LINEAR TECHNOLOGY LTC3559, LTC3559-1 Technical data

LTC3559/LTC3559-1

Linear USB Battery Charger

with Dual Buck Regulators

FEATURES

Battery Charger

n

Standalone USB Charger

n

Up to 950mA Charge Current Programmable via

Single Resistor

n

HPWR Input Selects 20% or 100% of Programmed

Charge Current

n

NTC Input for Temperature Qualifi ed Charging

n

Internal Timer Termination

n

Bad Battery Detection

n

CHRG Indicates C/10 or Timeout

Buck Regulators

n

400mA Output Current

n

2.25MHz Constant Frequency Operation

n

Zero Current in Shutdown

n

Low Noise Pulse Skip Operation or Power Saving

Burst Mode Operation

n

Low No-Load Quiescent Current: 35μA

n

Available in a Low Profi le Thermally Enhanced

16-Lead 3mm × 3mm QFN Package

APPLICATIONS

DESCRIPTION

The LTC®3559/LTC3559-1 are USB battery chargers with
dual high effi ciency buck regulators. The parts are ideally
suited to power single-cell Li-Ion/Polymer based handheld
applications needing multiple supply rails.

Battery charge current is programmed via the PROG pin
and the HPWR pin, with capability up to 950mA at the BAT
pin. The battery charger has an NTC input for temperature
qualifi ed charging. The CHRG pin allows battery status to
be monitored continuously during the charging process.
An internal timer controls charger termination.

Each monolithic synchronous buck regulator provides up
to 400mA of output current while operating at effi ciencies
greater than 90% over the entire Li-Ion/Polymer range.
A MODE pin provides the fl exibility to place both buck
regulators in a power saving Burst Mode
low noise pulse skip mode.

The LTC3559/LTC3559-1 are offered in a low profi le ther­mally enhanced 16-lead (3mm × 3mm) QFN package.

L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.

®

operation or a

n

SD/Flash-Based MP3 Players

n

Low Power Handheld Applications

TYPICAL APPLICATION

USB Charger Plus Dual Buck Regulators

USB (4.3V TO 5.5V)

OR AC ADAPTOR

DIGITAL

CONTROL

1μF

1.74k

V

CC

NTC

PROG

CHRG

SUSP

HPWR

EN1

EN2

MODE

GND

LTC3559

EXPOSED

PAD

BAT

PV

SW1

FB1

SW2

FB2

IN

UP TO 500mA

4.7μH

22pF

4.7μH

22pF

2.2μF

+

655k

309k

324k

649k

3559 TA01

SINGLE
Li-lon CELL
(2.7V TO 4.2V)

2.5V
400mA

10μF

1.2V
400mA

10μF

3559fb

1

LTC3559/LTC3559-1

ABSOLUTE MAXIMUM RATINGS

PIN CONFIGURATION

(Note 1)

VCC (Transient);

t < 1ms and Duty Cycle < 1% ....................... –0.3V to 7V

(Static) .................................................. –0.3V to 6V

V

CC

BAT, CHRG, SUSP ........................................ –0.3V to 6V

HPWR, NTC, PROG .......–0.3V to Max (V

, BAT) + 0.3V

CC

PROG Pin Current ...............................................1.25mA

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

................................................–0.3V to BAT + 0.3V

PV

IN

EN1, EN2, MODE .......................................... –0.3V to 6V

FB1, FB2, SW1, SW2 ............–0.3V to PV

, I

I

SW1

......................................................600mA DC

SW2

+ 0.3V or 6V

IN

Junction Temperature (Note 2) ............................. 125°C

BAT

MODE

FB1

16-LEAD (3mm s 3mm) PLASTIC QFN

EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB

TOP VIEW

VCCCHRG

16 15 14 13

1GND

2

17

3

4

5 6 7 8

EN1

SW1

UD PACKAGE

T

= 125°C, θJA = 68°C/W

JMAX

PROG

IN

PV

NTC

SW2

12

HPWR

SUSP

11

FB2

10

EN2

9

Operating Temperature Range (Note 3).... –40°C to 85°C

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

ORDER INFORMATION

LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE

LTC3559EUD#PBF LTC3559EUD#TRPBF LCMB

LTC3559EUD-1#PBF LTC3559EUD-1#TRPBF LDQD

Consult LTC Marketing for parts specifi ed with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based fi nish parts.

For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifi cations, go to: http://www.linear.com/tapeandreel/

16-Lead (3mm × 3mm) Plastic QFN

16-Lead (3mm × 3mm) Plastic QFN

–40°C to 85°C

–40°C to 85°C

The l denotes specifi cations that apply over the full operating temperature

ELECTRICAL CHARACTERISTICS

range, otherwise specifi cations are at TA = 25°C.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Battery Charger. V

V

CC

I

VCC

V

FLOAT

I

CHG

I

BAT

V

UVLO

ΔV
V

DUVLO

UVLO

Input Supply Voltage
Battery Charger Quiescent Current (Note 4) Standby Mode, Charge Terminated

BAT Regulated Output Voltage LTC3559

Constant-Current Mode Charge Current HPWR = 5V

Battery Drain Current Standby Mode, Charger Terminated

Undervoltage Lockout Threshold BAT = 3.5V, VCC Rising 3.85 4.0 4.125 V
Undervoltage Lockout Hysteresis BAT = 3.5V 200 mV

Differential Undervoltage Lockout
Threshold

= 5V, BAT = PVIN = 3.6V, R

CC

= 1.74k, HPWR = 5V, SUSP = NTC = EN1 = EN2 = 0V

PROG

Suspend Mode, V

0°C ≤ T

≤ 85°C, LTC3559

A

LTC3559-1

≤ 85°C, LTC3559-1

0°C ≤ T

A

HPWR = 0V

Shutdown, V
Suspend Mode, SUSP = 5V, BAT = V

BAT = 4.05V, (VCC – BAT) Falling (LTC3559)
BAT = 3.95V, (V

CC

= 5V

SUSP

< V

, BAT = V

UVLO

– BAT) Falling (LTC3559-1)

CC

FLOAT

FLOAT

l

4.3 5.5 V

4.179

4.165

4.079

4.065

l

4408446092500

30
30

200

8.5

4.200

4.200

4.100

4.100

–3.5
–2.5
–1.5

50
50

400

17

4.221

4.235

4.121

4.135

100

–7
–4
–3

70
70

μA
μA

V
V

V
V

mA
mA

μA
μA
μA

mV
mV

3559fb

2

LTC3559/LTC3559-1

ELECTRICAL CHARACTERISTICS

The l denotes specifi cations that apply over the full operating temperature
range, otherwise specifi cations are at T

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

ΔV

DUVLO

V

PROG

h

PROG

I

TRKL

V

TRKL

ΔV

TRKL

ΔV

RECHRG

t

RECHRG

t

TERM

t

BADBAT

h

C/10

t

C/10

R

ON(CHG)

T

LIM

NTC

V

COLD

V

HOT

V

DIS

I

NTC

Logic (HPWR, SUSP, CHRG)

V

IL

V

IH

R

DN

V

CHRG

I

CHRG

Buck Switching Regulators, BAT = PV

PV

IN

I

PVIN

PVIN UVLO PVIN Falling

f

OSC

V

IL

V

IH

I

LIMSW

Differential Undervoltage Lockout
Hysteresis

PROG Pin Servo Voltage HPWR = 5V

Ratio of I

to PROG Pin Current 800 mA/mA

BAT

Trickle Charge Current BAT < V
Trickle Charge Threshold Voltage BAT Rising 2.8 2.9 3.0 V
Trickle Charge Hysteresis Voltage 100 mV

Recharge Battery Threshold Voltage Threshold Voltage Relative to V

Recharge Comparator Filter Time BAT Falling 1.7 ms
Safety Timer Termination Period BAT = V
Bad Battery Termination Time BAT < V
End-of-Charge Indication Current Ratio (Note 5) 0.085 0.1 0.11 mA/mA
End-of-Charge Comparator Filter Time I
Battery Charger Power FET On-Resistance

(Between V

and BAT)

CC

Junction Temperature in Constant
Temperature Mode

Cold Temperature Fault Threshold Voltage Rising NTC Voltage

Hot Temperature Fault Threshold Voltage Falling NTC Voltage

NTC Disable Threshold Voltage Falling NTC Voltage

NTC Leakage Current V

Input Low Voltage HPWR, SUSP Pins 0.4 V
Input High Voltage HPWR, SUSP Pins 1.2 V
Logic Pin Pull-Down Resistance HPWR, SUSP Pins

CHRG Pin Output Low Voltage I
CHRG Pin Input Current BAT = 4.5V, V

IN

Input Supply Voltage LTC3559

Pulse Skip Supply Current
Burst Mode Supply Current
Shutdown Supply Current
Supply Current in UVLO

PV

Rising

IN

Switching Frequency MODE = 0V 1.91 2.25 2.59 MHz
Input Low Voltage MODE, EN1, EN2 0.4 V
Input High Voltage MODE, EN1, EN2 1.2 V
Peak PMOS Current Limit MODE = 0V or 3.8V 550 800 1050 mA

= 25°C.

