Linear Technology LTC3412EFE Datasheet

FEATURES

LTC3412

2.5A, 4MHz, Monolithic

Synchronous Step-Down Regulator

U

DESCRIPTIO

■

High Efficiency: Up to 95%

■

2.5A Output Current

■

Low Quiescent Current: 62µA

■

Low R

■

Programmable Frequency: 300kHz to 4MHz

■

No Schottky Diode Required

■

±2% Output Voltage Accuracy

■

0.8V Reference Allows Low Output Voltage

■

Selectable Forced Continuous/Burst Mode Operation

Internal Switches: 85mΩ

DS(ON)

with Adjustable Burst Clamp

■

Synchronizable Switching Frequency

■

Low Dropout Operation: 100% Duty Cycle

■

Power Good Output Voltage Monitor

■

Overtemperature Protection

■

Available in 16-Lead Thermally Enhanced TSSOP
Package

U

APPLICATIO S

■

Portable Instruments

■

Battery-Powered Equipment

■

Notebook Computers

■

Distributed Power Systems

■

Cellular Telephones

■

Digital Cameras

The LTC®3412 is a high efficiency monolithic synchro­nous, step-down DC/DC converter utilizing a constant
frequency, current mode architecture. It operates from an
input voltage range of 2.625V to 5.5V and provides an
adjustable regulated output voltage from 0.8V to 5V while
delivering up to 2.5A of output current. The internal
synchronous power switch with 85mΩ on-resistance
increases efficiency and eliminates the need for an exter­nal Schottky diode. Switching frequency is set by an
external resistor or can be sychronized to an external
clock. 100% duty cycle provides low dropout operation
extending battery life in portable systems. OPTI-LOOP

®

compensation allows the transient response to be opti­mized over a wide range of loads and output capacitors.

The LTC3412 can be configured for either Burst Mode

®

operation or forced continuous operation. Forced con­tinuous operation reduces noise and RF interference while
Burst Mode operation provides high efficiency by reduc­ing gate charge losses at light loads. In Burst Mode
operation, external control of the burst clamp level allows
the output voltage ripple to be adjusted according to the
requirements of the application. To further maximize
battery life, the P-channel MOSFET is turned on continu­ously in dropout (100% duty cycle).

, LTC and LT are registered trademarks of Linear Technology Corporation.

Burst Mode and OPTI-LOOP are registered trademarks of Linear Technology Corporation.

TYPICAL APPLICATIO

V

IN

2.7V TO 5.5V

SVINPV

R

T

4.7M

470pF

15k

1000pF

Figure 1. 2.5V, 2.5A Step-Down Regulator

309k

100pF

RUN/SS

I

TH

SYNC/MODE

LTC3412

110k

75k

U

PGOOD

V

FB

IN

PGND
SGND

SW

392k

1µH

3412 F01

22µF

100µF

V

2.5V

2.5A

OUT

Efficiency vs Load Current

100

80

60

40

EFFICIENCY (%)

20

0

0.001

Burst Mode OPERATION

FORCED CONTINUOUS

0.1 10.01

LOAD CURRENT (A)

VIN = 3.3V

= 2.5V

V

OUT

10

3412 G01

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1

LTC3412

WW

W

ABSOLUTE AXI U RATI GS

U

UUW

PACKAGE/ORDER I FOR ATIO

(Note 1)

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

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

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

IN
IN

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

Peak SW Sink and Source Current ......................... 6.5A

Operating Ambient Temperature

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

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

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

ELECTRICAL CHARACTERISTICS

The ● denotes the specifications which apply over the full operating

TOP VIEW

1

SV

IN

2

PGOOD

3

I

TH

4

V

FB

5

R

T

SYNC/MODE

RUN/SS

EXPOSED PAD IS SGND (MUST BE SOLDERED TO PCB)

