Datasheet LT1309 Datasheet (Linear Technology)

LT1309

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



500kHz Micropower

DC/DC Converter

for Flash Memory

EATU

F

■

60mA Output Current at 12V from 3V or 5V Supply

■

Shutdown to 9µA

■

VPP VALID Comparator

■

Up to 85% Efficiency

■

Switching Frequency: 500kHz (Typical)

■

Quiescent Current: 650µA

■

Low V

■

Soft Start Reduces Supply Current Transients

■

Uses Low Value, Small Size,

S

RE

Switch: 300mV at 0.5A (Typical)

CESAT

Surface Mount Inductors

■

Available in 8-Lead SO Package

U

O

PPLICATI

A

■

Flash Memory VPP Generators

■

Type II and III PCMCIA Card DC/DC Converters

■

3V to 12V, 5V to 12V Converters

■

Portable Computers and Instruments

■

Cellular Telephones

■

DC/DC Converter Module Replacements

S

DUESCRIPTIO

The LT®1309 is a 500kHz micropower DC/DC converter
for Flash Memory. The regulator features Burst Mode
operation with a 0.5A, 300mV switch, enabling 85%
efficiency at the fixed 12V output. High frequency opera­tion permits the use of small value, and therefore small
size, surface mount inductors and capacitors. The LT1309
comes in an 8-lead SO package allowing extremely
compact PC board layouts. These features make the
device attractive for PCMCIA cards, cellular phones and
other applications where PC board space is limited.

Quiescent current is 650µA decreasing to 9µA when the
part shuts down. The device includes a soft start feature
which limits supply current transients during turn-on.

The LT1309 contains a VPP VALID comparator with a
logic output that goes low when the output voltage is
ready to program 12V Flash Memory. This comparator
simplifies the interface to external control logic.

Burst Mode is a trademark of Linear Technology Corporation.

TM

A

PPLICATITYPICAL

12V, 60mA Flash Memory Programming Supply 12V Output Efficiency

L1*



V

IN

3.3V TO 5V

VPP VALID

+

*

**

†

ON/OFF

C1

4.7µF

MURATA ERIE LQH3C100K0YM00
CERAMIC
MOTOROLA MBR0530

10µH

V

IN

VPP VALID

LT1309

ON/OFF

PGND GND

O

V

SENSE

SOFT

START

U

SW

R1
1M

D1

†





VPP 12V, 60mA

C3

0.1µF

LT1309 • TA01

C2
1µF**

86

84

82

80

78

76

EFFICIENCY (%)

74

72

70

1

VIN = 5V

VIN = 3.3V

10 100

LOAD CURRENT (mA)

LT1309 • TA02

1

LT13 09

WU

U

PACKAGE

/

O

RDER I FOR ATIO

W

O

A

LUTEXI T

S

VCC Voltage............................................................... 7V

VSW Voltage............................................................ 20V

V
V
V
I

Voltage ....................................................... 20V

SENSE

Voltage......................................................... 7V

ON/OFF

Voltage ............................................................. 7V

SEL

Voltage .............................................................. 7V

LIM

Maximum Power Dissipation ............................ 500mW

Operating Temperature Range .....................0°C to 70°C

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

A

WUW

ARB

U
G

I

S

SOFT START

V

PGND

V

TOP VIEW

1



2

CC

3

4

SW

S8 PACKAGE

8-LEAD PLASTIC SO

T

= 150°C, θJA = 150°C/W

JMAX

8

7

6

5

ON/OFF
SENSE
VPP VALID
GND

ORDER PART

NUMBER

LT1309CS8

S8 PART MARKING

1309

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

Consult factory for Industrial and Military grade parts.

LECTRICAL C CHARA TERIST

E

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

I

Q

f

OSC

DC Maximum Duty Cycle ● 80 85 92 %
t

ON

V

CESAT

Quiescent Current V
Quiescent Current, Shutdown V
Input Voltage Range 2 6 V
Output Sense Voltage ● 11.5 12 12.6 V
Output Referred Comparator Hysteresis 35 mV
Oscillator Frequency Current Limit Not Asserted 400 500 700 kHz

Switch ON Time 1.7 µs
Reference Line Regulation 2V < VIN < 6V 0.06 0.15 %/V
Switch Saturation Voltage ISW = 0.5A 230 350 mV
Switch Leakage Current VSW = 12V, Switch Off 0.1 10 µA
Switch Current Limit VIN = 5V, Soft Start Floating 400 600 900 mA

Soft Start Current Soft Start Grounded 80 120 µA
ON/OFF Input Voltage Low 0.8 V
ON/OFF Input Voltage High 1.6 V
ON/OFF Bias Current V

Sense Pin Input Current 50.0 90 µA

VPP VALID Threshold V
VPP VALID Output Voltage Low I
VPP VALID Output Voltage High I

ICS

TA = 25°C, VCC = 5V, V

= 12V 650 900 µA

SENSE

= 0.2V 9 15 µA

ON/OFF

= 3V, Soft Start Floating 450 650 950 mA

V

IN

= 5V 16.0 24.0 µA

ON/OFF

= 3V 8.0 14.0 µA

V

ON/OFF

= 0V 0.1 1.0 µA

V

ON/OFF

= 0.2V 0.1 1 µA

V

ON/OFF

Rising (High to Low Transition) V

SENSE

= 100µA 0.13 0.3 V

SINK

= 2.5µA 4 4.5 V

SOURCE

= 3V, unless otherwise noted.

