Datasheet

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LT1505

1505fc

TYPICAL APPLICATION

DESCRIPTIO

FEATURES

APPLICATIO S

Constant-Current/Voltage

High Efficiency Battery Charger

Figure 1. Low Dropout 4A Lithium-Ion Battery Charger

■

Simple Charging of Li-Ion, NiMH and NiCd Batteries

■

Very High Efficiency: Up to 97%

■

Precision 0.5% Charging Voltage Accuracy

■

Preset Battery Voltages: 12.3V, 12.6V,

16.4V and 16.8V

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5% Charging Current Accuracy

■

Charging Current Programmed by Resistor or DAC

■

0.5V Dropout Voltage, Duty Cycle > 99.5%

■

AC Adapter Current Limit* Maximizes Charging Rate

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Flag Indicates Li-Ion Charge Completion

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Auto Shutdown with Adapter Removal

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Only 10µA Battery Drain When Idle

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Synchronizable Up to 280kHz

The LT

1505 PWM battery charger controller fast charges

multiple battery chemistries including lithium-ion (Li-Ion),

nickel-metal-hydride (NiMH) and nickel-cadmium (NiCd)

using constant-current or constant-voltage control. Maxi-

mum current can be easily programmed by resistors or a

DAC. The constant-voltage output can be selected for 3 or 4

series Li-Ion cells with 0.5% accuracy.

A third control loop limits the current drawn from the AC

adapter during charging*. This allows simultaneous opera-

tion of the equipment and fast battery charging without over-

loading the AC adapter.

The LT1505 can charge batteries ranging from 2.5V to 20V

with dropout voltage as low as 0.5V. Synchronous

N-channel FETs switching at 200kHz give high efficiency

and allow small inductor size. A diode is not required in

series with the battery because the charger automatically

enters a 10µA sleep mode when the wall adapter is un-

plugged. A logic output indicates Li-Ion full charge when

current drops to 20% of the programmed value.

The LT1505 is available in a 28-pin SSOP package.

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Notebook Computers

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Portable Instruments

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Chargers for Li-Ion, NiMH, NiCd and Lead Acid

Rechargeable Batteries

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

5Ω

PROG

1µF

300Ω

0.68µF

0.1µF

2.2µF

OUT

22µF

25V

×2

0.68µF

BAT

12.6V

BATTERY

* DBODY IS THE BODY DIODE OF M3

: SANYO OS-CON

L1: SUMIDA CDRH127-150

(CAN BE FROM 10µH TO 30µH)

Si4412

MBRS140

MMSD4148T1

500Ω

100k

*BODY DIODE

POLARITY MUST

BE AS SHOWN

0.025Ω

Si4435

DBODY*

SYSTEM POWER

(FROM

ADAPTER)

0.025Ω

15µH

1505 F01

PROG

4.93k

0.33µF

200Ω

47µF

35V

1µF

0.1µF

BAT2 BAT SENSE

LT1505

BOOST BOOSTC

SPIN

PGND

AGND

4.1V

4.2V

3 CELL

PROG

BGATE

COMP1

CAP

FLAG

SHDN

SYNC

INFET

TGATE

GBIAS

CLP

CLN

*US Patent No. 5,723,970

Summary of content (16 pages)

