LT1510IN - Linear Technology

LT1510/LT1510-5

Constant-Voltage/

Constant-Current Battery Charger

Figure 2. Charging Lithium Batteries (Efficiency at 1.3A > 87%)

* NiCd and NiMH batteries require charge termination circuitry (not shown in Figure 1).

TYPICAL APPLICATIONS

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

plest, most efficient solution to fast-charge modern re-

chargeable batteries including lithium-ion (Li-Ion), nickel-

metal-hydride (NiMH)* and nickel-cadmium (NiCd)* that

require constant-current and/or constant-voltage charg-

ing. The internal switch is capable of delivering 1.5A DC

current (2A peak current). The 0.1Ω onboard current

sense resistor makes the charging current programming

very simple. One resistor (or a programming current from

a DAC) is required to set the full charging current (1.5A) to

within 5% accuracy. The LT1510 with 0.5% reference

voltage accuracy meets the critical constant-voltage charg-

ing requirement for lithium cells.

The LT1510 can charge batteries ranging from 2V to 20V.

Ground sensing of current is not required and the battery’s

negative terminal can be tied directly to ground. A saturat-

ing switch running at 200kHz (500kHz for LT1510-5) gives

high charging efficiency and small inductor size. A block-

ing diode is not required between the chip and the battery

because the chip goes into sleep mode and drains only 3µA

when the wall adaptor is unplugged. Soft start and shutdown

features are also provided. The LT1510 is available in a 16-pin

fused lead power SO package with a thermal resistance of

50°C/W, an 8-pin SO and a 16-pin PDIP.

FEATURES

■

Charges NiCd, NiMH and Lithium-Ion Batteries ––

Only One

W Resistor Is Needed to Program

Charging Current

■

High Efficiency Current Mode PWM with 1.5A

Internal Switch and Sense Resistor

■

3% Typical Charging Current Accuracy

■

Precision 0.5% Voltage Reference for Voltage

Mode Charging or Overvoltage Protection

■

Current Sensing Can Be at Either Terminal of

the Battery

■

Low Reverse Battery Drain Current: 3µA

■

Charging Current Soft Start

■

Shutdown Control

■

500kHz Version Uses Small Inductor

With switching frequency as high as 500kHz, The LT

1510

current mode PWM battery charger is the smallest, sim-

APPLICATIONS

DESCRIPTION

■

Chargers for NiCd, NiMH and Lithium Batteries

■

Step-Down Switching Regulator with Precision

Adjustable Current Limit

Figure 1. 500kHz Smallest Li-Ion Cell Phone Charger (0.8A)

SW

BOOST

GND

SENSE



PROG



BAT

6.19k

8.2V TO 20V

R3

70.6k

0.25%

R4

100k

0.25%

†



2N7002

NOTE: COMPLETE LITHIUM-ION CHARGER, NO TERMINATION REQUIRED

TOKIN OR MARCON CERAMIC SURFACE MOUNT

COILTRONICS TP3-100, 10µH, 2.2mm HEIGHT (0.8A CHARGING CURRENT)

COILTRONICS TP1 SERIES, 10µH, 1.8mm HEIGHT (<0.5A CHARGING CURRENT)

PANASONIC EEFCD1B220 

OPTIONAL, SEE APPLICATIONS INFORMATION

1510 F01

C1

0.22µF

*

10µF

L1**

10µHLT1510-5

D1

MBRM120T3

D3

MBRM120T3

D2

MMBD914L

OVP

OUT***



22µF4.2V

–

0.1µF1k

1µF300Ω

*

**



***

†

SW

BOOST

GND

SENSE



PROG



BAT

3.83k

11V TO 28V

R3

240k

0.25%

R4

100k

0.25%

†



VN2222

NOTE: COMPLETE LITHIUM-ION CHARGER, NO TERMINATION REQUIRED

 * TOKIN OR MARCON CERAMIC SURFACE MOUNT

** COILTRONICS CTX33-2  



†

 OPTIONAL, SEE APPLICATIONS INFORMATION

1510 F02

C1

0.22µF

*

10µF

L1**

33µHLT1510

D1

1N5819

D3

1N5819

D2

1N914

OVP

OUT



22µF

TANT

4.2V

–

0.1µF1k

1µF300Ω

LT1510/LT1510-5

Supply Voltage (V

MAX

)............................................ 30V

Switch Voltage with Respect to GND ...................... –3V

Boost Pin Voltage with Respect to V

................... 30V

Boost Pin Voltage with Respect to GND ................. –5V

, PROG, OVP Pin Voltage ...................................... 8V

BAT

(Average)........................................................ 1.5A

Switch Current (Peak)............................................... 2A

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

ABSOLUTE MAXIMUM RATINGS

Operating Ambient Temperature Range

Commercial ............................................. 0°C to 70°C

Extended Commercial (Note 7)........... –40°C to 85°C

Industrial (Note 8) .............................. –40°C to 85°C

Operating Junction Temperature Range

LT1510C (Note 7)............................. –40°C to 125°C

LT1510I ............................................ –40°C to 125°C

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

PACKAGE/ORDER INFORMATION

Consult factory for Military grade parts.

ELECTRICAL CHARACTERISTICS

VCC = 16V, VBAT = 8V, VMAX (maximum operating VCC) = 28V, no load on any outputs, unless otherwise noted. (Notes 7, 8)

PARAMETER CONDITIONS MIN TYP MAX UNITS

Overall

Supply Current V

PROG

= 2.7V, V

≤ 20V ●2.90 4.3 mA

PROG

= 2.7V, 20V < V

≤ V

MAX

●2.91 4.5 mA

DC Battery Current, I

BAT

(Note 1) 8V ≤ V

≤ 25V, 0V ≤ V

BAT

≤ 20V, T

< 0°C●0.91 1.09 A

PROG

= 4.93k ●0.93 1.0 1.07 A

PROG

= 3.28k (Note 4) ●1.35 1.5 1.65 A

PROG

= 49.3k ●75 100 125 mA

< 0°C●70 130 mA

= 28V, V

BAT

= 20V

PROG

= 4.93k ●0.93 1.0 1.07 A

PROG

= 49.3k ●75 100 125 mA

LT1510CN

LT1510CS

LT1510IN

LT1510IS

ORDER PART

NUMBER

JMAX

= 125°C, θ

= 125°C/W

ORDER PART

NUMBER

GN PART

MARKING

CC1

AND V

CC2

SHOULD BE CONNECTED

TOGETHER CLOSE TO THE PINS.

