LTC4068X-4.2_技术文档

LTC4068-4.2/LTC4068X-4.2

Standalone Linear

Li-Ion Battery Charger with

Programmable Termination

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FEATURES

DESCRIPTIO

■

Programmable Charge Current Up to 950mA

The LTC^®4068 is a complete constant-current/constant-

voltage linear charger for single cell lithium-ion batteries.

Its DFN package and low external component count make

the LTC4068 ideally suited for portable applications. Fur-

thermore, the LTC4068 is designed to work within USB

power specifications.

■

Complete Linear Charger in DFN Package

■

No MOSFET, Sense Resistor or Blocking Diode

Required

■

Thermal Regulation Maximizes Charge Rate

Without Risk of Overheating*

■

Charges Directly from a USB Port

No external sense resistor or external blocking diode are

requiredduetotheinternalMOSFETarchitecture.Thermal

feedback regulates the charge current to limit the die

temperature during high power operation or high ambient

temperature conditions. The charge voltage is fixed at

4.2V and the charge current is programmed with a resis-

tor. The LTC4068 terminates the charge cycle when the

charge current drops below the programmed termination

threshold after the final float voltage is reached.

■

Programmable Charge Current Termination

■

Preset 4.2V Charge Voltage with ±1% Accuracy

■

Charge Current Monitor Output for Gas Gauging*

■

Automatic Recharge

■

Charge Status Output

■

“AC Present” Output

■

2.9V Trickle Charge Threshold (LTC4068)

■

Available Without Trickle Charge (LTC4068X)

■

Soft-Start Limits Inrush Current

■

When the input supply (wall adapter or USB supply) is

removed,theLTC4068entersalowcurrentstatedropping

the battery drain current to less than 2µA. Other features

include charge current monitor, undervoltage lockout,

automatic recharge and status pins to indicate charge

termination and the presence of adequate input voltage.

Low Profile (3mm × 3mm × 0.75mm) DFN Package

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APPLICATIO S

■

Cellular Telephones, PDAs, MP3 Players

Bluetooth Applications

■

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

Protected by U.S. Patents, including 6522118.

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TYPICAL APPLICATIO

Complete Charge Cycle (750mAh Battery)

700

600

500

400

300

200

100

0

4.75

4.50

4.25

4.00

3.75

3.50

3.25

3.00

CONSTANT

CURRENT

Single Cell Li-Ion Battery Charger with C/5 Termination

CONSTANT

VOLTAGE

600mA

V

IN

V

CC

BAT

4.5V TO 6.5V

LTC4068-4.2

1-CELL

Li-Ion

BATTERY

+

CHRG

ACPR

EN

ITERM

PROG

V

= 5V

825Ω

CC

θ

= 40°C/W

GND

JA

1µF

1.65k

R

= 1.65k

PROG

TERM

= 825Ω

406842 TA01

T

A

= 25°C

0.25 0.5 0.75 1.0 1.25

1.75 2.0 2.25

0

1.5

406842 TA02

TIME (HOURS)

406842fa

1

LTC4068-4.2/LTC4068X-4.2

W W

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ABSOLUTE AXI U RATI GS

PACKAGE/ORDER I FOR ATIO

(Note 1)

TOP VIEW

Input Supply Voltage (V_CC) ....................... –0.3V to 10V

PROG, ITERM ................................ –0.3V to V_CC+ 0.3V

BAT............................................................. –0.3V to 7V

CHRG, ACPR, EN ...................................... –0.3V to 10V

BAT Short-Circuit Duration .......................... Continuous

BAT Pin Current ........................................................ 1A

PROG Pin Current................................................... 1mA

Maximum Junction Temperature .......................... 125°C

Operating Temperature Range (Note 2) .. –40°C to 85°C

Storage Temperature Range ................. –65°C to 125°C

ORDER PART

NUMBER

ITERM

BAT

1

2

3

4

8

7

6

5

EN

ACPR

LTC4068EDD-4.2

LTC4068XEDD-4.2

9

CHRG

GND

V

CC

PROG

DD PART MARKING

DD PACKAGE

8-LEAD (3mm × 3mm) PLASTIC DFN

T_JMAX= 125°C, θ_JA= 40°C/W (NOTE 3)

EXPOSED PAD IS GROUND (PIN 9)

MUST BE SOLDERED TO PCB

LBHZ

LBQB

Consult LTC Marketing for parts specified with wider operating temperature ranges.

ELECTRICAL CHARACTERISTICS ^The● denotes specifications which apply over the full operating

temperature range, otherwise specifications are at T_A= 25°C. V_CC= 5V, unless otherwise noted.

