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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 APPLICATIONSU

, 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)* thatrequire constant-current and/or constant-voltage charg-ing. The internal switch is capable of delivering 1.5A DCcurrent (2A peak current). The 0.1 onboard currentsense resistor makes the charging current programmingvery simple. One resistor (or a programming current froma DAC) is required to set the full charging current (1.5A) towithin 5% accuracy. The LT1510 with 0.5% referencevoltage 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 batterysnegative terminal can be tied directly to ground. A saturat-ing switch running at 200kHz (500kHz for LT1510-5) giveshigh charging efficiency and small inductor size. A block-ing diode is not required between the chip and the batterybecause the chip goes into sleep mode and drains only 3Awhen the wall adaptor is unplugged. Soft start and shutdownfeatures are also provided. The LT1510 is available in a 16-pinfused lead power SO package with a thermal resistance of50C/W, an 8-pin SO and a 16-pin PDIP.

FEATURES

Charges NiCd, NiMH and Lithium-Ion Batteries Only One 1/10W Resistor Is Needed to ProgramCharging Current

High Efficiency Current Mode PWM with 1.5AInternal Switch and Sense Resistor

3% Typical Charging Current Accuracy Precision 0.5% Voltage Reference for Voltage

ModeCharging or Overvoltage Protection Current Sensing Can Be at Either Terminal of

the Battery Low Reverse Battery Drain Current: 3A Charging Current Soft Start Shutdown Control 500kHz Version Uses Small Inductor

With switching frequency as high as 500kHz, The LT 1510current mode PWM battery charger is the smallest, sim-

APPLICATIONSU

DESCRIPTIONU

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

VCC

PROG

VC

BAT

6.19k

8.2V TO 20V

+

R370.6k0.25%

R4100k0.25%

Q32N7002

NOTE: COMPLETE LITHIUM-ION CHARGER, NO TERMINATION REQUIRED

TOKIN OR MARCON CERAMIC SURFACE MOUNT

COILTRONICS TP3-100, 10H, 2.2mm HEIGHT (0.8A CHARGING CURRENT) COILTRONICS TP1 SERIES, 10H, 1.8mm HEIGHT (

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Supply Voltage (VMAX) ............................................ 30VSwitch Voltage with Respect to GND ...................... 3VBoost Pin Voltage with Respect to VCC ................... 30V

Boost Pin Voltage with Respect to GND ................. 5VVC, PROG, OVP Pin Voltage ...................................... 8VIBAT(Average)........................................................ 1.5ASwitch Current (Peak)............................................... 2AStorage Temperature Range ................. 65C to 150C

ABSOLUTE MAXIMUMRATINGSW WW U

Operating Ambient Temperature RangeCommercial ............................................. 0C to 70CExtended Commercial (Note 7) ........... 40C to 85C

Industrial (Note 8) .............................. 40C to 85COperating Junction Temperature RangeLT1510C (Note 7) ............................. 40C to 125CLT1510I ............................................ 40C to 125C

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

PACKAGE/ORDER INFORMATIONW UU

Consult factory for Military grade parts.

ELECTRICAL CHARACTERISTICSVCC= 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 VPROG= 2.7V, VCC20V 2.90 4.3 mAVPROG= 2.7V, 20V < VCCVMAX 2.91 4.5 mA

DC Battery Current, IBAT(Note 1) 8V VCC25V, 0V VBAT20V, TJ< 0C 0.91 1.09 ARPROG= 4.93k 0.93 1.0 1.07 ARPROG= 3.28k (Note 4) 1.35 1.5 1.65 ARPROG= 49.3k 75 100 125 mATJ< 0C 70 130 mA

VCC= 28V, VBAT= 20VRPROG= 4.93k 0.93 1.0 1.07 ARPROG= 49.3k 75 100 125 mA

LT1510CNLT1510CSLT1510INLT1510IS

ORDER PARTNUMBER

TJMAX= 125C, JA= 125C/ W

ORDER PARTNUMBER

GN PARTMARKING

* VCC1AND VCC2SHOULD BE CONNECTEDTOGETHER CLOSE TO THE PINS.

** FOUR CORNER PINS ARE FUSED TOINTERNAL DIE ATTACH PADDLE FORHEAT SINKING. CONNECT THESE FOURPINS TO EXPANDED PC LANDS FORPROPER HEAT SINKING.

