LTC1734ES6-4.1#TRPBF

LTC1734

Lithium-Ion Linear Battery

Charger in ThinSOT

FeaTures

DescripTion

The LTC^®1734 is a low cost, single cell, constant-current/

constant-voltage Li-Ion battery charger controller. When

combined with a few external components, the TSOT-23

package forms a very small, low cost charger for single

cell lithium-ion batteries.

n

Low Proﬁle (1mm) ThinSOT™ Package

n

No Blocking Diode Required

n

No Sense Resistor Required

1% Accurate Preset Voltages: 4.1V or 4.2V

n

Charge Current Monitor Output

for Charge Termination

The LTC1734 is available in 4.1V and 4.2V versions with

1% accuracy. Constant current is programmed using a

singleexternalresistorbetweenthePROGpinandground.

Manualshutdownisaccomplishedbyfloatingtheprogram

resistor while removing input power automatically puts

the LTC1734 into a sleep mode. Both the shutdown and

sleep modes drain near zero current from the battery.

n

Programmable Charge Current: 200mA to 700mA

n

Automatic Sleep Mode with Input Supply Removal

n

Manual Shutdown

n

Negligible Battery Drain Current in Shutdown

n

Undervoltage Lockout

n

Self Protection for Overcurrent/Overtemperature

Charge current can be monitored via the voltage on the

PROG pin allowing a microcontroller or ADC to read the

currentanddeterminewhentoterminatethechargecycle.

The output driver is both current limited and thermally

protected to prevent the LTC1734 from operating outside

of safe limits. No external blocking diode is required.

applicaTions

n

Cellular Telephones

n

Handheld Computers

n

Digital Cameras

Charging Docks and Cradles

Low Cost and Small Size Chargers

Programmable Current Sources

n

TheLTC1734canalsofunctionasageneralpurposecurrent

sourceorasacurrentsourceforchargingnickel-cadmium

(NiCd) and nickel-metal-hydride (NiMH) batteries using

external termination.

n

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and

ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the property

of their respective owners.

Typical applicaTion

300mA Li-Ion Battery Charger

PROG Pin Indicates Charge Status

5V

3

2

1

6

5

V

IN

V

BAT

V

I

SENSE

CC

5V

4V

3V

LTC1734

1µF

FMMT549

= 300mA

GND

DRIVE

I

BAT

4

PROG

BAT

SINGLE

+

CONSTANT

CURRENT

10µF

Li-Ion

CONSTANT

VOLTAGE

R

5k

PROG

BATTERY

2V

1.5V

V

PROG

1734 TA01

1V

0V

CHARGING

BEGINS

CHARGING

COMPLETE

1734 TA01b

1734fa

1

For more information www.linear.com/LTC1734

LTC1734

absoluTe MaxiMuM raTings

pin conFiguraTion

(Note 1)

Supply Voltage (V ) .................................–0.3V to 9V

CC

Input Voltage (BAT, PROG)........... –0.3V to (V + 0.3V)

CC

TOP VIEW

Output Voltage (DRIVE) ............... –0.3V to (V + 0.3V)

CC

I

1

6 DRIVE

5 BAT

SENSE

Output Current (I

).................................... –900mA

SENSE

GND 2

Short-Circuit Duration (DRIVE)....................... Indefinite

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

Operating Ambient Temperature Range

(Note 2) ...............................................–40°C to 85°C

Operating Junction Temperature (Note 2)............. 100°C

Storage Temperature Range ..................–65°C to 150°C

Lead Temperature (Soldering, 10 sec)...................300°C

V

3

4 PROG

CC

S6 PACKAGE

6-LEAD PLASTIC TSOT-23

T

= 125°C, θ = 230°C/W

JA

JMAX

orDer inForMaTion

LEAD FREE FINISH

LTC1734ES6-4.1#PBF

LTC1734ES6-4.2#PBF

TAPE AND REEL

PART MARKING

LTHD

PACKAGE DESCRIPTION

6-Lead Plastic SOT-23

TEMPERATURE RANGE

–40°C to 85°C

LTC1734ES6-4.1#TRPBF

LTC1734ES6-4.2#TRPBF

LTRG

–40°C to 85°C

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

Consult LTC Marketing for information on nonstandard lead based finish parts.

For more information on lead free part marking, go to: http://www.linear.com/leadfree/

For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/

elecTrical characTerisTics ^Thel denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at T_A= 25°C. V_CC= 5V, GND = 0V and V_BATis equal to the float voltage unless

otherwise noted. All current into a pin is positive and current out of a pin is negative. All voltages are referenced to GND, unless

otherwise specified.

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

V

CC

Supply

l

V

Operating Supply Range (Note 5)

4.55

8

V

CC

I

Quiescent V Pin Supply Current

V

PROG

= 5V, (Forces I

= I = 0),

670

1150

µA

CC

BAT

DRIVE

BAT

I

= 200µA,(7500Ω from PROG to GND)

l

I

V

Pin Supply Current in Manual Shutdown

CC

PROG Pin Open

450

0

900

1

µA

V

SHDN

BMS

BSL

Battery Drain Current in Manual Shutdown

Battery Drain Current in Sleep Mode (Note 4)

Undervoltage Lockout Exit Threshold

Undervoltage Lockout Entry Threshold

Undervoltage Lockout Hysteresis

PROG Pin Open (Note 3)

–1

V

= 0V

0

1

CC

V

Increasing

Decreasing

4.45

4.30

4.56

4.41

150

4.68

4.53

UVLOI

UVLOD

UVHYS

V

mV

1734fa

2

For more information www.linear.com/LTC1734

LTC1734

elecTrical characTerisTics ^Thel denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at T_A= 25°C. V_CC= 5V, GND = 0V and V_BATis equal to the float voltage unless

otherwise noted. All current into a pin is positive and current out of a pin is negative. All voltages are referenced to GND, unless

otherwise specified.