PAGE 1
LT1505 Constant-Current/Voltage High Efficiency Battery Charger DESCRIPTIO U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ The LT®1505 PWM battery charger controller fast charges multiple battery chemistries including lithium-ion (Li-Ion), nickel-metal-hydride (NiMH) and nickel-cadmium (NiCd) using constant-current or constant-voltage control. Maximum current can be easily programmed by resistors or a DAC. The constant-voltage output can be selected for 3 or 4 series Li-Ion cells with 0.5% accuracy.
PAGE 2
LT1505 U W W W ABSOLUTE MAXIMUM RATINGS (Note 1) VCC, CLP, CLN, INFET, UV, 3CELL, FLAG................ 27V SW Voltage with Respect to GND ........................... – 2V BOOST, BOOSTC Voltage with Respect to VCC ....... 10V GBIAS ..................................................................... 10V SYNC, BAT2, BAT, SENSE, SPIN ............................ 20V VC, PROG, VFB, 4.1V, 4.2V ........................................ 7V CAP, SHDN ..........................................................
PAGE 3
LT1505 ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 18V, VBAT = 12.6V, VCLN = VCC (LT1505), no load on any outputs unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS Preset Battery Voltage (12.3V, 16.4V, 12.6V, 16.8V) All Preset Battery Voltages Measured at BAT2 Pin Preset Battery Voltage Tolerance (VBAT + 0.3V) ≤ VCC ≤ 24V ● 0.
PAGE 4
LT1505 ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 18V, VBAT = 12.6V, VCLN = VCC (LT1505), no load on any outputs unless otherwise noted. PARAMETER Voltage Amplifier VA Transconductance (Note 3) CONDITIONS MIN TYP MAX UNITS 0.6 1.0 mho 25 mA nA Output Current from 50µA to 500µA 0.21 VFB = VPROG = VREF + 10mV At 0.5mA VA Output Current, TA < 70°C (3 CELL, 4.1V, 4.
PAGE 5
LT1505 U W TYPICAL PERFORMANCE CHARACTERISTICS Efficiency of Figure 1 Circuit VGBIAS vs IGBIAS 105 VIN = 19V VBAT = 12.6V 0.003 0°C 9.1 100 0°C ≤ TJ ≤ 125°C 25°C 0.002 9.0 125°C 8.9 90 0.001 8.8 ∆VREF (V) 95 VGBIAS (V) EFFICIENCY (%) VREF Line Regulation 9.2 8.7 8.6 0 –0.001 8.5 85 ALL TEMPERATURES 8.4 –0.002 8.3 80 –0.003 8.
PAGE 6
LT1505 U U U PIN FUNCTIONS BOOST (Pin 1): This pin is used to bootstrap and supply power for the topside power switch gate drive and control circuity. In normal operation, VBOOST is powered from an internally generated 8.6V regulator VGBIAS, VBOOST ≈ VCC + 9.1V when TGATE is high. Do not force an external voltage on BOOST pin. TGATE (Pin 2): This pin provides gate drive to the topside power FET. When TGATE is driven on, the gate voltage will be approximately equal to VSW + 6.6V.
PAGE 7
LT1505 U U U PIN FUNCTIONS the noninverting input to the amplifier, VA in the Block Diagram, that controls the charging current when the device operates in constant voltage mode. The amplifier VA controls the charging current to maintain the voltage on the VFB pin at the reference voltage (2.465V). Input bias current for VA is approximately 3nA. The LT1505 incorporates a resistor divider that can be used to select the correct voltage for either three or four 4.1V or 4.2V lithium-ion cells.
PAGE 8
LT1505 W BLOCK DIAGRAM (LT1505) VIN VCC 8 VCC INFET + VCC UV – 7 E8 – + 7.8V + E2 6.7V + Q4 A13 VCC 6.7V SHUTDOWN E3 + + BAT 0.2V – VCC 24 E1 A1 50k 3 – SW E7 + – BGATE A4 + A3 + + + – 4U 2.5V 4V 26 + A6 S 27 A9 R A7 ONE SHOT 28 + – 25 A12 Q2 Q3 22 + 0.02V + IVA 4 Q1 21 BGATE RS1 – + 12.6V BATTERY M2 PGND BOOSTC SPIN SENSE RS3 BAT RS2 IPROG CA1 – SLOPE COMP CAP 12 IBAT VRS1 50k A10 OSC 200k VRS1 GBIAS + A5 A8 1.
PAGE 9