1

23

4

5

6

7

8

TOP VIEW

N PACKAGE16-LEAD PDIP

16

1514

13

12

11

10

9

**GND

SWBOOST

GND

OVP

SENSE

GND

**GND

GND**

VCC2VCC1

PROG

VC

BAT

GND

GND**

S PACKAGE*16-LEAD PLASTIC SO

TJMAX= 125C, JA= 75C/W (N)TJMAX= 125C, JA= 50C/W (S)*

1

2

3

4

8

7

6

5

TOP VIEW

SW

BOOST

GND

SENSE

VCC

PROG

VC

BAT

S8 PACKAGE8-LEAD PLASTIC SO

LT1510CS8LT1510IS8

15101510I

ORDER PARTNUMBER

S8 PART MARKING

1

23

4

5

6

7

8

TOP VIEW

16

1514

13

12

11

10

9

**GND

SWBOOST

GND

OVP

NC

SENSE

**GND

GND**

VCC2VCC1

PROG

VC

NC

BAT

GND**

GN PACKAGE (0.015 IN)16-LEAD PLASTIC SSOP

TJMAX= 125C, JA= 75C/ W

** FOUR CORNER PINS ARE FUSED TOINTERNAL DIE ATTACH PADDLE FORHEAT SINKING. CONNECT THESE FOUR

PINS TO EXPANDED PC LANDS FORPROPER HEAT SINKING.

LT1510CGNLT1510IGNLT1510-5CGNLT1510-5IGN

15101510I

1510515105I

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


Overall

Minimum Input Operating Voltage Undervoltage Lockout 6.2 7 7.8 V

Reverse Current from Battery (When VCCIs Not VBAT20V, 0C TJ70C 3 15 AConnected, VSWIs Floating)

Boost Pin Current VCC VBOOST20V 0.10 20 A20V < VCC VBOOST28V 0.25 30 A2V VBOOST VCC8V (Switch ON) 6 11 mA8V < VBOOST VCC25V (Switch ON) 8 14 mA

Switch

Switch ON Resistance VCC= 10VISW= 1.5A, VBOOST VSW2V (Note 4) 0.3 0.5 ISW= 1A, VBOOST VSW< 2V (Unboosted) 2.0

IBOOST/ISWDuring Switch ON VBOOST= 24V, ISW1A 20 35 mA/A

Switch OFF Leakage Current VSW= 0V, VCC20V 2 100 A20V < VCC28V 4 200 A

Maximum VBATwith Switch ON VCC 2 V

Minimum IPROGfor Switch ON 2 4 20 A

Minimum IPROGfor Switch OFF at VPROG 1V 1 2.4 mA

Current Sense Amplifier Inputs (SENSE, BAT)

Sense Resistance (RS1) 0.08 0.12

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

BAT Bias Current (Note 5) VC< 0.3V 200 375 AVC> 0.6V 700 1300 A

Input Common Mode Limit (Low) 0.25 V

Input Common Mode Limit (High) VCC 2 V

Reference

Reference Voltage (Note 1) S8 Package RPROG= 4.93k, Measured at PROG Pin 2.415 2.465 2.515 V

Reference Voltage (Note 2) 16-Pin RPROG= 3.28k, Measured at OVP with 2.453 2.465 2.477 VVA Supplying IPROGand Switch OFF

Reference Voltage Tolerance, 16-Pin Only 8V VCC28V, 0C TJ70C 2.446 2.465 2.480 V8V VCC28V, 0C TJ125C 2.441 2.489 V8V VCC28V, TJ< 0C 2.430 2.489 V

Oscillator

Switching Frequency LT1510 180 200 220 kHzLT1510-5 440 500 550 kHz

Switching Frequency Tolerance All Conditions of VCC, Temperature, LT1510 170 200 230 kHzLT1510, TJ< 0C 160 230 kHzLT1510-5 425 500 575 kHzLT1510-5, TJ< 0C 400 575 kHz

Maximum Duty Cycle LT1510 87 %LT1510, TA= 25C (Note 8) 90 93 %LT1510-5 (Note 9) 77 81 %

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


Current Amplifier (CA2)

Transconductance VC= 1V, IVC= 1A 150 250 550 mho

Maximum VCfor Switch OFF 0.6 V

IVCCurrent (Out of Pin) VC0.6V 100 AVC< 0.45V 3 mA

Voltage Amplifier (VA), 16-Pin Only

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

Output Source Current, VCC= 10V VPROG= VOVP= VREF+ 10mV 1.3 mA

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

The denotes specifications which apply over the specifiedtemperature range.

Note 1:Tested with Test Circuit 1.

Note 2:Tested with Test Circuit 2.

Note 3:Sense resistor RS1and package bond wires.

Note 4:Applies to 16-pin only. 8-pin packages are guaranteed but nottested at 40C.Note 5:Current (700A) flows into the pins during normal operation andalso when an external shutdown signal on the VCpin is greater than 0.3V.Current decreases to 200A and flows out of the pins when externalshutdown holds the VCpin below 0.3V. Current drops to near zero wheninput voltage collapses. See external Shutdown in Applications Informationsection.

Note 6:A linear interpolation can be used for reference voltagespecification between 0C and 40C.