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

Charging Performance

l

V

Output Float Voltage in Constant Voltage Mode 4.1V Version, I = 10mA, 4.55V ≤ V ≤ 8V

4.059

4.158

4.10

4.20

4.141

4.242

V

BAT

BAT1

BAT2

BAT

CC

4.2V Version, I = 10mA, 4.55V ≤ V ≤ 8V

BAT

CC

l

I

Output Full-Scale Current When Programmed

for 200mA in Constant Current Mode

R

= 7500Ω, 4.55V ≤ V ≤ 8V,

155

200

700

0.15

240

770

0.28

mA

V

PROG

CC

Pass PNP Beta > 50

R = 2143Ω, 4.55V ≤ V ≤ 8V,

PROG

l

Output Full-Scale Current When Programmed

for 700mA in Constant Current Mode

620

CC

Pass PNP Beta > 50

= 10% of I , R = 7500Ω,

BAT1 PROG

V

Current Monitor Voltage on PROG Pin

Drive Output Current

I

0.045

CM1

BAT

4.55V ≤ V ≤ 8V, Pass PNP Beta > 50,

CC

0°C ≤ T ≤ 85°C

A

I

= 10% of I , R = 2143Ω,

BAT2 PROG

0.10

0.15

0.20

V

CM2

BAT

4.55V ≤ V ≤ 8V, Pass PNP Beta > 50,

CC

0°C ≤ T ≤ 85°C

A

l

I

V

= 3.5V

30

2.05

–6

mA

DSINK

DRIVE

Charger Manual Control

V

Manual Shutdown Threshold

Manual Shutdown Hysteresis

Programming Pin Pull-Up Current

V

Increasing

●

2.15

90

2.25

–1.5

130

V

mV

µA

MSDT

PROG

Decreasing from V

= 2.5V

MSHYS

PROGPU

MSDT

I

–3

Protection

I

Drive Output Short-Circuit Current Limit

V

= V

CC

●

35

65

mA

DSHRT

DRIVE

Note 1: Stresses beyond those listed under Absolute Maximum Ratings

may cause permanent damage to the device. Exposure to any Absolute

Maximum Rating condition for extended periods may affect device

reliability and lifetime.

Note 4: Assumes that the external PNP pass transistor has negligible B-E

reverse-leakage current when the emitter is biased at 0V (V ) and the

CC

base is biased at 4.2V (V ).

BAT

Note 5: The 4.68V maximum undervoltage lockout (UVLO) exit threshold

Note 2: The LTC1734E is guaranteed to meet performance specifications

from 0°C to 70°C ambient temperature range and 0°C to 100°C junction

temperature range. Specifications over the –40°C to 85°C operating

ambient temperature range are assured by design, characterization and

correlation with statistical process controls.

must first be exceeded before the minimum V specification applies.

CC

Short duration drops below the minimum V specification of several

CC

microseconds or less are ignored by the UVLO. If manual shutdown

is entered, then V must be higher than the 4.68V maximum UVLO

CC

threshold before manual shutdown can be exited. When operating near

the minimum V , a suitable PNP transistor with a low saturation voltage

CC

Note 3: Assumes that the external PNP pass transistor has negligible B-C

reverse-leakage current when the collector is biased at 4.2V (V ) and the

must be used.

BAT

base is biased at 5V (V ).

CC

1734fa

3

For more information www.linear.com/LTC1734

LTC1734

Typical perForMance characTerisTics

Float Voltage vs Temperature

and Supply Voltage

I_BAT1vs Temperature

and Supply Voltage

Float Voltage vs I_BAT

4.21

4.20

4.19

210

200

190

4.201

4.200

4.199

I

= 10mA

R

= 7.5k

PROG

V

A

= 5V

BAT

CC

PNP = FCX589

4.2V OPTION

PNP = FCX589

T

= 25°C

PNP = FCX589

4.2V OPTION

R

= 2150

PROG

V

CC

= 4.55V AND 8V

V

= 8V

CC

V

= 4.55V

25

CC

–50

0

50

75 100 125

–50

–25

0

25

50

75 100 125

–25

400

700

0

200 300

500 600

100

TEMPERATURE (°C)

I

(mA)

BAT

1734 G01

1734 G03

1734 G02

I_BAT2vs Temperature

and Supply Voltage

I

_BAT1vs V_BAT

I_BAT2vs V_BAT

740

700

660

750

700

650

210

200

190

R

= 2.15k

V

T

= 5V

CC

V

T

= 5V

PROG

CC

A

R

PNP = FCX589

= 25°C

A

R

= 2.15k

= 7.5k

PROG

PNP = FCX589

BAT PIN MUST BE DISCONNECTED

AND GROUNDED TO FORCE

CC MODE IN THIS REGION

BAT PIN MUST BE DISCONNECTED

AND GROUNDED TO FORCE

CC MODE IN THIS REGION

V

CC

= 4.55V AND 8V

–50

0

25

50

75 100 125

1

3

0

1

2

3

4

5

–25

0

2

4

5

TEMPERATURE (°C)

