Datasheet

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LTC4001

4001f

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Handheld Battery-Powered Devices

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Handheld Computers

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Charging Docks and Cradles

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Digital Cameras

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Smart Phones

2A Single Cell Li-Ion Battery Charger

2A Synchronous

Buck Li-Ion Charger

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Low Power Dissipation

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2A Maximum Charge Current

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No External MOSFETs, Sense Resistor or Blocking

Diode Required

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Remote Sensing at Battery Terminals

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Programmable Charge Termination Timer

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Preset 4.2V Float Voltage with ±0.5% Accuracy

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Programmable Charge Current Detection/Termination

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Automatic Recharge

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Thermistor Input for Temperature Qualified Charging

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Compatible with Current Limited Wall Adapters

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Low Profile 16-Lead (4mm × 4mm) QFN Package

Power Loss vs V

BAT

Charging (PWM Mode)

FEATURES

DESCRIPTIO

APPLICATIO S

TYPICAL APPLICATIO

The LTC

4001 is a 2A Li-Ion battery charger intended for

5V wall adapters. It utilizes a 1.5MHz synchronous buck

converter topology to reduce power dissipation during

charging. Low power dissipation, an internal MOSFET and

sense resistor allow a physically small charger that can be

embedded in a wide range of handheld applications. The

LTC4001 includes complete charge termination circuitry,

automatic recharge and a ±1% 4.2V float voltage. Input

short-circuit protection is included so no blocking diode is

required.

Battery charge current, charge timeout and end-of-charge

indication parameters are set with external components.

Additional features include shorted cell detection, tempera-

ture qualified charging and overvoltage protection. The

LTC4001 is available in a low profile (0.75mm) 16-lead

(4mm × 4mm) QFN package.

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

All other trademarks are the property of their respective owners.

PROG

FAULT

NTC

CHRG

PGND

INSENSE

BAT

BATSENS

IDET TIMER

274Ω

0.22µF

10µF

4001 TA01a

4.2V

Li-Ion

10µF

4.5V TO 5.5V

0.1µF

SW SENSE

LTC4001

1.5µH

GNDSENS

BAT

(V)

TOTAL APPLICATION CIRCUIT POWER

DISSIPATION (W)

0.75

1.00

1.25

4001 TA01b

0.50

0.25

3.25

3.5

3.75

4.25

= 5V

2A CHARGER

Summary of content (20 pages)

