Linear Technology LTC3545EUD-1, LTC3545 Datasheet

LTC3545/LTC3545-1

1

35451fa

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

Triple 800mA Synchronous

Step-Down Regulator–2.25MHz

The LTC®3545/LTC3545-1 are triple, high efficiency,
monolithic synchronous buck regulators using a constant
frequency, current mode architecture. The regulators op­erate independently with separate run pins. The 2.25V to

5.5V input voltage range makes the LTC3545/LTC3545-1
well suited for single Li-Ion battery-powered applications.
Low ripple pulse skip mode or high effi ciency Burst Mode
operation is externally selectable. PWM pulse skip mode
operation provides very low output ripple voltage while
Burst Mode operation increases effi ciency at low output
loads.

Switching frequency is internally set to 2.25MHz, or the
switching frequency can be synchronized to an external
1MHz to 3MHz clock. Power good indicators easily allow
power on sequencing between the three regulators.

The internal synchronous switches increase effi ciency and
eliminate external Schottky diodes. Low output voltages are
supported with the 0.6V feedback reference voltage.

The LTC3545-1 replaces the SYNC/MODE function with a
third PGOOD pin and forces Burst Mode operation.

■

Three 800mA Outputs

■

High Effi ciency: Up to 95%

■

2.25V to 5.5V Input Voltage Range

■

Low Ripple (<20mV

P-P

) Burst Mode® Operation

I

Q

: 58μA

■

2.25MHz Constant Frequency Operation or

■

Synchronizable to External 1MHz to 3MHz Clock

■

Power Good Indicators Ease Supply Sequencing

■

0.6V Reference Allows Low Output Voltages

■

Current Mode Operation/Excellent Transient Response

■

Low Profi le 16-Lead 3mm × 3mm QFN Package

■

Smart Phones

■

Wireless and DSL Modems

■

Digital Still Cameras

■

Portable Instruments

■

Point of Load Regulation

High Effi ciency Triple Step-Down Converter with Power Sequencing

Effi ciency and Loss vs Load Current

L, LT, LTC, LTM 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 6580258, 5481178, 6127815, 6498466, 6611131.

3545 TA01

L1

1.5µH

C5

10µF

PGNDGNDA

C4 10µF

C6

20pF

R2
255k

R1

511k

C1

10µF

V

OUT1

1.8V

V

IN

2.25V TO 5.5V

RUN1

PGOOD1

RUN2

PGOOD2

RUN3

L2

1.5µH

R4
226k

C2
10µF

V

OUT2

1.2V

SW2

V

FB2

SYNC/MODE

SW1

V

FB1

VINPV

IN

LTC3545

GNDA PGND

R7
500k

C7

20pF

R3

226k

R8
500k

L3

1.5µH

R6
200k

C3
10µF

V

OUT3

1.5V

SW3

V

FB3

C8

20pF

R5

301k

LOAD CURRENT (A)

30

EFFICIENCY (%)

LOSS (W)

90

100

20

10

80

50

70

60

40

0.0001 0.01 0.1 1

3545 TA01b

0

0.001

1

0.1

0.01

0.0001

0.001

VIN = 2.5V
V

IN

= 3.6V

V

IN

= 4.2V

TA = 25°C
V

OUT

= 2V
Burst Mode OPERATION
f

OSC

= 2.25MHz

SINGLE CHANNEL

LTC3545/LTC3545-1

2

35451fa

ELECTRICAL CHARACTERISTICS

ABSOLUTE MAXIMUM RATINGS

Input Supply Voltage .................................... –0.3V to 6V

RUNx, PGOODx ..............................–0.3V to (V

IN

+ 0.3V)

V

FBx

, SYNC/MODE .........................–0.3V to (VIN + 0.3V)

SWx ...............................................–0.3V to (V

IN

+ 0.3V)

P-Switch Source Current (DC) (Note 8) ...................1.1A

(Note 1)