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

V

Input Supply Voltage

Input Supply Current

●

4.25

6.5

V

CC

I

Charge Mode (Note 4), R

Standby Mode (Charge Terminated)

Shutdown Mode (EN = 5V, V < V

= 10k

●

0.4

200

25

1

500

50

mA

µA

CC

PROG

CC

BAT

or V < V

)

CC

UV

V

Regulated Output (Float) Voltage

BAT Pin Current

0°C ≤ T ≤ 85°C, 4.3V < V < 6.5V

4.158

4.2

4.242

V

FLOAT

A

CC

I

R

= 10k, Current Mode

= 2k, Current Mode

●

92

465

100

500

–2.5

±1

105

535

–6

mA

µA

BAT

PROG

Standby Mode, V

= 4.2V

BAT

Shutdown Mode (EN = 5V, V < V

or

±2

µA

CC

BAT

V

< V )

CC

UV

Sleep Mode, V = 0V

±1

45

±2

60

3

µA

mA

V

CC

I

Trickle Charge Current

V

< V , R = 2k (Note 5)

TRIKL PROG

●

30

TRIKL

BAT

V

Trickle Charge Threshold Voltage

Trickle Charge Hysteresis Voltage

R

= 10k, V Rising (Note 5)

BAT

2.8

2.9

80

TRIKL

TRHYS

UV

PROG

= 10k (Note 5)

mV

V

Undervoltage Lockout Voltage

Undervoltage Lockout Hysteresis

From V Low to High

●

3.7

150

0.4

3.8

200

0.7

2

3.92

300

CC

mV

V

UVHYS

EN(IL)

EN(IH)

EN Pin Input Low Voltage

EN Pin Input High Voltage

EN Pin Pull-Down Resistor

1

5

V

R

1.2

MΩ

EN

V

– V

Lockout Threshold

V

from Low to High

from High to Low

70

5

100

30

140

50

mV

ASD

CC

BAT

CC

I

Charge Termination Current Threshold

R

TERM

R

TERM

= 1k

= 5k

●

90

17.5

100

20

110

22.5

mA

TERM

V

PROG Pin Voltage

R

= 10k, Current Mode

= 5mA

0.93

1

1.07

0.6

V

PROG

CHRG

ACPR

PROG

CHRG

CHRG Pin Output Low Voltage

ACPR Pin Output Low Voltage

Recharge Battery Threshold Voltage

I

0.35

100

= 5mA

0.6

V

ACPR

∆V

V

– V

, 0°C ≤ T ≤ 85°C

60

140

mV

RECHRG

FLOAT

RECHRG

A

406842fa

2

LTC4068-4.2/LTC4068X-4.2

ELECTRICAL CHARACTERISTICS ^The● denotes specifications which apply over the full operating

temperature range, otherwise specifications are at T_A= 25°C. V_CC= 5V, unless otherwise noted.

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

T

Junction Temperature in Constant

Temperature Mode

120

°C

LIM

R

ON

Power FET “ON” Resistance

600

mΩ

(Between V and BAT)

CC

t

Soft-Start Time

I

= 0 to I

=1000V/R

PROG

100

2

µs

ms

µs

SS

BAT

Recharge Comparator Filter Time

Termination Comparator Filter Time

V

High to Low

0.75

400

4.5

RECHARGE

TERM

BAT

I

Drops Below Charge Termination Threshold

1000

2500

Note 1: Absolute Maximum Ratings are those values beyond which the life

of the device may be impaired.

Note 3: Failure to solder the exposed backside of the package to the PC

board will result in a thermal resistance much higher than 40°C/W.

Note 2: The LTC4068E-4.2/LTC4068XE-4.2 are guaranteed to meet

performance specifications from 0°C to 70°C. Specifications over the

–40°C to 85°C operating temperature range are assured by design,

characterization and correlation with statistical process controls.

Note 4: Supply current includes PROG pin current and ITERM pin current

(approximately 100µA each) but does not include any current delivered to

the battery through the BAT pin (approximately 100mA).

Note 5: This parameter is not applicable to the LTC4068X.