T

6
7
8

SGND

FE PACKAGE

16-LEAD PLASTIC TSSOP

= 125°C, θJA = 37.6°C/W, θJC = 10°C/W

JMAX

PV

16

IN

SW

15

SW

14

PGND

13

PGND

12

SW

11

SW

10

PV

9

IN

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

ORDER PART

NUMBER

LTC3412EFE

FE PART

MARKING

3412EFE

temperature range, otherwise specifications are at TA = 25°C. VIN = 3.3V unless otherwise specified.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

SV

IN

V

FB

I

FB

∆V

FB

V

LOADREG

∆V

PGOOD

R

PGOOD

I

Q

f

OSC

f

SYNC

R

PFET

R

NFET

I

LIMIT

V

UVLO

I

LSW

V

RUN

I

RUN

Signal Input Voltage Range 2.625 5.5 V
Regulated Feedback Voltage (Note 3) ● 0.784 0.800 0.816 V
Voltage Feedback Leakage Current 0.1 0.4 µA
Reference Voltage Line Regulation VIN = 2.7V to 5.5V (Note 3) ● 0.04 0.2 %/V
Output Voltage Load Regulation Measured in Servo Loop, V

Measured in Servo Loop, V

= 0.36V ● 0.02 0.2 %

ITH

= 0.84V ● –0.02 –0.2 %

ITH

Power Good Range ±7.5 ±9%
Power Good Pull-Down Resistance 120 200 Ω
Input DC Bias Current (Note 4)

Active Current V

= 0.78V, V

FB

Sleep VFB = 1V, V
Shutdown V

Switching Frequency R

RUN
OSC

= 0V, V
= 309kΩ 0.88 0.95 1.1 MHz

= 1V 250 330 µA

ITH

= 0V 62 80 µA

ITH

= 0V 0.02 1 µA

MODE

Switching Frequency Range (Note 6) 0.3 4 MHz
SYNC Capture Range (Note 6) 0.3 4 MHz
R

of P-Channel FET ISW = 1A 85 110 mΩ

DS(ON)

R

of N-Channel FET ISW = –1A 65 90 mΩ

DS(ON)

Peak Current Limit 4 5.4 A
Undervoltage Lockout Threshold 2.375 2.500 2.625 V
SW Leakage Current V

= 0V, VIN = 5.5V 0.1 1 µA

RUN

RUN Threshold 0.5 0.65 0.8 V
RUN/SS Leakage Current 1 µA

Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.

Note 2: The LTC3412E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.

Note 3: The LTC3412 is tested in a feedback loop that adjusts V

to

FB

2

achieve a specified error amplifier output voltage (ITH).
Note 4: Dynamic supply current is higher due to the internal gate charge

being delivered at the switching frequency.
Note 5: T

dissipation as follows: LTC3412: T

is calculated from the ambient temperature TA and power

J

= TA + PD (37.6°C/W).

J

Note 6: 4MHz operation is guaranteed by design and not production tested.

sn3412 3412fs

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Efficiency vs Load CurrentEfficiency vs Load Current Efficiency vs Load Current

100

80

60

40

EFFICIENCY (%)

20

0

0.001

Burst Mode OPERATION

FORCED CONTINUOUS

0.1 10.01

LOAD CURRENT (A)

VIN = 3.3V

= 2.5V

V

OUT

10

3412 G01

100

90
80
70
60
50
40

EFFICIENCY (%)

30
20

V

OUT

1MHz

10

Burst Mode OPERATION

0

0.001

VIN = 3.3V VIN = 5V

= 2.5V

0.1 10.01

LOAD CURRENT (A)

3412 G02

LTC3412

100

90
80

VIN = 3.3V VIN = 5V

70
60
50
40

EFFICIENCY (%)

30
20
10

10

0

0.001

V

= 2.5V

OUT

1MHz
FORCED CONTINUOUS

0.1 10.01

LOAD CURRENT (A)

10

3412 G03

98

LOAD = 100mA

96

94

92

EFFICIENCY (%)

90

88

86

OUT

V

LOAD = 2.5A

V

= 2.5V

OUT

1MHz
Burst Mode OPERATION

2.55 3.05 3.55 4.05 4.55 5.05

20mV/DIV

LOAD = 1A

INPUT VOLTAGE (V)

