Datasheet

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LTC4081

4081f

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Wireless Headsets

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Bluetooth Applications

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Portable MP3 Players

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Multifunction Wristwatches

Li-Ion Battery Charger with 1.8V Buck Regulator

500mA Li-Ion Charger

with NTC Input and

300mA Synchronous Buck

The LTC4081 is a complete constant-current/constant-

voltage linear battery charger for a single-cell 4.2V

lithium-ion/polymer battery with an integrated 300mA

synchronous buck converter. A 3mm × 3mm DFN pack-

age and low external component count make the LTC4081

especially suitable for portable applications. Furthermore,

the LTC4081 is speciﬁ cally designed to work within USB

power speciﬁ cations.

The

⎯

G pin indicates when charge current has

dropped to ten percent of its programmed value (C/10).

An internal 4.5 hour timer terminates the charge cycle.

The full-featured LTC4081 battery charger also includes

trickle charge, automatic recharge, soft-start (to limit inrush

current) and an NTC thermistor input used to monitor

battery temperature.

The LTC4081 integrates a synchronous buck converter

that is powered from the BAT pin. It has an adjustable

output voltage and can deliver up to 300mA of load cur-

rent. The buck converter also features low-current high-

efﬁ ciency Burst Mode operation that can be selected by

the MODE pin.

The LTC4081 is available in a 10-lead, low proﬁ le (0.75

mm) 3mm × 3mm DFN package.

Battery Charger:

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Constant-Current/Constant-Voltage Operation

with Thermal Feedback to Maximize Charge Rate

Without Risk of Overheating

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Internal 4.5 Hour Safety Timer for Termination

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Charge Current Programmable Up to 500mA with

5% Accuracy

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NTC Thermistor Input for Temperature Qualiﬁ ed

Charging

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C/10 Charge Current Detection Output

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5μA Supply Current in Shutdown Mode

Switching Regulator:

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High Efﬁ ciency Synchronous Buck Converter

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300mA Output Current (Constant-Frequency Mode)

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2.7V to 4.5V Input Range (Powered from BAT Pin)

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0.8V to V

BAT

Output Range

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MODE Pin Selects Fixed (2.25MHz) Constant-Frequency

PWM Mode or Low I

(23μA) Burst Mode

Operation

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2μA BAT Current in Shutdown Mode

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10-lead, low proﬁ le (0.75 mm) 3mm × 3mm DFN

package

APPLICATIO S

FEATURES

DESCRIPTIO

TYPICAL APPLICATIO

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

Burst Mode is a registered trademark of Linear Technology Corporation. All other

trademarks are the property of their respective owners. Protected by U.S. Patents,

including 6522118.

500mA

4.2V

Li-Ion/

POLYMER

BATTERY

4.7μF

806Ω

510Ω

806k

4.7μF

4081 TA01a

10pF

LTC4081

NTC

EN_CHRG

MODE

PROG

EN_BUCK

CHRG

BAT

100k

OUT

(1.8V/300mA)

1OμH

GND

4.7μF

(3.75V

TO 5.5V)

LOAD CURRENT (mA)

0.01

EFFICIENCY (%)

POWER LOSS (mW)

0.1 10 1001 1000

100

0.1

0.01

1000

4081 TA01b

BAT

= 3.8V

OUT

= 1.8V

L = 10μH

C = 4.7μF

EFFICIENCY

(Burst)

POWER LOSS

(Burst)

EFFICIENCY

(PWM)

POWER

LOSS

(PWM)

Buck Efﬁ ciency vs Load Current

OUT

= 1.8V)

Summary of content (24 pages)