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TYPICAL PERFOR A CE CHARACTERISTICS

PROG Pin Voltage vs Supply

Voltage (Constant Current Mode)

PROG Pin Voltage

vs Temperature

Charge Current

vs PROG Pin Voltage

1.015

1.010

1.005

1.000

0.995

0.990

0.985

600

500

400

300

200

100

0

1.0100

1.0075

1.0050

1.0025

V

T

= 5V

V

= 5V

V

= 5V

CC

= 4V

T

= 25°C

BAT

PROG

A

R

= 25°C

= 2k

R

= 10k

A

R

PROG

TERM

= 10k

PROG

1.0000

0.9975

0.9950

0.9925

0.9900

4

5

5.5

(V)

6

6.5

7

–50

–25

0

50

75

100

0

0.4

0.6

(V)

PROG

0.8

1

1.2

4.5

25

0.2

V

TEMPERATURE (°C)

CC

405842 G01

405842 G02

405842 G03

406842fa

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LTC4068-4.2/LTC4068X-4.2

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TYPICAL PERFOR A CE CHARACTERISTICS

Regulated Output (Float) Voltage

vs Charge Current

Regulated Output (Float) Voltage

vs Temperature

Regulated Output (Float) Voltage

vs Supply Voltage

4.26

4.215

4.210

4.205

4.200

4.195

4.190

4.185

4.215

4.210

4.205

4.200

4.195

4.190

4.185

V

A

R

= 5V

V

= 5V

PROG

T = 25°C

A

CC

R

T

= 25°C

= 10k

R

= 10k

PROG

4.24

4.22

= 1.25k

PROG

4.20

4.18

4.16

4.14

4.12

4.10

100 200

400 500 600 700

(mA)

–50

0

25

50

75

100

4

5

5.5

(V)

6

6.5

7

0

300

–25

4.5

TEMPERATURE (°C)

V

I

CC

BAT

405842 G04

405842 G05

405842 G06

CHRG Pin I-V Curve

(Pull-Down State)

ACPR Pin I-V Curve

(Pull-Down State)

Trickle Charge Current

vs Temperature

30

25

20

15

30

25

20

15

60

50

40

30

20

10

0

V

= 5V

BAT

LTC4068 ONLY

CC

T

= –40°C

T

A

= –40°C

A

= 2.5V

T

= 25°C

= 90°C

T

= 25°C

= 90°C

A

R

= 2k

PROG

A

10

5

10

5

R

= 10k

50

PROG

25

V

= 5V

CC

BAT

V

= 5V

CC

BAT

= 4V

0

4

6

7

4

6

7

–50

0

75

100

0

1

2

3

5

0

1

2

3

5

–25

TEMPERATURE (°C)

V

(V)

V

ACPR

(V)

CHRG

405842 G07

405842 G08

405842 G09

Trickle Charge Current

vs Supply Voltage

Trickle Charge Threshold Voltage

vs Temperature

Charge Current vs Battery Voltage

60

50

40

30

20

10

0

600

500

400

300

3.000

2.975

2.950

2.925

V

T

= 2.5V

LTC4068 ONLY

V

= 5V

PROG

LTC4068 ONLY

BAT

A

CC

= 25°C

R

= 10k

R

= 2k

PROG

2.900

2.875

200

100

0

2.850

2.825

2.800

R

= 10k

6

PROG

V

= 5V

CC

JA

θ

= 40°C/W

R

= 2k

PROG

3.3 3.6 3.9

(V)

4

5

5.5

(V)

6.5

7

–50

–25

0

50

75

100

2.4 2.7

3

4.2 4.5

4.5

25

V

TEMPERATURE (°C)

V

BAT

CC

405842 G10

405842 G11

405842 G12

406842fa

4

LTC4068-4.2/LTC4068X-4.2

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TYPICAL PERFOR A CE CHARACTERISTICS

Charge Current

vs Ambient Temperature

Charge Current vs Supply Voltage

600

500

400

300

200

100

0

600

ONSET OF THERMAL REGULATION

R

= 2k

PROG

500

400

300

R

PROG

= 2k

V

T

JA

= 4V

V

θ

= 5V

= 4V

BAT

A

CC

= 25°C

BAT

θ

= 40°C/W

JA

200

100

0

R

= 10k

50

R

= 10k

PROG

4

5

5.5

6

6.5

7

–50 –25

0

25

75

100 125

4.5

V

(V)

TEMPERATURE (°C)

CC

405842 G13

405842 G14

Power FET “ON” Resistance

vs Temperature

Recharge Threshold Voltage

vs Temperature

700

650

600

550

500

450

400

350

4.16

4.14

4.12

4.10

4.08

4.06

4.04

V

I

= 4.2V

V

= 5V

PROG

CC

BAT

R

CC

= 100mA

R

= 10k

= 2k

PROG

–50

0

25

50

75 100 125

–25

–50

0

25

50

75

100

–25

TEMPERATURE (°C)

405842 G17

405842 G15

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PI FU CTIO S

ITERM (Pin 1): Charge Termination Program. The charge voltage. Thisdividerisdisconnectedinshutdownmodeto

termination current threshold current is programmed by minimize current drain from the battery.

connecting a 1% resistor, R_TERM, to ground. The current

CHRG (Pin 3): Charge Status Open-Drain Output. When

threshold I_TERM, is set by the following formula:

the battery is charging, the CHRG pin is pulled low by an

internal N-channel MOSFET. When the charge cycle is

completed, CHRG becomes high impedance.