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

General Characteristics

V

IN

Input Voltage Range

●

2.25 5.5 V

V

FBx

Regulated Feedback Voltage (Note 5) TA = 25°C,

0°C ≤ T

A

≤ 85°C

●

0.592

0.588

0.6

0.6

0.608

0.612

V
V

ΔV

FBx

Reference Voltage Line Regulation (Note 5) VIN = 2.25V to 5.5V

●

0.08 0.15 %/V

V

LOADREG

Output Voltage Load Regulation (Note 6) 0.5 %

The ● denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at TA = 25°C. VIN = 3.6V unless otherwise noted. (Note 2)

N-Channel Sink Current (DC) (Note 8) .....................1.1A

Peak SW Sink and Source Current (Note 8) .............1.3A

Operating Temperature Range.................. –40°C to 85°C

Junction Temperature (Notes 3, 4)........................ 125°C

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

16 15 14 13

5 6 7 8

17

UD PACKAGE

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

TOP VIEW

9

10

11

12

4

3

2

1SW1

PGOOD1

RUN2

PGOOD2

V

FB2

V

FB3

RUN3

SYNC/MODE

GNDA

VINRUN1

V

FB1

SW2

PGND

PV

IN

SW3

T

JMAX

= 125°C, θJA = 68°C/W

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

16 15 14 13

5 6 7 8

TOP VIEW

17

UD PACKAGE

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

9

10

11

12

4

3

2

1SW1

PGOOD1

RUN2

PGOOD2

V

FB2

V

FB3

RUN3

PGOOD3

GNDA

VINRUN1

V

FB1

SW2

PGND

PV

IN

SW3

T

JMAX

= 125°C, θJA = 68°C/W

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

PIN CONFIGURATION

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

LTC3545EUD#PBF
LTC3545EUD-1#PBF

LTC3545EUD#TRPBF
LTC3545EUD-1#TRPBF

LCSR
LDDP

16-Lead (3mm × 3mm) Plastic QFN
16-Lead (3mm × 3mm) Plastic QFN

–40°C to 85°C
–40°C to 85°C

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/

ORDER INFORMATION

LTC3545 LTC3545-1

LTC3545/LTC3545-1

3

35451fa

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: The LTC3545/LTC3545-1 are 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: T

J

is calculated from the ambient temperature TA and power

dissipation P

D

according to the following formula:

T

J

= TA + (PD)(68°C/W)

This IC includes overtemperature protection that is intended to protect
the device during momentary overload conditions. Junction temperature
will exceed 125°C when overtemperature is active. Continuous operation
above the specifi ed maximum operating junction temperature may impair
device reliability.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

I

FB

Feedback Pin Leakage 80 nA

I

S

Input DC Bias Current Active Mode (Pulse Skip)
Burst Mode (All Regulators Sleeping)
Shutdown

VFB = 0.5V or V

OUT

= 90%, I

LOAD

= 0A,

2.25MHz, Three Regulators Enabled,

680

58

0.1

750

70

2.0

µA
µA
µA

f

OSC

Oscillator Frequency

●

1.8 2.25 2.7 MHz

f

SYNC

Synchronization Frequency LTC3545 Only

●

13MHz

V

RUN(HIGH)

RUNx Input High Voltage

●

1V

V

RUN(LOW)

RUNx Input Low Voltage

●

0.3 V

I

RUN

RUN Leakage Current ±0.1 ±1 µA

I

LSW

SWx Leakage V

RUN

= 0V, VSW = 0V or 5.5V, VIN = 5.5V ±0.1 ±1 µA

I

SYNC

SYNC Leakage V

RUNx

= 0V, V

SYNC

= 0V or 5.5V,

V

IN

= 5.5V

±0.1 ±1 µA

T

PGOOD

Power Good Threshold–Deviation From VFB
Steady State (0.6V)

V

FBx

Ramping Up

V

FBx

Ramping Down

–7.5

–10

%
%

R

PGOOD

Power Good Pull-Down On-Resistance I

PGD

= 50mA

●

14 50

Ω

MODE/SYNC Thresholds 0.93 V

Individual Regulator Characteristics

t

SS

Soft-Start Period VFB = 10% to 90% Fullscale 850 1100 µs

I

PK

Peak Switch Current Limit VFB < V

FBREG

, Duty Cycle < 35% 1 1.3 1.6 A

I

Q

Input DC Bias Current Active Mode (Pulse Skip)
Burst Mode Operation

VFB = 0.5V, I

LOAD

= 0A, 2.25MHz 310

31

µA
µA

R

PFET

R

DS(ON)

of P-Channel FET (Note 7) ISW = 100mA 0.35

Ω

R

NFET

R

DS(ON)

of N-Channel FET (Note 7) ISW = –100mA 0.35

Ω

V

UVLO

Undervoltage Lockout (High VCC to Low)