A

BAT = 4.05V (LTC3559)
BAT = 3.95V (LTC3559-1)

HPWR = 0V
BAT < V

Falling 2.2 ms

BAT

= 190mA 500

I

BAT

Hysteresis

Hysteresis

Hysteresis

= VCC = 5V –1 1 μA

NTC

= 5mA 100 250 mV

CHRG

= 3.8V, EN1 = EN2 = 3.8V

LTC3559-1
MODE = 0 (One Buck Enabled) (Note 6)

MODE = 1 (One Buck Enabled) (Note 6)
EN1 = EN2 = 0V
PV

= 2.0V

IN

TRKL

TRKL

FLOAT

TRKL

130
130

1.000

0.200

0.100

36 46 56 mA

FLOAT

–85 –100 –130 mV

3.5 4 4.5 Hour

0.4 0.5 0.6 Hour

105 °C

75 76.5

78 %V

1.6

33.4 34.9

36.4 %V

1.6

l

0.7 1.7

2.7 %V

50

l

1.9 4 6.3

= 5V 0 1 μA

CHRG

l

3

l

3

220

35

l

4.2

4.1

400

50
0
4

2
8

2.45

2.55

%V

%V

mV
mV

V
V
V

mΩ

CC
CC

CC
CC

CC

mV

MΩ

V
V

μA
μA
μA
μA

V
V

3559fb

3

LTC3559/LTC3559-1

ELECTRICAL CHARACTERISTICS

The l denotes specifi cations that apply over the full operating temperature
range, otherwise specifi cations are at T

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

FB

I

FB

D

MAX

R

PMOS

R

NMOS

R

SW(PD)

Feedback Voltage
FB Input Current FB1, FB2 = 0.82V –0.05 0.05 μA
Maximum Duty Cycle FB1, FB2 = 0V 100 %
R

of PMOS ISW = 150mA 0.65

DS(ON)

R

of NMOS ISW = –150mA 0.75

DS(ON)

SW Pull-Down in Shutdown 13

= 25°C.

A

l

780 800 820 mV

Ω

Ω

kΩ

Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.

Note 2: T
dissipation P

T

is calculated from the ambient temperature TA and power

J

according to the following formula:

D

= TA + (PD • θJA°C/W)

J

Note 3: The LTC3559/LTC3559-1 are guaranteed to meet specifi cations

temperature range are assured by design, characterization and correlation
with statistical process controls.

Note 4: V

CC

or any current delivered to the BAT pin. Total input current is equal to this
specifi cation plus 1.00125 • I

Note 5: I

C/10

with indicated PROG resistor.
Note 6: FB high, regulator not switching.

from 0°C to 85°C. Specifi cations over the –40°C to 85°C operating

TYPICAL PERFORMANCE CHARACTERISTICS

Suspend State Supply and BAT
Currents vs Temperature

10

9

8

7

6

VCC = 5V

5

BAT = 4.2V
SUSP = 5V

4

CURRENT (μA)

EN1 = EN2 = 0V

3

2

1

0

–55

–35

I

VCC

I

BAT

25

5

–15

TEMPERATURE (°C)

65

85

3559 G01

45

Battery Regulation (Float)
Voltage vs Temperature

4.250
VCC = 5V

4.225

4.200

4.175

(V)

4.150

FLOAT

V

4.125

4.100

4.075

4.050

–35 –15 25

–55

LTC3559

LTC3559-1

TEMPERATURE (°C)

5

45 65 85

supply current does not include current through the PROG pin

BAT

where I

is the charge current.

BAT

is expressed as a fraction of measured full charge current

Battery Regulation (Float) Voltage
vs Battery Charge Current,
Constant-Voltage Charging

4.205

4.200

4.195

4.190

4.185

4.180

(V)

BAT

4.175

V

4.170

4.165
VCC = 5V

4.160

HPWR = 5V

= 845Ω

R

PROG

4.155
EN1 = EN2 = 0V

4.150

3559 G02

100

300

400

2000

I

BAT

500

(mA)

600

700

800

900

3559 G03

1000

4

3559fb

TYPICAL PERFORMANCE CHARACTERISTICS

Battery Charge Current
vs Supply Voltage

500

VCC = 5V

495

HPWR = 5V

490

485

480

475

(mA)

470

BAT

I

465

460

455

450

445

440

= 1.74k

R

PROG

EN1 = EN2 = 0V

4.3

4.5

4.6 4.9 5.1

4.8 5.0 5.2 5.4 5.5

4.7
VCC (V)

Battery Charger Undervoltage
Lockout Threshold vs Temperature

4.2
BAT = 3.5V

(V)

CC

V

4.1

4.0

3.9

3.8

3.7

3.6

RISING

FALLING

5.34.4

3559 G04

Battery Charge Current
vs Battery Voltage (LTC3559)

500

450

400

350

300

(mA)

250

BAT

I

200

150

100

50

0

2

VCC = 5V
R

PROG

= 1.74k

2.5

HPWR = 5V

HPWR = 0V

3

V

BAT

Battery Drain Current in
Undervoltage Lockout
vs Temperature

3.0
EN1 = EN2 = 0V

(μA)

BAT

I

2.5

2.0

1.5

1.0

0.5

BAT = 4.2

(LTC3559)

3.5

(V)

BAT = 3.6

LTC3559/LTC3559-1

Battery Charge Current
vs Ambient Temperature in
Thermal Regulation

500

450

400

350

300

(mA)

250

BAT

I

200

150

VCC = 5V

100

HPWR = 5V

= 1.74k

R

PROG

50

EN1 = EN2 = 0

0

–35 5

–55

4

4.5

3559 G05

–15

25

TEMPERATURE (°C)

PROG Voltage
vs Battery Charge Current

1.2
VCC = 5V

HPWR = 5V

(V)

PROG

V

1.0

0.8

0.6

0.4

0.2

= 1.74k

R

PROG

EN1 = EN2 = 0V

85

45 125

105

65

3.5
–55

–35 –15

TEMPERATURE (°C)

Recharge Threshold
vs Temperature

115

VCC = 5V

111

107

103

99

(mV)

95

91

RECHARGE

V

87

83

79

75

–55

–35

–15

TEMPERATURE (°C)

25 65 85

545

3559 G07

25

5

45

65

3559 G10

0

–55

–35 –15

TEMPERATURE (°C)

25 65 85

545

3559 G08

Battery Charger FET
On-Resistance vs Temperature

700

VCC = 4V

= 200mA

I

BAT

650

EN1 = EN2 = 0V

600

550

(mΩ)

500

ON

R

450

400

350

300

85

–55

–15 5 25 45 65

–35

TEMPERATURE (°C)

85

3559 G11

0

100 200 300 400

I

BAT

SUSP/HPWR Pin Rising
Thresholds vs Temperature

1.2
VCC = 5V

1.1

1.0

0.9

0.8

0.7

THRESHOLD (V)

0.6

0.5

0.4

–35 –15 25

–55

5

TEMPERATURE (°C)

(mA)

500500 150 250 350 450

3559 G09

45 65 85

3559 G12

3559fb

5

LTC3559/LTC3559-1

TYPICAL PERFORMANCE CHARACTERISTICS

CHRG Pin Output Low Voltage
vs Temperature

140

VCC = 5V
I

CHRG

120

100

80

(mV)

60

CHRG

V

40

20

= 5mA

CHRG Pin I-V Curve

70

VCC = 5V
BAT = 3.8V

60

50

40

(mA)

30

CHRG

I

20

10

Timer Accuracy vs Supply Voltage

2.0

1.5

1.0

0.5

0

PERCENT ERROR (%)

–0.5

0

–55

–35 –15

TEMPERATURE (°C)

25 65 85

545

Timer Accuracy vs Temperature

7

VCC = 5V

6

5

4

3

2

1

PERCENT ERROR (%)

0

–1

–2

–55

–15

–35

TEMPERATURE (°C)

585

25

Buck Regulator Input Current vs
Temperature, Pulse Skip Mode
(LTC3559)

400

VFB = 0.82V

350

300

250

200

INPUT CURRENT (μA)

150

100

–35 5

–55

PVIN = 4.2V

–15

25

TEMPERATURE (°C)

PVIN = 2.7V

45 125

65

45 65

85

3559 G13

3559 G16

105

3559 G19

0

0

12

CHRG (V)

Complete Charge Cycle
2400mAh Battery (LTC3559)

1000

800
600

(mA)BAT (V)CHRG (V)

400

BAT

I

200

0

5.0

4.5

4.0

3.5

3.0

5.0

4.0

3.0

2.0

1.0
0

0

12 4 6

TIME (HOUR)

46

35

3559 G14

VCC = 5V

= 0.845k

R

PROG

HPWR = 5V

35

3559 G17

–1.0

4.3

4.7 4.9 5.1

4.5

Buck Regulator Input Current vs
Temperature, Burst Mode Operation

50

VFB = 0.82V

45

40

PVIN = 4.2V

35

30

INPUT CURRENT (μA)