LT1505 TEST CIRCUITS Test Circuit 1 SPIN LT1505 + – VC CA1 CA2 1k + 75k 0.047µF – SENSE RS3 200Ω BAT RS2 200Ω RS1 10Ω + VBAT VREF PROG 1µF RPROG 300Ω + LT1006 1k 1505 TC01 – + ≈ 0.65V 20k Test Circuit 2 LT1505 VFB OR BAT2 + VA – VREF PROG IPROG 2k 0.47µF RPROG – + + 2nF LT1013 1505 TC02 2.465V Test Circuit 3 LT1505 + CAP IVA 4 0.047µF – FLAG IPROG E6 2V 1k + – + + RS2 VRS1 200Ω – 10Ω + VBAT + VFB VA – IVA LT1013 BAT IPROG 3.3V 0.
PAGE 10
LT1505 U OPERATION The LT1505 is a synchronous current mode PWM stepdown (buck) switcher. The battery DC charge current is programmed by a resistor RPROG (or a DAC output current) at the PROG pin and the ratio of sense resistors RS2 over RS1 (see Block Diagram). Amplifier CA1 converts the charge current through RS1 to a much lower current IPROG (IPROG = IBAT • RS1/RS2) fed into the PROG pin.
PAGE 11
LT1505 U W U U APPLICATIONS INFORMATION EMI considerations usually make it desirable to minimize ripple current in the battery leads. Beads or inductors may be added to increase battery impedance at the 200kHz switching frequency. Switching ripple current splits between the battery and the output capacitor depending on the ESR of the output capacitor and the battery impedance. If the ESR of COUT is 0.
PAGE 12
LT1505 U U W U APPLICATIONS INFORMATION This is accomplished by sensing total adapter output current and adjusting charge current downward if a preset adapter current limit is exceeded. True analog control is used, with closed loop feedback ensuring that adapter load current remains within limits. Amplifier CL1 in Figure 2 senses the voltage across RS4, connected between the CLP and CLN pins.
PAGE 13
LT1505 U U W U APPLICATIONS INFORMATION Preset Battery Voltage Settings Lithium-Ion Charging Completion The LT1505 provides four preset battery voltages: 12.3V, 12.6V, 16.4V and 16.8V. See the Pin Functions section for pin setting voltage selection. An internal switch connects the resistor dividers to the battery sense pin, BAT2. When shutting down the LT1505 by removing adaptor power or by pulling the SHDN pin low, the resistor dividers will be disconnected and will not drain the battery.
PAGE 14
LT1505 U W U U APPLICATIONS INFORMATION amplifier CA1. They are not needed if VCC is at least 2.5V higher than VBAT. The PFET M3 is optional and can be replaced with a diode if VIN is at least 3V higher than VBAT. The gate control pin INFET turns on M3 when VIN gets up above the undervoltage lockout level set by R5 and R6 and is clamped internally to 8V below VCC. In sleep mode when VIN is removed, INFET will clamp M3 VSG to 0.2V.
PAGE 15
LT1505 U W U U APPLICATIONS INFORMATION All battery chargers with fast charge rates require some means to detect full charge state in the battery to terminate the high charge current. NiCd batteries are typically charged at high current until temperature rise or battery voltage decrease is detected as an indication of near full charge. The charge current is then reduced to a much lower value and maintained as a constant trickle charge.
PAGE 16
LT1505 U PACKAGE DESCRIPTION G Package 28-Lead Plastic SSOP (5.3mm) (Reference LTC DWG # 05-08-1640) 10.07 – 10.33* (.397 – .407) 28 27 26 25 24 23 22 21 20 19 18 17 16 15 7.65 – 7.90 (.301 – .311) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 5.20 – 5.38** (.205 – .212) 1.73 – 1.99 (.068 – .078) 0° – 8° .13 – .22 (.005 – .009) .65 (.0256) BSC .55 – .95 (.022 – .037) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS MILLIMETERS 2. DIMENSIONS ARE IN (INCHES) .25 – .38 (.010 – .015) .05 – .21 (.002 – .