100V

R_TERM

100V

I_TERM

=

, R_TERM=

GND (Pins 4, 9): Ground/Exposed Pad. The exposed

backside package pad (Pin 9) is electrical ground and

must be soldered to the PC board for maximum heat

transfer.

BAT (Pin 2): Charge Current Output. Provides charge

currenttothebatteryfromtheinternalP-channelMOSFET,

and regulates the final float voltage to 4.2V. An internal

precision resistor divider from this pin sets the float

406842fa

5

LTC4068-4.2/LTC4068X-4.2

U

PI FU CTIO S

PROG (Pin 5): Charge Current Program and Charge Cur-

rent Monitor. Charge current is programmed by connect-

ing a 1% resistor, R_PROG, to ground. When charging in

constant-currentmode,thispinservosto1V.Inallmodes,

the voltage on this pin can be used to measure the charge

current using the following formula:

When V_CCis within 100mV of the BAT pin voltage, the

LTC4068 enters shutdown mode dropping the battery

drain current to less than 2µA.

ACPR (Pin 7): Power Supply Status Open-Drain Output.

WhenV_CCisgreaterthantheundervoltagelockoutthresh-

old and at least 100mV above V_BAT, the ACPR pin is pulled

to ground; otherwise, the pin is high impedance.

I_BAT= (V_PROG/R_PROG) • 1000

Thispinisclampedtoapproximately2.4V. Drivingthispin

to voltages beyond the clamp voltage can draw large

currents and should be avoided.

EN(Pin8):EnableInput. AlogichighontheENpinwillput

the LTC4068 into shutdown mode where the battery drain

current is reduced to less than 2µA and the supply current

is reduced to less than 50µA. A logic low or floating the EN

pin (allowing an internal 2MΩ pull-down resistor to pull

this pin low) enables charging.

V_CC(Pin 6): Positive Input Supply Voltage. Provides

power to the charger. V_CCcan range from 4.25V to 6.5V.

This pin should be bypassed with at least a 1µF capacitor.

W

BLOCK DIAGRA

6

V

CC

120°C

T

A

1×

T

DIE

1000×

–

+

BAT

2

5µA

MA

R1

R2

ACPR

CHRG

+

7

3

VA

–

CA

+

REF

1.211V

–

R3

1V

*

CHARGE ACPR

LOGIC

R4

0.1V

R5

+

–

TERM

C1

EN

SHDN

EN

8

*TRICKLE

CHARGE

DISABLED

ON THE

LTC4068X

C2*

+

–

2.9V

TO BAT

ITERM

PROG

GND

4, 9

1

5

R

PROG

TERM

406842 BD

406842fa

6

LTC4068-4.2/LTC4068X-4.2

U

OPERATIO

The LTC4068 is a single cell lithium-ion battery charger

using a constant-current/constant-voltage algorithm. It

can deliver up to 950mA of charge current (using a good

thermal PCB layout) with a final float voltage accuracy of

±1%. The LTC4068 includes an internal P-channel power

MOSFET and thermal regulation circuitry. No blocking

diode or external current sense resistor is required; thus,

the basic charger circuit requires only two external com-

ponents. Furthermore, the LTC4068 is capable of operat-

ing from a USB power source.

Programming Charge Termination

The charge cycle terminates when the charge current

falls below the programmed termination threshold. This

threshold is set by connecting an external resistor, R_TERM

from the ITERM pin to ground. The charge termination

current threshold (I_TERM)is set by the following equation:

,

100V I_CHG

R

100V

I_TERM

=

•

^PROG,R_TERM

R_TERM10 R_TERM

=

The termination condition is detected by using an internal

filtered comparator to monitor the ITERM pin. When the

ITERM pin voltage drops below 100mV^*for longer than

t_TERM(typically 1ms), charging is terminated. The charge

current is latched off and the LTC4068 enters standby

mode where the input supply current drops to 200µA.

(Note: Termination is disabled in trickle charging and

thermal limiting modes.)

Normal Charge Cycle

AchargecyclebeginswhenthevoltageattheV_CCpinrises

abovetheUVLOthresholdlevelanda1%programresistor

is connected from the PROG pin to ground. If the BAT pin

is less than 2.9V, the charger enters trickle charge mode.