** FOUR CORNER PINS ARE FUSED TO

INTERNAL DIE ATTACH PADDLE FOR

HEAT SINKING. CONNECT THESE FOUR

PINS TO EXPANDED PC LANDS FOR

PROPER HEAT SINKING.

1

2

3

4

5

6

7

8



TOP VIEW

N PACKAGE

16-LEAD PDIP

16

15

14

13

12

11

10

9



**GND

SW

BOOST

GND

OVP

SENSE

GND

**GND

GND**

CC2



CC1



PROG



BAT

GND

GND**

S PACKAGE*

16-LEAD PLASTIC SO

JMAX

= 125°C, θ

= 75°C/ W (N)

JMAX

= 125°C, θ

= 50°C/W (S)*

1

2

3

8

7

6

5



TOP VIEW

SW

BOOST

GND

SENSE



PROG



BAT

S8 PACKAGE

8-LEAD PLASTIC SO

LT1510CS8

LT1510IS8

1510

1510I

ORDER PART

NUMBER

S8 PART MARKING

1

2

3

4

5

6

7

8



TOP VIEW

16

15

14

13

12

11

10

9



**GND

SW

BOOST

GND

OVP

NC

SENSE

**GND

GND**

VCC2

VCC1

PROG

VC

NC

BAT

GND**

GN PACKAGE (0.015 IN)

16-LEAD PLASTIC SSOP

JMAX

= 125°C, θ

= 75°C/ W

** FOUR CORNER PINS ARE FUSED TO

INTERNAL DIE ATTACH PADDLE FOR

HEAT SINKING. CONNECT THESE FOUR

PINS TO EXPANDED PC LANDS FOR

PROPER HEAT SINKING.

LT1510CGN

LT1510IGN

LT1510-5CGN

LT1510-5IGN

1510

1510I

15105

15105I

LT1510/LT1510-5

ELECTRICAL CHARACTERISTICS

VCC = 16V, VBAT = 8V, VMAX (maximum operating VCC) = 28V, no load on any outputs, unless otherwise noted.

PARAMETER CONDITIONS MIN TYP MAX UNITS

Overall

Minimum Input Operating Voltage Undervoltage Lockout ●6.2 7 7.8 V

Reverse Current from Battery (When V

Is Not V

BAT

≤ 20V, 0°C ≤ T

≤ 70°C●315 µA

Connected, V

Is Floating)

Boost Pin Current V

– V

BOOST

≤ 20V ●0.10 20 µA

20V < V

– V

BOOST

≤ 28V ●0.25 30 µA

2V ≤ V

BOOST

– V

≤ 8V (Switch ON) ●611 mA

8V < V

BOOST

– V

≤ 25V (Switch ON) ●814 mA

Switch

Switch ON Resistance V

= 10V

= 1.5A, V

BOOST

– V

≥ 2V (Note 4) ●0.3 0.5 Ω

= 1A, V

BOOST

– V

< 2V (Unboosted) ●2.0 Ω

∆I

BOOST

/∆I

During Switch ON V

BOOST

= 24V, I

≤ 1A 20 35 mA/A

Switch OFF Leakage Current V

= 0V, V

≤ 20V ●2 100 µA

20V < V

≤ 28V ●4 200 µA

Maximum V

BAT

with Switch ON ●V

– 2 V

Minimum I

PROG

for Switch ON 2420 µA

Minimum I

PROG

for Switch OFF at V

PROG

≤1V ●1 2.4 mA

Current Sense Amplifier Inputs (SENSE, BAT)

Sense Resistance (R

) 0.08 0.12 Ω

Total Resistance from SENSE to BAT (Note 3) 0.2 0.25 Ω

BAT Bias Current (Note 5) V

< 0.3V –200 –375 µA

> 0.6V 700 1300 µA

Input Common Mode Limit (Low) ●–0.25 V

Input Common Mode Limit (High) ●V

– 2 V

Reference

Reference Voltage (Note 1) S8 Package R

PROG

= 4.93k, Measured at PROG Pin ●2.415 2.465 2.515 V

Reference Voltage (Note 2) 16-Pin R

PROG

= 3.28k, Measured at OVP with 2.453 2.465 2.477 V

VA Supplying I

PROG

and Switch OFF

Reference Voltage Tolerance, 16-Pin Only 8V ≤ V

≤ 28V, 0°C ≤ T

≤ 70°C●2.446 2.465 2.480 V

8V ≤ V

≤ 28V, 0°C ≤ T

≤ 125°C●2.441 2.489 V

8V ≤ V

≤ 28V, T

< 0°C●2.430 2.489 V

Oscillator

Switching Frequency LT1510 180 200 220 kHz

LT1510-5 440 500 550 kHz

Switching Frequency Tolerance All Conditions of V

, Temperature, LT1510 ●170 200 230 kHz

LT1510, T

< 0°C●160 230 kHz

LT1510-5 ●425 500 575 kHz

LT1510-5, T

< 0°C●400 575 kHz

Maximum Duty Cycle LT1510 ●87 %

LT1510, T

= 25°C (Note 8) 90 93 %

LT1510-5 (Note 9) ●77 81 %

LT1510/LT1510-5

ELECTRICAL CHARACTERISTICS

VCC = 16V, VBAT = 8V, VMAX (maximum operating VCC) = 28V, no load on any outputs, unless otherwise noted.