PAGE 1
LTC4081 500mA Li-Ion Charger with NTC Input and 300mA Synchronous Buck DESCRIPTIO U FEATURES Battery Charger: Constant-Current/Constant-Voltage Operation with Thermal Feedback to Maximize Charge Rate Without Risk of Overheating ■ Internal 4.
PAGE 2
LTC4081 U W W W ABSOLUTE AXI U RATI GS (Note 1) VCC , t < 1ms and Duty Cycle < 1% .............. – 0.3V to 7V VCC Steady State ......................................... – 0.3V to 6V BAT, ⎯C⎯H⎯R⎯G .................................................. – 0.3V to 6V ⎯E⎯N⎯_⎯C⎯H⎯R⎯G, PROG, NTC ...................– 0.3V to VCC + 0.3V MODE, EN_BUCK .......................... – 0.3V to VBAT + 0.3V FB ............................................................... – 0.3V to 2V BAT Short-Circuit Duration..........
PAGE 3
LTC4081 ELECTRICAL CHARACTERISTICS The ● denotes speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C, VCC = 5V, VBAT = 3.8V, V⎯E⎯N⎯_⎯C⎯H⎯R⎯G = 0V, VNTC = 0V, VEN_BUCK = VBAT, VMODE = 0V. (Note 2) SYMBOL PARAMETER CONDITIONS MIN IBAT_SD Battery Current in Shutdown (Both Battery Charger and Switching Regulator Off) V⎯E⎯N⎯_⎯C⎯H⎯R⎯G = 5V, VEN_BUCK = 0, VCC > VBAT V⎯E⎯N⎯_⎯C⎯H⎯R⎯G = 4V, VEN_BUCK = 0, VCC (3.
PAGE 4
LTC4081 ELECTRICAL CHARACTERISTICS The ● denotes speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C, VCC = 5V, VBAT = 3.8V, V⎯E⎯N⎯_⎯C⎯H⎯R⎯G = 0V, VNTC = 0V, VEN_BUCK = VBAT, VMODE = 0V. (Note 2) SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS 0.78 0.80 0.82 V 2.25 2.
PAGE 5
LTC4081 TYPICAL PERFORMANCE CHARACTERISTICS (TA = 25°C, VCC = 5V, VBAT = 3.8V, unless otherwise speciﬁed) Battery Regulation (Float) Voltage vs Charge Current 4.21 Battery Regulation (Float) Voltage vs Temperature Battery Regulation (Float) Voltage vs VCC Supply Voltage 4.210 RPROG = 2k 4.25 4.205 4.20 4.20 4.200 4.18 4.17 4.16 4.15 4.15 4.195 FLOAT VOLTAGE (V) FLOAT VOLTAGE (V) FLOAT VOLTAGE (V) 4.19 4.190 4.185 4.180 4.175 0 50 200 150 100 CHARGE CURRENT (mA) 250 4.00 3.90 4.
PAGE 6
LTC4081 TYPICAL PERFORMANCE CHARACTERISTICS (TA = 25°C, VCC = 5V, VBAT = 3.8V, unless otherwise speciﬁed) ⎯C⎯H⎯R⎯G Pin Output Low Voltage vs Temperature Normalized Charge Termination Time vs Temperature 80 Buck Oscillator Frequency vs Battery Voltage 1.05 ICHRG = 5mA 2.28 VOLTAGE (mV) 60 50 40 30 20 2.27 1.00 FREQUENCY (MHz) NORMALIZED TIMER PERIOD 70 0.95 0.90 2.26 2.25 2.24 0.85 2.23 10 0 –50 –30 –10 10 30 50 TEMPERATURE (°C) 70 0.80 –50 90 –30 –10 10 30 50 70 2.22 2.
PAGE 7
LTC4081 TYPICAL PERFORMANCE CHARACTERISTICS speciﬁed) No-Load Buck Input Current (Burst Mode Operation) vs Temperature Buck Main Switch (PMOS) On-Resistance vs Battery Voltage 1.2 1.2 1.0 1.0 20 VBAT = 2.7V 15 10 ON-RESISTANCE (Ω) VBAT = 3.8V 25 0.8 0.6 0.4 0.2 5 30 50 –10 10 TEMPERATURE (˚C) 70 0 2.5 90 0.8 0.6 0.4 0.2 3.0 3.5 4.5 4.0 BATTERY VOLTAGE (V) 0 –50 –30 5.0 4081 G18 30 50 –10 10 TEMPERATURE (°C) 4081 G19 Buck Synchronous Switch (NMOS) On-Resistance vs Battery Voltage 1.
PAGE 8
LTC4081 TYPICAL PERFORMANCE CHARACTERISTICS speciﬁed) (TA = 25°C, VCC = 5V, VBAT = 3.
PAGE 9
LTC4081 U U U PI FU CTIO S BAT (Pin 1): Charge Current Output and Buck Regulator Input. Provides charge current to the battery and regulates the ﬁnal ﬂoat voltage to 4.2V. An internal precision resistor divider from this pin sets the ﬂoat voltage and is disconnected in charger shutdown mode. This pin must be decoupled with a low ESR capacitor for low-noise buck operation. VCC (Pin 2): Positive Input Supply Voltage. This pin provides power to the battery charger. VCC can range from 3.75V to 5.5V.