3412 G04

Efficiency vs FrequencyEfficiency vs Input Voltage

97

96

95

94

EFFICIENCY (%)

93

VIN = 3.3V

= 2.5V

V

92

OUT

LOAD = 1A
Burst Mode OPERATION

91

300

800 1300 1800 2300 2800 3300 3800

0.47µH

1µH

2.2µH

FREQUENCY (kHz)

Load Step Transient Forced
ContinuousBurst Mode Operation

OUT

V

100mV/DIV

3412 G05

Load Regulation

0.02

0.00
–0.02
–0.04
–0.06

OUT

/V

–0.08

OUT

–0.10

%∆V

–0.12
–0.14
–0.16
–0.18

0.5 1 1.5 2 2.5

0

LOAD CURRENT (A)

Load Step Transient Burst Mode
Operation

OUT

V

100mV/DIV

VIN = 3.3V
V

= 2.5V

OUT

3412 G06

L

I

200mA/DIV

VIN = 3.3V, V
LOAD = 50mA

OUT

4µs/DIV

= 2.5V

3412 G07

L

I

1A/DIV

20µs/DIV

VIN = 3.3V, V
LOAD STEP = NO LOAD TO 2.5A

OUT

= 2.5V

3412 G08

L

I

1A/DIV

VIN = 3.3V, V
LOAD STEP = 50mA TO 2.5A

OUT

= 2.5V

20µs/DIV

3412 G09

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3

LTC3412

R

OSC

(kΩ)

50

150 250 350 450 550 650 750 850 950

FREQUENCY (kHz)

3412 G15

4500

4000

3500

3000

2500

2000

1500

1000

500

0

VIN = 3.3V

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Start-Up, Burst Mode Operation

OUT

V

1V/DIV

RUN

V

1V/DIV

L

I

1A/DIV

1ms/DIV

VIN = 3.3V, V
LOAD = 1Ω

OUT

= 2.5V

3412 G10

Reference Voltage
vs Temperature

0.7960
VIN = 3.3V

0.7955

0.7950

0.7945

0.7940

0.7935

0.7930

REFERENCE VOLTAGE (V)

0.7925

0.7920

–45 –25 –5 15 35 55 75 95 115 120

TEMPERATURE (°C)

3412 G11

Switch On-Resistance
vs Input Voltage

120

100

80

60

40

ON-RESISTANCE (mΩ)

20

0

2.5 3

Switch On-Resistance
vs Temperature Switch Leakage vs Input Voltage Frequency vs R

120

VIN = 3.3V

110
100

PFET ON-RESISTANCE

90
80
70
60

NFET ON-RESISTANCE

50

ON-RESISTANCE (mΩ)

40
30
20

–20 0 20 40 60 80 100 120

–40

TEMPERATURE (°C)

3412 G13

2.5

2.0

1.5

1.0

LEAKAGE CURRENT (nA)

SYNCHRONOUS SWITCH

0.5

0

2.5 3

3.5 4 4.5 5 5.5

INPUT VOLTAGE (V)

MAIN SWITCH

3412 G14

PFET ON-RESISTANCE

NFET ON-RESISTANCE

3.5 4 4.5 5

INPUT VOLTAGE (V)

3412 G12

OSC

4

Frequency vs Input Voltage

1050

R = 309k

1040

1030

1020

1010

FREQUENCY (kHz)

1000

990

3 3.5 4 4.5 5 5.5

2.5
INPUT VOLTAGE (V)

3412 G16

Switching Frequency
vs Temperature

1010

VIN = 3.3V

1008
1006
1004
1002
1000

998

FREQUENCY (kHz)

996
994
992
990

–20 0 20 40 60 80 100 120

–40

TEMPERATURE (°C)

3412 G17

DC Supply Current
vs Input Voltage

350

300

250

200

150

DC SUPPLY CURRENT (µA)