V

(V)

V

(V)

BAT

1734 G04

1734 G06

1734 G05

Program Pin Pull-Up Current vs

Temperature and Supply Voltage

Program Pin Pull-Up Current

vs V_PROG

Program Pin Voltage

vs Charge Current (200mA)

3.6

3.5

3.4

3.3

3.6

3.4

3.2

3.0

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0

V

A

R

= 5V

CC

V

A

= 8V

V

= 2.5V

CC

PROG

T

= 25°C

T

= 25°C

= 7.5k

PROG

PNP = FCX589

V

= 8V

CC

V

= 4.55V

CC

3.2

3.1

3.0

LIMITS AT 25mV DUE TO

PROGRAMMING PIN PULL-UP

2.8

2.6

CURRENT (I

)

PROGPU

100

0

50

150

200

50

TEMPERATURE (°C)

100 125

2

4

5

6

7

8

–50 –25

0

25

75

3

V

(V)

I

(mA)

PROG

BAT1

1734 F09

1734 G07

1635 G08

1734fa

4

For more information www.linear.com/LTC1734

LTC1734

Typical perForMance characTerisTics

Program Pin Voltage

vs Charge Current (700mA)

Program Pin Voltage for I_BAT1/10

vs Temperature and Supply Voltage

Program Pin Voltage for I_BAT2/10

vs Temperature and Supply Voltage

1.6

160

150

140

160

150

140

V

T

= 5V

R

= 7.5k

CC

A

R

= 2.15k

PROG

= 25°C

PNP = FCX589

1.4

1.2

= 2.15k

PROG

PNP = FCX589

1.0

0.8

0.6

0.4

0.2

V

= 8V

CC

V

= 8V

CC

V

= 4.55V

CC

V

= 4.55V

CC

LIMITS AT 6mV DUE TO

PROGRAMMING PIN PULL-UP

CURRENT (I

)

PROGPU

0

100 200

400 500 600 700

0

300

–50

0

25

50

75 100 125

–25

–50

0

25

50

75

125

–25

100

I

(mA)

TEMPERATURE (°C)

BAT2

1734 G10

1734 G11

1734 G12

pin FuncTions

I

(Pin 1): Sense Node for Charge Current. Current

= 1500/R

). This pin also allows for the charge current

PROG

SENSE

fromV passesthroughtheinternalcurrentsenseresistor

to be monitored. The voltage on this pin is proportional

to the charge current where 1.5V corresponds to the full

programmed current. Floating this pin allows an internal

current source to pull the pin voltage above the shutdown

threshold voltage. Because this pin is in a signal path,

excessive capacitive loading can cause AC instability.

See the Applications Information section for more details.

CC

and reappears at I

to supply current to the external

SENSE

PNP emitter. The PNP collector provides charge current

to the battery.

GND (Pin 2): Ground. Provides a reference for the internal

voltageregulatorandareturnforallinternalcircuits.When

in the constant voltage mode, the LTC1734 will precisely

regulate the voltage between the BAT and GND pins. The

battery ground should connect close to the GND pin to

avoid voltage drop errors.

BAT (Pin 5): Battery Voltage Sense Input. A precision

internal resistor divider sets the final float voltage on this

pin. This divider is disconnected in the manual shutdown

or sleep mode. When charging, approximately 34µA

flows into the BAT pin. To minimize float voltage errors,

avoid excessive resistance between the battery and the

BAT pin. For dynamically stable operation, this pin usu-

ally requires a minimum bypass capacitance to ground

of 5µF to frequency compensate for the high frequency

inductive effects of the battery and wiring.

V

CC

(Pin 3): Positive Input Supply Voltage. This pin sup-

plies power to the internal control circuitry and external

PNPtransistorthroughtheinternalcurrentsenseresistor.

This pin should be bypassed to ground with a capacitor

in the range of 1µF to 10µF.

PROG (Pin 4): Charge Current Programming, Charge Cur-

rent Monitor and Manual Shutdown Pin. Provides a virtual

DRIVE (Pin 6): Base Drive Output for the External PNP

Pass Transistor. Provides a controlled sink current that

drives the base of the PNP. This pin has current limiting

protection for the LTC1734.

reference voltage of 1.5V for an external resistor (R

)