25

20

–35 5

–55

–15

TEMPERATURE (°C)

Buck Regulator PVIN Undervoltage
Thresholds vs Temperature Frequency vs Temperature

2.5

2.4

2.3

2.2

2.1

2.0

(MHz)

OSC

1.9

f

1.8

1.7

1.6

1.5
–55

PVIN = 3.8V

–35 –15 25

TEMPERATURE (°C)

5

(V)

IN

PV

2.85

2.75

2.65

2.55

2.45

2.35

2.25
–35 5

–55

RISING

FALLING

–15

25

TEMPERATURE (°C)

85

45 125

105

65

3559 G20

VCC (V)

PVIN = 2.7V

85

45 125

65

25

85

45

65

5.3 5.5

3559 G15

105

3559 G18

105

125

3559 G21

3559fb

6

TYPICAL PERFORMANCE CHARACTERISTICS

5

5

0

0

LTC3559/LTC3559-1

Buck Regulator Enable
Thresholds vs Temperature

1200

PVIN = 3.8V

1100

1000

900

(mV)

800

EN

V

700

600

500

400

–35 125

–55

–15

RISING

FALLING

25

45

5

TEMPERATURE (°C)

Buck Regulator Effi ciency vs I

105

65

85

3559 G22

LOAD

Buck Regulator PMOS R
vs Temperature (LTC3559)

1300

1200

1100

1000

900

(mΩ)

800

DS(ON)

R

700

600

500

400

–55

–35

–15

PVIN = 2.7V

5

TEMPERATURE (°C)

PVIN = 4.2V

25

45 12

(LTC3559) Buck Regulator Load Regulation

100

Burst Mode

90

OPERATION

80

70

60

50

40

EFFICIENCY (%)

30

20

10

0

0.1 10 100 1000

1

I

LOAD

PULSE SKIP
MODE

(mA)

V

OUT

PV

= 2.5V

= 4.2V

IN

3559 G25

(V)

OUT

V

2.60

2.58

2.56

2.54

2.52

2.50

2.48

2.46

2.44

PVIN = 3.8V

= 2.5V

V

OUT

1

Burst Mode

OPERATION

PULSE SKIP

MODE

10 100 100

I

(mA)

LOAD

65

DS(0N)

85

105

3559 G23

3559 G26

Buck Regulator NMOS R
vs Temperature (LTC3559)

1300

1200

1100

1000

900

(mΩ)

800

DS(ON)

R

700

600

500

400

–55

PVIN = 2.7V

–35

–15

PVIN = 4.2V

5

25

TEMPERATURE (°C)

45 12

Buck Regulator Line Regulation

2.60
V

= 2.5V

OUT

= 200mA

I

LOAD

2.58

2.56

2.54

(V)

2.52

OUT

V

2.50

2.48

2.46

2.44

3.0 3.3 3.9

2.7

3.6

PVIN (V)

65

DS(0N)

85

105

3559 G24

4.2

3559 G27

Buck Regulator Effi ciency vs I
(LTC3559)

100

Burst Mode

90

OPERATION

80

70

60

50

40

EFFICIENCY (%)

30

20

10

0

0.1 10 100 1000

PULSE SKIP

MODE

V

OUT

PVIN = 2.7V
PV

1

I

(mA)

LOAD

= 1.2V

= 4.2V

IN

LOAD

3559 G28

Buck Regulator Load Regulation

1.25
PVIN = 3.8V

(V)

OUT

V

1.24

1.23

1.22

1.21

1.20

1.19

1.18

1.17

1.16

1.15

= 1.2V

V

OUT

Burst Mode

OPERATION

PULSE SKIP

MODE

1

10 100 100

I

(mA)

LOAD

3559 G29

Buck Regulator Line Regulation

1.25
V

= 1.2V

OUT

(V)

OUT

V

1.24

1.23

1.22

1.21

1.20

1.19

1.18

1.17

1.16

1.15

2.7

I

LOAD

= 200mA

3.0

3.3
PVIN (V)

3.6

3.9

4.2

3559 G30

3559fb

7

LTC3559/LTC3559-1

TYPICAL PERFORMANCE CHARACTERISTICS

Buck Regulator Start-Up Transient

Buck Regulator Pulse Skip Mode
Operation

V

500mV/DIV

INDUCTOR

CURRENT

= 200mA/DIV

I

L

2V/DIV

V

20mV/DIV (AC)

2V/DIV

INDUCTOR

CURRENT

= 60mA/DIV

I

L

OUT

EN

= 3.8V

PV

IN

PULSE SKIP MODE
LOAD = 6Ω

50μs/DIV

Buck Regulator Burst Mode
Operation

OUT

SW

= 3.8V

PV

IN

LOAD = 60mA

2μs/DIV

3559 G33

3559 G35

V

SW

2V/DIV

INDUCTOR

CURRENT

= 50mA/DIV

I

L

INDUCTOR

CURRENT

= 200mA/DIV

V

LOAD STEP

OUT

OUT

20mV/DIV (AC)

I

L

50mV/DIV (AC)

5mA TO 290mA

= 3.8V

PV

IN

LOAD = 10mA

200ns/DIV

Buck Regulator Transient
Response, Pulse Skip Mode

= 3.8V 50μs/DIV

PV

IN

3559 G34

3559 G36

8

INDUCTOR

CURRENT

= 200mA/DIV

I

L

V

50mV/DIV (AC)

5mA TO 290mA

OUT

LOAD STEP

Buck Regulator Transient
Response, Burst Mode Operation

= 3.8V 50μs/DIV

PV

IN

3559 G37

3559fb

PIN FUNCTIONS

LTC3559/LTC3559-1

GND (Pin 1): Ground, Connect to Exposed Pad (Pin 17).

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

rent to the battery and regulates fi nal fl oat voltage to 4.2V
(LTC3559) or 4.1V (LTC3559-1).

MODE (Pin 3): MODE Pin for Buck Regulators. When held
high, both regulators are in Burst Mode operation. When
held low both regulators operate in pulse skip mode. This
pin is a high impedance input; do not fl oat.

FB1 (Pin 4): Buck 1 Feedback Voltage Pin. Receives feed­back by a resistor divider connected across the output.

EN1 (Pin 5): Enable Input Pin for Buck 1. This pin is a high
impedance input; do not fl oat. Active high.

SW1 (Pin 6): Buck 1 Switching Node. External inductor
connects to this node.

(Pin 7): Input Supply Pin for Buck Regulators.

PV

IN

Connect to BAT. A 2.2μF decoupling capacitor to GND is
recommended.

SW2 (Pin 8): Buck 2 Switching Node. External inductor
connects to this node.

can toggle between low power and high power modes per
USB specifi cation. A weak pull-down current is internally
applied to this pin to ensure it is low at power up when
the input is not being driven externally.

NTC (Pin 13): Input to the NTC Thermistor Monitoring
Circuit. The NTC pin connects to a negative temperature
coeffi cient thermistor which is typically co-packaged with
the battery pack to determine if the battery is too hot or
too cold to charge. If the battery temperature is out of
range, charging is paused until the battery temperature
re-enters the valid range. A low drift bias resistor is re­quired from V
NTC to ground. To disable the NTC function, the NTC pin
should be grounded.

PROG (Pin 14): Charge Current Program and Charge
Current Monitor Pin. Charge current is programmed by
connecting a resistor from PROG to ground. When charg­ing in constant-current mode, the PROG pin servos to 1V
if the HPWR pin is pulled high, or 200mV if the HPWR pin
is pulled low. The voltage on this pin always represents
the battery current through the following formula:

to NTC and a thermistor is required from

CC

EN2 (Pin 9): Enable Input Pin for Buck 2. This pin is a high
impedance input; do not fl oat. Active high.

FB2 (Pin 10): Buck 2 Feedback Voltage Pin. Receives feed­back by a resistor divider connected across the output.

SUSP (Pin 11): Suspend Battery Charging Operation.
A voltage greater than 1.2V on this pin puts the battery
charger into suspend mode, disables the charger and
resets the termination timer. A weak pull-down current is
internally applied to this pin to ensure it is low at power
up when the input is not being driven externally.

HPWR (Pin 12): High Current Battery Charging Enabled.
A voltage greater than 1.2V at this pin programs the
BAT pin current at 100% of the maximum programmed
charge current. A voltage less than 0.4V sets the BAT pin
current to 20% of the maximum programmed charge
current. When used with a 1.74k PROG resistor, this pin

I

CHRG (Pin 15): Open-Drain Charge Status Output. The

CHRG pin indicates the status of the battery charger. Four
possible states are represented by CHRG: charging, not
charging (i.e., the charge current is less than 1/10th of the
full-scale charge current), unresponsive battery (i.e., the
battery voltage remains below 2.9V after 1/2 hour of charg­ing) and battery temperature out of range. CHRG requires
a pull-up resistor and/or LED to provide indication.

V

CC

capacitor to GND is recommended.

Exposed Pad (Pin 17): Ground. The Exposed Pad must
be soldered to PCB ground to provide electrical contact
and rated thermal performance.