100

50

3 3.5 4 4.5 5 5.5

2.5

ACTIVE

SLEEP

INPUT VOLTAGE (V)

3412 G18

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INPUT VOLTAGE (V)

2.75

6.8

6.6

6.4

6.2

6.0

5.8

5.6

5.4

4.25 5.25

3412 G21

3.25 3.75

4.75

CURRENT LIMIT (A)

TYPICAL PERFOR A CE CHARACTERISTICS

Minimum Peak Inductor Current

DC Supply Current vs Temperature

350

VIN = 3.3V

300

250

200

150

100

SUPPLY CURRENT (µA)

50

0

–20 0 20 40 60 80 100 120

–40

ACTIVE

SLEEP

TEMPERATURE (°C)

3412 G19

vs Burst Clamp Voltage

4000

VIN = 3.3V

3500

3000

2500

2000

1500

1000

500

MINIMUM PEAK INDUCTOR CURRENT (mA)

0

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

0 0.1

BURST CLAMP VOLTAGE (V)

LTC3412

Current Limit vs Input Voltage

3412 G20

PI FU CTIO S

SVIN (Pin 1): Signal Input Supply. Decouple this pin to
SGND with a capacitor. Normally SVIN is equal to PVIN.
SVIN can be greater than PVIN but keep the voltage
difference between SVIN and PVIN less than 0.5V.

PGOOD (Pin 2): Power Good Output. Open-drain logic
output that is pulled to ground when the output voltage is
not within ±7.5% of regulation point.

ITH (Pin 3): Error Amplifier Compensation Point. The
current comparator threshold increases with this control
voltage. Nominal voltage range for this pin is from 0.2V to

1.4V with 0.2V corresponding to the zero-sense voltage
(zero current).

VFB (Pin 4): Feedback Pin. Receives the feedback voltage
from a resistive divider connected across the output.

RT (Pin 5): Oscillator Resistor Input. Connecting a resistor
to ground from this pin sets the switching frequency.

SYNC/MODE (Pin 6): Mode Select and External Clock
Synchronization Input. To select forced continuous, tie to
SVIN. Connecting this pin to a voltage between 0V and 1V
selects Burst Mode operation with the burst clamp set to
the pin voltage.

UUU

RUN/SS (Pin 7): Run Control and Soft-Start Input. Forcing
this pin below 0.5V shuts down the LTC3412. In shutdown
all functions are disabled drawing < 1µA of supply current.
A capacitor to ground from this pin sets the ramp time to
full output current.

SGND (Pin 8): Signal Ground. All small-signal compo­nents, compensation components and the exposed pad
on the bottom side of the IC should connect to this ground,
which in turn connects to PGND at one point.

PVIN (Pins 9, 16): Power Input Supply. Decouple this pin
to PGND with a capacitor.

SW (Pins 10, 11, 14, 15): Switch Node Connection to the
Inductor. This pin connects to the drains of the internal
main and synchronous power MOSFET switches.

PGND (Pins 12, 13): Power Ground. Connect this pin
close to the (–) terminal of CIN and C

OUT

.

sn3412 3412fs

5

LTC3412

UU

W

FU CTIO AL BLOCK DIAGRA

SGND

VOLTAGE

REFERENCE

0.8V

SV

IN

1

+

4

V

FB

0.74V

–

+

ERROR
AMPLIFIER

SYNC/MODE

–

+

RUNRUN/SS

7

0.86V

–

I

TH

3

+
–

–

+

OSCILLATOR

BCLAMP

BURST
COMPARATOR

SLOPE

COMPENSATION

RECOVERY

LOGIC

PMOS CURRENT
COMPARATOR

+

–

SLOPE

COMPENSATION

+

98

P-CH

N-CH

PV

IN

16

10

11

SW

14

15

PGOOD

2

NMOS

CURRENT

COMPARATOR

–

–

REVERSE

CURRENT

COMPARATOR

5

R

T

6

SYNC/MODE

+

3412 FBD

12

PGND

13

6

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