LTC1734LES6-4.2#TRMPBF [Linear]

LTC1734L - Lithium-Ion Linear Battery Charger in ThinSOT; Package: SOT; Pins: 6; Temperature Range: -40°C to 85°C;


型号：	LTC1734LES6-4.2#TRMPBF
厂家：	Linear
描述：	LTC1734L - Lithium-Ion Linear Battery Charger in ThinSOT; Package: SOT; Pins: 6; Temperature Range: -40°C to 85°C 电源电路电池电源管理电路
文件：	总12页 (文件大小：186K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

LTC1734L

Lithium-Ion Linear

Battery Charger in ThinSOT

FEATURES

DESCRIPTIO

Low Profile (1mm) ThinSOT^TMPackage

TheLTC^®1734Lisalowcost,singlecell,constant-current/

constant-voltage Li-Ion battery charger controller. When

combined with a few external components, the SOT-23

packageformsaverysmall,lowcostchargerforsinglecell

lithium-ion batteries. The LTC1734L is a lower charge

current version of the LTC1734.

■

Programmable Charge Current: 50mA to 180mA

■

No Blocking Diode Required

■

No Sense Resistor Required

■

1% Accurate Preset Voltage: 4.2V

■

Charge Current Monitor Output

for Charge Termination

The LTC1734L provides a fixed float voltage of 4.2V with

1% accuracy (for 4.1V and 4.15V float voltages, contact

LTC Marketing). Constant current is programmed using a

singleexternalresistorbetweenthePROGpinandground.

Manual shutdown is accomplished by floating the pro-

gram resistor while removing input power automatically

puts the LTC1734L into a sleep mode. Both the shutdown

and sleep modes drain near zero current from the battery.

■

Automatic Sleep Mode with Input Supply Removal

■

Manual Shutdown

■

Negligible Battery Drain Current in Shutdown

■

Undervoltage Lockout

■

Self Protection for Overcurrent/Overtemperature

APPLICATIO S

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

protectedtopreventtheLTC1734Lfromoperatingoutside

of safe limits. No external blocking diode is required.

■

Cellular Telephones

■

Handheld Computers

■

Digital Cameras

■

Charging Docks and Cradles

■

Low Cost and Small Size Chargers

■

Programmable Current Sources

The LTC1734L can also function as a general purpose

current source or as a current source for charging nickel-

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

ies using external termination.

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

ThinSOT is a trademark of Linear Technology Corporation.

TYPICAL APPLICATIO

PROG Pin Indicates Charge Status

BAT

80mA Li-Ion Battery Charger

SENSE

LTC1734L

1µF

UMT4403

GND

DRIVE

CONSTANT

CURRENT

CONSTANT

VOLTAGE

= 80mA

BAT

PROG

BAT

1.5V

PROG

SINGLE

Li-Ion

BATTERY

10µF

PROG

4.7k

1734 TA01

CHARGING

BEGINS

CHARGING

COMPLETE

1734 TA01b

1734lf

LTC1734L

W W U W

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ABSOLUTE MAXIMUM RATINGS

PACKAGE/ORDER INFORMATION

(Note 1)

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

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

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

Output Current (I_SENSE) ................................... –210mA

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

ORDER PART

NUMBER

TOP VIEW

LTC1734LES6-4.2

6 DRIVE

5 BAT

SENSE

GND 2

4 PROG

S6 PACKAGE

6-LEAD PLASTIC SOT-23

S6 PART MARKING

LTE6

T_JMAX= 125°C, θ_JA= 230°C/W

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

ELECTRICAL CHARACTERISTICS

The ● denotes the specifications which apply over the full operating

temperature range, unless otherwise noted 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

Supply

Input Supply Voltage (Note 5)

Quiescent V Pin Supply Current

●

4.55

BAT

= 5V, (Forces I

= I = 0),

BAT

670

1150

µA

DRIVE

= 200µA,(7500Ω from PROG to GND)

