LINEAR TECHNOLOGY LT1612 Technical data

FEATURES

LT1612

Synchronous, Step-Down

800kHz PWM

DC/DC Converter

U

DESCRIPTIO

■

Operates from Input Voltage As Low As 2V

■

Internal 0.7A Synchronous Switches

■

Uses Ceramic Input and Output Capacitors

■

620mV Reference Voltage

■

800kHz Fixed Frequency Switching

■

Programmable Burst Mode Operation

■

Low Quiescent Current: 160µA

■

8-Lead MSOP or SO Package

U

APPLICATIO S

■

Portable Devices

■

Lithium-Ion Step-Down Converters

■

5V to 3.3V Conversion

■

2-Cell Alkaline Step-Down Converters

U

TYPICAL APPLICATION

The LT®1612 is an 800kHz, synchronous step-down DC/
DC converter that operates from an input voltage as low
as 2V. Internal 0.45Ω switches deliver output currents up
to 500mA, and the 800kHz switching frequency allows the
use of small, low value ceramic input and output capaci­tors. Input voltage ranges from 5.5V down to 2V and
output voltage can be set as low as the 620mV reference.
The device features Burst ModeTM operation, keeping
efficiency high at light loads. Burst Mode operation can be
defeated by pulling the MODE pin high, enabling constant
switching throughout the load range for low noise.

No-load quiescent current is 160µA and shutdown current
is less than 1µA. The device is available in 8-lead SO and
MSOP packages.

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

Burst Mode is a trademark of Linear Technology Corporation.

V

IN

2V

10µF

C1

V

IN

SHDN

LT1612

MODE

V

C

33.2k

330pF

C1: TAIYO-YUDEN JMK325BJ106MN
C2: PANASONIC EEFCDOF680R
L1: SUMIDA CD43-100

Figure 1. 2V to 1.2V Converter

BOOST

SW

GND

Efficiency for LT1612 vs Linear Regulator

V

= 1.2V

0.1µF

L1

10µH

100pF

FB

R1

215k

R2

232k

1%

1%

V

1.2V
500mA

C2
68µF

3.15V

OUT

1612 F01a

90

80

70

60

EFFICIENCY (%)

50

40

30

OUT

VIN = 2V

VIN = 3V

VIN = 2V (LINEAR)

VIN = 3V (LINEAR)

10010 500

LOAD CURRENT (mA)

1612 • F01b

sn1612 1612fs

1

LT1612

TOP VIEW

SHDN
MODE
BOOST
SW

V

C

FB

V

IN

GND

S8 PACKAGE

8-LEAD PLASTIC SO

1

2

3

4

8

7

6

5

WW

W

ABSOLUTE MAXIMUM RATINGS

U

(Note 1)

Supply Voltage (VIN)............................................... 5.5V

SW Pin Voltage....................................................... 5.5V

FB Pin Voltage ............................................... VIN + 0.3V

VC Pin Voltage ........................................................... 2V

SHDN Pin Voltage................................................... 5.5V

MODE Pin Voltage .................................................. 5.5V

U

W

PACKAGE/ORDER INFORMATION

ORDER PART

NUMBER

TOP VIEW

8

V

1

C

2

FB

3

V

IN

4

GND

MS8 PACKAGE

8-LEAD PLASTIC MSOP

T

= 125°C, θJA = 200°C/W

JMAX

7
6
5

SHDN
MODE
BOOST
SW

LT1612EMS8

MS8 PART MARKING

LTMS

BOOST Pin Voltage ....................................... VIN + 5.5V

Junction Temperature........................................... 125°C

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

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

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

U

ORDER PART

NUMBER

LT1612ES8

S8 PART MARKING

T

= 125°C, θJA = 120°C/W

JMAX

1612

Consult factory for parts specified with wider operating temperature ranges.