PAGE 10
LTC4081 W BLOCK DIAGRA 2 VCC + 3 EN_CHRG 0.82V CHARGER SHUTDOWN C3 – MP3 MP1 D3 – 115°C + TDIE TA X1 REN X400 D1 PROG 0.1V + – D2 1 + BAT MA C1 R1 CA VA + + – – – MP4 6 1.22V 1V CHRG R2 PULSE LOGIC CHARGER ENABLE 0.1V + 2.9V C2 – BAT BADBAT + VCC C4 3.
PAGE 11
LTC4081 U OPERATIO The LTC4081 is a full-featured linear battery charger with an integrated synchronous buck converter designed primarily for handheld applications. The battery charger is capable of charging single-cell 4.2V Li-Ion batteries. The buck converter is powered from the BAT pin and has a programmable output voltage providing a maximum load current of 300mA. The converter and the battery charger can run simultaneously or independently of each other.
PAGE 12
LTC4081 U OPERATIO If the die temperature starts to creep up above 115°C due to internal power dissipation, the transconductance ampliﬁer, TA, limits the die temperature to approximately 115°C by reducing the charge current. Diode D3 ensures that TA does not affect the charge current when the die temperature is below 115°C. In thermal regulation, the PROG pin voltage continues to give an indication of the charge current.
PAGE 13
LTC4081 U OPERATIO Timer and Recharge The LTC4081’s battery charger has an internal charge termination timer that starts when the input voltage is greater than the undervoltage lockout threshold and at least 82mV above BAT, and the battery charger is leaving shutdown. At power-up or when exiting shutdown, the charge time is set to 4.5 hours. Once the charge cycle terminates, the battery charger continuously monitors the BAT pin voltage using a comparator with a 2ms ﬁlter time.
PAGE 14
LTC4081 U OPERATIO Constant-Frequency (PWM) Mode Operation The switching regulator operates in constant-frequency (PWM) mode when the MODE pin is pulled below VIL . In this mode, it uses a current mode architecture including an oscillator, an error ampliﬁer, and a PWM comparator for excellent line and load regulation. The main switch MP2 (P-channel MOSFET) turns on to charge the inductor at the beginning of each clock cycle if the FB pin voltage is less than the 0.8V reference voltage.
PAGE 15
LTC4081 U OPERATIO Zero Current Comparator The zero or reverse current comparator monitors the inductor current to the output and shuts off the synchronous rectiﬁer when this current reduces to a predetermined value (IZERO). In ﬁxed frequency mode, this is set to negative 15mA meaning that the regulator allows the inductor current to ﬂow in the reverse direction (from the output to ground through the synchronous rectiﬁer) to a maximum value of 15mA.
PAGE 16
LTC4081 U W U U APPLICATIO S I FOR ATIO BATTERY CHARGER Programming Charge Current The battery charge current is programmed using a single resistor from the PROG pin to ground. The charge current is 400 times the current out of the PROG pin.
PAGE 17
LTC4081 U W U U APPLICATIO S I FOR ATIO Operation from Current Limited Wall Adapter USB and Wall Adapter Power By using a current limited wall adapter as the input supply, the LTC4081 can dissipate signiﬁcantly less power when programmed for a current higher than the limit of the wall adapter. Although the LTC4081 allows charging from a USB port, a wall adapter can also be used to charge Li-Ion batteries. Figure 4 shows an example of how to combine wall adapter and USB power inputs.