●

1.8 2.25 V

ELECTRICAL CHARACTERISTICS

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

A

= 25°C. VIN = 3.6V unless otherwise noted. (Note 3)

Note 4: This IC includes overtemperature protection that is intended

to protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature is active.
Continuous operation above the specifi ed maximum operating junction
temperature may impair device reliability.

Note 5: The LTC3545/LTC3545-1 are tested in a proprietary test mode that
connects V

FB

to the output of the error amplifi er.

Note 6: Load regulation is inferred by measuring the regulation loop gain.
Note 7: The QFN switch-on resistance is guaranteed by correlation to

water level measurements.
Note 8: Guaranteed by long-term current density limitations.

LTC3545/LTC3545-1

4

35451fa

Burst Mode Operation Effi ciency vs Supply Voltage

Supply Current vs Temperature
Burst Mode Operation

TYPICAL PERFORMANCE CHARACTERISTICS

V

REF

vs Temperature at 2.25V,

3.6V, 5.5V

Switching Frequency vs Supply
Voltage and Temperature Load Regulation, All Channels

TEMPERATURE (°C)

–50

0.585

V

REF

(V)

0.590

0.595

0.600

0.605

0.610

0.615

0 50 100

3545 G01

2.25V

3.6V

5.5V

SUPPLY VOLTAGE (V)

2

1.5

SWITCHING FREQUENCY (MHz)

2.0

2.5

3.0

34

3545 G02

56

f

OSC

= –40°C

f

OSC

= 0°C

f

OSC

= 25°C

f

OSC

= 80°C

LOAD CURRENT (mA)

0

0.6

0.8

1.2

600

3545 G03

0.4

0.2

200 400 800

0

–0.4

–0.2

1.0

V

OUT

ERROR (%)

CHANNEL 1
CHANNEL 2
CHANNEL 3

TA = 25°C
V

IN

= 3.6V
UNTESTED CHANNELS OFF
PULSE SKIP MODE

1µs/DIV

SW

2V/DIV

I

L

100mA/DIV

V

OUT

20mV/DIV

3545 G04

VIN = 3.6V
V

OUT

= 1.8V

I

LOAD

= 50mA

f

OSC

= 2.25MHz

SUPPLY VOLTAGE (V)

2

EFFICIENCY (%)

90

95

6

3545 G05

85

80

3

4

5

100

V

OUT

= 2V

T

A

= 25°C
CHANNEL 3, ALL OTHERS OFF
f

OSC

= 2.25MHz

I

LOAD

= 250mA

TEMPERATURE (°C)

–40

0

SUPPLY CURRENT (µA)

5

15

20

25

40

45

3545 G06

10

0

–20

60

20 80

30

35

40

VIN = 5.5V
V

IN

= 4.5V

V

IN

= 3.5V

V

IN

= 2.5V

TA = 25°C
V

FB3

= 0.625V

I

LOAD

= 0V

CHANNEL 3 ONLY

LTC3545/LTC3545-1

5

35451fa

TYPICAL PERFORMANCE CHARACTERISTICS

Channel 1 Load Step Response Channel 2 Load Step Response Channel 3 Load Step Response

Supply Current vs Temperature,
Pulse Skipping

Effi ciency vs Load Current,
Burst Mode Operation

Effi ciency vs Load Current,
Pulse Skipping Operation

TEMPERATURE (°C)

–40

150

SUPPLY CURRENT (µA)

200

250

300

350

450

–20

02040

3545 G07

60 80

400

TA = 25°C
V

FB3

= 0.625V

I

LOAD

= 0V

CHANNEL 3 ONLY

VIN = 5.5V
V

IN

= 4.5V

V

IN

= 3.5V

V

IN

= 2.5V

LOAD CURRENT (mA)

30

EFFICIENCY (%)