ELECTRICAL CHARACTERISTICS

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

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

I

Q

V

FB

g

m

f

OSC

2

Quiescent Current MODE = 5V ● 12 mA

FB Voltage 0.605 0.62 0.635 V

FB Line Regulation ● 0.02 0.15 %/V
FB Pin Bias Current (Note 3) ● 750 nA
Error Amplifier Transconductance 250 µmhos
Min Input Voltage 2V

Max Input Voltage 5.5 V
Oscillator Frequency 700 800 900 kHz

f

Line Regulation 1%/V

OSC

Maximum Duty Cycle 85 90 %

Shutdown Threshold Minimum Voltage for Active

The ● denotes specifications which apply over the full operating

= V

IN

MODE = 0V, Not Switching
SHDN = 0V ● 1 µA

Maximum Voltage for Shutdown ● 0.2 V

SHDN

= 3V

● 160 220 µA

● 0.60 0.62 0.635 V

● 550 1100 kHz

● 80 %

● 2V

sn1612 1612fs

LT1612

ELECTRICAL CHARACTERISTICS

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

The ● denotes specifications which apply over the full operating

IN

= V

SHDN

= 3V

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

SHDN Pin Current SHDN = 2V

● 10 15 µA

SHDN = 5V ● 30 45 µA

BOOST Pin Current BOOST = VIN + 2V 4 mA
Switch Current Limit (Note 4) Duty Cycle = 0% MODE = OV 600 710 900 mA

MODE = 5V 550 650 900 mA
Burst Mode Operation Current Limit MODE = 0V 180 mA
Switch Voltage Drop ISW = 500mA 200 280 mV
Rectifier Voltage Drop I
SW Pin Leakage VSW = 5V, V

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

Note 2: The LT1612E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating

= 500mA 300 400 mV

RECT

= 0V ● 1 µA

SHDN

temperature range are assured by design, characterization and correlation
with statistical process controls.

Note 3: Bias current flows out of the FB pin.
Note 4: Duty cycle affects current limit due to slope compensation.

UW

TYPICAL PERFOR A CE CHARACTERISTICS

FB Voltage vs Temperature

0.64

0.63

0.62

0.61

FB VOLTAGE (V)

0.60

0.59
–50

02550

–25

TEMPERATURE (°C)

75 100

1612 • G01

Quiescent Current vs Temperature

190

MODE = 0V

180

170

160

150

140

130

120

QUIESCENT CURRENT (µA)

110

100

–50 –25 25 75

0 100

TEMPERATURE (°C)

50

1612 • G02

FB Pin Bias Current

0
–2
–4
–6
–8

–10
–12
–14

FB PIN CURRENT (nA)

–16
–18
–20

–50

–25

25

0

TEMPERATURE (°C)

50 75

100

1612 • G03

sn1612 1612fs

3

LT1612

TEMPERATURE (°C)

–50

OSCILLATOR FREQUENCY (kHz)

1000

900

800

700

600

500

400

–25

02550

1612 • G06

75 100

RECTIFIER CURRENT (mA)

0

RECTIFIER VOLTAGE DROP (mV)

600

500

400

300

200

100

0

100

200 300 400

1612 • G09

500 600

UW

TYPICAL PERFOR A CE CHARACTERISTICS

SHDN Pin Bias Current

80

70

60

50

40

30

20

SHDN PIN CURRENT (µA)

10

0

12 4

0

SHDN PIN VOLTAGE (V)

Maximum Duty Cycle vs
Temperature

94

90

86

Switch Current Limit vs
Temperature

800

700

600

500

400

SWITCH CURRENT (mA)

300

3

5

1612 • G04

200

–50

MODE = 5V

02550

–25

TEMPERATURE (°C)

MODE = 0V

75 100

1612 • G05

Switch Voltage Drop

600

500

400

Oscillator Frequency vs
Temperature

Rectifier Voltage Drop

82

78

MAXIMUM DUTY CYCLE (%)

74

70

–50

02550

–25

TEMPERATURE (°C)

75 100

1612 • G07

300

200

SWITCH VOLTAGE DROP (mV)

100

0

0

200 300 400

100

SWITCH CURRENT (mA)

500 600

1612 • G08

4

sn1612 1612fs