PROG

= •800

BAT

R

PROG

(Pin 16): Battery Charger Input. A 1μF decoupling

3559fb

9

LTC3559/LTC3559-1

BLOCK DIAGRAM

CHRG

15

HPWR

12

SUSP

11

NTC

13

MODE

3

EN1

5

EN2

9

FB1

4

TEMPERATURE

BANDGAP

UNDERVOLTAGE

LOCKOUT

DIE

16

V

CC

BAT

V

IN

BODY

MAXER

TA

T

DIE

–

G

m

+

CLK

V

C

0.8V

CA

V

FB

LOGIC

NTCA

NTC REF

OT

T

DIE

V

REF

800x

1x

–

+

BATTERY CHARGER

MODEEN

CONTROL

LOGIC

BUCK REGULATOR 1

BAT

PROG

PV

SW1

2

14

IN

7

6

10

OSCILLATOR

2.25MHz

FB2

10

CLK

V

–

FB

G

m

+

0.8V

GND EXPOSED PAD

1 17

CLK

V

C

MODEEN

CONTROL

LOGIC

BUCK REGULATOR 2

SW2

8

3559 BD

3559fb

OPERATION

LTC3559/LTC3559-1

The LTC3559/LTC3559-1 are linear battery chargers with
dual monolithic synchronous buck regulators. The buck
regulators are internally compensated and need no external
compensation components.

The battery charger employs a constant- current/constant­voltage charging algorithm and is capable of charging a
single Li-Ion battery at charging currents up to 950mA. The
user can program the maximum charging current available

USB (5V)

R

PROG

1.62k

LOW (PULSE SKIP MODE)

HIGH

HIGH
HIGH

V

CC

PROG

SUSP

HPWR

EN1
EN2
MODE

LTC3559/

LTC3559-1

at the BAT pin via a single PROG resistor. The actual BAT
pin current is set by the status of the HPWR pin.

For proper operation, the BAT and PV

pins must be tied

IN

together. If a buck regulator is also enabled during the
battery charging operation, the net current charging the
battery may be lower than the actual programmed value.
Refer to Figure 1 for an explanation.

500mA

300mA

BAT

PV

SW1

SW2

IN

200mA

+

3559 F01

2.2μF

V

OUT1

V

OUT2

+

SINGLE Li-lon
CELL 3.6V

Figure 1. Current Being Delivered at the BAT Pin Is 500mA. Both Buck Regulators Are Enabled. The Sum of the
Average Input Currents Drawn by Both Buck Regulators Is 200mA. This Makes the Effective Battery Charging Current
Only 300mA. If the HPWR Pin Were Tied LO, the BAT Pin Current Would Be 100mA. With the Buck Regulator
Conditions Unchanged, This Would Cause the Battery to Discharge at 100mA

APPLICATIONS INFORMATION

Battery Charger Introduction

The LTC3559/LTC3559-1 have a linear battery charger
designed to charge single-cell lithium-ion batteries. The
charger uses a constant-current/constant-voltage charge
algorithm with a charge current programmable up to
950mA. Additional features include automatic recharge,
an internal termination timer, low-battery trickle charge
conditioning, bad-battery detection, and a thermistor
sensor input for out of temperature charge pausing.

Furthermore, the battery charger is capable of operating
from a USB power source. In this application, charge
current can be programmed to a maximum of 100mA or
500mA per USB power specifi cations.

Input Current vs Charge Current

The battery charger regulates the total current delivered
to the BAT pin; this is the charge current. To calculate the
total input current (i.e., the total current drawn from the

pin), it is necessary to sum the battery charge current,

V

CC

charger quiescent current and PROG pin current.

Undervoltage Lockout (UVLO)

The undervoltage lockout circuit monitors the input volt­age (V
above V

) and disables the battery charger until VCC rises

CC

(typically 4V). 200mV of hysteresis prevents

UVLO

oscillations around the trip point. In addition, a differential
undervoltage lockout circuit disables the battery charger
when V

falls to within V

CC

(typically 50mV) of the

DUVLO

BAT voltage.

3559fb

11

LTC3559/LTC3559-1

APPLICATIONS INFORMATION

Suspend Mode

The battery charger can also be disabled by pulling the
SUSP pin above 1.2V. In suspend mode, the battery
drain current is reduced to 1.5μA and the input current is
reduced to 8.5μA.

Charge Cycle Overview

When a battery charge cycle begins, the battery charger
fi rst determines if the battery is deeply discharged. If the
battery voltage is below V

, typically 2.9V, an automatic

TRKL

trickle charge feature sets the battery charge current to
10% of the full-scale value.

Once the battery voltage is above 2.9V, the battery charger
begins charging in constant-current mode. When the
battery voltage approaches the 4.2V (LTC3559) or 4.1V
(LTC3559-1) required to maintain a full charge, otherwise
known as the fl oat voltage, the charge current begins to
decrease as the battery charger switches into constant­voltage mode.

mode, the 4-hour timer is started. After the safety timer
expires, charging of the battery will discontinue and no
more current will be delivered.

Automatic Recharge

After the battery charger terminates, it will remain off,
drawing only microamperes of current from the battery.
If the portable product remains in this state long enough,
the battery will eventually self discharge. To ensure that the
battery is always topped off, a charge cycle will automati­cally begin when the battery voltage falls below V

RECHRG

. In
the event that the safety timer is running when the battery
voltage falls below V

RECHRG

prevent brief excursions below V
safety timer, the battery voltage must be below V

, it will reset back to zero. To

RECHRG

from resetting the

RECHRG

for more than 1.7ms. The charge cycle and safety timer
will also restart if the V
then high (e.g., V

CC

UVLO or DUVLO cycles low and

CC

is removed and then replaced) or the

charger enters and then exits suspend mode.

Programming Charge Current

Trickle Charge and Defective Battery Detection

Any time the battery voltage is below V

, the charger

TRKL

goes into trickle charge mode and reduces the charge
current to 10% of the full-scale current. If the battery
voltage remains below V

for more than 1/2 hour, the

TRKL

charger latches the bad-battery state, automatically termi­nates, and indicates via the CHRG pin that the battery was
unresponsive. If for any reason the battery voltage rises
above V

, the charger will resume charging. Since the

TRKL

charger has latched the bad-battery state, if the battery
voltage then falls below V
V

RECHRG

fi rst, the charger will immediately assume that

again but without rising past

TRKL

the battery is defective. To reset the charger (i.e., when
the dead battery is replaced with a new battery), simply
remove the input voltage and reapply it or put the part in
and out of suspend mode.

Charge Termination

The battery charger has a built-in safety timer that sets the
total charge time for 4 hours. Once the battery voltage rises
above V

RECHRG

and the charger enters constant-voltage

The PROG pin serves both as a charge current program
pin, and as a charge current monitor pin. By design, the
PROG pin current is 1/800th of the battery charge current.
Therefore, connecting a resistor from PROG to ground
programs the charge current while measuring the PROG pin
voltage allows the user to calculate the charge current.

Full-scale charge current is defi ned as 100% of the con­stant-current mode charge current programmed by the
PROG resistor. In constant-current mode, the PROG pin
servos to 1V if HPWR is high, which corresponds to charg­ing at the full-scale charge current, or 200mV if HPWR
is low, which corresponds to charging at 20% of the full­scale charge current. Thus, the full-scale charge current
and desired program resistor for a given full-scale charge
current are calculated using the following equations:

800

I

=

CHG

R

PROG

R

=

PROG

800

I

CHG

V

V

12

3559fb

APPLICATIONS INFORMATION

LTC3559/LTC3559-1

In any mode, the actual battery current can be determined
by monitoring the PROG pin voltage and using the follow­ing equation:

I

BAT

PROG

= •800

R

PROG

Thermal Regulation

To prevent thermal damage to the IC or surrounding
components, an internal thermal feedback loop will auto­matically decrease the programmed charge current if the
die temperature rises to approximately 115°C. Thermal
regulation protects the battery charger from excessive
temperature due to high power operation or high ambient
thermal conditions and allows the user to push the limits
of the power handling capability with a given circuit board
design without risk of damaging the LTC3559/LTC3559-1
or external components. The benefi t of the LTC3559/
LTC3559-1 battery charger thermal regulation loop is that
charge current can be set according to actual conditions
rather than worst-case conditions with the assurance that
the battery charger will automatically reduce the current
in worst-case conditions.

Charge Status Indication

The CHRG pin indicates the status of the battery charger.
Four possible states are represented by CHRG: charging,
not charging, unresponsive battery and battery temperature
out of range.

The signal at the CHRG pin can be easily recognized as one
of the above four states by either a human or a micropro­cessor. The CHRG pin, which is an open-drain output, can
drive an indicator LED through a current limiting resistor
for human interfacing, or simply a pull-up resistor for
microprocessor interfacing.

To make the CHRG pin easily recognized by both humans
and microprocessors, the pin is either low for charging,
high for not charging, or it is switched at high frequency
(35kHz) to indicate the two possible faults: unresponsive
battery and battery temperature out of range.