PROG

tied between this pin and ground that programs the bat-

tery charge current when the charger is in the constant

current mode. The typical charge current will be 1000

times greater than the current through this resistor (I

BAT

1734fa

5

For more information www.linear.com/LTC1734

LTC1734

block DiagraM

V

IN

1F

V

CC

3

I

/1000

BAT

60

0.06

I

SENSE

1

6

SHUTDOWN

VOLTAGE

REFERENCE

REF

+

–

DRIVE

2.5V

OUTPUT

DRIVER

A3

UVLO

C1

SHUTDOWN

TEMPERATURE AND

CURRENT LIMITING

I

BAT

10F

2.15V

1.5V

2.5V

5

+

–

+

SINGLE

Li-Ion

CELL

SHUTDOWN

A2

A1

–

3A

SHUTDOWN

1734 BD

4

2

GND

PROG

R

PROG

1734fa

6

For more information www.linear.com/LTC1734

LTC1734

operaTion

The LTC1734 is a linear battery charger controller. Op-

eration can best be understood by referring to the Block

Diagram.ChargingbeginswhenV_CCrisesabovetheUVLO

(Undervoltage Lockout) threshold V_UVLOIand an external

current programming resistor is connected between the

PROG pin and ground. When charging, the collector of

the external PNP provides the charge current. The PNP’s

emitter current flows through the I_SENSEpin and through

the internal 0.06Ω current sense resistor. This current is

close in magnitude, but slightly more than the collector

current since it includes the base current. Amplifier A3,

along with the P-channel FET, will force the same voltage

that appears across the 0.06Ω resistor to appear across

the internal 60Ω resistor. The scale factor of 1000:1 in

resistor values will cause the FET’s drain current to be

1/1000 of the charge current and it is this current that

flows through the PROG pin. In the constant current

mode, amplifier A2 is used to limit the charge current to

4.2V (2.5V at amplifier A1’s input) the amplifier will divert

current away from the output driver thus limiting charge

current to that which will maintain 4.2V on the battery.

This is the constant voltage mode.

Whenintheconstantvoltagemode,the1000:1currentratio

is still valid and the voltage on the PROG pin will indicate

the charge current as a proportion of the maximum cur-

rent set by the current programming resistor. The battery

chargecurrentis1000•(V

/R

)amps.Thisfeature

PROG PROG

allows a microcontroller with an ADC to easily monitor

charge current and if desired, manually shut down the

charger at the appropriate time.

When V is applied, the charger can be manually shut

CC

down by floating the otherwise grounded end of R

.

PROG

An internal 3µA current source pulls the PROG pin above

the 2.15V threshold of voltage comparator C1 initiating

shutdown.

the maximum that is programmed by R_PROG

.

For charging NiMH or NiCd batteries, the LTC1734 can

function as a constant current source by grounding the

BAT pin. This will prevent amplifier A1 from trying to limit

charging current and only A2 will control the current.

The PROG pin current, which is 1/1000 of the charge

current, develops a voltage across the program resistor.

When this voltage reaches 1.5V, amplifier A2 begins di-

verting current away from the output driver, thus limiting

the charge current. This is the constant current mode. The

Faultconditionssuchasoverheatingofthedieorexcessive

DRIVE pin current are monitored and limited.

constant charge current is 1000 • (1.5V/R

).

PROG

When input power is removed or manual shutdown is

entered, the charger will drain only tiny leakage currents

from the battery, thus maximizing battery standby time.

As the battery accepts charge, its voltage rises. When it

reaches the preset float voltage of 4.2V (LTC1734-4.2

version), a precisely divided down version of this voltage

(2.5V) is compared to the 2.5V internal reference voltage

by amplifier A1. If the battery voltage attempts to exceed

With V removed the external PNP’s base is connected

CC

to the battery by the charger. In manual shutdown the

base is connected to V by the charger.

CC

1734fa

7

For more information www.linear.com/LTC1734

LTC1734

applicaTions inForMaTion

Charging Operation

resistorvaluewhenlowtopreventexcessivechargecurrent

errors. To reduce errors the program resistor value may

be adjusted to account for the impedance to ground. The

programming resistor will prevent potentially damaging

Charging begins when an input voltage is present that

exceeds the undervoltage lockout threshold (V_UVLOI),

a Li-Ion battery is connected to the charger output and

a program resistor is connected from the PROG pin to

ground. During the first portion of the charge cycle, when

the battery voltage is below the preset float voltage, the

charger is in the constant current mode. As the battery

voltage rises and reaches the preset float voltage, the

chargecurrentbeginstodecreaseandtheconstantvoltage

portion of the charge cycle begins. The charge current

will continue to decrease exponentially as the battery

approaches a fully charged condition.

currents if the PROG pin is forced above V . Under this

CC

condition V may float, be loaded down by other circuitry

CC

or be shorted to ground. If V is not shorted to ground

CC

thecurrentthroughtheresistorwillpullV upsomewhat.

CC

Another method is to directly switch the PROG pin to

a voltage source when shutdown is desired (Caution:

pulling the PROG below 1.5V with V applied will cause

CC

excessiveanduncontrolledchargecurrents).Thevoltage

source must be capable of sourcing the resulting current

through the program resistor. This has the advantage

of not adding any error to the program resistor during

normal operation. The voltage on the PROG pin must

Should the battery be removed during charging, a fast

built-in protection circuit will prevent the BAT pin from

rising above 5V, allowing the precision constant voltage

circuit time to respond.

be greater than 2.25V (V

) to ensure entering

MSDT(MAX)

shutdown, but no more than 0.3V above V to prevent

CC

damagingtheLTC1734fromexcessivePROGpincurrent.

Manual Shutdown

An exception is if V is allowed to float with no other

CC

Floating the program resistor allows an internal 3µA

circuitryloadingV down.Then,becausethecurrentwill

CC

current source (I

) to pull the PROG pin above the

PROGPU

be low, it is allowable to have the PROG pin shutdown

voltage applied. A three-state logic driver with sufficient

pull-up current can be used to perform this function by

enabling the high impedance state to charge or enabling

the pull-up device to enter shutdown.