Note 7:Commercial grade device specifications are guaranteed over the0C to 70C temperature range. In addition, commercial grade devicespecifications are assured over the 40C to 85C temperature range bydesign or correlation, but are not production tested.Maximum allowable ambient temperature may be limited by powerdissipation. Parts may not necessarily be operated simultaneously atmaximum power dissipation and maximum ambient temperature.Temperature rise calculations must be done as shown in the ApplicationsInformation section to ensure that maximum junction temperature doesnot exceed the 125C limit. With high power dissipation, maximumambient temperature may be less than 70C.Note 8:Industrial grade device specifications are guaranteed over the40C to 85C temperature range.Note 9:91% maximum duty cycle is guaranteed by design if VBATor VX(see Figure 8 in Application Information) is kept between 3V and 5V.

Note 10:VBAT= 4.2V.

Thermally Limited MaximumCharging Current, 8-Pin SO

INPUT VOLTAGE (V)

0

MAXIMUMC

HA

RGINGCURRENT(A)

1.3

1.1

0.9

0.7

0.5

0.320

1510 G12

5 10 15 25

16V BATTERY

12V BATTERY

8V BATTERY

4V BATTERY

(JA=125C/W)TAMAX=60CTJMAX=125C

Thermally Limited MaximumCharging Current, 16-Pin SO

INPUT VOLTAGE (V)

0

MAXIMUMCHA

RGINGCURRENT(A)

1.5

1.3

1.1

0.9

0.7

0.520

1510 G13

5 10 15 25

(JA=50C/W)TAMAX=60CTJMAX=125C

16V BATTERY

12V BATTERY

8V BATTERY

4V BATTERY

Thermally Limited MaximumCharging Current, 16-Pin GN

INPUT VOLTAGE (V)

0

MAXIMUMC

HARGINGCURRENT(A)

1.5

1.3

1.1

0.9

0.7

0.520

LT1510 TPC14

5 10 15 25

JA= 80C/WTAMAX= 60CTJMAX= 125C

4V BATTERY

8V BATTERY

12V BATTERY

16V BATTERY

TYPICAL PERFORMANCE CHARACTERISTICSUW

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Switching Frequency vsTemperature

DUTY CYCLE (%)

0 10 30 50 70

ICC(mA)

80

1510 G04

20 40 60

8

7

6

5

4

3

2

1

0

125C0C

25C

VCC= 16V

ICCvs Duty Cycle

TEMPERATURE (C)

20

FREQUENCY(kHz)

200 40 80 12060 100 140

1510 G05

210

205

200

195

190

185

180

IBAT(A)

0.1

EFFICIENCY(%)

100

98

96

94

92

90

88

86

84

82

800.5 0.9 1.51.31.1

1510 G01

0.3 0.7

VCC= 15V (EXCLUDING DISSIPATIONON INPUT DIODE D3)VBAT= 8.4V

Efficiency of Figure 2 Circuit

ICCvs VCC

VCC(V)

0

ICC(mA)

7.0

6.5

6.0

5.5

5.0

4.55 10 15 20

1510 G03

25 30

125C

25C

0C

MAXIMUM DUTY CYCLE

IVA(mA)

0

VOVP(mV)

4

3

2

1

00.8

1510 G08

0.20.1 0.3 0.5 0.7 0.90.4 0.6 1.0

125C

25C

IVAvs VOVP(Voltage Amplifier)

VCC(V)

0

VREF(V)

0.003

0.002

0.001

0

0.001

0.002

0.0035 10 15 20

1510 G02

25 30

ALL TEMPERATURES

VREFLine Regulation

TEMPERATURE (C)

0

DU

TYCYCLE(%)

120

1510 G09

40 80

98

97

96

95

94

93

92

91

9020 60 100 140

Maximum Duty Cycle

VPROG(V)

0 1 2 3 54

IPROG(mA)

6

0

6

1510 G11

125C

25C

PROG Pin Characteristic

VC(V)

0 0.2 0.6 1.0 1.4 1.8

IVC(mA)

1.20

1.08

0.96

0.84

0.72

0.60

0.48

0.36

0.24

0.12

0

0.121.6

1510 G10

0.4 0.8 1.2 2.0

VCPin Characteristic

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SWITCH CURRENT (A)

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.8 2.01.6

BOOSTCURRENT(mA)

50

45

40

35

30

25

20

15

10

5

0

1510 G07

VCC= 16V

VBOOST= 38V28V18V

Switch Current vs Boost Currentvs Boost Voltage

TEMPERATURE (C)

0

REFERENCEVOLTAGE(V)

2.470

2.468

2.466

2.464

2.462

2.460

2.45825 50 75 100

1510 G14

125 150

Reference Voltage vsTemperature

VBOOST(V)

42 6 8

MAXIMUMD

UTYCYCLE(%)

16 18 20

96

95

94

93

92

91

90

89

88

87

86

LT1510 TPC15

10 12 14 22

VBOOSTvsMaximum Duty Cycle

PINFUNCTIONSUUU

GND:Ground Pin.