PARAMETER CONDITIONS MIN TYP MAX UNITS

Current Amplifier (CA2)

Transconductance V

= 1V, I

= ±1µA 150 250 550 µmho

Maximum V

for Switch OFF ●0.6 V

Current (Out of Pin) V

≥ 0.6V 100 µA

< 0.45V 3 mA

Voltage Amplifier (VA), 16-Pin Only

Transconductance (Note 2) Output Current from 100µA to 500µA 0.5 1.2 2.5 mho

Output Source Current, V

= 10V V

PROG

= V

OVP

= V

REF

+ 10mV 1.3 mA

OVP Input Bias Current At 0.75mA VA Output Current ●50 150 nA

The ● denotes specifications which apply over the specified

temperature range.

Note 1: Tested with Test Circuit 1.

Note 2: Tested with Test Circuit 2.

Note 3: Sense resistor R

and package bond wires.

Note 4: Applies to 16-pin only. 8-pin packages are guaranteed but not

tested at –40°C.

Note 5: Current (≈ 700µA) flows into the pins during normal operation and

also when an external shutdown signal on the V

pin is greater than 0.3V.

Current decreases to ≈ 200µA and flows out of the pins when external

shutdown holds the V

pin below 0.3V. Current drops to near zero when

input voltage collapses. See external Shutdown in Applications Information

section.

Note 6: A linear interpolation can be used for reference voltage

specification between 0°C and –40°C.

Note 7: Commercial grade device specifications are guaranteed over the

0°C to 70°C temperature range. In addition, commercial grade device

specifications are assured over the –40°C to 85°C temperature range by

design or correlation, but are not production tested.

Maximum allowable ambient temperature may be limited by power

dissipation. Parts may not necessarily be operated simultaneously at

maximum power dissipation and maximum ambient temperature.

Temperature rise calculations must be done as shown in the Applications

Information section to ensure that maximum junction temperature does

not exceed the 125°C limit. With high power dissipation, maximum

ambient temperature may be less than 70°C.

Note 8: Industrial grade device specifications are guaranteed over the

–40°C to 85°C temperature range.

Note 9: 91% maximum duty cycle is guaranteed by design if V

BAT

or V

(see Figure 8 in Application Information) is kept between 3V and 5V.

Note 10: V

BAT

= 4.2V.

Thermally Limited Maximum

Charging Current, 8-Pin SO

INPUT VOLTAGE (V)

MAXIMUM CHARGING CURRENT (A)

1.3

1.1

0.9

0.7

0.5

0.3 20

1510 G12

510 15 25

16V BATTERY

12V BATTERY

8V BATTERY

4V BATTERY

(θ

=125°C/W)

AMAX

=60°C

JMAX

=125°C

Thermally Limited Maximum

Charging Current, 16-Pin SO

INPUT VOLTAGE (V)

MAXIMUM CHARGING CURRENT (A)

1.5

1.3

1.1

0.9

0.7

0.5 20

1510 G13

510 15 25

(θ

=50°C/W)

AMAX

=60°C

JMAX

=125°C

16V BATTERY

12V BATTERY

8V BATTERY

4V BATTERY

Thermally Limited Maximum

Charging Current, 16-Pin GN

INPUT VOLTAGE (V)

MAXIMUM CHARGING CURRENT (A)

1.5

1.3

1.1

0.9

0.7

0.5 20

LT1510 • TPC14

510 15 25

= 80°C/W

AMAX

= 60°C

JMAX

= 125°C

4V BATTERY

8V BATTERY

12V BATTERY

16V BATTERY

TYPICAL PERFORMANCE CHARACTERISTICS

LT1510/LT1510-5

TYPICAL PERFORMANCE CHARACTERISTICS

Switching Frequency vs

Temperature

DUTY CYCLE (%)

010305070

(mA)

1510 G04

20 40 60

8

7

6

5

4

3

2

1

125°C

0°C

25°C

= 16V

ICC vs Duty Cycle

TEMPERATURE (°C)

–20

FREQUENCY (kHz)

200 40 80 12060 100 140

1510 G05

210

205

200

195

190

185

180

BAT

(A)

0.1

EFFICIENCY (%)

100

98

96

94

92

90

88

86

84

82

80 0.5 0.9 1.51.31.1

1510 G01

0.3 0.7

= 15V (EXCLUDING DISSIPATION

ON INPUT DIODE D3)

BAT

= 8.4V

Efficiency of Figure 2 Circuit

ICC vs VCC

VCC (V)

ICC (mA)

7.0

6.5

6.0

5.5

5.0

4.5 510 15 20

1510 G03

25 30

125°C

25°C

0°C

MAXIMUM DUTY CYCLE

(mA)

∆V

OVP

(mV)

4

3

2

1

00.8

1510 G08

0.20.1 0.3 0.5 0.7 0.9

0.4 0.6 1.0

125°C

25°C

IVA vs ∆VOVP (Voltage Amplifier)

(V)

∆V

REF

(V)

0.003

0.002

0.001

0

–0.001

–0.002

–0.003 510 15 20

1510 G02

25 30

ALL TEMPERATURES

VREF Line Regulation

TEMPERATURE (°C)

DUTY CYCLE (%)

120

1510 G09

40 80

98

97

96

95

94

93

92

91

90 20 60 100 140

Maximum Duty Cycle

PROG

(V)

0123 54

PROG

(mA)

–6

1510 G11



125°C

25°C

PROG Pin Characteristic

(V)

0 0.2 0.6 1.0 1.4 1.8

(mA)

–1.20

–1.08

–0.96

–0.84

–0.72

–0.60

–0.48

–0.36

–0.24

–0.12

0

0.12 1.6

1510 G10

0.4 0.8 1.2 2.0

VC Pin Characteristic

LT1510/LT1510-5

TYPICAL PERFORMANCE CHARACTERISTICS

SWITCH CURRENT (A)

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.8 2.01.6

BOOST CURRENT (mA)

50

45

40

35

30

25

20

15

10

5

0



1510 G07



= 16V

BOOST

= 38V

28V

18V

Switch Current vs Boost Current

vs Boost Voltage

TEMPERATURE (°C)

REFERENCE VOLTAGE (V)

2.470

2.468

2.466

2.464

2.462

2.460

2.458 25 50 75 100

1510 G14

125 150

Reference Voltage vs

Temperature

BOOST

(V)

4268

MAXIMUM DUTY CYCLE (%)

16 18 20

96

95

94

93

92

91

90

89

88

87

LT1510 • TPC15

10 12 14 22

VBOOST vs

Maximum Duty Cycle

PIN FUNCTIONS

UUU

GND: Ground Pin.