2.15V shutdown threshold (V

), thus shutting down

MSDT

the charger. In this mode, the LTC1734 continues to draw

somecurrentfromthesupply(I ),butonlyanegligible

SHDN

leakage current is delivered to the battery (I

).

BMS

Shutdown can also be accomplished by pulling the oth-

erwise grounded end of the program resistor to a voltage

An NPN transistor or a diode can also be utilized to imple-

ment shutdown from a voltage source. These have the

advantage of blocking current when the voltage source

goes low, thus automatically disconnecting the voltage

source for normal charging operation. The use of an NPN

allows for use of a weak voltage source due to the current

gain of the transistor. For an NPN connect the collector to

greaterthan2.25V(V

Max).Chargingwillceaseabove

MSDT

1.5V, but the internal battery voltage resistor divider will

draw about 34µA from the battery until shutdown is en-

tered. Figure 1 illustrates a microcontroller configuration

that can either float the resistor or force it to a voltage. The

voltage should be no more than 8V when high and have

an impedance to ground of less than 10% of the program

V

the base to the voltage source and the emitter to the

CC,

PROG pin. For a diode, connect the anode to the voltage

source and cathode to the PROG pin. An input high level

R

PROG

ranging from 3.3V to V should be adequate to enter

PROG

LTC1734

OPEN DRAIN

OR TOTEM

POLE OUTPUT

CC

shutdown while a low level of 0.5V or less should allow

for normal charging operation. Use of inexpensive small

signal devices such as the 2N3904 or 1N914 is recom-

mended to prevent excessive capacitive loading on the

PROG pin (see Stability section).

C

ADC INPUT

1734 F01

Figure 1. Interfacing with a Microcontroller

1734fa

8

For more information www.linear.com/LTC1734

LTC1734

applicaTions inForMaTion

Sleep Mode

Programming Constant Current

When the input supply is disconnected, the IC enters the

When in the constant current mode, the full-scale charge

current(C)isprogrammedusingasingleexternalresistor

between the PROG pin and ground. This charge current

will be 1000 times greater than the current through the

program resistor. The program resistor value is selected

by dividing the voltage forced across the resistor (1.5V)

by the desired resistor current.

sleep mode. In this mode, the battery drain current (I

)

BSL

is a negligible leakage current, allowing the battery to re-

main connected to the charger for an extended period of

time without discharging the battery. The leakage current

is due to the reverse-biased B-E junction of the external

PNP transistor.

The LTC1734 is designed for a maximum current of ap-

proximately 700mA. This translates to a maximum PROG

pin current of 700µA and a minimum program resistor of

approximately 2.1k. Because the PROG pin is in a closed-

loop signal path, the pole frequency must be kept high

enough to maintain adequate AC stability by avoiding

excessive capacitance on the pin. See the Stability section

for more details.

Undervoltage Lockout

Undervoltage lockout (UVLO) keeps the charger off until

the input voltage exceeds a predetermined threshold level

(V

) that is typically 4.56V. Approximately 150mV

UVLOI

of hysteresis is built in to prevent oscillation around the

threshold level. In undervoltage lockout, battery drain

current is very low (<1µA).

3

1

V

IN

CHARGE CURRENT CONTROL 1 CONTROL 2

V

I

SENSE

CC

5V

0

LOW

HIGH

LOW

HIGH

LOW

HIGH

LTC1734

1F

200mA

500mA

700mA

2

4

6

5

FZT549

GND

DRIVE

OPTIONAL FILTER

1k

I

BAT

CHARGE

CURRENT

MONITOR

(FILTERED)

CHARGE

CURRENT

PIN 4

PROG

BAT

SINGLE

MONITOR

0.1F TO

0.5F

10F

Li-Ion

(UNFILTERED)

3k

7.5k

Q2

BATTERY

Q1

2N7002

1734 F02

2N7002

CONTROL 1

CONTROL 2

Figure 2. Logic Control Programming of Output Current to 0mA, 200mA, 500mA or 700mA

3

2

4

1

6

5

V

IN

V

I

SENSE

CC

5V

LTC1734

1F

FZT549*

GND

DRIVE

CURRENT CONTROL 1 CONTROL 2

I

LOAD

PROG

BAT

0

LOW

HIGH

LOW

HIGH

LOW

HIGH

200mA

500mA

700mA

LOAD

3k

7.5k

1734 F03

Q1

2N7002

Q2

2N7002

*OBSERVE MAXIMUM TEMPERATURE

CONTROL 1

CONTROL 2

Figure 3. Programmable Current Source with Output Current of 0mA, 200mA, 500mA or 700mA

1734fa

9

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LTC1734

applicaTions inForMaTion

The minimum full-scale current that can be reliably

programmed is approximately 50mA, which requires a

program resistor of 30k. Limiting capacitive loading on

the program pin becomes more important when high

value program resistors are used. In addition, the cur-

rent monitoring accuracy can degrade considerably at

very low current levels. If current monitoring is desired,

a minimum full-scale current of 200mA is recommended.

Dynamic loads on the battery will cause transients to ap-

pear on the PROG pin. Should they cause excessive errors

in charge current monitoring, a simple RC filter as shown

in Figure 2 can be used to filter the transients. The filter

will also quiet the PROG pin to help prevent inadvertent

momentary entry into the manual shutdown mode.