PROG

Pin Supply Current in Manual Shutdown

PROG Pin Open

●

450

900

µA

SHDN

BMS

Battery Drain Current in Manual Shutdown

(Note 3)

–1

Battery Drain Current in Sleep Mode (Note 4)

Undervoltage Lockout Exit Threshold

Undervoltage Lockout Entry Threshold

Undervoltage Lockout Hysteresis

= 0V

●

–1

µA

BSL

Increasing

Decreasing

4.45

4.30

4.56

4.41

150

4.68

4.53

UVLOI

UVLOD

UVHYS

Charging Performance

Output Float Voltage in Constant Voltage Mode

= 10mA, 4.55V ≤ V ≤ 8V

●

4.158 4.20

4.242

BAT

Output Full-Scale Current When Programmed

for 50mA in Constant Current Mode

= 7500Ω, 4.55V ≤ V ≤ 8V,

BAT1

PROG

Pass PNP Beta > 50

Output Full-Scale Current When Programmed

for 180mA in Constant Current Mode

= 2100Ω, 4.55V ≤ V ≤ 8V,

●

160

180

200

BAT2

PROG

Pass PNP Beta > 50

= 10% of I , R = 7500Ω,

BAT1 PROG

Current Monitor Voltage on PROG Pin

Drive Output Current

0.045 0.15

0.28

CM1

CM2

BAT

4.55V ≤ V ≤ 8V, Pass PNP Beta > 50,

0°C ≤ T ≤ 85°C

= 10% of I

, R = 2100Ω,

BAT2 PROG

0.10

0.15

0.20

BAT

4.55V ≤ V ≤ 8V, Pass PNP Beta > 50,

0°C ≤ T ≤ 85°C

DRIVE

= 3.5V

●

DSINK

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LTC1734L

ELECTRICAL CHARACTERISTICS

The ● 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

Charger Manual Control

CONDITIONS

MIN

2.05

–6

TYP

MAX

2.25

–1.5

130

UNITS

Manual Shutdown Threshold

Manual Shutdown Hysteresis

Program Pin Pull-Up Current

PROG

Increasing

●

2.15

µA

MSDT

Decreasing from V

= 2.5V

MSHYS

PROGPU

MSDT

–3

Protection

Drive Output Short-Circuit Current Limit

DRIVE

= V

DSHRT

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

of a device may be impaired.

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

base is biased at 4.2V (V ).

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

must first be exceeded before the minimum V specification applies.

Short duration drops below the minimum V specification of several

BAT

Note 2: The LTC1734LE 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.

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

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

threshold before manual shutdown can be exited. When operating near the

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

BAT

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

base is biased at 5V (V ).

must be used.

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TYPICAL PERFOR A CE 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

4.201

4.200

4.199

= 10mA

= 5V

= 7.5k

BAT

PROG

PNP = FCX589

= 25°C

PNP = FCX589

= 2100Ω

PROG

= 4.55V AND 8V

= 8V

= 4.55V

–50

75 100 125

–25

100

175

125

125 150

–50

75 100

–25

TEMPERATURE (°C)

(mA)

TEMPERATURE (°C)

BAT

1734 G01

1734 G02

1734 G03

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LTC1734L

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TYPICAL PERFOR A CE CHARACTERISTICS

I_BAT2vs Temperature

and Supply Voltage

I_BAT1vs V_BAT

I_BAT2vs V_BAT

190

180

170

190

180

170

= 5V

= 2.1k

= 5V

PROG

= 25°C

PNP = FCX589

= 25°C

= 7.5k

= 2.1k

PROG

PNP = FCX589

BAT PIN MUST BE DISCONNECTED

AND GROUNDED TO FORCE

CC MODE IN THIS REGION

= 4.55V AND 8V

BAT PIN MUST BE DISCONNECTED

AND GROUNDED TO FORCE

CC MODE IN THIS REGION

–50

75 100 125

–25

TEMPERATURE (°C)