In this mode, the LTC4068 supplies approximately 1/10th

the programmed charge current to bring the battery volt-

age up to a safe level for full current charging. (Note: The

LTC4068X does not include this trickle charge feature.)

I_TERMcanbesettobe1/10thofI_CHGbyshortingtheITERM

pin to the PROG pin, thus eliminating the need for external

resistor R_TERM. When configured in this way, I_TERMis

alwayssettoI_CHG/10,andtheprogrammedchargecurrent

is set by the equation:

When the BAT pin voltage rises above 2.9V, the charger

enters constant-current mode where the programmed

chargecurrentissuppliedtothebattery.WhentheBATpin

approaches the final float voltage (4.2V), the LTC4068

enters constant-voltage mode and the charge current

begins to decrease. When the charge current drops to the

programmed termination threshold (set by the external

resistor R_TERM), the charge cycle ends.

500V

R_PROG

500V^**

I_CHG

=

,R_PROG=

When charging, transient loads on the BAT pin can cause

the ITERM pin to fall below 100mV for short periods of

time before the DC charge current has dropped to 10% of

the programmed value. The 1ms filter time (t_TERM) on the

termination comparator ensures that transient loads of

this nature do not result in premature charge cycle termi-

nation. Once the average charge current drops below the

programmed termination threshold, the LTC4068 termi-

nates the charge cycle and ceases to provide any current

out of the BAT pin. In this state, any load on the BAT pin

must be supplied by the battery.

Programming Charge Current

The charge current is programmed using a single resistor

from the PROG pin to ground. The charge current out of

the BAT pin is 1000 times the current out of the PROG pin.

The program resistor and the charge current are calcu-

lated using the following equations:

1000V

I_CHG

1000V

R_PROG

=

, I_CHG=

ChargecurrentoutoftheBATpincanbedeterminedatany

time by monitoring the PROG pin voltage and using the

following equation:

The LTC4068 constantly monitors the BAT pin voltage in

standbymode.Ifthisvoltagedropsbelowthe4.1Vrecharge

*

Any external sources that hold the ITERM pin above 100mV will prevent the LTC4068 from

terminating a charge cycle.

V_PROG

R_PROG

I_BAT

=

•1000

**

These equations apply only when the ITERM pin is shorted to the PROG pin.

406842fa

7

LTC4068-4.2/LTC4068X-4.2

U

OPERATIO

Thermal Limiting

threshold (V_RECHRG), another charge cycle begins and

charge current is once again supplied to the battery. To

manuallyrestartachargecyclewheninstandbymode, the

inputvoltagemustberemovedandreappliedorthecharger

mustbeshutdownandrestartedusingtheENpin.Figure 1

shows the state diagram of a typical charge cycle.

Aninternalthermalfeedbackloopreducestheprogrammed

chargecurrentifthedietemperatureattemptstoriseabove

apresetvalueofapproximately120°C.Thisfeatureprotects

the LTC4068 from excessive temperature and allows the

user to push the limits of the power handling capability of

agivencircuitboardwithoutriskofdamagingtheLTC4068.

Thechargecurrentcanbesetaccordingtotypical(notworst

case) ambient temperature with the assurance that the

chargerwillautomaticallyreducethecurrentinworst-case

conditions. DFN power considerations are discussed fur-

ther in the Applications Information section.

POWER ON

BAT < 2.9V

TRICKLE CHARGE

MODE

EN DRIVEN LOW

OR

UVLO CONDITION

STOPS

LTC4068

ONLY

1/10TH FULL CURRENT

CHRG: STRONG

PULL-DOWN

BAT > 2.9V

Undervoltage Lockout (UVLO)

BAT > 2.9V

SHUTDOWN MODE

CHARGE MODE

Aninternalundervoltagelockoutcircuitmonitorstheinput

voltageandkeepsthechargerinshutdownmodeuntilV_CC

risesabovetheundervoltagelockoutthreshold. TheUVLO

circuit has a built-in hysteresis of 200mV. Furthermore, to

protect against reverse current in the power MOSFET, the

UVLO circuit keeps the charger in shutdown mode if V_CC

falls to within 30mV of the BAT voltage. If the UVLO com-

parator is tripped, the charger will not come out of shut-

down mode until V_CCrises 100mV above the BAT voltage.