Because the PROG pin is in a closed-loop signal path the

pole frequency must be kept high enough to maintain

adequate AC stability. This means that the maximum

resistance and capacitance presented to the PROG pin

must be limited. See the Stability section for more details.

Different charge currents can be programmed by various

meanssuchasbyswitchingindifferentprogramresistors

as shown in Figures 2 and 3. A voltage DAC connected

through a resistor to the PROG pin or a current DAC

connected in parallel with a resistor to the PROG pin can

also be used to program current (the resistor is required

Constant Current Source

The LTC1734 can be used as a constant current source

by disabling the voltage control loop as shown in Figure

3. This is done by pulling the BAT pin below the preset

float voltages of 4.1V or 4.2V by grounding the BAT pin.

The program resistor will determine the output current.

The output current range can be between approximately

50mA and 700mA, depending on the maximum power

rating of the external PNP pass transistor.

with the I

to maintain AC stability as discussed in the

DAC

Stability section). Another means is to use a PWM output

from a microcontroller to duty cycle the charger into and

out of shutdown to create an average current (see Manual

Shutdown section for interfacing examples). Because

chargers are generally slow to respond, it can take up to

approximately 300µs for the charger to fully settle after a

shutdown is de-asserted. This delay must be accounted

for unless the minimum PWM low duration is about 3ms

or more. Shutdown occurs within a few microseconds of

a shutdown command. The use of PWM can extend the

average current to less than the normal 200mA minimum

constant current.

External PNP Transistor

The external PNP pass transistor must have adequate

beta,lowsaturationvoltageandsufficientpowerdissipa-

tion capability (including any heat sinking, if required).

To provide 700mA of charge current with the minimum

availablebasedriveofapproximately30mArequiresaPNP

betagreaterthan23.IflowerbetaPNPtransistorsareused,

more base current is required from the LTC1734. This can

result in the output drive current limit being reached, or

thermal shutdown due to excessive power dissipation.

ExcessivebetacanaffectACstability(seeStabilitysection)

Monitoring Charge Current

The voltage on the PROG pin indicates the charge cur-

rent as a proportion of the maximum current set by the

program resistor. The charge current is equal to 1000 •

(V

/R

)amps.Thisfeatureallowsamicrocontroller

PROG PROG

with an ADC to easily monitor charge current and if de-

sired, manually shut down the charger at the appropriate

time. See Figure 1 for an example. The minimum PROG

With low supply voltages, the PNP saturation voltage

(V_CESAT) becomes important. The V_CESATmust be less

than the minimum supply voltage minus the maximum

voltage drop across the internal sense resistor and bond

wires(0.1Ω)andbatteryfloatvoltage.IfthePNPtransistor

can not achieve the low saturation voltage required, base

current will dramatically increase. This is to be avoided

for a number of reasons: output drive may reach current

pin current is about 3µA (I

).

PROGPU

Errors in the charge current monitor voltage on the PROG

pin are inversely proportional to battery current and can

be statistically approximated as follows:

One Sigma Error(%) ≅ 1 + 0.3/I (A)

BAT

1734fa

10

For more information www.linear.com/LTC1734

LTC1734

applicaTions inForMaTion

Table 1. PNP Pass Transistor Selection Guide

MAXIMUM P (W) MOUNTED

D

ON BOARD AT T = 25°C

PACKAGE STYLE

SOT-23

SOT-89

SOT-23-6

SOT-89

SOT-223

FTR

ZETEX PART NUMBER

FMMT549

ROHM PART NUMBER

COMMENTS

Low V

A

0.5

0.625

1

CESAT

FMMT720

Very Low V

High Beta

CESAT,

FCX589 or BCX69

ZXT10P12DE6

FCX717

1.1

1 to 2

2

Very Low V

High Beta, Small

CESAT,

Very Low V

High Beta

CESAT,

FZT589

Low V

CESAT

2

BCP69 or FZT549

0.75

1

2SB822

2SB1443

2SA1797

2SB1182

Low V

CESAT

ATV

2

SOT-89

TO-252

10 (T = 25°C)

Low V

High Beta

C

CESAT,

limit resulting in the charger’s characteristics to go out of

specifications, excessivepowerdissipationmayforcethe

IC into thermal shutdown, or the battery could become

discharged because some of the current from the DRIVE

pin could be pulled from the battery through the forward

biased collector base junction.

V

is the maximum supply voltage and V

is

DD(MAX)

BAT(MIN)

the minimum battery voltage when discharged.

Once the maximum power dissipation and V

known, Table 1 can be used as a guide in selecting some

PNPs to consider. In the table, very low V

0.25V, low V

are

CE(MIN)

is less than

CESAT

is 0.25V to 0.5V and the others are 0.5V

CESAT

For example, to program a charge current of 500mA

with a minimum supply voltage of 4.75V, the minimum

to 0.8V all depending on the current. See the manufac-

turer’s data sheet for details. All of the PNP transistors

are rated to carry at least 1A continuously as long as the

power dissipation is within limits. The Stability section

addresses caution in the use of high beta PNPs.

operating V is:

CE

V (V) = 4.75 – (0.5)(0.1) – 4.2 = 0.5V

CE(MIN)

The actual battery charge current (I ) is slightly smaller

BAT

Should overheating of the PNP transistor be a concern,

protection can be achieved with a positive temperature

coefficient (PTC) thermistor, wired in series with the cur-

rent programming resistor and thermally coupled to the

transistor. The PTH9C chip series from Murata has a steep

resistanceincreaseattemperaturethresholdsfrom85°Cto

145°Cmakingitbehavesomewhatlikeathermostatswitch.