SW: Switch Output. The Schottky catch diode must be

placed with very short lead length in close proximity to SW

pin and GND.

: Supply for the Chip. For good bypass, a low ESR

capacitor of 10µF or higher is required, with the lead length

kept to a minimum. V

should be between 8V and 28V

and at least 2V higher than V

BAT

for V

BAT

less than 10V, and

2.5V higher than V

BAT

for V

BAT

greater than 10V. Under-

voltage lockout starts and switching stops when V

goes

below 7V. Note that there is a parasitic diode inside from

SW pin to V

pin. Do not force V

below SW by more

than 0.7V with battery present. All V

pins should be

shorted together close to the pins.

BOOST: This pin is used to bootstrap and drive the switch

power NPN transistor to a low on-voltage for low power

dissipation. In normal operation, V

BOOST

= V

+ V

BAT

when switch is on. Maximum allowable V

BOOST

is 55V.

SENSE: Current Amplifier CA1 Input. Sensing can be at

either terminal of the battery. Note that current sense

resistor R

(0.08Ω) is between Sense and BAT pins.

BAT: Current Amplifier CA1 Input.

PROG: This pin is for programming the charging current

and for system loop compensation. During normal opera-

tion, V

PROG

stays close to 2.465V. If it is shorted to GND

the switching will stop. When a microprocessor-controlled

DAC is used to program charging current, it must

capable of sinking current at a compliance up to 2.465V.

: This is the control signal of the inner loop of the current

mode PWM. Switching starts at 0.7V and higher V

corresponds to higher charging current in normal opera-

tion. A capacitor of at least 0.1µF to GND filters out noise

and controls the rate of soft start. To shut down switching,

pull this pin low. Typical output current is 30µA.

OVP: This is the input to the amplifier VA with a threshold

of 2.465V. Typical input current is about 50nA into pin. For

charging lithium-ion batteries, VA monitors the battery

voltage and reduces charging current when battery volt-

age reaches the preset value. If it is not used, the OVP pin

should be grounded.

LT1510/LT1510-5

BLOCK DIAGRAM

TEST CIRCUITS



Test Circuit 1

–

REF

≈ 0.65V

BAT

2N3055

LT1010

CA2

–

CA1

3.3k

20k

BAT

SENSE

1510 TC01

PROG

0.047µF

LT1510

0.22µF

56µF

60k

LT1006

–

0.7V

1.5V

BAT

REF

GND SLOPE

COMPENSATION

PWM B1

CA2

–

CA1

REF

2.465V

SHUTDOWN

200kHz

OSCILLATOR

R1

BAT

PROG

BOOST

SENSE

BAT

0VP

1510 BD

PROG

60k

PROG

BAT

= 500µA/A

= 0.64

Ω

CHARGING CURRENT I

BAT



= (I

PROG

)(2000)



= 2.465V

PROG

(2000)

()

LT1510/LT1510-5

TEST CIRCUITS



REF

2.465V

–

10k

OVP

1510 TC02

PROG

LT1510

PROG

LT1013

0.47µF

Test Circuit 2

OPERATIO

The LT1510 is a current mode PWM step-down (buck)

switcher. The battery DC charging current is programmed

by a resistor R

PROG

(or a DAC output current) at the PROG

pin (see Block Diagram). Amplifier CA1 converts the

charging current through R

to a much lower current

PROG

(500µA/A) fed into the PROG pin. Amplifier CA2

compares the output of CA1 with the programmed current

and drives the PWM loop to force them to be equal. High

DC accuracy is achieved with averaging capacitor C

PROG

Note that I

PROG

has both AC and DC components. I

PROG

goes through R1 and generates a ramp signal that is fed to

the PWM control comparator C1 through buffer B1 and

level shift resistors R2 and R3, forming the current mode

inner loop. The Boost pin drives the switch NPN Q

into

saturation and reduces power loss. For batteries like

lithium-ion that require both constant-current and con-

stant-voltage charging, the 0.5%, 2.465V reference and

the amplifier VA reduce the charging current when battery

voltage reaches the preset level. For NiMH and NiCd, VA

can be used for overvoltage protection. When input volt-

age is not present, the charger goes into low current (3µA

typically) sleep mode as input drops down to 0.7V below

battery voltage. To shut down the charger, simply pull the

pin low with a transistor.

APPLICATIONS INFORMATION

WUU U

Application Note 68, the LT1510 design manual, contains

more in depth appications examples.

Input and Output Capacitors

In the chargers in Figures 1 and 2 on the first page of this

data sheet, the input capacitor C

is assumed to absorb all

input switching ripple current in the converter, so it must

have adequate ripple current rating. Worst-case RMS

ripple current will be equal to one half of output charging

current. Actual capacitance value is not critical. Solid

tantalum capacitors such as the AVX TPS and Sprague

593D series have high ripple current rating in a relatively

small surface mount package, but

caution must be used

when tantalum capacitors are used for input bypass

. High

input surge currents can be created when the adapter is

hot-plugged to the charger and solid tantalum capacitors

have a known failure mechanism when subjected to very

high turn-on surge currents. Highest possible voltage

rating on the capacitor will minimize problems. Consult with

the manufacturer before use. Alternatives include new high

LT1510/LT1510-5

APPLICATIONS INFORMATION

WUU U

capacity ceramic capacitor (5µF to 10µF) from Tokin or

United Chemi-Con/MARCON, et al., and the old standby,

aluminum electrolytic, which will require more microfarads

to achieve adequate ripple rating. OS-CON can also be used.

