LINEAR TECHNOLOGY LTC3542 Technical data

FEATURES

LTC3542

500mA, 2.25MHz

Synchronous Step-Down

DC/DC Converter

U

DESCRIPTIO

■

High Effi ciency: Up to 96%

■

High Peak Switch Current: 1000mA

■

Low Output Ripple (<20mV

Typical)

P-P

Burst Mode Operation: Only 26µA

■

Very Low Quiescent Current: Only 26µA

■

2.5V to 5.5V Input Voltage Range

■

2.25MHz Constant Frequency Operation

■

1MHz to 3MHz External Frequency Synchronization

■

Low Dropout Operation: 100% Duty Cycle

■

No Schottky Diode Required

■

Internal Soft-Start Limits Inrush Current

■

0.6V Reference Allows Low Output Voltages

■

Shutdown Mode Draws <1µA Supply Current

■

±2% Output Voltage Accuracy

■

Current Mode Operation for Excellent Line and Load

Transient Response

■

Overtemperature Protected

■

Available in 6-Lead 2mm × 2mm DFN and Small TSOT

U

APPLICATIO S

■

Cellular Telephones

■

Wireless and DSL Modems

■

Digital Cameras

■

MP3 Players

■

PDAs and Other Handheld Devices

The LTC®3542 is a high effi ciency monolithic synchronous
buck converter using a constant frequency, current mode
architecture. Supply current during operation is only
26µA, dropping to <1µA in shutdown. The 2.5V to 5.5V
input voltage range makes the LTC3542 ideally suited for
single Li-Ion battery-powered applications. 100% duty
cycle provides low dropout operation, extending battery
life in portable systems. The output voltage is adjustable
from 0.6V to V

. Internal power switches are optimized

IN

to provide high effi ciency and eliminate the need for an
external Schottky diode.

Switching frequency is internally set at 2.25MHz, allowing
the use of small surface mount inductors and capacitors,
and it can synchronize to an external clock signal with a
frequency range of 1MHz to 3MHz through the MODE/
SYNC pin. The LTC3542 is specifi cally designed to work
well with ceramic output capacitors, achieving very low
output voltage ripple and a small PCB footprint.

The LTC3542 can be confi gured for the power saving Burst

®

Mode

Operation. For reduced noise and RF interference,
the MODE/SYNC pin can be confi gured for pulse skipping
operation.

, LTC, LT and Burst Mode are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents, including 5481178, 6580258, 6304066, 6127815, 6498466,
6611131, 5994885.

TYPICAL APPLICATIO

V

2.7V TO 5.5V

IN

C
10µF
CER

IN

V

IN

LTC3542

RUN

MODE/SYNC

GND

SW

V

FB

U

2.2µH

75k

22pF

150k

V

1.8V
500mA

C

OUT

10µF
CER

3542 TA01a

OUT

Effi ciency and Power Loss vs Output Current

100

VIN = 3.6V

90

= 1.8V

V

OUT

80

70

60

50

40

EFFICIENCY (%)

30

20

10

0

0.1 10 100 1000

1
OUTPUT CURRENT (mA)

1000

100

10

1

0.1

3542 TA01b

POWER LOSS (mW)

3542f

1

LTC3542

/

WWWU

ABSOLUTE AXI U RATI GS

(Note 1)

Input Supply Voltage (VIN) ........................... –0.3V to 6V

, RUN Voltages .......................................–0.3V to V

V

FB

MODE Voltage ................................–0.3V to (VIN + 0.3V)

SW Voltage ....................................–0.3V to (V

+ 0.3V)

IN

Operating Ambient Temperature Range

Junction Temperature (Note 7) ............................. 125°C

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

IN

Lead Temperature (Soldering, 10 sec)

TSOT-23 ............................................................ 300°C

Refl ow Peak Body Temperature (DFN) .................. 260°C

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

UU

W

PACKAGE/ORDER I FOR ATIO

TOP VIEW

6

V

1

FB

2

3

DC PACKAGE

7

V

IN

GND

6-LEAD (2mm × 2mm) PLASTIC DFN

T

= 125°C, θJA = 40°C/W, θJC = 3°C/W (SOLDERED TO A 4-LAYER BOARD, NOTE 3)

JMAX

EXPOSED PAD (PIN 7) IS PGND, MUST BE SOLDERED TO PCB

RUN

MODE

5

SYNC

SW

4

GND 2

ORDER PART NUMBER DC PART MARKING ORDER PART NUMBER S6 PART MARKING

LTC3542EDC LCFR LTC3542ES6 LCFS

Order Options Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking: http://www.linear.com/leadfree/

Consult LTC Marketing for parts specifi ed with wider operating temperature ranges.