SW:Switch Output. The Schottky catch diode must beplaced with very short lead length in close proximity to SWpin and GND.

VCC:Supply for the Chip. For good bypass, a low ESRcapacitor of 10F or higher is required, with the lead length

kept to a minimum. VCCshould be between 8V and 28Vand at least 2V higher than VBATfor VBATless than 10V, and2.5V higher than VBATfor VBATgreater than 10V. Under-voltage lockout starts and switching stops when VCCgoesbelow 7V. Note that there is a parasitic diode inside fromSW pin to VCCpin. Do not force VCCbelow SW by morethan 0.7V with battery present. All VCCpins should beshorted together close to the pins.

BOOST:This pin is used to bootstrap and drive the switchpower NPN transistor to a low on-voltage for low powerdissipation. In normal operation, VBOOST = VCC + VBATwhen switch is on. Maximum allowable VBOOSTis 55V.

SENSE:Current Amplifier CA1 Input. Sensing can be ateither terminal of the battery. Note that current senseresistor RS1(0.08) is between Sense and BAT pins.

BAT:Current Amplifier CA1 Input.

PROG:This pin is for programming the charging currentand for system loop compensation. During normal opera-tion, VPROGstays close to 2.465V. If it is shorted to GNDthe switching will stop. When a microprocessor-controlledDAC is used to program charging current, it must becapable of sinking current at a compliance up to 2.465V.

VC:This is the control signal of the inner loop of the currentmode PWM. Switching starts at 0.7V and higher VCcorresponds to higher charging current in normal opera-tion. A capacitor of at least 0.1F to GND filters out noiseand controls the rate of soft start. To shut down switching,pull this pin low. Typical output current is 30A.

OVP:This is the input to the amplifier VA with a thresholdof 2.465V. Typical input current is about 50nA into pin. Forcharging lithium-ion batteries, VA monitors the batteryvoltage and reduces charging current when battery volt-age reaches the preset value. If it is not used, the OVP pinshould be grounded.

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BLOCK DIAGRAMW

TEST CIRCUITS

Test Circuit 1

+

VREF

0.65V

VBAT

VC

2N3055

1k

LT1010

CA2

+

+

CA1

++

3.3k

20k

1k

1k

RS1

IBAT

BAT

SENSE

1510 TC01

PROG

RPROG

0.047F

LT1510

0.22F

56F60k

LT1006

+

+

+

+

+

+

VSW

0.7V

1.5V

VBAT

VREF

VC

GND SLOPECOMPENSATION

R2

R3

C1

PWM B1

CA2

+

+

CA1

VA

+

+

VREF2.465V

SHUTDOWN

200kHzOSCILLATOR

S

RR

R11k

RS1IBAT

IPROG

IPROG

VCC

VCC

BOOST

SW

SENSE

BAT

0VP

1510 BD

PROG

RPROG

CPROG

60k

IPROGIBAT

= 500A/A

QSW

gm= 0.64

CHARGING CURRENT IBAT= (IPROG)(2000)

= 2.465V RPROG

(2000)( )

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TEST CIRCUITS

VREF

2.465V

+

+

VA

+

10k

10k

OVP

1510 TC02

IPROG

RPROG

LT1510

PROG

LT1013

0.47F

Test Circuit 2

OPERATIOU

The LT1510 is a current mode PWM step-down (buck)switcher. The battery DC charging current is programmedby a resistor RPROG(or a DAC output current) at the PROGpin (see Block Diagram). Amplifier CA1 converts thecharging current through RS1 to a much lower currentIPROG (500A/A) fed into the PROG pin. Amplifier CA2compares the output of CA1 with the programmed currentand drives the PWM loop to force them to be equal. HighDC accuracy is achieved with averaging capacitor CPROG.Note that IPROGhas both AC and DC components. IPROGgoes through R1 and generates a ramp signal that is fed tothe PWM control comparator C1 through buffer B1 and

level shift resistors R2 and R3, forming the current modeinner loop. The Boost pin drives the switch NPN QSWintosaturation and reduces power loss. For batteries likelithium-ion that require both constant-current and con-stant-voltage charging, the 0.5%, 2.465V reference andthe amplifier VA reduce the charging current when battery

voltage reaches the preset level. For NiMH and NiCd, VAcan be used for overvoltage protection. When input volt-age is not present, the charger goes into low current (3Atypically) sleep mode as input drops down to 0.7V belowbattery voltage. To shut down the charger, simply pull theVCpin low with a transistor.