When charging begins, CHRG is pulled low and remains
low for the duration of a normal charge cycle. When the

charge current has dropped to below 10% of the full-scale
current, the CHRG pin is released (high impedance). If a
fault occurs after the CHRG pin is released, the pin re­mains high impedance. However, if a fault occurs before
the CHRG pin is released, the pin is switched at 35kHz.
While switching, its duty cycle is modulated between a high
and low value at a very low frequency. The low and high
duty cycles are disparate enough to make an LED appear
to be on or off thus giving the appearance of “blinking”.
Each of the two faults has its own unique “blink” rate for
human recognition as well as two unique duty cycles for
microprocessor recognition.

Table 1 illustrates the four possible states of the CHRG
pin when the battery charger is active.

Table 1. CHRG Output Pin

MODULATION

STATUS FREQUENCY

Charging 0Hz 0 Hz (Lo-Z) 100%

< C/10 0Hz 0 Hz (Hi-Z) 0%

I

BAT

NTC Fault

Bad Battery

35kHz

35kHz

(BLINK)

FREQUENCY DUTY CYCLE

1.5Hz at 50% 6.25% to 93.75%

6.1Hz at 50% 12.5% to 87.5%

An NTC fault is represented by a 35kHz pulse train whose
duty cycle varies between 6.25% and 93.75% at a 1.5Hz
rate. A human will easily recognize the 1.5Hz rate as a
“slow” blinking which indicates the out of range battery
temperature while a microprocessor will be able to decode
either the 6.25% or 93.75% duty cycles as an NTC fault.

If a battery is found to be unresponsive to charging (i.e.,
its voltage remains below V

for over 1/2 hour), the

TRKL

CHRG pin gives the battery fault indication. For this fault,
a human would easily recognize the frantic 6.1Hz “fast”
blinking of the LED while a microprocessor would be able
to decode either the 12.5% or 87.5% duty cycles as a bad
battery fault.

Although very improbable, it is possible that a duty cycle
reading could be taken at the bright-dim transition (low
duty cycle to high duty cycle). When this happens the
duty cycle reading will be precisely 50%. If the duty cycle
reading is 50%, system software should disqualify it and
take a new duty cycle reading.

3559fb

13

LTC3559/LTC3559-1

APPLICATIONS INFORMATION

NTC Thermistor

The battery temperature is measured by placing a nega­tive temperature coeffi cient (NTC) thermistor close to the
battery pack. The NTC circuitry is shown in Figure 3.

To use this feature, connect the NTC thermistor, R
between the NTC pin and ground, and a bias resistor, R
from V

to NTC. R

CC

should be a 1% resistor with a

NOM

NTC

NOM

,
,

value equal to the value of the chosen NTC thermistor at
25°C (R25). A 100k thermistor is recommended since
thermistor current is not measured by the battery charger
and its current will have to be considered for compliance
with USB specifi cations.

The battery charger will pause charging when the re­sistance of the NTC thermistor drops to 0.54 times the

POWER

ON

FAULT

BAT b 2.9V

DUVLO, UVLO AND SUSPEND DISABLE MODE

IF SUSP < 0.4V AND

> 4V AND

V

CC

> BAT + 130mV

V

CC

BATTERY CHARGING SUSPENDED
CHRG PULSES

value of R25 or approximately 54k (for a Vishay “Curve
1” thermistor, this corresponds to approximately 40°C). If
the battery charger is in constant-voltage mode, the safety
timer will pause until the thermistor indicates a return to
a valid temperature.

As the temperature drops, the resistance of the NTC
thermistor rises. The battery charger is also designed
to pause charging when the value of the NTC thermistor
increases to 3.25 times the value of R25. For a Vishay
“Curve 1” thermistor, this resistance, 325k, corresponds
to approximately 0°C. The hot and cold comparators each
have approximately 3°C of hysteresis to prevent oscillation
about the trip point. Grounding the NTC pin disables all
NTC functionality.

NO

CHRG HIGH IMPEDANCE

YES

NTC FAULT

NO FAULT

2.9V < BAT < V

RECHRG

STANDBY MODE

NO CHARGE CURRENT
CHRG HIGH IMPEDANCE

14

TRICKLE CHARGE MODE

1/10 FULL CHARGE CURRENT
CHRG STRONG PULL-DOWN
30 MINUTE TIMER BEGINS

30 MINUTE

TIMEOUT

DEFECTIVE BATTERY

NO CHARGE CURRENT
CHRG PULSES

Figure 2. State Diagram of the Battery Charger Operation

BAT > 2.9V

CONSTANT CURRENT MODE

FULL CHARGE CURRENT
CHRG STRONG PULL-DOWN

CONSTANT VOLTAGE MODE

4-HOUR TERMINATION TIMER
BEGINS

BAT DROPS BELOW V

4-HOUR TERMINATION TIMER RESETS

4-HOUR
TIMEOUT

RECHRG

3559 F02

3559fb

APPLICATIONS INFORMATION

LTC3559/LTC3559-1

Alternate NTC Thermistors and Biasing

The battery charger provides temperature qualifi ed
charging if a grounded thermistor and a bias resistor are
connected to the NTC pin. By using a bias resistor whose
value is equal to the room temperature resistance of the
thermistor (R25) the upper and lower temperatures are
pre-programmed to approximately 40°C and 0°C, respec­tively (assuming a Vishay “Curve 1” thermistor).

The upper and lower temperature thresholds can be ad­justed by either a modifi cation of the bias resistor value
or by adding a second adjustment resistor to the circuit.
If only the bias resistor is adjusted, then either the upper
or the lower threshold can be modifi ed but not both. The
other trip point will be determined by the characteristics
of the thermistor. Using the bias resistor in addition to an
adjustment resistor, both the upper and the lower tempera­ture trip points can be independently programmed with
the constraint that the difference between the upper and
lower temperature thresholds cannot decrease. Examples
of each technique are given below.

NTC thermistors have temperature characteristics which
are indicated on resistance-temperature conversion tables.
The Vishay-Dale thermistor NTHS0603N011-N1003F, used
in the following examples, has a nominal value of 100k
and follows the Vishay “Curve 1” resistance-temperature
characteristic.

In the explanation below, the following notation is used.

R25 = Value of the thermistor at 25°C

R

NTC|COLD

R

NTC|HOT

r

COLD

r

HOT

R

NOM

= Value of thermistor at the cold trip point

= Value of the thermistor at the hot trip point

= Ratio of R

= Ratio of R

NTC|COLD

NTC|HOT

to R25

to R25

= Primary thermistor bias resistor (see Figure 3)

R1 = Optional temperature range adjustment resistor (see
Figure 4)

The trip points for the battery charger’s temperature quali­fi cation are internally programmed at 0.349 • V
hot threshold and 0.765 • V

for the cold threshold.

CC

for the

CC

Therefore, the hot trip point is set when:

R

NTC HOT

+

RR

NOM NTCHOT

|

•.•

= 0 349

VV

|

CC CC

and the cold trip point is set when:

R

NTC COLD

+

RR

NOM NTC COLD

|

•.•

= 0 765

VV

|

CC CC

R

NOM

100k

R
100k

NTC

16

13

V

CC

NTC

(NTC FALLING)

0.765 • V

(NTC RISING)

0.349 • V

(NTC FALLING)

0.017 • V

NTC BLOCK

CC

CC

CC

V

CC

16

0.765 • V

CC

NTC

(NTC FALLING)

(NTC RISING)

0.349 • V

CC

(NTC FALLING)

0.017 • V

CC

–

TOO_COLD

+

–

TOO_HOT

+

+

NTC_ENABLE

–

–

TOO_COLD

+

R

NOM

105k

R1

12.7k

13

–

R

NTC

TOO_HOT

100k

+

+

NTC_ENABLE

–

3559 F03

Figure 3. Typical NTC Thermistor Circuit Figure 4. NTC Thermistor Circuit with Additional Bias Resistor

3559 F04

3559fb

15

LTC3559/LTC3559-1

Y

APPLICATIONS INFORMATION

Solving these equations for R

NTC|COLD

and R

NTC|HOT

results in the following:

R

NTC|HOT

= 0.536 • R

NOM

and

R

NTC|COLD

By setting R
in r

HOT

= 3.25 • R

equal to R25, the above equations result

NOM

= 0.536 and r

NOM

= 3.25. Referencing these ratios

COLD

to the Vishay Resistance-Temperature Curve 1 chart gives
a hot trip point of about 40°C and a cold trip point of about
0°C. The difference between the hot and cold trip points
is approximately 40°C.

By using a bias resistor, R

, different in value from

NOM

R25, the hot and cold trip points can be moved in either
direction. The temperature span will change somewhat due
to the nonlinear behavior of the thermistor. The following
equations can be used to easily calculate a new value for
the bias resistor:

r

=

HOT

0 536

.

R

25

•

R

NOM

For example, to set the trip points to 0°C and 45°C with
a Vishay Curve 1 thermistor choose:

3 266 0 4368

Rkk

NOM

.–.

==

2 714

.