TOP VIEW

VIN 1

V

3

FB

S6 PACKAGE

6-LEAD PLASTIC TSOT-23

T

= 125°C, θJA = 250°C/W

JMAX

6 SW

5 MODE/SYNC

4 RUN

●

The

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifi cations are at T

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

IN

I

FB

V

FB

ΔV

LINE_REG

ΔV

LOAD_REG

I

S

f

OSC

f

SYNC

I

LIM

R

DS(ON)

Operating Voltage Range

Feedback Input Current ±30 nA

Feedback Voltage (Note 4)

Reference Voltage Line Regulation (Note 4) VIN = 2.5V to 5.5V 0.04 0.2 %/V

Output Voltage Load Regulation (Note 4) I

Input DC Supply Current (Note 5)
Active Mode
Sleep Mode
Shutdown

Oscillator Frequency VFB = 0.6V

Synchronous Frequency VFB = 0.6V 1 3 MHz

Peak Switch Current VIN = 3V, VFB = 0.5V, Duty Cycle < 35% 650 1000 mA

P-Channel On Resistance (Note 6)
N-Channel On Resistance (Note 6)

= 25°C. VIN = 3.6V unless otherwise noted.

A

denotes the specifi cations which apply over the full operating

●

2.5 5.5 V

●

0.588 0.6 0.612 V

= 100mA to 500mA 0.02 0.2 %

LOAD

V

= 0.5V

FB

V

= 0.7V, MODE = 0V

FB

RUN = 0V

ISW = 100mA
I

= –100mA

SW

26

0.1

●

1.8 2.25 2.7 MHz

0.5

0.35

500

35

1

0.65

0.55

µA
µA
µA

3542f

2

Ω
Ω

LTC3542

The

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifi cations are at T

= 25°C. VIN = 3.6V unless otherwise noted.

A

●

denotes the specifi cations which apply over the full operating

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

I

SW(LKG)

V

UVLO

V

RUN

RUN Leakage Current

I

RUN

V

MODE/SYNC

I

MODE/SYNC

Switch Leakage Current VIN = 5V, V

Undervoltage Lockout Threshold VIN Rising

V

Falling 1.8

IN

RUN Threshold

MODE/SYNC Threshold

MODE/SYNC Leakage Current

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. No pin should exceed 6V.

Note 2: The LTC3542 is guaranteed to meet performance specifi cations
from 0°C to 85°C. Specifi cations over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.

Note 3: Failure to solder the Exposed Pad of the package to the PC board
will result in a thermal resistance much higher than 40°C/W.

= 0V, VSW = 0V or 5V ±0.01 ±1 µA

RUN

2.0

2.3 V

1.9

●

0.3 1.5 V

●

●

0.3 1.2 V

●

±0.01 ±1 µA

±0.01 ±1 µA

Note 4: The converter is tested in a proprietary test mode that connects
the output of the error amplifi er to the SW pin, which is connected to an
external servo loop.

Note 5: Dynamic supply current is higher due to the internal gate charge
being delivered at the switching frequency.

Note 6: The DFN switch on resistance is guaranteed by correlation to wafer
level measurements.

Note 7: T
dissipation P

T

is calculated from the ambient temperature TA and power

J

according to the following formula:

D

= TA + (PD) • (θJA).

J

UW

TYPICAL PERFOR A CE CHARACTERISTICS

TA = 25°C unless otherwise specifi ed.

V

SW

2V/DIV

V

OUT

50mV/DIV

AC COUPLED

100mA/DIV

Burst Mode Operation Pulse Skip Mode Operation Start-Up from Shutdown

RUN

2V/DIV

V

OUT

1V/DIV

100mA/DIV

I

L

V

= 3.6V

IN

= 1.8V

V

OUT

= 0A

I

LOAD

FIGURE 3a CIRCUIT

400µs/DIV

I

L

V

= 3.6V

IN

= 1.8V

V

OUT

= 25mA

I

LOAD

FIGURE 3a CIRCUIT

2µs/DIV

3542 G01

SW

2V/DIV

V

OUT

50mV/DIV

AC COUPLED

100mA/DIV

I

L

= 3.6V

V

IN

= 1.8V

V

OUT

= 25mA

I

LOAD

FIGURE 3a CIRCUIT

400ns/DIV

3542 G02

3542 G03

3542f

3

LTC3542

UW

TYPICAL PERFOR A CE CHARACTERISTICS

TA = 25°C unless otherwise specifi ed.