APPLICATIONS INFORMATIONWU UU

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 thisdata sheet, the input capacitor CINis assumed to absorb allinput switching ripple current in the converter, so it musthave adequate ripple current rating. Worst-case RMSripple current will be equal to one half of output chargingcurrent. Actual capacitance value is not critical. Solid

tantalum capacitors such as the AVX TPS and Sprague593D series have high ripple current rating in a relativelysmall surface mount package, but caution must be usedwhen tantalum capacitors are used for input bypass. Highinput surge currents can be created when the adapter ishot-plugged to the charger and solid tantalum capacitorshave a known failure mechanism when subjected to veryhigh turn-on surge currents. Highest possible voltagerating on the capacitor will minimize problems. Consult withthe manufacturer before use. Alternatives include new high

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capacity ceramic capacitor (5F to 10F) from Tokin orUnited 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 COUT is also assumed to absorboutput switching current ripple. The general formula forcapacitor current is:

I

V V

V

L fRMS

BATBAT

CC=( )

( )( )

0 29 1

1

.

For example, with VCC= 16V, VBAT= 8.4V, L1 = 30H and

f = 200kHz, IRMS= 0.2A.EMI considerations usually make it desirable to minimizeripple current in the battery leads, and beads or inductorsmay be added to increase battery impedance at the 200kHzswitching frequency. Switching ripple current splits be-tween the battery and the output capacitor depending onthe ESR of the output capacitor and the battery impedance.If the ESR of COUTis 0.2and the battery impedance israised to 4with a bead of inductor, only 5% of the currentripple will flow in the battery.

Soft Start

The LT1510 is soft started by the 0.1F capacitor on VCpin. On start-up, VCpin voltage will rise quickly to 0.5V,then ramp at a rate set by the internal 45A pull-up currentand the external capacitor. Battery charging current startsramping up when VCvoltage reaches 0.7V and full currentis achieved with VCat 1.1V. With a 0.1F capacitor, time toreach full charge current is about 3ms and it is assumedthat input voltage to the charger will reach full value in lessthan 3ms. Capacitance can be increased up to 0.47F iflonger input start-up times are needed.

In any switching regulator, conventional timer-based softstarting can be defeated if the input voltage rises muchslower than the time-out period. This happens because theswitching regulators in the battery charger and the com-puter power supply are typically supplying a fixed amountof power to the load. If input voltage comes up slowlycompared to the soft start time, the regulators will try to

deliver full power to the load when the input voltage is stillwell 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 theadapter output stays in a current limited state at reducedoutput voltage. For instance, if maximum charger pluscomputer load power is 20W, a 24V adapter might becurrent limited at 1A. If adapter voltage is less than (20W/1A= 20V) when full power is drawn, the adapter voltage will besucked down by the constant 20W load until it reaches alower stable state where the switching regulators can nolonger supply full load. This situation can be prevented byutilizing 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 VCCpin.Internal lockout is performed by clamping the VCpin low.The VCpin is released from its clamped state when the VCCpin rises above 7V. The charger will start delivering currentabout 2ms after VCis released, as set by the 0.1F at VCpin. Higher lockout voltage can be implemented with aZener diode (see Figure 3 circuit).

Figure 3. Undervoltage Lockout

GND

VCC

VC

VIN

1510 F03

LT1510

2k

D11N4001VZ

The lockout voltage will be VIN= VZ+ 1V.

For example, for a 24V adapter to start charging at 22VIN,choose VZ= 21V. When VINis less than 22V, D1 keeps VC

low and charger off.

Charging Current Programming

The basic formula for charging current is (see BlockDiagram):

I I V

RBAT PROG

PROG

=( )( ) =

( )2000

2 4652000

.

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where RPROG is the total resistance from PROG pin toground.

For example, 1A charging current is needed.

RV

AkPROG =

( )( )=

2 465 2000

14 93

..

Charging current can also be programmed by pulse widthmodulating IPROGwith a switch Q1 to RPROGat a frequencyhigher than a few kHz (Figure 4). Charging current will beproportional to the duty cycle of the switch with full currentat 100% duty cycle.

When a microprocessor DAC output is used to control

charging current, it must be capable of sinking currentat a compliance up to 2.5V if connected directly to thePROG pin.


even this low current drain. A 47k resistor from adapteroutput to ground should be added if Q3 is used to ensurethat the gate is pulled to ground.

With divider current set at 25A, R4 = 2.465/25A = 100kand,

RR V

R A

k

k A

k

BAT3

4 2 465

2 465 4 0 05

100 8 4 2 465

2 465 100 0 05

240

= ( ) ( )

+ ( )=

( )+ ( )

=

.

. .

. .

. .

Lithium-ion batteries typically require float voltage accu-racy of 1% to 2%. Accuracy of the LT1510 OVP voltage is0.5% at 25C and 1% over full temperature. This leadsto the possibility that very accurate (0.1%) resistors mightbe needed for R3 and R4. Actually, the temperature of theLT1510 will rarely exceed 50C in float mode becausecharging currents have tapered off to a low level, so 0.25%resistors will normally provide the required level of overallaccuracy.

