Linear Technology LTC1707 Datasheet

LTC1707

Final Electrical Specifications

High Efficiency Monolithic

Synchronous Step-Down

Switching Regulator

FEATURES

■

600mA Output Current (VIN ≥ 4V)

■

High Efficiency: Up to 96%

■

Constant Frequency: 350kHz Synchronizable
to 550kHz

■

2.85V to 8.5V VIN Range

■

0.8V Feedback Reference Allows Low Voltage
Outputs: 0.8V ≤ V

■

No Schottky Diode Required

■

1.19V ±1% Reference Output Pin

■

Selectable Burst ModeTM Operation/Pulse

OUT

≤ V

IN

Skipping Mode

■

Low Dropout Operation: 100% Duty Cycle

■

Precision 2.7V Undervoltage Lockout

■

Current Mode Control for Excellent Line and
Load Transient Response

■

Low Quiescent Current: 200µA

■

Shutdown Mode Draws Only 15µA Supply Current

■

Available in 8-Lead SO Package

U

APPLICATIO S

■

Cellular Telephones

■

Portable Instruments

■

Wireless Modems

■

RF Communications

■

Distributed Power Systems

■

Single and Dual Cell Lithium

U

December 1999

DESCRIPTIO

The LTC®1707 is a high efficiency monolithic current
mode synchronous buck regulator using a fixed frequency
architecture. The operating supply range is from 8.5V
down to 2.85V, making it suitable for both single and dual
lithium-ion battery-powered applications. Burst Mode op­eration provides high efficiency at low load currents.
100% duty cycle provides low dropout operation, extend­ing operating time in battery-powered systems.

The switching frequency is internally set at 350kHz,
allowing the use of small surface mount inductors. For
noise sensitive applications it can be externally synchro­nized up to 550kHz. Burst Mode operation is inhibited
during synchronization or when the SYNC/MODE pin is
pulled low preventing low frequency ripple from interfer­ing with audio circuitry. Soft-start is provided by an
external capacitor.

The internal synchronous MOSFET switch increases effi­ciency and eliminates the need for an external Schottky
diode, saving components and board space. Low output
voltages down to 0.8V are easily achieved due to the 0.8V
internal reference. The LTC1707 comes in an 8-lead SO
package.

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

Burst Mode is a trademark of Linear Technology Corporation.

TYPICAL APPLICATIO

V

*

IN

3V TO

+

8.5V

22µF
16V

Figure 1a. High Efficiency Low Dropout Step-Down Converter

47pF

6

V

IN

2

RUN

7

SYNC/MODE

1

I

TH

LTC1707

GND

4

SW

V

REF

V

FB

U

15µH

5

8

3

*V

OUT

3V < VIN < 3.3V

+

249k

80.6k

FOLLOWS VIN FOR

100µF

6.3V

V

OUT

3.3V

1707 F01a

100

V

OUT

95

90

85

EFFICIENCY (%)

80

75

70

1

= 3.3V

10 100 1000

OUTPUT CURRENT (mA)

Figure 1b. Efficiency vs Output Load Current

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.

VIN = 3.6V

= 6V

V

IN

VIN = 8.4V

1707 F01b

1

LTC1707

WWWU

ABSOLUTE AXI U RATI GS

PACKAGE/ORDER I FOR ATIO

UU

W

(Note 1)

Input Supply Voltage ................................ –0.3V to 10V

I

Voltage ................................................. –0.3V to 5V

TH

RUN/SS, VFB Voltages ............................... – 0.3V to V

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

IN
IN

P-Channel Switch Source Current (DC) .............. 800mA

N-Channel Switch Sink Current (DC) .................. 800mA

Peak SW Sink and Source Current ......................... 1.5A

Operating Ambient Temperature Range

Commercial ............................................ 0°C to 70°C

I

RUN/SS

V

GND

TOP VIEW

1

TH

2

3

FB

4

S8 PACKAGE

8-LEAD PLASTIC SO

T

= 125°C, θJA = 110°C/ W

JMAX

8

V
SYNC/MODE

7

V

6

SW

5

REF

IN

ORDER PART

NUMBER

LTC1707CS8
LTC1707IS8

S8 PART MARKING

1707
1707I

Industrial ........................................... –40°C to 85°C

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

Consult factory for Military grade parts.