RUN

2V/DIV

V

OUT

1V/DIV

500mA/DIV

0.6150

0.6125

0.6100

0.6075

0.6050

0.6025

0.6000

(V)

0.5975

REF

V

0.5950

0.5925

0.5900

0.5875

0.5850

0.5825

Start-Up from Shutdown Load Step

V

OUT

100mV/DIV

AC COUPLED

I

L

500mA/DIV

I

L

V

= 3.6V

IN

= 1.8V

V

OUT

= 500mA

I

LOAD

FIGURE 3a CIRCUIT

Reference Voltage
vs Temperature

25

–50

0

–25

TEMPERATURE (°C)

400µs/DIV

50

3542 G04

100

125

3542 G07

75

I

LOAD

500mA/DIV

V

= 3.6V

IN

V

OUT

I

LOAD

FIGURE 3a CIRCUIT

Oscillator Frequency
vs Temperature

2.7

2.6

2.5

2.4

2.3

2.2

2.1

FREQUENCY (MHz)

2.0

1.9

1.8
–50 –30 –10 10 30 50 70 90 110

= 1.8V

= 30mA TO 500mA

20µs/DIV

TEMPERATURE (°C)

3542 G08

3542 G05

V

OUT

100mV/DIV

AC COUPLED

500mA/DIV

I

LOAD

500mA/DIV

2.7

2.6

2.5

2.4

2.3

2.2

2.1

FREQUENCY (MHz)

2.0

1.9

1.8
2

Load Step

I

L

= 3.6V

V

IN

= 1.8V

V

OUT

= 0mA TO 500mA

I

LOAD

FIGURE 3a CIRCUIT

20µs/DIV

Oscillator Frequency
vs Supply Voltage

3

4

SUPPLY VOLTAGE (V)

3542 G06

56

3542 G09

Output Voltage vs Supply Voltage

0.5
V

= 1.8V

OUT

0.4

= 100mA

I

OUT

0.3

0.2

0.1

0

ERROR (%)

–0.1

OUT

V

–0.2

–0.3

–0.4

–0.5

2

2.5 3.5

3

4

INPUT VOLTAGE (V)

4

4.5

vs Input Voltage

0.9

0.8

0.7

0.6

)

9

(

0.5

0.4

DS(ON)

R

0.3

0.2

0.1

0

R

1

DS(ON)

MAIN SWITCH

SYNCHRONOUS

SWITCH

32647

V

5

(V)

IN

3542 G12

3542f

Output Voltage vs Load Current

2.0
VIN = 3.6V

= 1.8V

V

OUT

1.5

1.0

0.5

0

ERROR (%)

–0.5

OUT

V

–1.0

–1.5

5.5

5

6

3542 G10

–2.0

1

Burst Mode

OPERATION

PULSE SKIP

MODE

10 100 1000

LOAD CURRENT (mA)

3542 G11

UW

TYPICAL PERFOR A CE CHARACTERISTICS

R

0.9

0.8

0.7

0.6

(Ω)

0.5

0.4

DS(ON)

R

0.3

0.2

0.1

0

–50

vs Temperature

DS(ON)

MAIN SWITCH

0

–25

TEMPERATURE (°C)

SYNCHRONOUS

SWITCH

VIN = 2.7V

= 3.6V

V

IN

= 4.2V

V

IN

25 125

50

75 100

3542 G13

Switch Leakage vs Input Voltage

1000

900

800

700

600

500

400

300

LEAKAGE CURRENT (pA)

200

100

0

0

SYNCHRONOUS

1

SWITCH

2

MAIN SWITCH

34

VIN (V)

TA = 25°C unless otherwise specifi ed.

Switch Leakage vs Temperature

300

250

200

150

100

SWITCH LEAKAGE (nA)

MAIN SWITCH
SYNCHRONOUS SWITCH

–25 0

25 75

TEMPERATURE (°C)

5

3542 G14

50

6

0

–50

LTC3542

50 100 125

3542 G15

Effi ciency vs Input Voltage

100

90

80

70

60

EFFICIENCY (%)

50

40

30

2.5

I

= 500mA

OUT

= 100mA

I

OUT

= 10mA

I

OUT

= 1mA

I

OUT

= 0.1mA

I

OUT

3 3.5

INPUT VOLTAGE (V)

V

= 1.8V

OUT

Burst Mode OPERATION
FIGURE 3a CIRCUIT

4.5 5.5

45

3542 G16

Effi ciency vs Load Current

100

90

80

70

60

50

40

EFFICIENCY (%)

30

20

V

= 1.8V

OUT

Burst Mode OPERATION

10

FIGURE 3a CIRCUIT

0

0.1 10 100 1000

1

OUTPUT CURRENT (mA)

Effi ciency vs Load Current Effi ciency vs Load Current

100

90

80

70

60

50

40

EFFICIENCY (%)

30

20

V

= 1.2V

OUT

Burst Mode OPERATION

10

FIGURE 3a CIRCUIT

0

0.1 10 100 1000

1
OUTPUT CURRENT (mA)

VIN = 2.7V
V
V

= 3.6V

IN

= 4.2V

IN

3542 G18

100

Burst Mode

90

OPERATION

80

70

60

50

40

EFFICIENCY (%)

30

20

10

0

0.1 10 100 1000

PULSE SKIP

1
OUTPUT CURRENT (mA)

VIN = 2.7V
V
V

MODE

VIN = 3.6V

= 1.8V

V

OUT

FIGURE 3a CIRCUIT

= 3.6V

IN

= 4.2V

IN

3542 G17

3542 G19

3542f

5