LINEAR TECHNOLOGY LTC3548 Technical data

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FEATURES

LTC3548

Dual Synchronous,

400mA/800mA, 2.25MHz

Step-Down DC/DC Regulator

U

DESCRIPTIO

■

High Efficiency: Up to 95%

■

Very Low Quiescent Current: Only 40µA

■

2.25MHz Constant Frequency Operation

■

High Switch Current: 0.7A and 1.2A

■

No Schottky Diodes Required

■

Low R

■

Current Mode Operation for Excellent Line

Internal Switches: 0.35Ω

DS(ON)

and Load Transient Response

■

Short-Circuit Protected

■

Low Dropout Operation: 100% Duty Cycle

■

Ultralow Shutdown Current: IQ < 1µA

■

Output Voltages from 5V down to 0.6V

■

Power-On Reset Output

■

Externally Synchronizable Oscillator

■

Small Thermally Enhanced MSOP and 3mm × 3mm
DFN Packages

U

APPLICATIO S

■

PDAs/Palmtop PCs

■

Digital Cameras

■

Cellular Phones

■

Portable Media Players

■

PC Cards

■

Wireless and DSL Modems

The LTC®3548 is a dual, constant frequency, synchronous
step down DC/DC converter. Intended for low power
applications, it operates from 2.5V to 5.5V input voltage
range and has a constant 2.25MHz switching frequency,
allowing the use of tiny, low cost capacitors and inductors
with a profile ≤1.2mm. Each output voltage is adjustable
from 0.6V to 5V. Internal synchronous 0.35Ω, 0.7A/1.2A
power switches provide high efficiency without the need
for external Schottky diodes.

A user selectable mode input is provided to allow the user
to trade-off noise ripple for low power efficiency. Burst
Mode® operation provides high efficiency at light loads,
while Pulse Skip Mode provides low noise ripple at light
loads.

To further maximize battery runtime, the P-channel
MOSFETs are turned on continuously in dropout (100%
duty cycle), and both channels draw a total quiescent
current of only 40µA. In shutdown, the device draws <1µA.

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

TYPICAL APPLICATIO

V

= 2.8V

IN

TO 5.5V

10µF

= 2.5V

V

OUT2

AT 400mA

4.7µF 10µF

887k 604k

Figure 1. 2.5V/1.8V at 400mA/800mA Step-Down Regulators

RUN2 V

MODE/SYNC

SW2

V

FB2

U

IN

LTC3548

GND

RUN1

POR

SW1

V

FB1

LTC3548 Efficiency Curve

100

100k

RESET

2.2µH4.7µH

33pF68pF

301k280k

V

= 1.8V

OUT1

AT 800mA

3548 TA01

95

90

85

80

POWER LOSS

75

EFFICIENCY (%)

70

65

60

1

EFFICIENCY

VIN = 3.3V, V
Burst Mode OPERATION
CHANNEL 1, NO LOAD ON CHANNEL 2

LOAD CURRENT (mA)

= 1.8V

OUT

10 100 1000

3548 TA02

1000

100

POWER LOSS (mW)

10

1

0.1

3548f

1

LTC3548

TOP VIEW

1
2
3
4
5

V

FB1

RUN1

V

IN

SW1
GND

10
9
8
7
6

V

FB2

RUN2
POR
SW2

MODE/
SYNC

11

MSE PACKAGE

10-LEAD PLASTIC MSOP

MSE PIN 11, EXPOSED PAD: PGND

MUST BE CONNECTED TO GND

WW

W

U

ABSOLUTE AXI U RATI GS

(Note 1)

VIN Voltages.................................................–0.3V to 6V

, V

V

FB1

, RUN1, RUN2

FB2

Voltages ..................................... – 0.3V to VIN + 0.3V

MODE/SYNC Voltage ...................... – 0.3V to V

SW1, SW2 Voltage ......................... – 0.3V to V

+ 0.3V

IN

+ 0.3V

IN

POR Voltage ................................................ – 0.3V to 6V

UUW

PACKAGE/ORDER I FOR ATIO

TOP VIEW

V

1

FB1

RUN1

2

11

3

V

IN

4

SW1

5

GND

10-LEAD (3mm × 3mm) PLASTIC DFN

T

JMAX

DD PACKAGE

DD PIN 11, EXPOSED PAD: PGND

MUST BE CONNECTED TO GND

= 125°C, θJA = 45°C/W, θJC = 3°C/W

(Soldered to a 4-layer board)

10

V

RUN2

9

POR

8

7

SW2

6

MODE/
SYNC

FB2

ORDER PART

NUMBER

LTC3548EDD

DD PART MARKING

LBNJ

Ambient Operating Temperature

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

Junction Temperature (Note 5)............................. 125°C

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

Lead Temperature (Soldering, 10 sec)

LTC3548EMSE only .......................................... 300°C

ORDER PART

NUMBER

LTC3548EMSE

MSE PART MARKING

LTBNH

T

= 125°C, θJA = 45°C/W, θJC = 10°C/W

JMAX

(Soldered to a 4-layer board)