(V)

BAT

1734 G04

1734 G05

1734 G06

Program Pin Pull-Up Current vs

Temperature and Supply Voltage

Program Pin Pull-Up Current

vs V_PROG

Program Pin Voltage

vs Charge Current (50mA)

3.6

3.4

3.2

3.0

3.6

3.5

3.4

3.3

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

= 5V

= 8V

PROG

= 2.5V

= 25°C

= 7.5k

PROG

PNP = FCX589

= 8V

= 4.55V

3.2

3.1

3.0

LIMITS AT 25mV DUE TO

PROGRAMMING PIN PULL-UP

2.8

2.6

CURRENT (I

)

PROGPU

TEMPERATURE (°C)

100 125

–50 –25

(V)

PROG

(mA)

BAT1

1635 G08

1734 G07

1734 F09

Program Pin Voltage for I_BAT1/10

vs Temperature and Supply Voltage

Program Pin Voltage for I_BAT2/10

vs Temperature and Supply Voltage

Program Pin Voltage

vs Charge Current (180mA)

160

150

140

160

150

140

1.6

= 5V

= 7.5k

= 2.1k

PROG

PNP = FCX589

= 25°C

PNP = FCX589

1.4

1.2

= 2.1k

PROG

PNP = FCX589

1.0

0.8

0.6

0.4

0.2

= 8V

= 4.55V

LIMITS AT 6mV DUE TO

PROGRAMMING PIN PULL-UP

CURRENT (I

)

PROGPU

135

180

75 100

TEMPERATURE (°C)

125

TEMPERATURE (°C)

125

–50

75 100

–25

(mA)

BAT2

1734 G10

1734 G11

1734 G12

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LTC1734L

PIN FUNCTIONS

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

from V_CCpasses through the internal current sense resis-

tor and reappears at I_SENSEto supply current to the

external PNP emitter. The PNP collector provides charge

current to the battery.

(I_BAT= 375/R_PROG). This pin also allows for the charge

current to be monitored. The voltage on this pin is propor-

tionaltothechargecurrentwhere1.5Vcorrespondstothe

full programmed currrent. Floating this pin allows an

internal current source to pull the pin voltage above the

shutdownthresholdvoltage. Becausethispinisinasignal

path, excessive capacitive loading can cause AC instabil-

ity. See the Applications Information section for more

details.

GND(Pin2):Ground. Providesareferencefortheinternal

voltage regulator and a return for all internal circuits.

When in the constant voltage mode, the LTC1734L 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

BATpin. Fordynamicallystableoperation, thispinusually

requires a minimum bypass capacitance to ground of 5µF

tofrequencycompensateforthehighfrequencyinductive

effects of the battery and wiring.

V_CC(Pin 3): Positive Input Supply Voltage. Supplies

power to the internal control circuitry and external PNP

transistorthroughtheinternalcurrentsenseresistor. This

pin should be bypassed to ground with a capacitor in the

range of 1µF to 10µF.

PROG (Pin 4): Charge Current Programming, Charge

Current Monitor and Manual Shutdown Pin. Provides a

virtual reference voltage of 1.5V for an external resistor

(R_PROG) tied between this pin and ground that programs

the battery charge current when the charger is in the

constant current mode. The typical charge current will be

250 times greater than the current through this resistor

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 LTC1734L.

BLOCK DIAGRA

1µF

/250

BAT

60Ω

0.24Ω

BAT

SENSE

SHUTDOWN

VOLTAGE

REFERENCE

2.5V

REF

–

DRIVE

OUTPUT

DRIVER

UVLO

SHUTDOWN

TEMPERATURE AND

CURRENT LIMITING

BAT

2.15V

1.5V

2.5V

SINGLE

Li-Ion

CELL

10µF

SHUTDOWN

–

3µA

SHUTDOWN

1734 BD

GND

PROG

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LTC1734L

OPERATIO

The LTC1734L is a linear battery charger controller.