The output capacitor C

OUT

is also assumed to absorb

output switching current ripple. The general formula for

capacitor current is:

RMS

BAT BAT

()

−











()()

029 1

For example, with V

= 16V, V

BAT

= 8.4V, L1 = 30µH and

f = 200kHz, I

RMS

= 0.2A.

EMI considerations usually make it desirable to minimize

ripple current in the battery leads, and beads or inductors

may be added to increase battery impedance at the 200kHz

switching frequency. Switching ripple current splits be-

tween the battery and the output capacitor depending on

the ESR of the output capacitor and the battery impedance.

If the ESR of C

OUT

is 0.2Ω and the battery impedance is

raised to 4Ω with a bead of inductor, only 5% of the current

ripple will flow in the battery.

Soft Start

The LT1510 is soft started by the 0.1µF capacitor on V

pin. On start-up, V

pin voltage will rise quickly to 0.5V,

then ramp at a rate set by the internal 45µA pull-up current

and the external capacitor. Battery charging current starts

ramping up when V

voltage reaches 0.7V and full current

is achieved with V

at 1.1V. With a 0.1µF capacitor, time to

reach full charge current is about 3ms and it is assumed

that input voltage to the charger will reach full value in less

than 3ms. Capacitance can be increased up to 0.47µF if

longer input start-up times are needed.

In any switching regulator, conventional timer-based soft

starting can be defeated if the input voltage rises much

slower than the time-out period. This happens because the

switching regulators in the battery charger and the com-

puter power supply are typically supplying a fixed amount

of power to the load. If input voltage comes up slowly

compared to the soft start time, the regulators will try to

deliver full power to the load when the input voltage is still

well below its final value. If the adapter is current limited,

it cannot deliver full power at reduced output voltages and

the possibility exists for a quasi “latch” state where the

adapter output stays in a current limited state at reduced

output voltage. For instance, if maximum charger plus

computer load power is 20W, a 24V adapter might be

current limited at 1A. If adapter voltage is less than (20W/1A

= 20V) when full power is drawn, the adapter voltage will be

sucked down by the constant 20W load until it reaches a

lower stable state where the switching regulators can no

longer supply full load. This situation can be prevented by

utilizing

undevoltage lockout

, set higher than the minimum

adapter voltage where full power can be achieved.

A fixed undervoltage lockout of 7V is built into the V

pin.

Internal lockout is performed by clamping the V

pin low.

The V

pin is released from its clamped state when the V

pin rises above 7V. The charger will start delivering current

about 2ms after V

is released, as set by the 0.1µF at V

pin. Higher lockout voltage can be implemented with a

Zener diode (see Figure 3 circuit).

Figure 3. Undervoltage Lockout

GND

1510 F03

LT1510

D1

1N4001

The lockout voltage will be V

= V

+ 1V.

For example, for a 24V adapter to start charging at 22V

choose V

= 21V. When V

is less than 22V, D1 keeps V

low and charger off.

Charging Current Programming

The basic formula for charging current is (see Block

Diagram):

II V

BAT PROG PROG

()()











()

2000 2 465 2000

LT1510/LT1510-5

where R

PROG

is the total resistance from PROG pin to

ground.

For example, 1A charging current is needed.

PROG

()()

2 465 2000

1493

Charging current can also be programmed by pulse width

modulating I

PROG

with a switch Q1 to R

PROG

at a frequency

higher than a few kHz (Figure 4). Charging current will be

proportional to the duty cycle of the switch with full current

at 100% duty cycle.

When a microprocessor DAC output is used to control

charging current, it must be capable of sinking current

at a compliance up to 2.5V if connected directly to the

PROG pin.

APPLICATIONS INFORMATION

WUU U

even this low current drain. A 47k resistor from adapter

output to ground should be added if Q3 is used to ensure

that the gate is pulled to ground.

With divider current set at 25µA, R4 = 2.465/25µA = 100k

and,

RRV

BAT

34 2 465

2 465 4 0 05

100 8 4 2 465

2 465 100 0 05

240

()

−

()

=−

()

..µµ

Lithium-ion batteries typically require float voltage accu-

racy of 1% to 2%. Accuracy of the LT1510 OVP voltage is

±0.5% at 25°C and ±1% over full temperature. This leads

to the possibility that very accurate (0.1%) resistors might

be needed for R3 and R4. Actually, the temperature of the

LT1510 will rarely exceed 50°C in float mode because

charging currents have tapered off to a low level, so 0.25%

resistors will normally provide the required level of overall

accuracy.

External Shutdown

The LT1510 can be externally shut down by pulling the V

pin low with an open drain MOSFET, such as VN2222. The

pin should be pulled below 0.8V at room temperature

to ensure shutdown. This threshold decreases at about

2mV/°C. A diode connected between the MOSFET drain

and the V

pin will still ensure the shutdown state over all

temperatures, but it results in slightly different conditions

as outlined below.

If the V

pin is held below threshold, but above ≈ 0.4V, the

current flowing

into

the BAT pin will remain at about

700µA. Pulling the V

pin below 0.4V will cause the current

to drop to ≈ 200µA and reverse, flowing

out

of the BAT pin.

Although these currents are low, the long term effect may

need to be considered if the charger is held in a shutdown

state for very long periods of time, with the charger input

voltage remaining. Removing the charger input voltage

causes all currents to drop to near zero.

If it is acceptable to have 200µA flowing into the battery

while the charger is in shutdown, simply pull the V

directly to ground with the external MOSFET. The resistor

divider used to sense battery voltage will pull current out

Figure 4. PWM Current Programming

PWM

PROG

4.64k

300Ω

PROG

PROG

1µF

Q1

VN2222

LT1510

1510 F04

BAT

= (DC)(1A)

Lithium-Ion Charging

The circuit in Figure 2 uses the 16-pin LT1510 to charge

lithium-ion batteries at a constant 1.3A until battery volt-

age reaches a limit set by R3 and R4. The charger will then

automatically go into a constant-voltage mode with cur-

rent decreasing to zero over time as the battery reaches full

charge. This is the normal regimen for lithium-ion charg-

ing, with the charger holding the battery at “float” voltage

indefinitely. In this case no external sensing of full charge

is needed.