100 104 2

•.

the nearest 1% value is 105k.

R1 = 0.536 • 105k – 0.4368 • 100k = 12.6k

the nearest 1% value is 12.7k. The fi nal solution is shown
in Figure 4 and results in an upper trip point of 45°C and
a lower trip point of 0°C.

USB and Wall Adapter Power

Although the battery charger is designed to draw power
from a USB port to charge Li-Ion batteries, a wall adapter
can also be used. Figure 5 shows an example of how to
combine wall adapter and USB power inputs. A P-channel
MOSFET, MP1, is used to prevent back conduction into
the USB port when a wall adapter is present and Schottky
diode, D1, is used to prevent USB power loss through the
1k pull-down resistor.

r

HOT

=

and r

COLD

325

.

R

25

•

are the resistance ratios at the

COLD

de-

R

NOM

where r

hot and cold trip points. Note that these equations

sired
are linked. Therefore, only one of the two trip points can
be chosen, the other is determined by the default ratios
designed in the IC. Consider an example where a 60°C
hot trip point is desired.

From the Vishay Curve 1 R-T characteristics, r
at 60°C. Using the above equation, R
to 46.4k. With this value of R

NOM

NOM

, the cold trip point is

is 0.2488

HOT

should be set

about 16°C. Notice that the span is now 44°C rather than
the previous 40°C.

The upper and lower temperature trip points can be inde­pendently programmed by using an additional bias resistor
as shown in Figure 4. The following formulas can be used

•

NOM

R

25

and R1:

to compute the values of R

rr

–

R

NOM

COLD HOT

=

.

2 714

Typically, a wall adapter can supply signifi cantly more
current than the 500mA-limited USB port. Therefore, an
N-channel MOSFET, MN1, and an extra program resistor are
used to increase the maximum charge current to 950mA
when the wall adapter is present.

5V WALL

ADAPTER

950mA I

CHG

USB

POWER

500mA I

Figure 5. Combining Wall Adapter and USB Power

CHG

MP1

D1

BATTERY

CHARGER

V

CC

PROG

1.65k

MN1

1k

BAT

I

BAT

1.74k

+

Li-Ion
BATTER

3559 F05

RRr

=

.• – •

1 0 536 RR25

NOM HOT

16

3559fb

APPLICATIONS INFORMATION

LTC3559/LTC3559-1

Power Dissipation

The conditions that cause the LTC3559/LTC3559-1 to
reduce charge current through thermal feedback can be
approximated by considering the power dissipated in the
IC. For high charge currents, the LTC3559/LTC3559-1
power dissipation is approximately:

PVV I

=

D CC BAT BAT

where PD is the power dissipated, VCC is the input supply
voltage, V
current. It is not necessary to perform any worst-case power
dissipation scenarios because the LTC3559/LTC3559-1
will automatically reduce the charge current to maintain
the die temperature at approximately 105°C. However, the
approximate ambient temperature at which the thermal
feedback begins to protect the IC is:

TCP

=°

ADJA

TCVVI

=°

A CC BAT BAT JA

Example: Consider an LTC3559/LTC3559-1 operating from
a USB port providing 500mA to a 3.5V Li-Ion battery.
The ambient temperature above which the LTC3559/
LTC3559-1 will begin to reduce the 500mA charge cur­rent is approximately:

TCVVmACW

=°

A

TC

=°

A

=°

TC

A

The LTC3559/LTC3559-1 can be used above 70°C, but
the charge current will be reduced from 500mA. The
approximate current at a given ambient temperature can
be calculated:

I

BAT

Using the previous example with an ambient tem­perature of 88°C, the charge current will be reduced to
approximately:

I

BAT

–•

()

is the battery voltage, and I

BAT

105

105––– ••

105 5 3 5 500 68

105 0
54

=

VV

()

CC BAT JA

=

VV CWCCA

535 68

()

θ

()

––.• • /

()()

–.. • / –75 68 105 51

CT

°

105 –

–•θ

CC

°°

105 88

–. • / /

–

°=° °

WCW C

A

°

=

θ

102

17

BAT

°

°

is the charge

°

Furthermore, the voltage at the PROG pin will change
proportionally with the charge current as discussed in
the Programming Charge Current section.

It is important to remember that LTC3559/LTC3559-1
applications do not need to be designed for worst-case
thermal conditions since the IC will automatically reduce
power dissipation when the junction temperature reaches
approximately 105°C.

Battery Charger Stability Considerations

The LTC3559/LTC3559-1 battery charger contains two
control loops: the constant-voltage and constant-cur­rent loops. The constant-voltage loop is stable without
any compensation when a battery is connected with low
impedance leads. Excessive lead length, however, may add
enough series inductance to require a bypass capacitor
of at least 1.5μF from BAT to GND. Furthermore, a 4.7μF
capacitor with a 0.2Ω to 1Ω series resistor from BAT to
GND is required to keep ripple voltage low when the bat­tery is disconnected.

High value capacitors with very low ESR (especially
ceramic) reduce the constant-voltage loop phase margin,
possibly resulting in instability. Ceramic capacitors up to
22μF may be used in parallel with a battery, but larger
ceramics should be decoupled with 0.2Ω to 1Ω of series
resistance.

In constant-current mode, the PROG pin is in the feedback
loop, not the battery. Because of the additional pole created
by the PROG pin capacitance, capacitance on this pin must
be kept to a minimum. With no additional capacitance on
the PROG pin, the charger is stable with program resistor
values as high as 25K. However, additional capacitance
on this node reduces the maximum allowed program
resistor. The pole frequency at the PROG pin should be
kept above 100kHz. Therefore, if the PROG pin is loaded
with a capacitance, C
be used to calculate the maximum resistance value for

:

R

PROG

R

PROG

≤

π ••

210

, the following equation should

PROG

1

5

C

PROG

= 167

IImA

BAT

3559fb

17

LTC3559/LTC3559-1

APPLICATIONS INFORMATION

Average, rather than instantaneous, battery current may be
of interest to the user. For example, if a switching power
supply operating in low-current mode is connected in
parallel with the battery, the average current being pulled
out of the BAT pin is typically of more interest than the
instantaneous current pulses. In such a case, a simple RC
fi lter can be used on the PROG pin to measure the average
battery current as shown in Figure 6. A 10k resistor has
been added between the PROG pin and the fi lter capacitor
to ensure stability.

LTC3559/

LTC3559-1

PROG

GND

Figure 6. Isolated Capacitive Load on PROG Pin and Filtering

R

10k

PROG

3559 F06

C

FILTER

CHARGE
CURRENT
MONITOR
CIRCUITRY

USB Inrush Limiting

When a USB cable is plugged into a portable product,
the inductance of the cable and the high-Q ceramic input
capacitor form an L-C resonant circuit. If there is not
much impedance in the cable, it is possible for the voltage
at the input of the product to reach as high as twice the
USB voltage (~10V) before it settles out. In fact, due to
the high voltage coeffi cient of many ceramic capacitors
(a nonlinearity), the voltage may even exceed twice the
USB voltage. To prevent excessive voltage from damaging
the LTC3559/LTC3559-1 during a hot insertion, the soft
connect circuit in Figure 7 can be employed.

In the circuit of Figure 7, capacitor C1 holds MP1 off when
the cable is fi rst connected. Eventually C1 begins to charge
up to the USB voltage applying increasing gate support
to MP1. The long time constant of R1 and C1 prevents

MP1

5V USB

INPUT

Si2333

C1
100nF

USB CABLE

R1
40k

Figure 7. USB Soft Connect Circuit

C2
10μF

V

CC

LTC3559/

LTC3559-1

GND

3559 F07

the current from building up in the cable too fast thus
dampening out any resonant overshoot.

Buck Switching Regulator General Information

The LTC3559/LTC3559-1 contain two 2.25MHz constant­frequency current mode switching regulators that provide
up to 400mA each. Both switchers can be programmed
for a minimum output voltage of 0.8V and can be used
to power a microcontroller core, microcontroller I/O,
memory or other logic circuitry. Both regulators support
100% duty cycle operation (dropout mode) when the
input voltage drops very close to the output voltage and
are also capable of operating in Burst Mode operation for
highest effi ciencies at light loads (Burst Mode operation
is pin selectable). The switching regulators also include
soft-start to limit inrush current when powering on, short
circuit current protection, and switch node slew limiting
circuitry to reduce radiated EMI.

A single MODE pin sets both regulators in Burst Mode
operation or pulse skip operating mode while each regula­tor is enabled individually through their respective enable
pins EN1 and EN2. The buck regulators input supply (PV

IN

)
should be connected to the battery pin (BAT). This allows
the undervoltage lockout circuit on the BAT pin to disable
the buck regulators when the BAT voltage drops below

2.45V. Do not drive the buck switching regulators from
a voltage other than BAT. A 2.2μF decoupling capacitor
from the PV

pin to GND is recommended.