Operation can best be understood by referring to the

Block Diagram. Charging begins when V_CCrises above

the UVLO (Undervoltage Lockout) threshold V_UVLOIand

an external program resistor is connected between the

PROGpinandground.Whencharging,thecollectorofthe

external PNP provides the charge current. The PNP’s

emitter current flows through the I_SENSEpin and through

the internal 0.24Ω 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 0.24Ω resistor to appear across

the internal 60Ω resistor. The scale factor of 250:1 in

resistor values will cause the FET’s drain current to be 1/

250 of the charge current and it is this current that flows

through the PROG pin. In the constant current mode,

amplifierA2isusedtolimitthechargecurrenttothevalue

A1’s input) the amplifier will divert current away from the

output driver thus maintaining 4.2V on the battery. This is

the constant voltage mode.

Whenintheconstantvoltagemode,the250:1currentratio

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

charge current is 250 • (V_PROG/R_PROG) amps. This feature

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_CCis applied, the charger can be manually shut

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.

For charging NiMH or NiCd batteries, the LTC1734L can

function as a constant current source by grounding the

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

charge current and only A2 will control the current.

that is programmed by R_PROG

The PROG pin current, which is 1/250 of the charge

current, develops a voltage across the program resistor.

When this voltage reaches 1.5V, amplifier A2 begins

diverting current away from the output driver, thus limit-

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

The constant charge current is 250 • (1.5V/R_PROG).

Fault conditions such as overheating of the die or exces-

sive DRIVE pin current are monitored and limited.

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.

WithV_CCremovedtheexternalPNP’sbaseisconnectedto

the battery by the charger. In manual shutdown the base

is connected to V_CCby the charger.

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

reachesthepresetfloatvoltageof4.2V,apreciselydivided

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 4.2V (2.5V at amplifier

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APPLICATIO S I FOR ATIO

Charger Operation

charge current begins to decrease and the constant

voltage portion of the charge cycle begins. The charge

current will continue to decrease exponentially as the

battery approaches a fully charged condition.

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

Should the battery be removed during charging, a fast

built-inprotectioncircuitwillpreventtheBATpinfromris-

ing above 5V, allowing the precision constant voltage

circuit time to respond.

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LTC1734L

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APPLICATIONS INFORMATION

Manual Shutdown

must be greater than 2.25V (V_MSDT(MAX)) to ensure

entering shutdown, but no more than 0.3V above V_CCto

prevent damaging the LTC1734L from excessive PROG

pin current. An exception is if V_CCis allowed to float with

no other circuitry loading V_CCdown. Then, because the

current will 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.

Floating the program resistor allows an internal 3µA

current source (I_PROGPU) to pull the PROG pin above the

2.15V shutdown threshold (V_MSDT), thus shutting down

the charger. In this mode, the LTC1734L continues to

draw quiescent current from the supply (I_SHDN), but only

a negligible leakage current is delivered to the battery

(I_BMS).

Shutdown can also be accomplished by pulling the other-

wise grounded end of the program resistor to a voltage

greaterthan2.25V(V_MSDTMax).Chargingwillceaseabove

1.5V, but the internal battery voltage resistor divider will

draw about 34µA from the battery until shutdown is

entered. Figure 1 illustrates a microcontroller configura-

tion 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 resistor value when low to prevent excessive

charge current errors. To reduce errors the program

resistor value may be adjusted to account for the imped-

ance to ground. The programming resistor will prevent

potentially damaging currents if the PROG pin is forced

above V_CC. Under this condition V_CCmay float, be loaded

down by other circuitry or be shorted to ground. If V_CCis

notshortedtoground, thecurrentthroughtheresistorwill

pull V_CCup slightly.

An NPN transistor or a diode can also be utilized to

implement shutdown from a voltage source. These have

theadvantageofblockingcurrentwhenthevoltagesource

goes low, thus automatically disconnecting the voltage

source for normal charging operation. Using an NPN

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

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

V_CC,the base to the voltage source and the emitter to the

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

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

ranging from 3.3V to V_CCshould be adequate to enter

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).