Current through the R3/R4 divider is set at a compromise

value of 25µA to minimize battery drain when the charger

is off and to avoid large errors due to the 50nA bias current

of the OVP pin. Q3 can be added if it is desired to eliminate

LT1510/LT1510-5

APPLICATIONS INFORMATION

WUU U

period, after which the LT1510 can be shut down by

pulling the V

pin low with an open collector or drain.

Some external means must be used to detect the need for

additional charging if needed, or the charger may be

turned on periodically to complete a short float-voltage

cycle.

Current trip level is determined by the battery voltage, R1

through R3, and the internal LT1510 sense resistor

(≈ 0.18Ω pin-to-pin). D2 generates hysteresis in the trip

level to avoid multiple comparator transitions.

Nickel-Cadmium and Nickel-Metal-Hydride Charging

The circuit in Figure 6 uses the 8-pin LT1510 to charge

NiCd or NiMH batteries up to 12V with charging currents

of 0.5A when Q1 is on and 50mA when Q1 is off.

of the battery, canceling part or all of the 200µA. Note that

if net current is into the battery and the battery is removed,

the charger output voltage will float high, to near input

voltage. This could be a problem when reinserting the

battery, if the resulting output capacitor/battery surge

current is high enough to damage either the battery or the

capacitor.

If net current into the battery must be less than zero in

shutdown, there are several options. Increasing divider

current to 300µA - 400µA will ensure that net battery

current is less than zero. For long term storage conditions

however, the divider may need to be disconnected with a

MOSFET switch as shown in Figures 2 and 5. A second

option is to connect a 1N914 diode in series with the

MOSFET drain. This will limit how far the V

pin will be pulled

down, and current (≈ 700µA) will flow

into

the BAT pin, and

therefore out of the battery. This is not usually a problem

unless the charger will remain in the shutdown state with

input power applied for very long periods of time.

Removing input power to the charger will cause the BAT

pin current to drop to near zero, with only the divider

current remaining as a small drain on the battery. Even

that current can be eliminated with a switch as shown in

Figures 2 and 5.

Figure 5. Disconnecting Voltage Divider

Some battery manufacturers recommend termination of

constant-voltage float mode after charging current has

dropped below a specified level (typically 50mA to 100mA)

and

a further time-out period of 30 minutes to 90 minutes

has elapsed. This may extend the life of the battery, so

check with manufacturers for details. The circuit in Figure

7 will detect when charging current has dropped below

75mA. This logic signal is used to initiate a time-out

Figure 6. Charging NiMH or NiCd Batteries

(Efficiency at 0.5A ≈ 90%)

For a 2-level charger, R1 and R2 are found from:

BAT PROG

()( )

2000 2 465.

RIRII

LOW HI LOW

12 465 2000 22 465 2000

()()

−

All battery chargers with fast-charge rates require some

means to detect full charge state in the battery to terminate

the high charging current. NiCd batteries are typically

charged at high current until temperature rise or battery

R3

12k

R4

4.99k

0.25%

R5

220k

OVP V

–

4.2V

BAT

Q3

VN2222

LT1510

1510 F05

SW

BOOST

GND

SENSE



PROG



BAT

R2

11k

R1

100k

Q1

VN2222



 * TOKIN OR MARCON CERAMIC

 SURFACE MOUNT

** COILTRONICS CTX33-2

WALL

ADAPTER

1510 F05.5

C1

0.22µF

*

10µF

L1**

33µHLT1510

D1

1N5819

D3

1N5819

D2

1N914

OUT



22µF

TANT

0.1µF

1µF300Ω

2V TO

20V

BAT

ON: I

BAT

= 0.5A

OFF: I

BAT

= 0.05A



LT1510/LT1510-5

APPLICATIONS INFORMATION

WUU U

Figure 7. Current Comparator for Initiating Float Time-Out

0.18Ω

GND

NEGATIVE EDGE

TO TIMER

INTERNAL

SENSE

RESISTOR

1510 F06

3.3V OR 5V

ADAPTER

OUTPUT

LT1510

D1

1N4148

C1

0.1µF

BAT

SENSE

R1*

1.6k R4

470k

R3

430k

R2

560k

LT1011

D2

1N4148

* TRIP CURRENT = R1(VBAT)

(R2 + R3)(0.18Ω)

–

voltage decrease is detected as an indication of near full

charge. The charging current is then reduced to a much

lower value and maintained as a constant trickle charge.

An intermediate “top off” current may be used for a fixed

time period to reduce 100% charge time.

NiMH batteries are similar in chemistry to NiCd but have

two differences related to charging. First, the inflection

characteristic in battery voltage as full charge is ap-

proached is not nearly as pronounced. This makes it more

difficult to use dV/dt as an indicator of full charge, and

change of temperature is more often used with a tempera-

ture sensor in the battery pack. Secondly, constant trickle

charge may not be recommended. Instead, a moderate

level of current is used on a pulse basis (≈ 1% to 5% duty

cycle) with the time-averaged value substituting for a

constant low trickle.

Thermal Calculations

If the LT1510 is used for charging currents above 0.4A, a

thermal calculation should be done to ensure that junction

temperature will not exceed 125°C. Power dissipation in

the IC is caused by bias and driver current, switch resis-

tance, switch transition losses and the current sense

resistor. The following equations show that maximum

practical charging current for the 8-pin SO package

(125° C/W thermal resistance) is about 0.8A for an 8.4V

battery and 1.1A for a 4.2V battery. This assumes a 60°C

maximum ambient temperature. The 16-pin SO, with a

thermal resistance of 50°C/W, can provide a full 1.5A

charging current in many situations. The 16-pin PDIP falls

between these extremes. Graphs are shown in the Typical

Performance Characteristics section.

