LINEAR TECHNOLOGY LT1616 Technical data

FEATURES

■

Wide Input Range: 3.6V to 25V

■

5V at 400mA from 7V to 25V Input

■

3.3V at 400mA from 4.7V to 25V Input

■

Fixed Frequency 1.4MHz Operation

■

Uses Tiny Capacitors and Inductors

■

Internally Compensated

■

Low Shutdown Current: <1µA

■

Low V

■

Tiny 6-Lead SOT-23 Package

Switch: 220mV at 300mA

CESAT

U

APPLICATIO S

■

Wall Transformer Regulation

■

Local Logic Supply Conversion:

12V to 5V
12V or 5V to 3.3V, 2.5V or 1.8V

■

Distributed Supply Regulation

■

Digital Cameras

■

Battery-Powered Equipment

LT1616

600mA, 1.4MHz Step-Down

Switching Regulator

in SOT-23

U

DESCRIPTIO

The LT®1616 is a current mode PWM step-down DC/DC
converter with internal 0.6A power switch, packaged in a
tiny 6-lead SOT-23. The wide input range of 3.6V to 25V
makes the LT1616 suitable for regulating a wide variety of
power sources, from 4-cell batteries and 5V logic rails to
unregulated wall transformers and lead-acid batteries. Its
high operating frequency allows the use of tiny, low cost
inductors and ceramic capacitors. With its internal com­pensation eliminating additional components, a complete
400mA step-down regulator fits onto 0.15 square inches
of PC board area.

The constant frequency current mode PWM architecture
and stable operation with ceramic capacitors results in
low, predictable output ripple. Current limiting provides
protection against shorted outputs. The low current (<1µ A)
shutdown provides complete output disconnect, enabling
easy power management in battery-powered systems.

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

TYPICAL APPLICATIO

3.3V Step-Down Converter

V

4.5V TO 25V

OFF ON

IN

5

V

IN

LT1616

4

SHDN SW

GND FB

23

C1
1µF

C1: TAIYO-YUDEN TMK316BJ105
C2: TAIYO-YUDEN JMK316BJ106ML
D1: ON SEMICONDUCTOR MBR0530
D2: 1N4148
L1: SUMIDA CR43-100

BOOST

1

6

R1

16.5k

R2
10k

U

C3

0.01µF

D1

Efficiency

D2

L1

10µH

V

OUT

3.3V
300mA: V
400mA: V

C2
10µF

1616 TA01

= 4.5V TO 25V

IN

= 4.7V TO 25V

IN

100

90

80

70

60

EFFICIENCY (%)

50

40

30

0

VIN = 5V

100 200 500

LOAD CURRENT (mA)

VIN = 12V

VIN = 20V

300 400

1616 G02

1

LT1616

PACKAGE/ORDER I FOR ATIO

UU

W

BOOST 1

GND 2

FB 3

6 SW
5 V

IN

4 SHDN

TOP VIEW

S6 PACKAGE

6-LEAD PLASTIC SOT-23

WWWU

ABSOLUTE AXI U RATI GS

(Note 1)

Input Voltage (VIN) ................................................. 25V

BOOST Pin Voltage ................................................. 35V

ORDER PART

NUMBER

BOOST Pin Above SW Pin ...................................... 25V

SHDN Pin ............................................................... 25V

LT1616ES6

FB Voltage ................................................................ 6V

Current Into FB Pin ...............................................±1mA

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

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

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

T

= 125°C, θJA = 250°C/ W

JMAX

S6 PART MARKING

LTNB

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

Consult factory for parts specified with wider operating temperature ranges.

ELECTRICAL CHARACTERISTICS

The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
VIN = 10V, V

= 15V, unless otherwise noted. (Note 2)

BOOST

PARAMETER CONDITIONS MIN TYP MAX UNITS

Undervoltage Lockout 3.35 3.6 V
Feedback Voltage ● 1.225 1.25 1.275 V
FB Pin Bias Current VFB = Measured V
Quiescent Current Not Switching 1.9 2.5 mA
Quiescent Current in Shutdown V
Reference Line Regulation VIN = 5V to 25V 0.005 %/V
Switching Frequency VFB = 1.1V ● 1 1.4 1.8 MHz
Frequency Shift Threshold on FB Pin fSW = 700kHz 0.44 V
Maximum Duty Cycle ● 80 87 %
Switch Current Limit (Note 3) 630 850 mA
Switch V

CESAT

Switch Leakage Current 10 µA
Minimum Boost Voltage Above Switch ISW = 300mA 1.6 2.5 V
BOOST Pin Current ISW = 300mA 7 12 mA
SHDN Input Voltage High 1.8 V
SHDN Input Voltage Low 0.4 V
SHDN Bias Current V

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

Note 2: The LT1616E 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.

= 0V 0.01 2 µA

SHDN

ISW = 300mA 220 350 mV

= 3V 8 15 µA

SHDN

= 0V 0.01 0.1 µA

V

SHDN

+ 10mV ● 150 600 nA

REF

Note 3: Current limit guaranteed by design and/or correlation to static test.
Slope compensation reduces current limit at higher duty cycle.