Another method is to directly switch the PROG pin to a

voltage source when shutdown is desired (Caution: pull-

ing the PROG below 1.5V with V_CCapplied will cause

excessive and uncontrolled charge currents). The volt-

age source must be capable of sourcing the resulting

current through the program resistor. This has the ad-

vantage of not adding any error to the program resistor

during normal operation. The voltage on the PROG pin

Sleep Mode

When the input supply is disconnected, the IC enters the

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.

)

PROG

Undervoltage Lockout

PROG

LTC1734L

OPEN DRAIN

OR TOTEM

Undervoltage lockout (UVLO) keeps the charger off until

the input voltage exceeds a predetermined threshold level

(V_UVLOI) that is typically 4.56V. Approximately 150mV of

hysteresis is built in to prevent oscillation around the

threshold level. In undervoltage lockout, battery drain

current is very low (<1µA).

POLE OUTPUT

µC

ADC INPUT

1734 F01

Figure 1. Interfacing with a Microcontroller

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LTC1734L

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APPLICATIONS INFORMATION

Programming Constant Current

monitoring accuracy can degrade considerably at very

low current levels. If current monitoring is desired, a

minimum full-scale current of 50mA is recommended.

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

current is programmed using a single external resistor

between the PROG pin and ground. This charge current

will be 250 times the current through the program resis-

tor. The program resistor value is selected by dividing the

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

resistor current:

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

with the I_DACto maintain AC stability as discussed in the

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 deasserted. 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 50mA minimum

constant current.

_PROG= 375/I_BAT

The LTC1734L is designed for an absolute maximum

currentof210mA.ThistranslatestoamaximumPROGpin

currentof840µAandaminimumprogramresistorof1.8k.

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.

The minimum full-scale current that can be reliably pro-

grammed is approximately 10mA, which requires a pro-

gram resistor of 37.4k. Limiting capacitive loading on the

program pin becomes more important when high value

program resistors are used. In addition, the current

CHARGE CURRENT CONTROL 1 CONTROL 2

SENSE

LOW

HIGH

LOW

HIGH

LOW

HIGH

LTC1734L

1µF

50mA

125mA

175mA

FZT549

GND

DRIVE

OPTIONAL FILTER

BAT

CHARGE

CURRENT

MONITOR

(FILTERED)

CHARGE

CURRENT

PIN 4

PROG

BAT

SINGLE

MONITOR

0.1µF TO

0.5µF

10µF

Li-Ion

(UNFILTERED)

7.5k

BATTERY

2N7002

1734 F02

2N7002

CONTROL 1

CONTROL 2

Figure 2. Logic Control Programming of Output Current to 0mA, 50mA, 125mA or 175mA

SENSE

LTC1734L

1µF

FZT549*

GND

DRIVE

CURRENT CONTROL 1 CONTROL 2

LOAD

PROG

BAT

LOW

HIGH

LOW

HIGH

LOW

HIGH

50mA

125mA

175mA

LOAD

7.5k

1734 F03

2N7002

*OBSERVE MAXIMUM TEMPERATURE

CONTROL 1

CONTROL 2

Figure 3. Programmable Current Source with Output Current of 0mA, 50mA, 125mA or 175mA

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LTC1734L

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APPLICATIONS INFORMATION

Monitoring Charge Current

To provide 180mA of charge current with the minimum

available base drive of approximately 20mA requires a

PNP beta greater than 9.

The voltage on the PROG pin indicates the charge current

as a proportion of the maximum current set by the

program resistor. The charge current is equal to 250 •

(V_PROG/R_PROG) amps. This feature allows a microcontrol-

ler with an ADC to easily monitor charge current and if

desired, manually shut down the charger at the appropri-

ate time. The minimum PROG pin current is about 3µA

(I_PROGPU).