External Shutdown

The LT1510 can be externally shut down by pulling the VCpin low with an open drain MOSFET, such as VN2222. The

VCpin should be pulled below 0.8V at room temperatureto ensure shutdown. This threshold decreases at about2mV/C. A diode connected between the MOSFET drainand the VCpin will still ensure the shutdown state over alltemperatures, but it results in slightly different conditionsas outlined below.

If the VCpin is held below threshold, but above 0.4V, thecurrent flowing into the BAT pin will remain at about700A. Pulling the VCpin below 0.4V will cause the currentto drop to 200A and reverse, flowing out of the BAT pin.

Although these currents are low, the long term effect mayneed to be considered if the charger is held in a shutdownstate for very long periods of time, with the charger inputvoltage remaining. Removing the charger input voltagecauses all currents to drop to near zero.

If it is acceptable to have 200A flowing into the batterywhile the charger is in shutdown, simply pull the VCpindirectly to ground with the external MOSFET. The resistordivider used to sense battery voltage will pull current out

Figure 4. PWM Current Programming

PWM

RPROG4.64k

300

PROG

CPROG1F

Q1VN2222

5V

0V

LT1510

1510 F04IBAT= (DC)(1A)

Lithium-Ion Charging

The circuit in Figure 2 uses the 16-pin LT1510 to chargelithium-ion batteries at a constant 1.3A until battery volt-age reaches a limit set by R3 and R4. The charger will thenautomatically go into a constant-voltage mode with cur-

rent decreasing to zero over time as the battery reaches fullcharge. This is the normal regimen for lithium-ion charg-ing, with the charger holding the battery at float voltageindefinitely. In this case no external sensing of full chargeis needed.

Current through the R3/R4 divider is set at a compromisevalue of 25A to minimize battery drain when the chargeris off and to avoid large errors due to the 50nA bias currentof the OVP pin. Q3 can be added if it is desired to eliminate

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period, after which the LT1510 can be shut down bypulling the VCpin 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 beturned on periodically to complete a short float-voltagecycle.

Current trip level is determined by the battery voltage, R1through R3, and the internal LT1510 sense resistor(0.18pin-to-pin). D2 generates hysteresis in the triplevel 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 currentsof 0.5A when Q1 is on and 50mA when Q1 is off.

of the battery, canceling part or all of the 200A. Note thatif 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 thebattery, if the resulting output capacitor/battery surgecurrent is high enough to damage either the battery or thecapacitor.

If net current into the battery must be less than zero inshutdown, there are several options. Increasing dividercurrent to 300A - 400A will ensure that net batterycurrent is less than zero. For long term storage conditionshowever, the divider may need to be disconnected with aMOSFET switch as shown in Figures 2 and 5. A second

option is to connect a 1N914 diode in series with theMOSFET drain. This will limit how far the VCpin will be pulleddown, and current (700A) will flow into the BAT pin, andtherefore out of the battery. This is not usually a problemunless the charger will remain in the shutdown state withinput power applied for very long periods of time.

Removing input power to the charger will cause the BATpin current to drop to near zero, with only the dividercurrent remaining as a small drain on the battery. Eventhat current can be eliminated with a switch as shown in

Figures 2 and 5.

Figure 5. Disconnecting Voltage Divider

Some battery manufacturers recommend termination ofconstant-voltage float mode after charging current hasdropped below a specified level (typically 50mA to 100mA)anda further time-out period of 30 minutes to 90 minuteshas elapsed. This may extend the life of the battery, socheck with manufacturers for details. The circuit in Figure7 will detect when charging current has dropped below75mA. 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:

I

R

BAT

PROG

=( )( )2000 2 465.

RI

RI ILOW HI LOW

12 465 2000

22 465 2000

=( )( )

=( )( )

. .

All battery chargers with fast-charge rates require somemeans to detect full charge state in the battery to terminatethe high charging current. NiCd batteries are typicallycharged at high current until temperature rise or battery

R312k

R44.99k0.25%

R5220k

OVPVIN

+

+

4.2V

4.2V

VBAT

Q3VN2222

LT1510

1510 F05

SW

BOOST

GND

SENSE

VCC

PROG

VC

BAT

R211k

+

R1100k

Q1

VN2222

* TOKIN OR MARCON CERAMIC SURFACE MOUNT** COILTRONICS CTX33-2

WALLADAPTER

1510 F05.5

C10.22F

CIN*10F

L1**33H LT1510

D11N5819

D31N5819

D21N914

+

COUT22FTANT

0.1F

+

1k

1F300

2V TO20V

IBAT

ON: IBAT= 0.5AOFF: IBAT= 0.05A

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Figure 7. Current Comparator for Initiating Float Time-Out

0.18

GND

NEGATIVE EDGETO TIMER

INTERNALSENSE

RESISTOR

1510 F06

3.3V OR 5VADAPTEROUTPUT

3 8

7

1

42

LT1510

D11N4148

C10.1F

BAT

SENSE

R1*1.6k R4

470k

R3430k

R2560k

LT1011

D21N4148

* TRIP CURRENT =R1(VBAT)

(R2 + R3)(0.18)

+

voltage decrease is detected as an indication of near fullcharge. The charging current is then reduced to a muchlower value and maintained as a constant trickle charge.An intermediate top off current may be used for a fixedtime period to reduce 100% charge time.