2

UW

TYPICAL PERFOR A CE CHARACTERISTICS

LT1616

Efficiency, V

100

90

80

70

60

EFFICIENCY (%)

50

40

30

0

VIN = 8V

VIN = 24V

100 200 500

LOAD CURRENT (mA)

Maximum Load Current
at V

= 5V BOOST Pin Current

OUT

500

L = 15µH

400

300

LOAD CURRENT (mA)

200

100

5

0

INPUT VOLTAGE (V)

OUT

10

= 5V

L = 6.8µH

300 400

L = 10µH

OUTPUT LIMITED

BY DISSIPATION

15

VIN = 12V

20

1616 G01

1616 G04

Efficiency, V

100

90

80

70

60

EFFICIENCY (%)

50

40

30

0

100 200 500

= 3.3V Switch Voltage Drop

OUT

VIN = 5V

LOAD CURRENT (mA)

VIN = 12V

VIN = 20V

300 400

1616 G02

500

400

300

200

SWITCH VOLTAGE (mV)

100

0

0

200 400

SWITCH CURRENT (mA)

600

1616 G03

Maximum Load Current
at V

= 3.3V

OUT

500

L = 10µH

400

300

LOAD CURRENT (mA)

200

100

25

0

L = 4.7µH

5

10

INPUT VOLTAGE (V)

OUTPUT LIMITED

BY DISSIPATION

15

20

25

1616 G05

16

14

12

10

8

6

4

BOOST PIN CURRENT (mA)

2

0

0

200 400

SWITCH CURRENT (mA)

600

1616 G06

Switch Current Limit

1000

800

600

400

200

SWITCH CURRENT LIMIT (mA)

0

20

0

TYPICAL

40

DUTY CYCLE (%)

MINIMUM

60

Feedback Pin Voltage

1.27

1.26

1.25

1.24

FEEDBACK PIN VOLTAGE (V)

1.23

1.22

80

100

1616 G07

–50

02550

–25

TEMPERATURE (°C)

75 100

1616 G08

Undervoltage Lockout

3.7

3.6

3.5

3.4

3.3

UNDERVOLTAGE LOCKOUT (V)

3.2

3.1
–50

02550

–25

TEMPERATURE (°C)

75 100

1616 G11

3

LT1616

SHDN PIN VOLTAGE

0

0

SHDN PIN CURRENT (µA)

20

40

60

80

100

120

5101520

1616 G10

25

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Oscillator Frequency

2.00

1.75

1.50

1.25

1.00

0.75

0.50

SWITCHING FREQUENCY (MHz)

0.25

0

U

–25 0 50

–50

25

TEMPERATURE (°C)

UU

100

75

1616 G09

PI FU CTIO S

BOOST (Pin 1): The BOOST pin is used to provide a drive
voltage, higher than the input voltage, to the internal
bipolar NPN power switch.

GND (Pin 2): Tie the GND pin to a local ground plane below
the LT1616 and the circuit components. Return the feed­back divider to this pin.

FB (Pin 3): The LT1616 regulates its feedback pin to 1.25V.
Connect the feedback resistor divider tap to this pin. Set
the output voltage according to V
A good value for R2 is 10k.

= 1.25V (1 + R1/R2).

OUT

SHDN Pin Current

SHDN (Pin 4): The SHDN pin is used to put the LT1616 in

shutdown mode. Tie to ground to shut down the LT1616.
Tie to 2V or more for normal operation. If the shutdown
feature is not used, tie this pin to the VIN pin.

VIN (Pin 5): The VIN pin supplies current to the LT1616’s
internal regulator and to the internal power switch. This pin
must be locally bypassed.

SW (Pin 6): The SW pin is the output of the internal power
switch. Connect this pin to the inductor, catch diode and
boost capacitor.

4

BLOCK DIAGRA

5

V

IN

INT REG

4

SHDN

AND

UVLO

W

LT1616

BOOST

1

SLOPE

COMP

OSC

FREQUENCY
FOLDBACK

Σ

2

GND

R

S

V

C

g

m

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OPERATIO

The LT1616 is a constant frequency, current mode Buck
regulator. The 1.4MHz oscillator enables an RS flip-flop,
turning on the internal 600mA power switch Q1. An ampli­fier and comparator monitor the current flowing between
the VIN and SW pins, turning the switch off when this current
reaches a level determined by the voltage at VC. An error
amplifier measures the output voltage through an external
resistor divider tied to the FB pin. This amplifier servos the
switch current to regulate the FB pin voltage to 1.25V. An
active clamp on the VC node provides current limit.

An internal regulator provides power to the control cir­cuitry. This regulator includes an undervoltage lockout to
prevent switching when VIN is less than ~3.5V. The

(Refer to Block Diagram)

Q

Q

1.25V

3

1616BD

FB

DRIVER

Q1

SW

6

SHDN pin is used to place the LT1616 in shutdown,
disconnecting the output and reducing the input current
to less than 1µA.

The switch driver operates from either the input or from
the BOOST pin. An external capacitor and diode are used
to generate a voltage at the BOOST pin that is higher than
the input supply. This allows the driver to fully saturate the
internal bipolar NPN power switch for efficient operation.

The oscillator reduces the LT1616’s operating frequency
when the voltage at the FB pin is low. This frequency
foldback helps to control the output current during start­up and overload.

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