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 (0.3Ω) and battery float voltage. If the PNP transis-

tor 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 limit resulting in the charger’s characteristics to

gooutofspecifications, excessivepowerdissipationmay

force the IC into thermal shutdown, or the battery could

becomedischargedbecausesomeofthecurrentfromthe

DRIVE pin could be pulled from the battery through the

forward biased collector base junction.

Errors in the charge current monitor voltage on the PROG

pin and in the full-scale charge current are inversely

proportional to battery current and can be statistically

approximated as follows:

One Sigma Error(%) 1 + 0.08/I_BAT(A)

Dynamic loads on the battery will cause transients to

appear 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 momen-

tary entry into the manual shutdown mode.

For example, to program a charge current of 100mA with

a minimum supply voltage of 4.75V, the minimum operat-

ing V_CEis:

V_CE(MIN)(V) = 4.75 – (0.1)(0.3) – 4.2 = 0.52V

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.

The actual battery charge current (I_BAT) is slightly less

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_C/I_B),

I_BATcan be calculated as follows:

Constant Current Source

I_BAT(A) = 250 • I_PROG[β/(β + 1)]

The LTC1734L 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

voltage of 4.2V by grounding the BAT pin. The program

resistor will determine the output current. The output

current range can be between approximately 10mA and

180mA, depending on the maximum power rating of the

external PNP pass transistor.

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

be compensated for by increasing I_PROGby 2%.

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:

External PNP Transistor

_D(MAX)(W) = I_BAT(V_DD(MAX)– V_BAT(MIN))

The external PNP pass transistor must have adequate

beta, lowsaturationvoltageandsufficientpowerdissipa-

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

V_DD(MAX)is the maximum supply voltage and V_BAT(MIN)is

the minimum battery voltage when discharged.

1734lf

LTC1734L

W U U

APPLICATIONS INFORMATION

Table 1. PNP Pass Transistor Selection Guide

Maximum P (W)

Mounted on Board

at T = 25°C

Package Style

SC-70

ZETEX Part Number

ROHM Part Number

UMT4403

Comments

0.2

0.5

0.625

Smallest Size

SC-70

UMT2907A

SOT-23

SOT-89

SOT-23-6

SOT-89

SOT-223

FTR

FMMT549

FMMT720

Low V

CESAT

Very Low V

High Beta

CESAT,

FCX589 or BCX69

ZXT10P12DE6

FCX717

1.1

1 to 2

Very Low V

High Beta, Small

High Beta

CESAT,

FZT589

Low V

CESAT

BCP69 or FZT549

0.75

2SB822

2SB1443

2SA1797

Low V

CESAT

ATV

SOT-89

Once the maximum power dissipation and V_CE(MIN)are

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

suitable PNP transistor. In the table, very low V_CESATis

lessthan0.25V,lowV_CESATis0.25Vto0.5Vandtheothers

are0.5Vto0.8Valldependingonthecurrentrequired. See

the manufacturer’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.

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

usually required from BAT to ground. The battery and

interconnecting wires appear inductive at high frequen-

cies, and since these are in the feedback loop, this capaci-

tancemaybenecessarytocompensatefortheinductance.

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.

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

current programming resistor and thermally coupled to

the transistor. The PRF chip series from Murata has a

steep resistance increase at temperature thresholds from

85°C to 145°C making it behave somewhat like a thermo-

stat switch. For example, the model PRF18BA471QB1RB

thermistor is 470Ω at 25°C, but abruptly increase its

resistance to 4.7k at 125°C. Below 125°C, the device

exhibits a small negative TC. The 470Ω thermistor can be

added in series with a 1.6k resistor to form the current

programming resistor for a 180mA charger. Should the

thermistor reach 125°C, the charge current will drop to

60mA and inhibit any further increase in temperature.

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.