For example, the model PTH9C16TBA471Q thermistor is

470Ω at 25°C, but abruptly increase its resistance to 4.7k

at125°C.Below125°C,thedeviceexhibitsasmallnegative

TC. The 470Ω thermistor can be added in series with a

1.6kresistortoformthecurrentprogrammingresistorfor

a 700mA charger. Should the thermistor reach 125°C, the

charge current will drop to 238mA and inhibit any further

increase in temperature.

than the expected charge current because the charger

senses the emitter current and the battery charge current

will be reduced by the base current. In terms of β (I /I ),

C B

I

can be calculated as follows:

BAT

I

(A) = 1000 • I [β/(β + 1)]

PROG

BAT

If β = 50, then I is 2% low. If desired, the 2% loss can

BAT

be compensated for by increasing I

by 2%.

PROG

Another important factor to consider when choosing the

PNP pass transistor is the power handling capability. The

transistor’sdatasheetwillusuallygivethemaximumrated

power dissipation at a given ambient temperature with a

power derating for elevated temperature operation. The

maximum power dissipation of the PNP when charging is:

P

(W) = I (V

– V

)

D(MAX)

BAT DD(MAX)

BAT(MIN)

1734fa

11

For more information www.linear.com/LTC1734

LTC1734

applicaTions inForMaTion

Stability

first, then if the battery voltage is near the programmed

voltage of 4.1V or 4.2V, the constant voltage mode will

begin. The resulting waveform on the PROG pin is an

indication of stability.

The LTC1734 contains two control loops: constant volt-

age and constant current. To maintain good AC stability

in the constant voltage mode, a capacitor of at least 4.7µF

is usually required from BAT to ground. The battery and

interconnectingwiresappearinductiveathighfrequencies,

and since these are in the feedback loop, this capacitance

may be necessary to compensate for the inductance.

This capacitor need not exceed 100µF and its ESR can

range from near zero to several ohms depending on the

inductance to be compensated. In general, compensation

is optimal with a capacitance of 4.7µF to 22µF and an ESR

of 0.5Ω to 1.5Ω.

The double exposure photo in Figure 5 shows the effects

of capacitance on the program pin. The middle waveform

is typical while the lower waveform indicates excessive

program pin capacitance resulting in constant current

mode instability. Although not common, ringing on the

constant voltage portion of the waveform is an indication

of instability due to any combination of extremely low ESR

values, high capacitance values of the output capacitor

or very high PNP transistor beta. To minimize the effect

of the scope probe capacitance, a 10k resistor is used to

isolatetheprobefromtheprogrampin.Also,anadjustable

load resistor or current sink can be used to quickly alter

the charge current when a fully charged battery is used.

Using high beta PNP transistors (>300) and very low ESR

output capacitors (especially ceramic) reduces the phase

margin, possibly resulting in oscillation. Also, using high

value capacitors with very low ESRs will reduce the phase

margin. Adding a resistor of 0.5Ω to 1.5Ω in series with

the capacitor will restore the phase margin.

10k

TO SCOPE

PROG

BAT

+

6 TO

20

R

PROG

3k

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

back loop, not the battery. Because of this, capacitance

on this pin must be limited. Locating the program resis-

tor near the PROG pin and isolating the charge current

monitoring circuitry (if used) from the PROG pin with a

1k to 10k resistor may be necessary if the capacitance is

greater than that given by the following equation:

Li-Ion*

LTC1734

2.5V

0V

1734 F04

f = 1kHz

*FULLY CHARGED CELL

Figure 4. Setup for AC Stability Testing

5V

0V

400k

R_PROG

PULSE

GENERATOR

C_MAX(pF)

=

Higher charge currents require lower program resistor

values which can tolerate more capacitive loading on the

PROG pin. Maximum capacitance can be as high as 50pF

2V

1V

0V

2V

1V

0V

PROG PIN

(20pF ON PIN)

for a charge current of 200mA (R

= 7.5k).

PROG

PROG PIN

(200pF ON PIN)

Figure 4 is a simple test circuit for checking stability in

both the constant current and constant voltage modes.

With input power applied and a near fully charged battery

connected to the charger, driving the PROG pin with a

pulse generator will cycle the charger in and out of the

manualshutdownmode.ReferringtoFigure5,afterashort

delay, the charger will enter the constant current mode

SHUT DELAY

DOWN

CONSTANT

CURRENT

CONSTANT

VOLTAGE

HORIZONTAL SCALE: 100s/DIV

Figure 5. Stability Waveforms

1734fa

12

For more information www.linear.com/LTC1734

LTC1734

applicaTions inForMaTion

Reverse Input Voltage Protection

the charger input to a hot power source. To prevent these

transients from exceeding the absolute maximum voltage

rating, several ohms of resistance can be added in series

with the ceramic input capacitor.