P mA V mA V

VmA I

IV V

PIRV

VtVI f

BIAS IN BAT

BAT

IN BAT

DRIVER

BAT BAT BAT

BAT SW BAT

IN OL IN BAT

SENSE

()()

()

()()

[]

()( )











()

()( )( )

()()()()

35 15

75 0012

130

.. 18

Ω

()()

BAT

= Switch ON resistance ≈ 0.35Ω

= Effective switch overlap time ≈ 10ns

f = 200kHz (500kHz for LT1510-5)

LT1510/LT1510-5

APPLICATIONS INFORMATION

WUU U

Example: V

= 15V, V

BAT

= 8.4V, I

BAT

= 1.2A;

PmAmA

mA W

BIAS

DRIVER

()()

()

()()

[]

()()











()

35 15 15 84

15 75 0012 12 017

12 84 1 84

55 15 013

...

....

.. .

kHz

SENSE

()( )()







()( )( )

=+=

()()

−

12 035 84

10 10 15 1 2 200

028 004 032

018 12 026

...

•.

...

.. .

Total power in the IC is:

0.17 + 0.13 + 0.32+ 0.26 = 0.88W

Temperature rise will be (0.88W)(50°C/W) = 44°C. This

assumes that the LT1510 is properly heat sunk by con-

necting the four fused ground pins to the expanded traces

and that the PC board has a backside or internal plane for

heat spreading.

The P

DRIVER

term can be reduced by connecting the boost

diode D2 (see Figures 2 and 6 circuits) to a lower system

voltage (lower than V

BAT

) instead of V

BAT

(see Figure 8).

Then,

IVV V

DRIVER

BAT BAT X X

()( )()











()

For example, V

= 3.3V,

AVV V

DRIVER

()()()











()

12 84 33 1 33

55 15 0 045

... .

The average I

required is:

VmA

DRIVER

0 045

33 14

Total board area becomes an important factor when the

area of the board drops below about 20 square inches. The

graph in Figure 9 shows thermal resistance vs board area

for 2-layer and 4-layer boards. Note that 4-layer boards

have significantly lower thermal resistance, but both types

show a rapid increase for reduced board areas. Figure 10

shows actual measured lead temperature for chargers

operating at full current. Battery voltage and input voltage

will affect device power dissipation, so the data sheet

power calculations must be used to extrapolate these

readings to other situations.

Vias should be used to connect board layers together.

Planes under the charger area can be cut away from the

rest of the board and connected with vias to form both a

BOARD AREA (IN

)



60

55

50

45

40

35

30

25 15 25

1510 F08

510 20 30 35

THERMAL RESISTANCE (°C/W)

S16, MEASURED FROM AIR AMBIENT

TO DIE USING COPPER LANDS AS 

SHOWN ON DATA SHEET

2-LAYER BOARD

4-LAYER BOARD

Figure 9. LT1510 Thermal Resistance

BOOST

SENSE

1510 F07

LT1510

10µF

Figure 8

LT1510/LT1510-5

APPLICATIONS INFORMATION

WUU U

BOARD AREA (IN

)



90

80

70

60

50

40

30

20 15 25

1510 F09

510 20 30 35

LEAD TEMPERATURE (°C)

CHRG

= 1.3A

= 16V

BAT

= 8.4V

BOOST

= V

BAT



= 25°C

NOTE: PEAK DIE TEMPERATURE WILL BE

ABOUT 10°C HIGHER THAN LEAD TEMPER-

ATURE AT 1.3A CHARGING CURRENT

2-LAYER BOARD

4-LAYER BOARD

event of an input short. The body diode of Q2 creates the

necessary pumping action to keep the gate of Q1 low

during normal operation (see Figure 11).

Figure 12. High Speed Switching Path

1510 F12

BAT

HIGH

FREQUENCY

CIRCULATING

PATH

BAT

SWITCH NODE

OUT

Figure 10. LT1510 Lead temperature

low thermal resistance system and to act as a ground

plane for reduced EMI.

Higher Duty Cycle for the LT1510 Battery Charger

Maximum duty cycle for the LT1510 is typically 90% but

this may be too low for some applications. For example, if

an 18V ±3% adapter is used to charge ten NiMH cells, the

charger must put out 15V maximum. A total of 1.6V is lost

in the input diode, switch resistance, inductor resistance

and parasitics so the required duty cycle is 15/16.4 =

91.4%. As it turns out, duty cycle can be extended to 93%

by restricting boost voltage to 5V instead of using V

BAT

is normally done. This lower boost voltage V

(see Figure

8) also reduces power dissipation in the LT1510, so it is a

win-win decision.

Even Lower Dropout

For even lower dropout and/or reducing heat on the board,

the input diode D3 (Figures 2 and 6) should be replaced

with a FET. It is pretty straightforward to connect a

P-channel FET across the input diode and connect its gate

to the battery so that the FET commutates off when the

input goes low. The problem is that the gate must be

pumped low so that the FET is fully turned on even when

the input is only a volt or two above the battery voltage.

Also there is a turn off speed issue. The FET should turn off

instantly when the input is dead shorted to avoid large

current surges form the battery back through the charger

into the FET. Gate capacitance slows turn off, so a small

P-FET (Q2) discharges the gate capacitance quickly in the

Figure 11. Replacing the Input Diode

VX

3V TO 6V

HIGH DUTY CYCLE

CONNECTION

VIN

1510 F10

RX

50k

Q1: Si4435DY

Q2: TP0610L

CX

10µFVBAT

BOOST

SENSE

VCC

LT1510

BAT

Layout Considerations

Switch rise and fall times are under 10ns for maximum

efficiency. To prevent radiation, the catch diode, SW pin

and input bypass capacitor leads should be kept as short

as possible. A ground plane should be used under the

switching circuitry to prevent interplane coupling and to

act as a thermal spreading path. All ground pins should be

connected to expand traces for low thermal resistance.