90

100

20

10

80

50

70

60

40

0.1 10 100 1000

3545 G08

0

1

VIN = 2.7V
V

IN

= 3.6V

V

IN

= 4.2V

TA = 25°C
V

OUT

= 1.8V
CHANNEL 3, OTHER CHANNELS OFF
f

OSC

= 2.25MHz

LOAD CURRENT (mA)

30

EFFICIENCY (%)

90

100

20

10

80

50

70

60

40

0.1 10 100 1000

3545 G09

0

1

VIN = 2.7V
V

IN

= 3.6V

V

IN

= 4.2V

TA = 25°C
V

OUT

= 1.8V
CHANNEL 3, OTHER CHANNELS OFF
f

OSC

= 2.25MHz

10µs/DIV

I

LOAD

500mA/DIV

I

L

500mA/DIV

V

OUT1

100mV/DIV

3545 G10

TA = 25°C
V

IN

= 3.6V

V

OUT

= 1.2V
LOAD STEP 0mA TO 600mA
Burst Mode OPERATION

10µs/DIV

I

LOAD

500mA/DIV

I

L

500mA/DIV

V

OUT2

100mV/DIV

3545 G11

TA = 25°C
V

IN

= 3.6V

V

OUT

= 1.5V
LOAD STEP 0mA TO 600mA
Burst Mode OPERATION

10µs/DIV

I

LOAD

500mA/DIV

I

L

500mA/DIV

V

OUT3

100mV/DIV

3545 G12

TA = 25°C
V

IN

= 3.6V

V

OUT

= 1.8V
LOAD STEP 0mA TO 600mA
Burst Mode OPERATION

LTC3545/LTC3545-1

6

35451fa

TYPICAL PERFORMANCE CHARACTERISTICS

Start-Up From Shutdown
Loaded

PFET R

DS(ON)

vs Supply Voltage PFET R

DS(ON)

vs Temperature

NFET R

DS(ON)

vs Supply Voltage

Start-Up From Shutdown
No Load Load Step Crosstalk

NFET R

DS(ON)

vs Temperature

200µs/DIV

I

SUPPLY

1A/DIV

RUNX

5V/DIV

V

OUT1

V

OUT2

V

OUT3

(ALL 1V/DIV)

3545 G13

TA = 25°C
V

IN

= 3.6V

I

LOAD

= 600mA, ALL CHANNELS

200µs/DIV

I

SUPPLY

50mA/DIV

V

OUT1

1V/DIV

V

OUT2

1V/DIV

V

OUT3

1V/DIV

3545 G14

TA = 25°C
V

IN

= 3.6V

I

LOAD

= 0, ALL CHANNELS

200µs/DIV

I

LOAD

CH1

50mA/DIV

V

OUT2

2mV/DIV

V

OUT3

2mV/DIV

V

OUT1

100mV/DIV

3545 G15

TA = 25°C
V

IN

= 3.6V
500mA LOAD STEP IN CHANNEL1
CHANNELS 2 AND 3 LOADED AT 400mA EACH

SUPPLY VOLTAGE (V)

2

0

R

DS(ON)

()

0.05

0.15

0.20

0.25

0.50

0.35

3

4

3545 G16

0.10

0.40

0.45

0.30

5

6

TA = 85°C
T

A

= 25°C

T

A

= –25°C

TEMPERATURE (°C)

–50

0

R

DS(ON)

()

0.05

0.15

0.20

0.25

0.50

0.35

0

3545 G17

0.10

0.40

0.45

0.30

50

100

VIN = 2.5V
V

IN

= 3.6V

V

IN

= 5.5V

SUPPLY VOLTAGE (V)

2

0

R

DS(ON)

()

0.05

0.15

0.20

0.25

0.50

0.35

3

4

3545 G18

0.10

0.40

0.45

0.30

5

6

TA = 85°C
T

A

= 25°C

T

A

= –25°C

TEMPERATURE (°C)

–50

0

R

DS(ON)

()

0.05

0.15

0.20

0.25

0.50

0.35

0

3545 G19

0.10

0.40

0.45

0.30

50

100

VIN = 2.5V
V

IN

= 3.6V

V

IN

= 5.5V