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

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V, unless otherwise specified. (Note 2)

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

IN

I

FB

V

FB

∆V

LINE REG

∆V

LOAD REG

I

S

f

OSC

f

SYNC

I

LIM

R

DS(ON)

I

SW(LKG)

2

The ● denotes the specifications which apply over the full operating

Operating Voltage Range ● 2.5 5.5 V
Feedback Pin Input Current ● 30 nA
Feedback Voltage (Note 3) 0°C ≤ TA ≤ 85°C 0.588 0.6 0.612 V

–40°C ≤ T

Reference Voltage Line Regulation VIN = 2.5V to 5.5V (Note 3) 0.3 0.5 %/V
Output Voltage Load Regulation (Note 3) 0.5 %
Input DC Supply Current

Active Mode V
Sleep Mode V

FB1
FB1

Shutdown RUN = 0V, V
Oscillator Frequency VFB = 0.6V ● 1.8 2.25 2.7 MHz
Synchronization Frequency 2.25 MHz
Peak Switch Current Limit Channel 1 VIN = 3V, VFB = 0.5V, Duty Cycle <35% 0.95 1.2 1.6 A

Peak Switch Current Limit Channel 2 V

IN

Top Switch On-Resistance (Note 6) 0.35 0.45 Ω
Bottom Switch On-Resistance (Note 6) 0.30 0.45 Ω

Switch Leakage Current VIN = 5V, V

≤ 85°C ● 0.585 0.6 0.612 V

A

= V

= 0.5V 700 950 µA

FB2

= V

= 0.63V, MODE/SYNC = 3.6V 40 60 µA

FB2

= 5.5V, MODE/SYNC = 0V 0.1 1 µA

IN

= 3V, VFB = 0.5V, Duty Cycle <35% 0.6 0.7 0.9 A

= 0V, VFB = 0V 0.01 1 µA

RUN

3548f

LTC3548

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifications are at T

The ● denotes the specifications which apply over the full operating

= 25°C. VIN = 3.6V, unless otherwise specified. (Note 2)

A

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

POR Power-On Reset Threshold VFB Ramping Down, MODE/SYNC = 0V –8.5 %

Power-On Reset On-Resistance 100 200 Ω
Power-On Reset Delay 262,144 Cycles

V

RUN

I

RUN

Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired. No pin shall exceed 6V.

Note 2: The LTC3548 is guaranteed to meet specified performance from
0°C to 70°C. Specifications over the – 40°C and 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.

Note 3: The LTC3548 is tested in a proprietary test mode that connects

RUN Threshold ● 0.3 1 1.5 V
RUN Leakage Current ● 0.01 1 µA

to the output of the error amplifier.

V

FB

Note 4: Dynamic supply current is higher due to the internal gate charge
being delivered at the switching frequency.

Note 5: T

is calculated from the ambient TA and power dissipation P

J

D

according to the following formula: TJ = TA + (PD • θJA).
Note 6: The DFN switch on-resistance is guaranteed by correlation to

wafer level measurements.

UW

TYPICAL PERFOR A CE CHARACTERISTICS

TA = 25°C unless otherwise specified.

Load StepBurst Mode Operation Pulse Skipping Mode

SW

5V/DIV

V

OUT

20mV/DIV

I

L

200mA/DIV

VIN = 3.6V

= 1.8V

V

OUT

= 180mA

I

LOAD

CHANNEL 1; CIRCUIT OF FIGURE 3

Efficiency vs Input Voltage

100

95

90

85

80

75

EFFICIENCY (%)

70

V

65

Burst Mode OPERATION
CIRCUIT OF FIGURE 3

60

2

100mA

10mA

1mA

800mA

= 1.8V, CHANNEL 1

OUT

3

INPUT VOLTAGE (V)

SW

5V/DIV

V

OUT

10mV/DIV

I

L

200mA/DIV

2µs/DIV 1µs/DIV

3548 G01 3548 G02

V

= 3.6V

IN

= 1.8V

V

OUT

= 30mA

I

LOAD

CHANNEL 1; CIRCUIT OF FIGURE 3

Oscillator Frequency vs
Temperature

2.5

VIN = 3.6V

2.4

2.3

2.2

FREQUENCY (MHz)

2.1

456

3548 G04

2.0

–50 25 75

–25 0

TEMPERATURE (°C)

50 100 125

3548 G05

V

OUT

200mV/DIV

I

L

500mA/DIV

I

LOAD

500mA/DIV

V

= 3.6V

IN

= 1.8V

V

OUT

= 80mA TO 800mA

I

LOAD

CHANNEL 1; CIRCUIT OF FIGURE 3

Oscillator Frequency vs Supply
Voltage

10

8

6

4

2

0

–2

–4

FREQUENCY DEVIATION (%)

–6

–8

–10

2

20µs/DIV

3

SUPPLY VOLTAGE (V)

456

3548 G03

3548 G06

3548f

3

LTC3548

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Reference Voltage vs
Temperature R

0.615
VIN = 3.6V

0.610

0.605

0.600

0.595

REFERENCE VOLTAGE (V)