PAGE 18
LTC4081 U W U U APPLICATIO S I FOR ATIO Where VOUT is the regulated output of the switching regulator, IOUT is the regulator load and η is the regulator efﬁciency at that particular load. It is not necessary to perform worst-case power dissipation scenarios because the LTC4081 will automatically reduce the charge current to maintain the die temperature at approximately 115°C.
PAGE 19
LTC4081 U W U U APPLICATIO S I FOR ATIO Power conscious designs may want to use thermistors whose room temperature value is greater than 10k. Vishay Dale has a number of values of thermistor from 10k to 100k that follow the “R-T Curve 1.” Using different R-T curves, such as Vishay Dale “R-T Curve 2”, is also possible. This curve, combined with LTC4081 internal thresholds, gives temperature trip points of approximately 0°C (falling) and 40°C (rising), a delta of 40°C.
PAGE 20
LTC4081 U W U U APPLICATIO S I FOR ATIO NTC Trip Point Error SWITCHING REGULATOR When a 1% resistor is used for RHOT, the major error in the 40°C trip point is determined by the tolerance of the NTC thermistor. A typical 100k NTC thermistor has ±10% tolerance. By looking up the temperature coefﬁcient of the thermistor at 40°C, the tolerance error can be calculated in degrees centigrade. Consider the Vishay NTHS0603N01N1003J thermistor, which has a temperature coefﬁcient of –4%/°C at 40°C.
PAGE 21
LTC4081 U W U U APPLICATIO S I FOR ATIO Accepting larger values of ΔIL allows the use of low inductances, but results in higher output voltage ripple, greater core losses, and lower output current capability. A reasonable starting point for setting ripple current is ΔIL =0.3 • ILIM, where ILIM is the peak switch current limit. The largest ripple current occurs at the maximum input voltage.
PAGE 22
LTC4081 U W U U APPLICATIO S I FOR ATIO There are several types of ceramic capacitors with considerably different characteristics. Y5V ceramic capacitors have apparently higher packing density but poor performance over their rated voltage or temperature ranges. Under given voltage and temperature conditions, X5R and X7R ceramic capacitors should be compared directly by case size rather than speciﬁed value for a desired minimum capacitance.
PAGE 23
LTC4081 U PACKAGE DESCRIPTIO DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699) R = 0.115 TYP 6 0.38 ± 0.10 10 0.675 ±0.05 3.50 ±0.05 1.65 ±0.05 2.15 ±0.05 (2 SIDES) 3.00 ±0.10 (4 SIDES) PACKAGE OUTLINE 1.65 ± 0.10 (2 SIDES) PIN 1 TOP MARK (SEE NOTE 6) (DD) DFN 1103 5 0.25 ± 0.05 0.200 REF 0.50 BSC 2.38 ±0.05 (2 SIDES) 1 0.75 ±0.05 0.00 – 0.05 0.25 ± 0.05 0.50 BSC 2.38 ±0.10 (2 SIDES) BOTTOM VIEW—EXPOSED PAD RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS NOTE: 1.
PAGE 24
LTC4081 U TYPICAL APPLICATIO Li-Ion Battery Charger with 1.5V Buck Regulator Buck Efﬁciency vs Load Current (VOUT = 1.5V) D1 100 R3 510Ω 80 RNOM 100k CHRG EN_BUCK NTC CIN 4.7μF RNTC 100k BAT LTC4081 EN_CHRG T 500mA L1 1OμH CBAT 4.7μF + SW CPL 10pF FB R1 715k MODE GND PROG RPROG 806Ω R2 806k 4.2V Li-Ion/ POLYMER BATTERY VOUT (1.5V/300mA) COUT 4.7μF 4081 TA02a EFFICIENCY (%) VCC EFFICIENCY (Burst) EFFICIENCY (PWM) 100 POWER LOSS 10 (PWM) 60 40 20 0 0.