In some applications, protection from reverse voltage

on V is desired. If the supply voltage is high enough, a

CC

series blocking diode can be used. In other cases, where

the voltage drop must be kept low, a P-channel FET as

shown in Figure 6 can be used.

Internal Protection

Internal protection is provided to prevent excessive

V

Bypass Capacitor

DRIVE pin currents (I

) and excessive self-heating

CC

DSHRT

of the LTC1734 during a fault condition. The faults can

be generated from a shorted DRIVE pin or from exces-

sive DRIVE pin current to the base of the external PNP

Many types of capacitors with values ranging from 1µF to

10µF located close to the LTC1734 will provide adequate

input bypassing. However, caution must be exercised

when using multilayer ceramic capacitors. Because of the

self resonant and high Q characteristics of some types of

ceramic capacitors, high voltage transients can be gener-

ated under some start-up conditions, such as connecting

transistor when it’sindeep saturation from too lowa V .

CE

This protection is not designed to prevent overheating

of the external pass transistor. Indirectly though, self-

heating of the PNP thermally conducting to the LTC1734

and resulting in the IC’s junction temperature to rise

above 150°C, thus cutting off the PNP’s base current.

This action will limit the PNP’s junction temperature to

some temperature well above 150°C. The temperature

depends on how well the IC and PNP are thermally

*

V

IN

CC

LTC1734

1734 F06

*DRAIN-BULK DIODE OF FET

connected and on the transistor’s θ . See the External

JA

PNP Transistor section for information on protecting the

Figure 6. Low Loss Reverse Voltage Protection

transistor from overheating.

1734fa

13

For more information www.linear.com/LTC1734

LTC1734

package DescripTion

Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.

S6 Package

6-Lead Plastic TSOT-23

(Reference LTC DWG # 05-08-1636)

2.90 BSC

(NOTE 4)

0.62

MAX

0.95

REF

1.22 REF

1.4 MIN

1.50 – 1.75

(NOTE 4)

2.80 BSC

3.85 MAX 2.62 REF

PIN ONE ID

RECOMMENDED SOLDER PAD LAYOUT

PER IPC CALCULATOR

0.30 – 0.45

6 PLCS (NOTE 3)

0.95 BSC

0.80 – 0.90

0.20 BSC

DATUM ‘A’

0.01 – 0.10

1.00 MAX

0.30 – 0.50 REF

1.90 BSC

0.09 – 0.20

(NOTE 3)

S6 TSOT-23 0302

NOTE:

1. DIMENSIONS ARE IN MILLIMETERS

2. DRAWING NOT TO SCALE

3. DIMENSIONS ARE INCLUSIVE OF PLATING

4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR

5. MOLD FLASH SHALL NOT EXCEED 0.254mm

6. JEDEC PACKAGE REFERENCE IS MO-193

1734fa

14

For more information www.linear.com/LTC1734

LTC1734

revision hisTory

REV

DATE

DESCRIPTION

PAGE NUMBER

A

9/15

Revised package drawing and reference.

1, 2, 14

1734fa

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 representa-

tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

15

For more information www.linear.com/LTC1734

LTC1734

relaTeD parTs

PART NUMBER

DESCRIPTION

COMMENTS

LT^®1510-5

500kHz Constant-Current/Constant-Voltage Battery

Charger

Up to 1A Charge Current for Li-Ion, NiCd, NiMH or Lead-Acid Batteries

LT1571-1/LT1571-2

LT1571-5

200kHz/500kHz Constant-Current/Constant-Voltage

Battery Charger Family

Up to 1.5A Charge Current for 1-, 2- or Multiple Cell Li-Ion Batteries,

Preset and Adjustable Battery Voltages, C/10 Charge Detection

LTC1729

LTC1730

LTC1731

LTC1732

LT1769

Li-Ion Battery Charger Termination Controller

Can be Used with LTC Battery Chargers to Provide Charge Termination,

Preset Voltages, C/10 Charge Detection and Timer Functions

Li-Ion Battery Pulse Charger

Minimizes Heat Dissipation, No Blocking Diode Required, Limits

Maximum Current for Safety

Linear Constant-Current/Constant-Voltage Charger

Controller

Simple Charger Uses External FET. Features Preset Voltages, C/10 Charge

Detection and Programmable Timer

Linear Constant-Current/Constant-Voltage Charger

Controller

Simple Charger Uses External FET. Input Power Good Indication Features

Preset Voltages, C/10 Charge Detection and Programmable Timer

200kHz Constant-Current/Constant-Voltage Battery

Charger

Up to 2A Charge Current for Li-Ion, NiCd, NiMH or Lead-Acid Batteries

with Input Current Limit

1734fa

LT 0915 REV A • PRINTED IN USA

LinearTechnology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

16

For more information www.linear.com/LTC1734

(408)432-1900 FAX: (408) 434-0507 www.linear.com/LTC1734

l

 LINEAR TECHNOLOGY CORPORATION 2001


型号：	LTC1734ES6-4.1#TRPBF
厂家：	Linear
描述：	LTC1734 - Lithium-Ion Linear Battery Charger in ThinSOT; Package: SOT; Pins: 6; Temperature Range: -40°C to 85°C 电池光电二极管
文件：	总16页 (文件大小：203K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

LTC1734ES6-4.1#TRPBF [Linear]

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