I

CC

DROPS TO <25µA

FULL CURRENT

CHRG: Hi-Z

CHRG: STRONG

PULL-DOWN

ITERM < 100mV

STANDBY MODE

NO CHARGE CURRENT

CHRG: Hi-Z

EN DRIVEN HIGH

OR

UVLO CONDITION

2.9V < BAT < 4.1V

406842 F01

Figure 1. State Diagram of a Typical Charge Cycle

Manual Shutdown

At any point in the charge cycle, the LTC4068 can be put

into shutdown mode by driving the EN pin high. This

reduces the battery drain current to less than 2µA and the

supply current to less than 50µA. When in shutdown

mode, the CHRG pin is in the high impedance state. A new

charge cycle can be initiated by driving the EN pin low. An

internal resistor pull-down on this pin forces the LTC4068

to be enabled if the pin is allowed to float.

Charge Status Indicator (CHRG)

The charge status output has two states: pull-down and

high impedance. The pull-down state indicates that the

LTC4068 is in a charge cycle. Once the charge cycle has

terminated or the LTC4068 is disabled, the pin state

becomes high impedance.

Power Supply Status Indicator (ACPR)

Automatic Recharge

The power supply status output has two states: pull-down

and high impedance. The pull-down state indicates that

Oncethechargecycleisterminated,theLTC4068continu-

ously monitors the voltage on the BAT pin using a com-

parator with a 2ms filter time (t_RECHARGE). A charge cycle

restarts when the battery voltage falls below 4.10V (which

corresponds to approximately 80% to 90% battery capac-

ity). This ensures that the battery is kept at, or near, a fully

V

_CCisabovetheUVLOthreshold(3.8V)andisalso100mV

above the battery voltage. If these conditions are not met,

theACPRpinishighimpedanceindicatingthattheLTC4068

is unable to charge the battery.

406842fa

8

LTC4068-4.2/LTC4068X-4.2

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APPLICATIO S I FOR ATIO

charged condition and eliminates the need for periodic filter can be used on the PROG pin to measure the average

charge cycle initiations. The CHRG output enters a pull- battery current, as shown in Figure 2. A 10k resistor has

down state during recharge cycles.

been added between the PROG pin and the filter capacitor

to ensure stability.

If the battery is removed from the charger, a sawtooth

waveformofapproximately100mVappearsatthecharger

output. This is caused by the repeated cycling between

termination and recharge events. This cycling results in

pulsing at the CHRG output; an LED connected to this pin

will exhibit a blinking pattern, indicating to the user that a

battery is not present. The frequency of the sawtooth is

dependent on the amount of output capacitance.

LTC4068-4.2

CHARGE

10k

CURRENT

PROG

MONITOR

CIRCUITRY

R

PROG

C

FILTER

GND

406842 F02

Figure 2. Isolating Capacitive Load on PROG Pin and Filtering

Stability Considerations

The constant-voltage mode feedback loop is stable with-

out an output capacitor, provided a battery is connected to

the charger output. With no battery present, an output

capacitor on the BAT pin is recommended to reduce ripple

voltage. When using high value, low ESR ceramic capaci-

tors, it is recommended to add a 1Ω resistor in series with

the capacitor. No series resistor is needed if tantalum

capacitors are used.

Power Dissipation

It is not necessary to design for worst-case power dissi-

pation scenarios because the LTC4068 automatically

reducesthechargecurrentduringhighpowerconditions.

The conditions that cause the LTC4068 to reduce charge

current through thermal feedback can be approximated

by considering the power dissipated in the IC. Nearly all

of this power dissipation is generated by the internal

MOSFET—this is calculated to be approximately:

In constant-current mode, the PROG pin is in the feedback

loop, not the battery. The constant-current mode stability

is affected by the impedance at the PROG pin. With no

additional capacitance on the PROG pin, the charger is

stable with program resistor values as high as 20k; how-

ever, additional capacitance on this node reduces the

maximum allowed program resistor. The pole frequency

at the PROG pin should be kept above 100kHz. Therefore,

if the PROG pin is loaded with a capacitance, C_PROG, the

following equation can be used to calculate the maximum

P_D= (V_CC– V_BAT) • I_BAT

where P_Dis the power dissipated, V_CCis the input supply

voltage, V_BATis the battery voltage and I_BATis the charge

current. The approximate ambient temperature at which

the thermal feedback begins to protect the IC is:

T_A= 120°C – P_Dθ_JA

T_A= 120°C – (V_CC– V_BAT) • I_BAT• θ_JA

Example: An LTC4068 operating from a 5V supply is

programmed to supply 800mA full-scale current to a

dischargedLi-Ionbatterywithavoltageof3.3V.Assuming

θ_JAis 50°C/W (see Thermal Considerations), the ambient

temperatureatwhichtheLTC4068willbegintoreducethe

charge current is approximately:

resistance value for R_PROG

:

1

R_PROG

≤

2π •10⁵•C_PROG

Average, ratherthaninstantaneouschargecurrentmaybe

of interest to the user. For example, if a switching power

supply operating in low current mode is connected in

parallel with the battery, the average current being pulled

out of the BAT pin is typically of more interest than the

instantaneous current pulses. In such a case, a simple RC

T_A= 120°C – (5V – 3.3V) • (800mA) • 50°C/W

T_A= 120°C – 1.36W • 50°C/W = 120°C – 68°C

T_A= 52°C

406842fa

9

LTC4068-4.2/LTC4068X-4.2

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APPLICATIO S I FOR ATIO

The LTC4068 can be used above 52°C ambient but the

charge current will be reduced from the programmed

800mA. The approximate current at a given ambient

temperature can be approximated by:

ceramiccapacitors. Becauseoftheself-resonantandhigh

Q characteristics of some types of ceramic capacitors,

high voltage transients can be generated under some

start-up conditions such as connecting the charger input

to a live power source. Adding a 1.5Ω resistor in series

with an X5R ceramic capacitor will minimize start-up

voltage transients. For more information, see Application

Note 88.

120°C – T_A

I_BAT

=

V_CC– V_BAT• θ_JA

(

)

Using the previous example with an ambient temperature

of 60°C, the charge current will be reduced to

approximately:

Charge Current Soft-Start

The LTC4068 includes a soft-start circuit to minimize the

inrushcurrentatthestartofachargecycle.Whenacharge

cycle is initiated, the charge current ramps from zero to

full-scale current over a period of approximately 100µs.

Thishastheeffectofminimizingthetransientcurrentload

on the power supply during start-up.

120°C – 60°C

60°C

85°C/A

I_BAT

=

5V – 3.3V • 50°C/W

(

)

I_BAT= 706mA

Moreover,whenthermalfeedbackreducesthechargecur-

rentthevoltageatthePROGpinisalsoreducedproportion-

ally as discussed in the Operation section. It is important

to remember that LTC4068 applications do not need to be

designedforworst-casethermalconditionssincetheICwill

automatically reduce power dissipation when the junction

temperature reaches approximately 120°C.

USB and Wall Adapter Power

The LTC4068 allows charging from both a wall adapter

and a USB port. Figure 3 shows how to combine wall

adapter and USB power inputs. A P-channel MOSFET,

MP1, isusedtopreventbackconductingintotheUSBport

when a wall adapter is present and a Schottky diode, D1,

is used to prevent USB power loss through the 1k pull-

down resistor.

Thermal Considerations

I

n order to deliver maximum charge current under all

Typically a wall adapter can supply more current than

the 500mA-limited USB port. Therefore, an N-channel

MOSFET, MN1, and an extra 3.3k program resistor are

used to increase the charge current to 800mA when the

walladapterispresent.Thechargeterminationthreshold

remains fixed at 80mA.

conditions, it is critical that the exposed metal pad on the

backside of the LTC4068 package is soldered to the PC

board ground. Correctly soldered to a 2500mm²double-

sided 1oz copper board, the LTC4068 has a thermal

resistance of approximately 40°C/W. Failure to make

thermal contact between the exposed pad on the back-

side of the package and the copper board will result in

thermal resistances far greater than 40°C/W. As an

example, a correctly soldered LTC4068 can deliver over

800mA to a battery from a 5V supply at room tempera-

ture. Without a good backside thermal connection, this

number will drop considerably.

5V WALL

ADAPTER

I

CHG

800mA I

LTC4068-4.2

BAT

CHG

2

1

5

SYSTEM

LOAD

D1

6

USB POWER

V

CC

ITERM

500mA I

CHG

4, 9

MP1

GND PROG

1.25k

+

Li-Ion

BATTERY

3.3k

1k

2k

MN1

406842 F03

V_CCBypass Capacitor

Many types of capacitors can be used for input bypassing;

however,cautionmustbeexercisedwhenusingmultilayer

Figure 3. Combining Wall Adapter and USB Power

406842fa

10

LTC4068-4.2/LTC4068X-4.2

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U

APPLICATIO S I FOR ATIO

DRAIN-BULK

DIODE OF FET

Reverse Polarity Input Voltage Protection

LTC4068

CC

In some applications, protection from reverse polarity

voltage on V_CCis desired. If the supply voltage is high

enough, a series blocking diode can be used. In other

cases,wherethevoltagedropmustbekeptlow,aP-channel

MOSFET can be used (as shown in Figure 4).