Storage Temperature Range ................ –65°C to 150°C

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

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifications are at TA = 25°C. V

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

I

VFB

V

FB

∆V

OVL

∆V

FB

V

LOADREG

I

S

V

RUN/SS

I

RUN/SS

I

SYNC/MODE

f

OSC

V

UVLO

R

PFET

R

NFET

I

PK

I

LSW

V

REF

∆V

REF

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

Note 2: T
dissipation P

TJ = TA + (PD • 110°C/W)

Feedback Current (Note 3) 6 60 nA
Regulated Feedback Voltage (Note 3) ● 0.78 0.80 0.82 V
Output Overvoltage Lockout ∆V
Reference Voltage Line Regulation VIN = 3V to 8.5V (Note 3) 0.002 0.01 %/V
Output Voltage Load Regulation ITH Sinking 2µA (Note 3) 0.5 0.8 %

Input DC Bias Current (Note 4)

Pulse Skipping Mode VIN = 8.5V, V
Burst Mode Operation V
Shutdown V

Shutdown V
Run/SS Threshold V
Soft-Start Current Source V
SYNC/MODE Pull-Up Current V
Oscillator Frequency V

Undervoltage Lockout VIN Ramping Down from 3V (0°C to 70°C) 2.55 2.70 2.85 V

R

of P-Channel FET ISW = –100mA 0.5 0.7 Ω

DS(ON)

R

of N-Channel FET ISW = –100mA 0.6 0.8 Ω

DS(ON)

Peak Inductor Current VIN = 4V, ITH = 1.4V, Duty Cycle < 40% 0.70 0.915 1.10 A
SW Leakage V
Reference Output Voltage I
Reference Output Load Regulation 0V ≤ I

is calculated from the ambient temperature TA and power

J

according to the following formula:

D

I

TH

ITH
RUN/SS
RUN/SS

RUN/SS
RUN/SS
SYNC/MODE
FB

V

FB

V

IN

VIN Ramping Down from 3V (–40°C to 85°C) 2.45 2.70 2.85 V
V

IN

RUN/SS

REF

The ● denotes specifications which apply over the full operating

= 5V unless otherwise specified.

IN

= V

OVL

Sourcing 2µA (Note 3) –0.5 –0.8 %

= 0V, VIN = 8.5V, V

= 0.7V 315 350 385 kHz
= 0V 35 kHz

Ramping Up from 0V (0°C to 70°C) 2.60 2.80 3.00 V

Ramping Up from 0V (–40°C to 85°C) 2.50 2.80 3.00 V

= 0µA ● 1.178 1.19 1.202 mV

– V

OVL

FB

= 3.3V, V

OUT

= 0V, 3V < VIN < 8.5V 11 35 µA
= 0V, VIN < 3V 6 µA

Ramping Positive 0.4 0.7 1.0 V
= 0V 1.2 2.25 3.3 µA

= 0V 0.5 1.5 2.5 µA

= 0V ±10 ±1000 nA

≤ 100µA ● 2.3 15 mV

REF

SYNC/MODE

SYNC/MODE

Note 3: The LTC1707 is tested in a feedback loop that servos V
balance point for the error amplifier (V

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

= 0V 300 µA

= Open 200 320 µA

20 60 110 mV

to the

= 0.8V).

ITH

FB

2

INPUT VOLTAGE (V)

2.5

4

SUPPLY CURRENT IN SHUTDOWN (µA)

6

10

12

14

6.5

22

1707 G06

8

4.5

3.5

7.5

5.5 8.5

16

18

20

V

RUN/SS

= 0V

T

J

= 85°C

TJ = 25°C

TJ = –40°C

UW

TYPICAL PERFOR A CE CHARACTERISTICS

LTC1707

Efficiency vs Input Voltage

100

95

90

85

EFFICIENCY (%)

80

V

OUT

L = 15µH
Burst Mode OPERATION

75

0

I

LOAD

= 2.5V

2

I

= 100mA

LOAD

I

LOAD

= 10mA

6

4

INPUT VOLTAGE (V)

Undervoltage Lockout Threshold
vs Temperature

3.00

2.95

2.90

2.85

2.80

2.75

2.70

2.65

2.60

2.55

UNDERVOLTAGE LOCKOUT THRESHOLD (V)

2.50
–50 –25

V

IN

RAMPING UP

V

IN

RAMPING DOWN

0 25 50 125

TEMPERATURE (°C)

75 100

= 300mA

8

1707 G04

1707 G01

10

Efficiency vs Load Current

100

95

Burst Mode

90

OPERATION
85
80
75
70

EFFICIENCY (%)

65
60
55
50

1

PULSE SKIPPING
MODE

10 100 1000

OUTPUT CURRENT (mA)

DC Supply Current
vs Input Voltage

350

300

250

200

150

100

DC SUPPLY CURRENT (µA)

TJ = 25°C

50

V

OUT

LOAD CURRENT = 0A

0

2.5

PULSE SKIPPING

= 1.8V

4.5

3.5
INPUT VOLTAGE (V)

MODE

Burst Mode

OPERATION

VIN = 3.6V

= 2.5V

V

OUT

L = 15µH

1707 G02

5.5 8.5

6.5

7.5

1707 G05

Efficiency vs Load Current

100

95

90

85

EFFICIENCY (%)

80

75

70

1

VIN = 7.2V

V

OUT

L = 15µH
Burst Mode OPERATION

10 100 1000

OUTPUT CURRENT (mA)

Supply Current in Shutdown
vs Input Voltage

VIN = 2.8V

VIN = 3.6V

= 2.5V

1707 G03

Reference Voltage
vs Temperature

1.200
VIN = 5V

1.195

1.190

1.185

REFERENCE VOLTAGE (V)