PAGE 1
LTC4001 2A Synchronous Buck Li-Ion Charger U FEATURES DESCRIPTIO ■ The LTC®4001 is a 2A Li-Ion battery charger intended for 5V wall adapters. It utilizes a 1.5MHz synchronous buck converter topology to reduce power dissipation during charging. Low power dissipation, an internal MOSFET and sense resistor allow a physically small charger that can be embedded in a wide range of handheld applications. The LTC4001 includes complete charge termination circuitry, automatic recharge and a ±1% 4.
PAGE 2
LTC4001 W W W AXI U U ABSOLUTE RATI GS U U W PACKAGE/ORDER I FOR ATIO (Note 1) PVIN, VINSENSE t < 1ms, DC < 1% .................................... –0.3V to 7V Steady State ............................................ –0.3V to 6V SW, SENSE, BAT, BATSENS, SS, FAULT, CHRG, EN, NTC, PROG, IDET, TIMER Voltage .............. – 0.3V to 6V Operating Temperature Range (Note 3) .. – 40°C to 85°C Operating Junction Temperature (Note 5) ...............................................
PAGE 3
LTC4001 ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C. VIN = 5V, VEN = 0V, RPROG = 549Ω, RIDET = 549Ω, unless otherwise specified. SYMBOL PARAMETER CONDITIONS tTIMER Timer Accuracy CTIMER = 0.22µF VEN Enable Input Threshold Voltage VEN Rising ∆VEN Enable Input Hysteresis VPROG PROG Pin Voltage RPROG = 549Ω 1.213 V VIDET IDET Pin Voltage RIDET = 549Ω 1.
PAGE 4
LTC4001 U W TYPICAL PERFOR A CE CHARACTERISTICS (TA = 25°C unless otherwise noted) Oscillator Frequency vs Temperature 1.00 FREQUENCY VARIATION FROM 25°C (%) 0.75 PERCENT VARIATION (%) 0.8 VBAT = 3.2V VSS = 1V 0.50 0.25 0 –0.25 –0.50 –0.75 –1.00 3.5 3 4 5 4.5 VIN (V) 6 5.5 0.6 Dissipation of Figure 8 Circuit vs IBAT 1.25 VIN = 5V VBAT = 3.2V VSS = 1V TOTAL APPLICATION CIRCUIT POWER DISSIPATION (W) Oscillator Frequency vs VIN 0.4 0.2 0 0.50 0.
PAGE 5
LTC4001 U W TYPICAL PERFOR A CE CHARACTERISTICS IDET Threshold vs RIDET for RPROG = 549Ω Soft-Start (PWM Mode) CHRG Pin Temperature Fault Behavior (Detail) 400 350 INPUT CURRENT (IIN) 0.5A/DIV 300 IDET (mA) 0 INDUCTOR CURRENT (IL) 0.5A/DIV 0 SOFT-START VOLTAGE (VSS) 1V/DIV 0 EN PIN (VEN) 5V/DIV 0 250 CHRG 1V/DIV 200 150 100 VBAT = 3.
PAGE 6
LTC4001 U U U PI FU CTIO S FAULT (Pin 10): Battery Fault. This pin is a logic high if a shorted battery is detected or if a temperature fault is detected. A temperature fault occurs with the temperature monitor circuit enabled and the thermistor temperature is either below 0°C or above 50°C (typical). IDET (Pin 13): Charge Rate Detection Threshold. Connecting a resistor, RIDET to GNDSENS programs the charge rate detection threshold. If RIDET = RPROG, CHRG provides an IBAT/10 indication.
PAGE 7
11 15 10 7 6 14 NTC TIMER FAULT CHRG EN SS PWM ON RD Q + DRIVER CHIP OVER TEMP CONNECT OVERVOLTAGE CHIP OVERTEMP COMPARATOR SS LOW PROG SHORTED DISCHARGE SS LOGIC LOW CURRENT VIN GOOD RECHARGE TFAULT TIMER FAULT CHRG EN TRICKLE ON NTC COMPARATOR SS + S OVERCURRENT RAMP PWM COMPARATOR SHUTDOWN CLK – OSCILLATOR PROG SHORT COMPARATOR 1.2V + – – LOW BATTERY 5 + 1.
PAGE 8
LTC4001 U OPERATIO The LTC4001 is a constant current, constant voltage Li-Ion battery charger based on a synchronous buck architecture. Low power dissipation makes continuous high rate (2A) battery charging practical. The battery DC charge current is programmed by a resistor RPROG (or a DAC output current) at the PROG pin. The final battery float voltage is internally set to 4.2V. battery temperature and suspend charging when battery temperature is outside the 0°C to 50°C window.
PAGE 9
LTC4001 U OPERATIO Overvoltage, Chip Overtemperature and Short-Circuit Current Protection The LTC4001 includes overvoltage, chip overtemperature and several varieties of short-circuit protection. A comparator turns off both chargers (high rate and trickle) if battery voltage exceeds the float voltage by approximately 5%. This may occur in situations where the battery is accidentally disconnected while battery charging is underway.
PAGE 10
LTC4001 U W U U APPLICATIO S I FOR ATIO Soft-Start and Compensation Capacitor Selection The IDET threshold (a charge current threshold used to determine when the battery is nearly fully charged) is programmed in much the same way as the PROG pin, except that the IDET threshold is 91.5 times the current delivered by the IDET pin. This current is usually set with an external resistor from IDET to ground, but it may also be set with a current output DAC. The voltage on the PROG pin is nominally 1.213V.