NiMH batteries are similar in chemistry to NiCd but havetwo 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 moredifficult to use dV/dt as an indicator of full charge, andchange of temperature is more often used with a tempera-ture sensor in the battery pack. Secondly, constant tricklecharge may not be recommended. Instead, a moderatelevel of current is used on a pulse basis (1% to 5% dutycycle) with the time-averaged value substituting for aconstant low trickle.

Thermal Calculations

If the LT1510 is used for charging currents above 0.4A, athermal calculation should be done to ensure that junctiontemperature will not exceed 125C. Power dissipation inthe IC is caused by bias and driver current, switch resis-tance, switch transition losses and the current senseresistor. The following equations show that maximumpractical charging current for the 8-pin SO package(125C/W thermal resistance) is about 0.8A for an 8.4V

battery and 1.1A for a 4.2V battery. This assumes a 60Cmaximum ambient temperature. The 16-pin SO, with athermal resistance of 50C/W, can provide a full 1.5Acharging current in many situations. The 16-pin PDIP fallsbetween these extremes. Graphs are shown in the TypicalPerformance Characteristics section.

P mA V mA V

V

VmA I

P

I V V

V

PI R V

Vt V I f

P

BIAS IN BAT

BAT

IN

BAT

DRIVER

BAT BATBAT

IN

SW

BAT SW BAT

INOL IN BAT

SENSE

=( )( ) + ( )

+( )

+ ( )( )[ ]

=( )( ) +

( )

=

( ) ( )( )+ ( )( )( )( )

=

3 5 1 5

7 5 0 012

130

55

0

2

2

2

. .

. .

..182

( )( )IBAT

RSW= Switch ON resistance 0.35tOL= Effective switch overlap time 10nsf = 200kHz (500kHz for LT1510-5)

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Example: VIN= 15V, VBAT= 8.4V, IBAT= 1.2A;

P mA mA

mA W

P W

BIAS

DRIVER

=( )( )+ ( )

+( )

+( )( )[ ]=

=( ) ( ) +

( ) =

3 5 15 1 5 8 4

8 4

157 5 0 012 1 2 0 17

1 2 8 4 18 4

30

55 150 13

2

2

. . .

.. . . .

. . .

.

P

kHz

W

P W

SW

SENSE

=( ) ( )( )

+

( )( )( )= + =

=( )( ) =

1 2 0 35 8 4

15

10 10 15 1 2 200

0 28 0 04 0 32

0 18 1 2 0 26

2

9

2

. . .

.

. . .

. . .

Total power in the IC is:

0.17 + 0.13 + 0.32+ 0.26 = 0.88W

Temperature rise will be (0.88W)(50C/W) = 44C. Thisassumes that the LT1510 is properly heat sunk by con-

necting the four fused ground pins to the expanded tracesand that the PC board has a backside or internal plane forheat spreading.

The PDRIVERterm can be reduced by connecting the boostdiode D2 (see Figures 2 and 6 circuits) to a lower systemvoltage (lower than VBAT) instead of VBAT(see Figure 8).

Then,

P

I V V V

VDRIVER

BAT BAT XX

IN=

( )( )( ) +

( )

130

55

For example, VX= 3.3V,

P

A V V V

VWDRIVER=

( )( )( ) +

( ) =

1 2 8 4 3 3 1 3 3

30

55 150 045

. . . .

.

The average IVXrequired is:

P

V

W

V

mADRIVER

X

= =0 045

3 3

14.

.Total board area becomes an important factor when thearea of the board drops below about 20 square inches. Thegraph in Figure 9 shows thermal resistance vs board areafor 2-layer and 4-layer boards. Note that 4-layer boardshave significantly lower thermal resistance, but both typesshow a rapid increase for reduced board areas. Figure 10shows actual measured lead temperature for chargersoperating at full current. Battery voltage and input voltagewill affect device power dissipation, so the data sheet

power calculations must be used to extrapolate thesereadings to other situations.