0.590

0.585

–50 25 75

–25 0

TEMPERATURE (°C)

50 100 125

3548 G07

500

450

400

(mΩ)

350

DS(ON)

R

300

250

200

1

vs Input Voltage R

DS(ON)

TA = 25°C

MAIN
SWITCH

SYNCHRONOUS

SWITCH

3

2

V

57

46

(V)

IN

3548 G08

550

500

450

400

350

(mΩ)

300

DS(ON)

R

250

200

150

100

vs Junction Temperature

DS(ON)

VIN = 4.2V

MAIN SWITCH
SYNCHRONOUS SWITCH

–50

–25 0

25 75

JUNCTION TEMPERATURE (°C)

VIN = 2.7V

VIN = 3.6V

50 100 150125

3548 G09

Efficiency vs Load Current

100

95

90

Burst Mode OPERATION

85

80

75

EFFICIENCY (%)

70

65

60

1

NO LOAD ON OTHER CHANNEL

CHANNEL 1; CIRCUIT OF FIGURE 3

10 100 1000

LOAD CURRENT (mA)

Efficiency vs Load Current

100

2.7V

90

80

70

EFFICIENCY (%)

60

V

50

Burst Mode OPERATION
NO LOAD ON OTHER CHANNEL
CIRCUIT OF FIGURE 3

40

1

3.6V

4.2V

= 2.5V, CHANNEL 1

OUT

10 100 1000

LOAD CURRENT (mA)

PULSE SKIP MODE

VIN = 3.6V, V

OUT

= 1.8V

3548 G11

3548 G10

Load Regulation

2.0

1.5

Burst Mode OPERATION

1.0

0.5

0

PULSE SKIP MODE

ERROR (%)

–0.5

OUT

V

–1.0

–1.5

–2.0

1

NO LOAD ON OTHER CHANNEL

CHANNEL 1; CIRCUIT OF FIGURE 3

10 100 1000

LOAD CURRENT (mA)

Efficiency vs Load Current

100

95

90

2.7V

85

80

75

EFFICIENCY (%)

70

V

= 1.5V, CHANNEL 1

OUT

Burst Mode OPERATION

65

NO LOAD ON OTHER CHANNEL
CIRCUIT OF FIGURE 3

60

1

3.6V

4.2V

10 100 1000

LOAD CURRENT (mA)

VIN = 3.6V, V

OUT

= 1.8V

3548 G12

3548 G14

Line Regulation

0.5
V

= 1.8V

OUT

0.4

= 200mA

I

OUT

= 25°C

T

A

0.3

0.2

0.1

0

ERROR (%)

–0.1

OUT

V

–0.2

–0.3

–0.4

–0.5

2

35

Efficiency vs Load Current

100

95

90

2.7V

85

80

75

EFFICIENCY (%)

70

65

60

4.2V

V

= 1.2V, CHANNEL 1

OUT

Burst Mode OPERATION
NO LOAD ON OTHER CHANNEL
CIRCUIT OF FIGURE 3

1

10 100 1000

LOAD CURRENT (mA)

4

VIN (V)

6

3548 G15

3.6V

3548 G13

4

3548f

LTC3548

U

UU

PI FU CTIO S

V

(Pin 1): Output Feedback. Receives the feedback

FB1

voltage from the external resistive divider across the
output. Nominal voltage for this pin is 0.6V.

RUN1 (Pin 2): Regulator 1 Enable. Forcing this pin to V
enables regulator 1, while forcing it to GND causes regu­lator 1 to shut down. This pin must be driven; do not float.

VIN (Pin 3): Main Power Supply. Must be closely decoupled
to GND.

SW1 (Pin 4): Regulator 1 Switch Node Connection to the
Inductor. This pin swings from VIN to GND.

GND (Pin 5): Main Ground. Connect to the (–) terminal of
C

, and (–) terminal of CIN.

OUT

MODE/SYNC (Pin 6): Combination Mode Selection and
Oscillator Synchronization. This pin controls the operation
of the device. When tied to VIN or GND, Burst Mode
operation or pulse skipping mode is selected, respec­tively. Do not float this pin. The oscillation frequency can

IN

be synchronized to an external oscillator applied to this pin
and pulse skipping mode is automatically selected.

SW2 (Pin 7): Regulator 2 Switch Node Connection to the
Inductor. This pin swings from VIN to GND.

POR (Pin 8): Power-On Reset . This common-drain logic
output is pulled to GND when the output voltage falls
below –8.5% of regulation and goes high after 117ms
when both channels are within regulation.

RUN2 (Pin 9): Regulator 2 Enable. Forcing this pin to V
enables regulator 2, while forcing it to GND causes regu­lator 2 to shut down. This pin must be driven; do not float.

V

(Pin 10): Output Feedback. Receives the feedback

FB2

voltage from the external resistive divider across the
output. Nominal voltage for this pin is 0.6V.

Exposed Pad (GND) (Pin 11): Power Ground. Connect to
the (–) terminal of C
connected to electrical ground on PCB.

, and (–) terminal of CIN. Must be

OUT

IN

3548f

5