The fast-switching high current ground path including the

switch, catch diode and input capacitor should be kept

very short. Catch diode and input capacitor should be

close to the chip and terminated to the same point. This

path contains nanosecond rise and fall times with several

amps of current. The other paths contain only DC and /or

200kHz triwave and are less critical. Figure 13 shows

critical path layout. Figure 12 indicates the high speed,

high current switching path.

LT1510/LT1510-5

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-

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

APPLICATIONS INFORMATION

WUU U

GND

1510 F11

LT1510

GND

CC2



CC1



PROG



BAT

GND

GND

GND

SW

BOOST

GND

OVP

SENSE

GND

GND

Figure 13. Critical Electrical and Thermal Path Layer

Dimensions in inches (millimeters) unless otherwise noted.

PACKAGE DESCRIPTION

GN Package

16-Lead Plastic SSOP (Narrow 0.150)

(LTC DWG # 05-08-1641)

GN16 (SSOP) 0895

 * DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH

 SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE

 ** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD

 FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE

345

678

0.229 – 0.244

(5.817 – 6.198)

0.150 – 0.157**

(3.810 – 3.988)

16 15 14 13

0.189 – 0.196*

(4.801 – 4.978)

12 11 10 9

0.016 – 0.050

(0.406 – 1.270)

0.015 ± 0.004

(0.38 ± 0.10)



× 45°

0° – 8° TYP

0.0075 – 0.0098

(0.191 – 0.249)

0.053 – 0.069

(1.351 – 1.748)

0.008 – 0.012

(0.203 – 0.305)

0.004 – 0.009

(0.102 – 0.249)

0.025

(0.635)

BSC

N Package

16-Lead PDIP (Narrow 0.300)

(LTC DWG # 05-08-1510)

N16 0695

0.255 ± 0.015*

(6.477 ± 0.381)

0.770*

(19.558)

MAX

12345678

910

0.015

(0.381)

MIN

0.125

(3.175)

MIN

0.130 ± 0.005

(3.302 ± 0.127)

0.065

(1.651)

TYP

0.045 – 0.065

(1.143 – 1.651)

0.018 ± 0.003

(0.457 ± 0.076)

0.005

(0.127)

MIN

0.100 ± 0.010

(2.540 ± 0.254)

0.009 – 0.015

(0.229 – 0.381)

0.300 – 0.325

(7.620 – 8.255)

0.325 +0.025

–0.015

+0.635

–0.381

8.255

()

*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.

MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)

S8 Package

8-Lead Plastic Small Outline (Narrow 0.150)

(LTC DWG # 05-08-1610)

1234

0.150 – 0.157**

(3.810 – 3.988)

8765

0.189 – 0.197*

(4.801 – 5.004)

0.228 – 0.244

(5.791 – 6.197)

0.016 – 0.050

0.406 – 1.270

0.010 – 0.020

(0.254 – 0.508)× 45°

0°– 8° TYP

0.008 – 0.010

(0.203 – 0.254)

SO8 0695

0.053 – 0.069

(1.346 – 1.752)

0.014 – 0.019

(0.355 – 0.483)

0.004 – 0.010

(0.101 – 0.254)

0.050

(1.270) BSC

DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE

DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE



*

LT1510/LT1510-5

1510fc LT/GP 1197 REV C 4K • PRINTED IN USA

 LINEAR TECHN OLOGY CORPORATION 1995

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

●

(408) 432-1900

FAX: (408) 434-0507

●

TELEX: 499-3977

●

www.linear-tech.com

PART NUMBER DESCRIPTION COMMENTS

LTC®1325 Microprocessor-Controlled Battery Management Can Charge, Discharge and Gas Gauge NiCd, NiMH and Pb-Acid

System Batteries with Software Charging Profiles

LT1372/LT1377 500kHz/1MHz Step-Up Switching Regulators High Frequency, Small Inductor, High Efficiency Switchers, 1.5A Switch

LT1373 250kHz Step-Up Switching Regulator High Efficiency, Low Quiescent Current, 1.5A Switch

LT1376 500kHz Step-Down Switching Regulator High Frequency, Small Inductor, High Efficiency Switcher, 1.5A Switch

LT1511 3A Constant-Voltage/Constant-Current Battery Charger High Efficiency, Minimal External Components to Fast Charge Lithium,

NiMH and NiCd Batteries

LT1512 SEPIC Battery Charger V

Can Be Higher or Lower Than Battery Voltage

RELATED PARTS

TYPICAL APPLICATION

Dimensions in inches (millimeters) unless otherwise noted.

PACKAGE DESCRIPTION

S Package

16-Lead Plastic Small Outline (Narrow 0.150)

(LTC DWG # 05-08-1610)

0.016 – 0.050

0.406 – 1.270

0.010 – 0.020

(0.254 – 0.508)× 45°

0° – 8° TYP

0.008 – 0.010

(0.203 – 0.254)

12345678

0.150 – 0.157**

(3.810 – 3.988)

16 15 14 13

0.386 – 0.394*

(9.804 – 10.008)

0.228 – 0.244

(5.791 – 6.197)

12 11 10 9

S16 0695

0.053 – 0.069

(1.346 – 1.752)

0.014 – 0.019

(0.355 – 0.483)

0.004 – 0.010

(0.101 – 0.254)

0.050

(1.270)

TYP

DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH 

SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE

DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD 

FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE



*

Adjustable Voltage Regulator with Precision Adjustable Current Limit

SW

BOOST

CC2



18V TO 25V

OUT



2.5V TO 15V

CURRENT LIMIT LEVEL

50mA TO 1A

1510 TA01

0.22µF

0.1µF

100µF

30µH

LT1510

1N5819

1N914

POT

5k



POT

100k

PROG



4.93k

0.01µF

500µF

1µF

GND

CURRENT LIMIT LEVEL = (2000)

2.465V

PROG

CC1

PROG

BAT

OVP

SENSE

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