V

IN

405842 F04

Figure 4. Low Loss Input Reverse Polarity Protection

U

PACKAGE DESCRIPTIO

DD Package

8-Lead Plastic DFN (3mm × 3mm)

(Reference LTC DWG # 05-08-1698)

0.675 ±0.05

3.5 ±0.05

2.15 ±0.05 (2 SIDES)

1.65 ±0.05

PACKAGE

OUTLINE

0.28 ± 0.05

0.50

BSC

2.38 ±0.05

(2 SIDES)

RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS

R = 0.115

0.38 ± 0.10

TYP

5

8

3.00 ±0.10

(4 SIDES)

1.65 ± 0.10

(2 SIDES)

PIN 1

TOP MARK

(DD8) DFN 0203

4

1

0.28 ± 0.05

0.75 ±0.05

0.200 REF

0.50 BSC

2.38 ±0.10

(2 SIDES)

0.00 – 0.05

BOTTOM VIEW—EXPOSED PAD

NOTE:

1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-1)

2. ALL DIMENSIONS ARE IN MILLIMETERS

3. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE

MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE

4. EXPOSED PAD SHALL BE SOLDER PLATED

406842fa

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-

tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.

11

LTC4068-4.2/LTC4068X-4.2

U

TYPICAL APPLICATIO S

Full Featured Single Cell Li-Ion Charger

Li-Ion Battery Charger with Reverse Polarity Input Protection

V

IN

5V

WALL

ADAPTER

6

1k

6

500mA

V

CC

2

500mA

V

CC

BAT

2

1

7

3

ACPR

BAT

LTC4068-4.2

ITERM

1

5

CHRG ITERM

LTC4068-4.2

1µF

1-CELL

Li-Ion

+

8

1µF

1k

EN

PROG

GND

4, 9

1µF

8

5

BATTERY

EN

PROG

GND

4, 9

1-CELL

Li-Ion

BATTERY

1k

+

2k

406842 TA04

405642 TA03

USB/Wall Adapter Power Li-Ion Charger

I

BAT

5V WALL

ADAPTER

2

BAT

1-CELL

Li-Ion

BATTERY

+

LTC4068-4.2

1

5

6

USB

POWER

V

ITERM

PROG

GND

4, 9

CC

1µF

1.25k

5k

1k

100mA/

500mA

µC

406842 TA05

RELATED PARTS

PART NUMBER

DESCRIPTION

COMMENTS

Simple Charger uses External FET, Features Preset Voltages, C/10

LTC1732

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Standalone Charger with Programmable Timer, Up to 1.5A Charge Current

Simple ThinSOT Charger, No Blocking Diode, No Sense Resistor Needed

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LTC1734

LTC1734L

LTC1998

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Low Current Version of LTC1734; 50mA ≤ I

≤ 180mA

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Standalone Charger, 6V ≤ V ≤ 28V, Up to 96% Efficiency,

IN

±0.8% Charging Voltage Accuracy

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LTC4052

LTC4053

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No Blocking Diode or External Power FET Required, ≤1.5A Charge Current

Standalone Charger with Programmable Timer, Up to 1.25A Charge Current

Standalone Linear Li-Ion Battery Charger

in ThinSOT

Thermal Regulation Prevents Overheating, C/10 Termination,

C/10 Indicator, Up to 800mA Charge Current

LTC4057

Li-Ion Linear Battery Charger

Up to 800mA Charge Current, Thermal Regulation, ThinSOT Package

LTC4058

LTC4058X

Standalone Li-Ion Linear Charger in DFN

Up to 950mA Charge Current, Kelvin Sense for High Accuracy,

C/10 Charge Termination

LTC4410

USB Power Manager

For Simultaneous Operation of USB Peripheral and Battery Charging from USB

Port, Keeps Current Drawn from USB Port Constant, Keeps Battery Fresh, Use

with the LTC4053, LTC1733, or LTC4054

LTC4411

LTC4412

Low Loss PowerPath^TMController in ThinSOT

Automatic Switching Between DC Sources, Load Sharing,

Replaces ORing Diodes

ThinSOT and PowerPath are trademarks of Linear Technology Corporation.

406842fa

LT/TP 0904 1K REV A • PRINTED IN USA

12 ^{LinearTechnology Corporation}

1630 McCarthy Blvd., Milpitas, CA 95035-7417

●

(408) 432-1900 FAX: (408) 434-0507 www.linear.com


型号：	LTC4068X-4.2
厂家：	Linear
描述：	Standalone Linear Li-Ion Battery Charger with Programmable Termination 电池
文件：	总12页 (文件大小：149K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

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