Vias should be used to connect board layers together.Planes under the charger area can be cut away from therest of the board and connected with vias to form both a

BOARD AREA (IN2)

0

60

55

50

45

40

35

30

2515 25

1510 F08

5 10 20 30 35

THERMALR

ESISTANCE(C/W)

S16, MEASURED FROM AIR AMBIENTTO DIE USING COPPER LANDS AS SHOWN ON DATA SHEET

2-LAYER BOARD

4-LAYER BOARD

Figure 9. LT1510 Thermal Resistance

BOOST

SW

SENSE

VXIVX

1510 F07

LT1510C1

L1

D2

10F+

Figure 8

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BOARD AREA (IN2)

0

90

80

70

60

50

40

30

2015 25

1510 F09

5 10 20 30 35

LEADTEMPERATURE

(C)

ICHRG= 1.3AVIN= 16VVBAT= 8.4VVBOOST= VBATTA= 25C

NOTE: PEAK DIE TEMPERATURE WILL BEABOUT 10C 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 thenecessary pumping action to keep the gate of Q1 lowduring normal operation (see Figure 11).

Figure 12. High Speed Switching Path

1510 F12

VBAT

L1

VIN

HIGHFREQUENCY

CIRCULATINGPATH

BAT

SWITCH NODE

CIN COUT

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% butthis may be too low for some applications. For example, ifan 18V 3% adapter is used to charge ten NiMH cells, thecharger must put out 15V maximum. A total of 1.6V is lostin the input diode, switch resistance, inductor resistanceand 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 VBATasis normally done. This lower boost voltage VX (see Figure8) also reduces power dissipation in the LT1510, so it is awin-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 replacedwith a FET. It is pretty straightforward to connect aP-channel FET across the input diode and connect its gateto the battery so that the FET commutates off when the

input goes low. The problem is that the gate must bepumped low so that the FET is fully turned on even whenthe input is only a volt or two above the battery voltage.Also there is a turn off speed issue. The FET should turn offinstantly when the input is dead shorted to avoid largecurrent surges form the battery back through the chargerinto the FET. Gate capacitance slows turn off, so a smallP-FET (Q2) discharges the gate capacitance quickly in the

Figure 11. Replacing the Input Diode

VX3V TO 6V

HIGH DUTY CYCLE

CONNECTION

VIN

1510 F10

C3

L1

D2

D1

Q2

Q1

RX50k

Q1: Si4435DYQ2: TP0610L

CX10F VBAT

BOOST

SW

SENSE

VCC

LT1510

BAT

+

+

Layout Considerations

Switch rise and fall times are under 10ns for maximumefficiency. To prevent radiation, the catch diode, SW pinand input bypass capacitor leads should be kept as shortas possible. A ground plane should be used under theswitching circuitry to prevent interplane coupling and toact 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 theswitch, catch diode and input capacitor should be keptvery short. Catch diode and input capacitor should beclose to the chip and terminated to the same point. Thispath contains nanosecond rise and fall times with severalamps of current. The other paths contain only DC and /or200kHz triwave and are less critical. Figure 13 showscritical path layout. Figure 12 indicates the high speed,high current switching path.

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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.


D1

L1

CIN

GND

1510 F11

LT1510

GND

VCC2

VCC1

PROG

VC

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 DESCRIPTIONU

GN Package16-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

1 2 3 4 5 6 7 8

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 8TYP0.0075 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 Package16-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

16

1 2 3 4 5 6 7 8

9101112131415

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)

MIN0.100 0.010

(2.540 0.254)

0.009 0.015

(0.229 0.381)

0.300 0.325

(7.620 8.255)

0.325+0.0250.015

+0.6350.381

8.255( )*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)

S8 Package8-Lead Plastic Small Outline (Narrow 0.150)

(LTC DWG # 05-08-1610)

1 2 3 4

0.150 0.157**

(3.810 3.988)

8 7 6 5

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 8TYP0.008 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

*

**

8/10/2019 LT1510CS

16/16

LT1510/LT1510-5

1510fc LT/GP 1197 REV C 4K PRINTED IN USALinear Technology Corporation

PART NUMBER DESCRIPTION COMMENTS

LTC1325 Microprocessor-Controlled Battery Management Can Charge, Discharge and Gas Gauge NiCd, NiMH and Pb-AcidSystem 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 VINCan Be Higher or Lower Than Battery Voltage

RELATED PARTS

TYPICAL APPLICATIONU

Dimensions in inches (millimeters) unless otherwise noted.PACKAGE DESCRIPTIONU

S Package16-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 8TYP0.008 0.010

(0.203 0.254)

1 2 3 4 5 6 7 8

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

VCC2

1k

1k

VIN

18V TO 25V

VOUT2.5V TO 15VCURRENT LIMIT LEVEL50mA TO 1A

1510 TA01

0.22F

0.1F

100F

30H

LT15101N5819

1N914

+

+POT5k

POT100k

RPROG4.93k0.01F

500F

1F

GND

CURRENT LIMIT LEVEL = (2000)2.465V

RPROG

VCC1

PROG

BAT

OVP

SENSE

VC

( )

Documents

LT1510CS