IN

Buck Switching Regulator
Output Voltage Programming

Both switching regulators can be programmed for output
voltages greater than 0.8V. The output voltage for each
buck switching regulator is programmed using a resistor
divider from the switching regulator output connected to
the feedback pins (FB1 and FB2) such that:

V

= 0.8(1 + R1/R2)

OUT

Typical values for R1 are in the range of 40k to 1M. The
capacitor C

cancels the pole created by feedback re-

FB

sistors and the input capacitance of the FB pin and also
helps to improve transient response for output voltages
much greater than 0.8V. A variety of capacitor sizes can
be used for C

but a value of 10pF is recommended for

FB

3559fb

18

APPLICATIONS INFORMATION

LTC3559/LTC3559-1

most applications. Experimentation with capacitor sizes
between 2pF and 22pF may yield improved transient
response if so desired by the user.

Buck Switching Regulator Operating Modes

The step-down switching regulators include two possible
operating modes to meet the noise/power needs of a
variety of applications.

In pulse skip mode, an internal latch is set at the start of
every cycle, which turns on the main P-channel MOSFET
switch. During each cycle, a current comparator compares
the peak inductor current to the output of an error amplifi er.
The output of the current comparator resets the internal
latch, which causes the main P-channel MOSFET switch to
turn off and the N-channel MOSFET synchronous rectifi er
to turn on. The N-channel MOSFET synchronous rectifi er
turns off at the end of the 2.25MHz cycle or if the current
through the N-channel MOSFET synchronous rectifi er
drops to zero. Using this method of operation, the error
amplifi er adjusts the peak inductor current to deliver the
required output power. All necessary compensation is
internal to the step-down switching regulator requiring
only a single ceramic output capacitor for stability. At
light loads in pulse skip mode, the inductor current may
reach zero on each pulse which will turn off the N-channel
MOSFET synchronous rectifi er. In this case, the switch
node (SW1 or SW2) goes high impedance and the switch
node voltage will “ring”. This is discontinuous operation,
and is normal behavior for a switching regulator. At very
light loads in pulse skip mode, the step-down switching

P

VIN

EN

PWM

CONTROL

MODE

MP

MN

SW

L

V

OUT

+

C

C

FB

O

R1

regulators will automatically skip pulses as needed to
maintain output regulation. At high duty cycle (V

/2) in pulse skip mode, it is possible for the inductor

PV

IN

OUT

>

current to reverse causing the buck converter to switch
continuously. Regulation and low noise operation are
maintained but the input supply current will increase to a
couple mA due to the continuous gate switching.

During Burst Mode operation, the step-down switching
regulators automatically switch between fi xed frequency
PWM operation and hysteretic control as a function of
the load current. At light loads the step-down switching
regulators control the inductor current directly and use a
hysteretic control loop to minimize both noise and switching
losses. During Burst Mode operation, the output capacitor
is charged to a voltage slightly higher than the regulation
point. The step-down switching regulator then goes into
sleep mode, during which the output capacitor provides
the load current. In sleep mode, most of the switching
regulator’s circuitry is powered down, helping conserve
battery power. When the output voltage drops below a
pre-determined value, the step-down switching regulator
circuitry is powered on and another burst cycle begins. The
sleep time decreases as the load current increases. Beyond
a certain load current point (about 1/4 rated output load
current) the step-down switching regulators will switch to
a low noise constant frequency PWM mode of operation,
much the same as pulse skip operation at high loads. For
applications that can tolerate some output ripple at low
output currents, Burst Mode operation provides better
effi ciency than pulse skip at light loads.

The step-down switching regulators allow mode transition
on-the-fl y, providing seamless transition between modes
even under load. This allows the user to switch back and
forth between modes to reduce output ripple or increase
low current effi ciency as needed. Burst Mode operation is
set by driving the MODE pin high, while pulse skip mode
is achieved by driving the MODE pin low.

FB

GND

0.8V

Figure 8. Buck Converter Application Circuit

R2

3559 F08

Buck Switching Regulator in Shutdown

The buck switching regulators are in shutdown when
not enabled for operation. In shutdown, all circuitry in
the buck switching regulator is disconnected from the
regulator input supply, leaving only a few nanoamps of

3559fb

19

LTC3559/LTC3559-1

APPLICATIONS INFORMATION

leakage pulled to ground through a 10k resistor on the
switch (SW1 or SW2) pin when in shutdown.

Buck Switching Regulator Dropout Operation

It is possible for a step-down switching regulator’s input
voltage to approach its programmed output voltage (e.g., a
battery voltage of 3.4V with a programmed output voltage
of 3.3V). When this happens, the PMOS switch duty cycle
increases until it is turned on continuously at 100%. In this
dropout condition, the respective output voltage equals the
regulator’s input voltage minus the voltage drops across
the internal P-channel MOSFET and the inductor.

Buck Switching Regulator Soft-Start Operation

Soft-start is accomplished by gradually increasing the
peak inductor current for each switching regulator over
a 500μs period. This allows each output to rise slowly,
helping minimize the battery in-rush current required to
charge up the regulator’s output capacitor. A soft-start
cycle occurs whenever a switcher fi rst turns on, or after a
fault condition has occurred (thermal shutdown or UVLO).
A soft-start cycle is not triggered by changing operating
modes using the MODE pin. This allows seamless output
operation when transitioning between operating modes.

Buck Switching Regulator
Switching Slew Rate Control

The buck switching regulators contain circuitry to limit the
slew rate of the switch node (SW1 and SW2). This circuitry
is designed to transition the switch node over a period of
a couple of nanoseconds, signifi cantly reducing radiated
EMI and conducted supply noise while maintaining high
effi ciency.

Buck Switching Regulator Low Supply Operation

An undervoltage lockout (UVLO) circuit on PV
down the step-down switching regulators when BAT drops
below 2.45V. This UVLO prevents the step-down switching
regulators from operating at low supply voltages where loss
of regulation or other undesirable operation may occur.

shuts

IN

Buck Switching Regulator Inductor Selection

The buck regulators are designed to work with inductors
in the range of 2.2μH to 10μH, but for most applications
a 4.7μH inductor is suggested. Larger value inductors
reduce ripple current which improves output ripple voltage.
Lower value inductors result in higher ripple current which
improves transient response time. To maximize effi ciency,
choose an inductor with a low DC resistance. For a 1.2V
output effi ciency is reduced about 2% for every 100mΩ
series resistance at 400mA load current, and about 2%
for every 300mΩ series resistance at 100mA load current.
Choose an inductor with a DC current rating at least 1.5
times larger than the maximum load current to ensure that
the inductor does not saturate during normal operation.
If output short circuit is a possible condition the induc­tor should be rated to handle the maximum peak current
specifi ed for the buck regulators.

Different core materials and shapes will change the size/cur­rent and price/current relationship of an inductor. Toroid or
shielded pot cores in ferrite or permalloy materials are small
and don’t radiate much energy, but generally cost more
than powdered iron core inductors with similar electrical
characteristics. Inductors that are very thin or have a very
small volume typically have much higher DCR losses, and
will not give the best effi ciency. The choice of which style
inductor to use often depends more on the price vs size,
performance, and any radiated EMI requirements than on
what the buck regulator requires to operate.

The inductor value also has an effect on Burst Mode
operation. Lower inductor values will cause Burst Mode
switching frequency to increase.

Table 2 shows several inductors that work well with the
LTC3559/LTC3559-1. These inductors offer a good compro­mise in current rating, DCR and physical size. Consult each
manufacturer for detailed information on their entire
selection of inductors.

20

3559fb

APPLICATIONS INFORMATION

Table 2 Recommended Inductors

INDUCTOR TYPE L (μH) MAX IDC(A)

DB318C

D312C

DE2812C

CDRH3D16

CDRH2D11

CLS4D09

SD3118

SD3112

SD12

SD10

LPS3015 4.7

*Typical DCR

4.7

3.3

4.7

3.3

4.7

3.3

4.7

3.3

4.7

3.3

4.7

4.7

3.3

4.7

3.3

4.7

3.3

4.7

3.3

3.3

1.07

1.20

0.79

0.90

1.15

1.37

0.9

1.1

0.5

0.6

0.75

1.3

1.59

0.8

0.97

1.29

1.42

1.08

1.31

1.1

1.3

LTC3559/LTC3559-1

MAX DCR(Ω) SIZE IN MM (L × W × H)

0.1

0.07

0.24

0.20

0.13*

0.105*

0.11

0.085

0.17

0.123

0.19

0.162

0.113

0.246

0.165

0.117*

0.104*

0.153*

0.108*

0.2

0.13

3.8 × 3.8 × 1.8

3.8 × 3.8 × 1.8

3.6 × 3.6 × 1.2

3.6 × 3.6 × 1.2

3.0 × 2.8 × 1.2

3.0 × 2.8 × 1.2

4 × 4 × 1.8
4 × 4 × 1.8

3.2 × 3.2 × 1.2

3.2 × 3.2 × 1.2

4.9 × 4.9 × 1

3.1 × 3.1 × 1.8

3.1 × 3.1 × 1.8

3.1 × 3.1 × 1.2

3.1 × 3.1 × 1.2

5.2 × 5.2 × 1.2

5.2 × 5.2 × 1.2

5.2 × 5.2 × 1.0

5.2 × 5.2 × 1.0

3.0 × 3.0 × 1.5

3.0 × 3.0 × 1.5

MANUFACTURER

Toko

www.toko.com

Sumida

www.sumida.com

Cooper

www.cooperet.com

Coilcraft

www.coilcraft.com

Buck Switching Regulator
Input/Output Capacitor Selection

Low ESR (equivalent series resistance) ceramic capaci­tors should be used at both switching regulator outputs
as well as the switching regulator input supply. Only
X5R or X7R ceramic capacitors should be used because
they retain their capacitance over wider voltage and
temperature ranges than other ceramic types. A 10μF
output capacitor is suffi cient for most applications.
For good transient response and stability the output
capacitor should retain at least 4μF of capacitance over
operating temperature and bias voltage. The switching
regulator input supply should be bypassed with a 2.2μF
capacitor. Consult manufacturer for detailed information
on their selection and specifi cations of ceramic capaci­tors. Many manufacturers now offer very thin (< 1mm
tall) ceramic capacitors ideal for use in height-restricted
designs. Table 3 shows a list of several ceramic capacitor
manufacturers.

