8
LT1769 TEST CIRCUITS Test Circuit 1 SPIN LT1769 CA1 CA2 1k + 0.047µF + – VC 60k – SENSE RS3 200Ω BAT RS2 200Ω RS1 100Ω + VBAT VREF PROG 1µF RPROG 300Ω + LT1006 1k + 1769 TC01 – ≈ 0.65V 20k Test Circuit 2 LT1769 OVP + VA – VREF PROG 10k IPROG 10k 0.47µF RPROG – + + LT1013 2.465V 1769 TC02 U OPERATION The LT1769 is a current mode PWM step-down (buck) switcher.
PAGE 9
LT1769 U U W U APPLICATIONS INFORMATION Input and Output Capacitors In the 2A Lithium-Ion Battery Charger (Figure 1), the input capacitor (CIN) is assumed to absorb all input switching ripple current in the converter, so it must have adequate ripple current rating. Worst-case RMS ripple current will be equal to one half of the output charge current. Actual capacitance value is not critical.
PAGE 10
LT1769 U U W U APPLICATIONS INFORMATION VUV = Rising lockout threshold on the UV pin VIN = Charger input voltage that will sustain full load power Example: With R6 = 5k, VUV = 6.7V and setting VIN at 12V; R5 = 5k (12V – 6.7V)/6.7V = 4k The resistor divider should be connected directly to the adapter output as shown, not to the VCC pin, to prevent battery drain with no adapter voltage.
PAGE 11
LT1769 U U W U APPLICATIONS INFORMATION LT1769 PROG 300Ω Q3 VN2222 LT1769 RPROG 4.7k 5V 0V CPROG 1µF 8.4V VIN R5 220k OVP R4 4.99k 0.25% Q1 VN2222 PWM IBAT = (DC)(2A) VBAT + R3 12k 0.25% 1769 F04 1769 F03 Figure 3. PWM Current Programming Figure 4. Disconnecting Voltage Divider holding the battery at “float” voltage indefinitely. In this case no external sensing of full charge is needed.
PAGE 12
LT1769 U U W U APPLICATIONS INFORMATION charger may be turned on periodically to complete a short float-voltage cycle. Current trip level is determined by the battery voltage, R1 through R3 and the sense resistor (RS1). D2 generates hysteresis in the trip level to avoid multiple comparator transitions. Nickel-Cadmium and Nickel-Metal-Hydride Charging The 2A Lithium-Ion Battery Charger shown in Figure 1 can be modified to charge NiCd or NiMH batteries.
PAGE 13
LT1769 U U W U APPLICATIONS INFORMATION Example: VIN = 19V, VBAT = 12.6V, IBAT = 2A: SW PBIAS = (3.5mA )(19) + 1.5mA(12.6) 2 12.6) ( + 19 C2 [7.5mA + (0.012)(2000mA)] = 0.35W (2)(12.6)2  1+ 1230.6  = 0.43W PDRIVER = 55(19) 2 2) (0.16)(12.6) ( + 10 −9 (19)(2)(200kHz) PSW = 19 = 0.42 + 0.08 = 0.5W Total Power in the IC is: 0.35 + 0.43 + 0.5 = 1.3W Temperature rise will be (1.3W)(35°C/W) = 46°C.
PAGE 14
LT1769 U U W U APPLICATIONS INFORMATION STANDARD CONNECTION THERMAL RESISTANCE (°C/W) 45 40 SW C3 0.47µF 35 C3 0.47µF BOOST LT1769 D2 30 HIGH DUTY CYCLE CONNECTION D2 SPIN SENSE VX 3V TO 6V BAT SENSE BAT CX 10µF 4-LAYER BOARD 20 VBAT MEASURED FROM AIR AMBIENT TO DIE USING COPPER LANDS AS SHOWN ON DATA SHEET 15 BOOST LT1769 SPIN 2-LAYER BOARD 25 SW VBAT + + 10 0 5 20 15 25 10 BOARD AREA (IN2) 30 35 1769 F10 1769 F08 Figure 10. High Duty Cycle Figure 8.
PAGE 15
LT1769 U U W U APPLICATIONS INFORMATION Optional Diode Connections Layout Considerations The typical application in Figure 1 shows a single diode (D3) to isolate the VCC pin from the adaptor input and to block reverse input voltage (both steady state and transient). This simple connection may be unacceptable in situations where the system load must be powered from the battery when the adapter input power is removed.
PAGE 16
LT1769 U PACKAGE DESCRIPTION FE Package 20-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1663) Exposed Pad Variation CB 3.86 (.152) 6.60 ±0.10 2.74 (.108) 4.50 ±0.10 SEE NOTE 4 0.45 ±0.05 1.05 ±0.10 6.40 – 6.60* (.252 – .260) 3.86 (.152) 0.65 BSC RECOMMENDED SOLDER PAD LAYOUT 1.20 (.047) MAX 4.30 – 4.50* (.169 – .177) 20 1918 17 16 15 14 13 12 11 0° – 8° 0.09 – 0.20 (.0036 – .0079) 0.65 (.0256) BSC 0.45 – 0.75 (.018 – .030) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS MILLIMETERS 2.