1.180

–50 –25

0 25 50 125

TEMPERATURE (°C)

75 100

1707 G07

Oscillator Frequency
vs Temperature

390

VIN = 5V

380

370

360

350

340

330

320

OSCILLATOR FREQUENCY (kHz)

310

300

–50 –25

0 25 50 125

TEMPERATURE (°C)

75 100

1707 G08

Oscillator Frequency
vs Input Voltage

390

380

370

360

350

340

330

320

OSCILLATOR FREQUENCY (kHz)

310

300

2.5

4.5

3.5
INPUT VOLTAGE (V)

5.5 8.5

6.5

7.5

1627 G09

3

LTC1707

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Maximum Output Current vs
Input Voltage

1000

V

= 1.8V

800

600

400

OUTPUT CURRENT (mA)

200

OUT

= 1.5V

V

OUT

V

= 3.3V

V

OUT

V

= 2.5V

OUT

V

= 2.9V

OUT

0

2.5

4.5

3.5
INPUT VOLTAGE (V)

5.5 8.5

OUT

= 5V

6.5

TJ = 85°C
L = 15µH

7.5

1707 G10

Switch Leakage Current
vs Temperature

1800

VIN = 8.4V

1600

1400

1200

1000

800

600

SWITCH LEAKAGE (nA)

400

200

0

–50 –25

0 25 50 125

TEMPERATURE (°C)

SYNCHRONOUS

Switch Resistance
vs Input Voltage Load Step Transient Response

0.9

0.8

0.7

0.6

0.5

0.4

0.3

SWITCH RESISTANCE (Ω)

0.2

0.1

MAIN SWITCH

0

2.5

4.5

3.5
INPUT VOLTAGE (V)

SYNCHRONOUS SWITCH

5.5 8.5

6.5

7.5

1707 G13

I

0.5V/DIV

V

OUT

50mV/DIV

AC COUPLED

I

LOAD

500mA/DIV

TH

FIGURE 1A VIN = 5V FIGURE 1A I

25µs/DIV

SWITCH

SWITCH

75 100

MAIN

1707 G11

1707 G14

0.9

0.8

0.7

0.6

0.5

0.4

0.3

SWITCH RESISTANCE (Ω)

0.2

0.1

SW

5V/DIV

V

OUT

20mV/DIV

AC COUPLED

I

LOAD

200mA/DIV

Switch Resistance
vs Temperature

VIN = 5V

SYNCHRONOUS

SWITCH

0

–50 –25

0 25 50 125

TEMPERATURE (°C)

Burst Mode Operation

10µs/DIV

MAIN
SWITCH

75 100

VIN = 5V

= 50mA

LOAD

1707 G12

1707 G15

4

LTC1707

U

UU

PI FU CTIO S

I

(Pin 1): Error Amplifier Compensation Point. The

TH

current comparator threshold increases with this control
voltage. Nominal voltage range for this pin is 0V to 1.2V.

RUN/SS (Pin 2): Combination of Soft-Start and Run
Control Inputs. A capacitor to ground at this pin sets the
ramp time to full current output. The time is approximately

0.5s/µF. Forcing this pin below 0.4V shuts down the
LTC1707.

VFB (Pin 3): Feedback Pin. Receives the feedback voltage
from an external resistive divider across the output.

GND (Pin 4): Ground Pin.
SW (Pin 5): Switch Node Connection to Inductor. This pin

connects to the drains of the internal main and synchro­nous power MOSFET switches.

U

U

W

FU CTIO AL DIAGRA

VIN (Pin 6): Main Supply Pin. Must be closely decoupled

to GND, Pin 4.

SYNC/MODE (Pin 7):

This pin performs two functions:

1) synchronize with an external clock and 2) select be­tween two modes of low load current operation. To
synchronize with an external clock, apply a TTL/CMOS
compatible clock with a frequency between 385kHz and
550kHz. To select Burst Mode operation, float the pin or
tie it to VIN. Grounding Pin 7 forces pulse skipping mode
operation.

V

(Pin 8): The Output of a 1.19V ±1% Precision

REF

Reference. May be loaded up to 100µA and is stable with
up to 2000pF load capacitance.

SYNC/MODE

7

V

FB

3

V

REF

8

SHUTDOWN

V

IN

1.5µA

0.6V

V

IN

1.19V
REF

UVLO

TRIP = 2.7V

BURST

DEFEAT

–

+

Y = “0” ONLY WHEN X IS A CONSTANT “1”

Y

X

SLOPE

OSC

FREQ

SHIFT

V

IN

RUN/SS

2.25µA

2

COMP

0.8V

0.86V

+

EA

–

RUN/SOFT

START

+

OVDET

–

V

IN

–

EN

+

0.12V

I

1

TH

–

+

BURST

SLEEP

QRS

SWITCHING

Q

LOGIC

AND

BLANKING

CIRCUIT

V

0.4V

IN

–

+

I

COMP

ANTI-

SHOOT-THRU

I

RCMP

6

V

IN

6Ω

+

–

SW

5

GND

4

1707 BD

5