Table 3: Recommended Ceramic Capacitor Manufacturers

AVX [phone] www.avxcorp.com

Murata [phone] www.murata.com

Taiyo Yuden [phone] www.t-yuden.com

TDK [phone] www.tdk.com

PCB Layout Considerations

As with all DC/DC regulators, careful attention must be
paid while laying out a printed circuit board (PCB) and to
component placement. The inductors, input PV

capacitor

IN

and output capacitors must all be placed as close to the
LTC3559/LTC3559-1 as possible and on the same side as
the LTC3559/LTC3559-1. All connections must be made on
that same layer. Place a local unbroken ground plane below
these components that is tied to the Exposed Pad (Pin 17)
of the LTC3559/LTC3559-1. The Exposed Pad must also
be soldered to system ground for proper operation.

3559fb

21

LTC3559/LTC3559-1

TYPICAL APPLICATIONS

The Output Voltage of a Buck Regulator Is Programmed for 3.3V. When BAT Voltage Approaches 3.3V, the Regulator Operates in

Dropout and the Output Voltage Will Be BAT – (I

A 3-Resistor Bias Network for NTC Sets Hot and Cold Trip Points at Approximately 55°C and 0°C

ADAPTER

4.5V TO 5.5V
110k510Ω

28.7k

DIGITALLY

CONTROLLED

• 0.6). An LED at CHRG Gives a Visual Indication of the Battery Charger State.

LOAD

UP TO

1μF

100k
NTC
NTH50603N01

887Ω

V

CC

NTC

LTC3559/

LTC3559-1

CHRG

PROG

SUSP

HPWR

MODE

EN1

EN2

GND EXPOSED PAD

BAT

PV

IN

SW1

FB1

SW2

FB2

3559 TA03

950mA

4.7μH

4.7μH

1.02M

806k

2.2μF

SINGLE

+

Li-lon CELL

2.7V TO 4.2V (LTC3559)

2.7V TO 4.1V (LTC3559-1)

22pF

324k

22pF

649k

10μF

10μF

3.3V AT
400mA

1.8V AT
400mA

Buck Regulator Effi ciency vs I

100

Burst Mode

90

OPERATION

80

70

60

50

40

EFFICIENCY (%)

30

20

10

0

0.1 10 100 1000

PULSE SKIP
MODE

V

OUT

PVIN = 2.7V
PV

1

I

(mA)

LOAD

= 1.8V

= 4.2V

IN

LOAD

3559 TA02b

Buck Regulator Effi ciency vs I

100

90

80

70

60

50

40

EFFICIENCY (%)

30

20

10

0

0.1 10 100 1000

Burst Mode
OPERATION

1

I

LOAD

PULSE SKIP
MODE

(mA)

PVIN = 4.2V
V

OUT

LOAD

= 3.3V

3559 TA02c

22

3559fb

TYPICAL APPLICATIONS

LTC3559/LTC3559-1

The Battery Can be Charged with Up to 950mA of Charge Current. Buck Regulator 2 Is Enabled Only After V

Is Up to Approximately

OUT1

0.7V. This Provides a Sequencing Function Which May Be Desirable in Applications Where a Microprocessor Needs to Be Powered Up

Before Peripherals. CHRG Interfaces to a Microprocessor Which Decodes the Battery Charger State

UP TO

ADAPTER

4.5V TO 5.5V

MICROPROCESSOR

TO

100k

100k

100k
NTC
NTH50603NO1

DIGITALLY

CONTROLLED

887Ω

1μF

V

CC

NTC

CHRG

PROG

SUSP

HPWR

MODE

EN1

EN2

LTC3559/

LTC3559-1

GND EXPOSED PAD

BAT

PV

SW1

FB1

SW2

FB2

950mA

SINGLE

+

IN

2.2μF

4.7μH

655k

4.7μH

324k

Li-lon CELL

2.7V TO 4.2V (LTC3559)

2.7V TO 4.1V (LTC3559-1)

22pF

309k

22pF

649k

10μF

1.2V AT
400mA

10μF

3559 TA02

2.5V AT
400mA

PACKAGE DESCRIPTION

0.70 p0.05

3.50 p 0.05

2.10 p 0.05

1.45 p 0.05
(4 SIDES)

0.25 p0.05

0.50 BSC

RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
NOTE:

1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE MO-220 VARIATION (WEED-2)

2. DRAWING NOT TO SCALE

3. ALL DIMENSIONS ARE IN MILLIMETERS

4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE

5. EXPOSED PAD SHALL BE SOLDER PLATED

6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON THE TOP AND BOTTOM OF PACKAGE

UD Package

16-Lead Plastic QFN (3mm × 3mm)

(Reference LTC DWG # 05-08-1691)

3.00 p 0.10
(4 SIDES)

PIN 1
TOP MARK
(NOTE 6)

PACKAGE
OUTLINE

0.75 p 0.05

1.45 p 0.10
(4-SIDES)

0.200 REF

0.00 – 0.05

BOTTOM VIEW—EXPOSED PAD

R = 0.115

TYP

15 16

0.50 BSC

PIN 1 NOTCH R = 0.20 TYP
OR 0.25 s 45o CHAMFER

0.40 p 0.10

1

2

(UD16) QFN 0904

0.25 p 0.05

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

3559fb

23

LTC3559/LTC3559-1

RELATED PARTS

PART NUMBER DESCRIPTION COMMENTS

LTC3550 Dual Input USB/AC Adapter Li-Ion Battery Charger with

Adjustable Output 600mA Buck Converter

LTC3552 Standalone Linear Li-Ion Battery Charger with Adjustable

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LTC3552-1 Standalone Linear Li-Ion Battery Charger with Dual

Synchronous Buck Converter

LTC3455 Dual DC/DC Converter with USB Power Manager and

Li-Ion Battery Charger

LTC3456 2-Cell, Multi-Output DC/DC Converter with USB Power

Manager

LTC4080 500mA Standalone Charger with 300mA Synchronous

Buck

Hot Swap is a trademark of Linear Technology Corporation.

Synchronous Buck Converter, Effi ciency: 93%, Adjustable Output at
600mA, Charge Current: 950mA Programmable, USB Compatible,
Automatic Input Power Detection and Selection

Synchronous Buck Converter, Effi ciency: >90%, Adjustable Outputs at
800mA and 400mA, Charge Current Programmable Up to 950mA, USB
Compatible, 5mm × 3mm DFN16 Package

Synchronous Buck Converter, Effi ciency: >90%, Outputs 1.8V at 800mA
and 1.575 at 400mA, Charge Current Programmable Up to 950mA, USB
Compatible

Seamless Transition Between Input Power Sources: Li-Ion Battery, USB
and 5V Wall Adapter, Two High Effi ciency DC/DC Converters: Up to 96%,
Full-Featured Li-Ion Battery Charger with Accurate USB Current Limiting
(500mA/100mA) Pin-Selectable Burst Mode
Output for SDIO and Memory Cards, 4mm × 4mm QFN24 Package

Seamless Transition Between 2-Cell Battery, USB and AC Wall Adapter
Input Power Sources, Main Output: Fixed 3.3V Output, Core Output:
Adjustable From 0.8V to V
Power Supply Sequencing: Main and Hot Swap Accurate USB Current
Limiting, High Frequency Operation: 1MHz, High Effi ciency: Up to 92%,
4mm × 4mm QFN24 Package

Charges Single-Cell Li-Ion Batteries, Timer Termination +C/10, Thermal
Regulation, Buck Output: 0.8V to V
× 3mm DFN10 Package

Operation, Hot SwapTM

, Hot Swap Output for Memory Cards,

BATT(MIN)

, Buck Input VIN: 2.7V to 5.5V, 3mm

BAT

24

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

[phone] ● FAX: [phone] ● www.linear.com

3559fb

LT 0508 REV B • PRINTED IN USA

© LINEAR TECHNOLOGY CORPORATION 2007