PAGE 11
LTC4001 U W U U APPLICATIO S I FOR ATIO The equations for calculating R1 (used in single resistor programming) differ from the equations for calculating RPROG and RIDET (2-resistor programming) and reflect the fact that the current from both the IDET and PROG pins must flow through a single resistor R1 when a single programming resistor is used. CHRG Status Output Pin When a charge cycle starts, the CHRG pin is pulled to ground by an internal N-channel MOSFET which is capable of driving an LED.
PAGE 12
LTC4001 U W U U APPLICATIO S I FOR ATIO The battery temperature is measured by placing a negative temperature coefficient (NTC) thermistor close to the battery pack. To use this feature, connect the NTC thermistor, RNTC, between the NTC pin and GNDSENS and the resistor, RNOM, from the NTC pin to VINSENSE. RNOM should be a 1% resistor with a value equal to the value of the chosen NTC thermistor at 25°C. The LTC4001 goes into hold mode when the resistance, RHOT, of the NTC thermistor drops to 0.
PAGE 13
LTC4001 U W U U APPLICATIO S I FOR ATIO VINSENSE 9 LTC4001 NTC BLOCK 0.74 • VINSENSE RNOM 121k – TOO COLD NTC + 11 R1 13.3k – TOO HOT 0.29 • VINSENSE RNTC 100k + + 0.02 • VINSENSE NTC ENABLE – GNDSENS 4 4001 F04 Figure 4. Extending the Delta Temperature where RNOM is the value of the bias resistor, RHOT and RCOLD are the values of RNTC at the desired temperature trip points. Continuing the example from before with a desired hot trip point of 50°C: RNOM = RCOLD – RHOT 100k • (3.2636 – 0.
PAGE 14
LTC4001 U W U U APPLICATIO S I FOR ATIO Inductor Selection Remote Sensing A high (1.5MHz) operating frequency was chosen for the buck switcher in order to minimize the size of the inductor. However, take care to use inductors with low core losses at this frequency. A good choice is the IHLP-2525AH-01 from Vishay Dale. For highest float voltage accuracy, tie GNDSENS and BATSENS directly to the battery terminals. In a similar fashion, tie BAT and PGND directly to the battery terminals.
PAGE 15
LTC4001 U W U U APPLICATIO S I FOR ATIO LINEAR CHARGING VADAPTER WALL ADAPTER IN CURRENT LIMIT PWM CHARGING VBAT + VDROP VIN ILIMIT IBAT ITRICKLE VTRIKL VFLOAT 4001 F05 VBAT Figure 5. Charging Characteristic Battery charging current continues to drop as the VBAT rises, dropping to zero at VFLOAT. Because the voltage drop in the LTC4001 is very low when charge current is highest, power dissipation is also very low.
PAGE 16
LTC4001 U W U U APPLICATIO S I FOR ATIO Insert the highest power dissipation figure into the following equation to determine maximum junction temperature: TJ = TA + (PD • 37°C/W) The LTC4001 includes chip overtemperature protection. If junction temperature exceeds 160°C (typical), the chip will stop battery charging until chip temperature drops below 150°C.
PAGE 17
LTC4001 U W U U APPLICATIO S I FOR ATIO VBAT (V) 4 3 2 1 0 0 2 4 6 8 10 12 14 TIME (ms) 16 18 20 22 24 0 2 4 6 8 10 12 14 TIME (ms) 16 18 20 22 24 0 2 4 6 8 10 12 14 TIME (ms) 16 18 20 22 VSS (mV) 500 250 0 PWM CHARGE TRICKLE CHARGE 24 4001 F07 Figure 7.
PAGE 18
LTC4001 U W U U APPLICATIO S I FOR ATIO Layout Considerations With the exception of the input and output filter capacitors (which should be connected to PGND) all other components that return to ground should be connected to GNDSENS. Switch rise and fall times are kept under 5ns for maximum efficiency. To minimize radiation, the SW pin and input bypass capacitor leads (between PVIN and PGND) should be kept as short as possible.
PAGE 19
LTC4001 U PACKAGE DESCRIPTIO UF Package 16-Lead Plastic QFN (4mm × 4mm) (Reference LTC DWG # 05-08-1692) 0.72 ±0.05 4.35 ± 0.05 2.15 ± 0.05 2.90 ± 0.05 (4 SIDES) PACKAGE OUTLINE 0.30 ±0.05 0.65 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS BOTTOM VIEW—EXPOSED PAD 4.00 ± 0.10 (4 SIDES) 0.75 ± 0.05 R = 0.115 TYP 15 PIN 1 NOTCH R = 0.20 TYP OR 0.35 × 45° CHAMFER 16 0.55 ± 0.20 PIN 1 TOP MARK (NOTE 6) 1 2.15 ± 0.10 (4-SIDES) 2 (UF16) QFN 10-04 0.200 REF 0.00 – 0.05 0.30 ± 0.05 0.
PAGE 20
LTC4001 RELATED PARTS PART NUMBER ® DESCRIPTION COMMENTS LT 1511 3A Constant Current/Constant Voltage Battery Charger High Efficiency, Minimum External Components to Fast Charge Lithium, NIMH and NiCd Batteries, 24-Lead SO Package LT1513 SEPIC Constant or Programmable Current/Constant Voltage Battery Charger Charger Input Voltage May Be Higher, Equal to or Lower Than Battery Voltage, 500kHz Switching Frequency, DD Pak and TO-220 Packages LT1571 1.