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

feedback loop, not the battery. Because of this, capaci-

tance on this pin must be limited. Locating the program

resistor 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 capaci-

tance is greater than that given by the following equation:

400k

R_PROG

C_MAX(pF)

Stability

The LTC1734L contains two control loops: constant volt-

age and constant current. To maintain good AC stability in

1734lf

LTC1734L

W U U

APPLICATIONS INFORMATION

of instability due to any combination of extremely low ESR

values, high capacitance values of the output capacitor or

veryhighPNPtransistorbeta. Tominimizetheeffectofthe

scope probe capacitance, a 10k resistor is used to isolate

the probe from the program pin. Also, an adjustable load

resistor or current sink can be used to quickly alter the

charge current when a fully charged battery is used.

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

for a charge current of 50mA (R_PROG= 7.5k).

Figure4isasimpletestcircuitforcheckingstabilityinboth

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

manual shutdown mode. Referring to Figure 5, after a

short delay, the charger will enter the constant current

mode first, then if the battery voltage is near the pro-

grammed voltage of 4.2V, the constant voltage mode will

begin. The resulting waveform on the PROG pin is an

indication of stability.

Reverse Input Voltage Protection

In some applications, protection from reverse voltage on

V_CCis desired. If the supply voltage is high enough, a

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.

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

LTC1734L

1734 F06

*DRAIN-BULK DIODE OF FET

Figure 6. Low Loss Reverse Voltage Protection

V_CCBypass Capacitor

Many types of capacitors with values ranging from 1µF to

10µF located close to the LTC1734L 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

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.

10k

TO SCOPE

PROG

BAT

20Ω TO

200Ω

PROG

Li-Ion*

LTC1734L

2.5V

1734 F04

f = 1kHz

*FULLY CHARGED CELL

Figure 4. Setup for AC Stability Testing

PULSE

GENERATOR

Internal Protection

PROG PIN

(20pF ON PIN)

InternalprotectionisprovidedtopreventexcessiveDRIVE

pin currents (I_DSHRT) and excessive self-heating of the

LTC1734L during a fault condition. The faults can be

generated from a shorted DRIVE pin or from excessive

DRIVE pin current to the base of the external PNP

transistor when it’s in deep saturation from a very low

V_CE. This protection is not designed to prevent overheat-

ingoftheexternalpasstransistor. Indirectlythough, self-

PROG PIN

(200pF ON PIN)

SHUT DELAY

DOWN

CONSTANT

CURRENT

CONSTANT

VOLTAGE

HORIZONTAL SCALE: 100µs/DIV

heatingofthePNPthermallyconductingtotheLTC1734L

Figure 5. Stability Waveforms

1734lf

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.

LTC1734L

W U U

APPLICATIONS INFORMATION

and resulting in the IC’s junction temperature to rise

above 150°C, thus cutting off the base current to the PNP

transistor. This action will limit the transistor junction

temperature to a temperature well above 150°C. The

temperature depends on how well the IC and PNP are

thermally connected and on the transistor’s θ_JA. See the

External PNP Transistor section for information on pro-

tecting the transistor from overheating.

PACKAGE DESCRIPTIO

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

1.50 – 1.75

(NOTE 4)

2.80 BSC

1.4 MIN

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

NOTE:

0.20 BSC

DATUM ‘A’

1. DIMENSIONS ARE IN MILLIMETERS

2. DRAWING NOT TO SCALE

0.01 – 0.10

1.00 MAX

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

0.30 – 0.50 REF

1.90 BSC

0.09 – 0.20

(NOTE 3)

S6 TSOT-23 0302

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COMMENTS

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200mA to 700mA Li-Ion Linear Charger in ThinSot

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1734lf

LT/TP 0802 2K • PRINTED IN THE USA

12 ^{LinearTechnology Corporation}

1630 McCarthy Blvd., Milpitas, CA 95035-7417

●

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

LINEAR TECHNOLOGY CORPORATION 2001

LTC1734LES6-4.2#TRMPBF [Linear]

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