ON/OFF

SENSE

– 200mV

The ● denotes specifications which apply over the full operating
temperature range.

2

W

TEMPERATURE (°C)

–50

100

SWITCH SATURATION VOLTAGE (mV)

125

150

175

200

250

–25

02550

1309 G03

75 100

225

ISW = 500mA

TEMPERATURE (°C)

–50

300

SUPPLY CURRENT (µA)

400

500

600

700

800

–25

02550

1309 G05

75 100

VCC = 5V
V

CC

= 3V

U

TYPICAL PERFORMANCE CHARACTERISTICS

LT1309

Oscillator Frequency

800

700

600

500

400

OSCILLATOR FREQUENCY (kHz)

300

–50

02550

–25

TEMPERATURE (°C)

Sense Voltage

12.20

12.15

12.10

12.05

12.00

11.95

SENSE VOLTAGE (V)

11.90

11.85

11.80
–25 0 50

–50

75 100

1309 G01

25

TEMPERATURE (°C)

Switch Current Limit

1000

900

800

700

600

SWITCH CURRENT (mA)

500

400

–50

–25

75

100

1309 G04

VCC = 3V

VCC = 5V

02550

TEMPERATURE (°C)

Switch Saturation Voltage

75 100

1309 G02

Supply Current

14

12

10

8



SUPPLY CURRENT (µA)

6

4

2

0

–50

Supply Current in Shutdown

VCC = 5V

VCC = 3V

50 100

–25 0

25 75

TEMPERATURE (°C)

1309 G06

Maximum Duty Cycle

95

90

85

80

MAXIMUM DUTY CYCLE (%)

75

70

–50

02550

–25

TEMPERATURE (°C)

75 100

1309 G07

3

LT13 09

W

U

TYPICAL PERFORMANCE CHARACTERISTICS

12V

V

OUT

2V/DIV

VPP VALID

10V/DIV

V

ON/OFF

10V/DIV

Start-Up Waveforms, I

50µs/DIV 1309 G08

= 1mA

LOAD

12V OUTPUT

AC COUPLED

I

LOAD

Load Transient Response,
C

OUT

1V/DIV

60mA
10mA

50µs/DIV 1309 G10

= 1µF

V

OUT

5V/DIV

500mA/DIV

V

ON/OFF

10V/DIV

Start-Up Waveforms, I

I

L

50µs/DIV 1309 G09

LOAD

= 10mA

UU U

PI FU CTIO S

SOFT START (Pin 1): A 0.1µ F/1MΩ parallel RC from this
pin to GND provides a Soft Start function upon device
turn-on. Initially about 80µ A will flow from the pin into the
capacitor. When the voltage at the pin reaches approxi­mately 0.4V, current ceases flowing out of the pin.

V

(Pin 2): Input Supply. At least 1µF input bypass

CC

capacitance is required. More capacitance reduces ring­ing on the supply line.

PGND (Pin 3): Power Ground. Connect to ground plane.
VSW (Pin 4): Collector of Power Switch. High dV/dt

present on this pin. To minimize radiated noise keep
layout short and direct.

GND (Pin 5): Signal Ground. Connect to ground plane.
VPP VALID (Pin 6): This pin provides a logic signal

indicating that output voltage has reached 12V. Active low
with internal 200k pull-up resistor.

SENSE (Pin 7): Output Sense Pin. This pin connects to a
resistive divider that sets the output voltage. In shutdown,
the resistor string is disconnected and current into this pin
reduces to < 1µA.

ON/OFF (Pin 8): Shutdown Control. When pulled below

1.5V, this pin disables the LT1309 and reduces supply
current to 9µ A. All circuitry is disabled in shutdown. The
part is enabled when ON/OFF is greater than 1.5V.

4

BLOCK DIAGRA

7

864k

4k

100k

W

ON/OFFSENSE

8

POWER ON

–

C2

+

–

C1

+

LT1309

V

CC

R2

700Ω

BIAS

2

R1
3Ω

SW

4

Q2
× 1

Q1
× 50

36mV

+

–

+

V

CC

200k

VPP VALID

6

OFF

500kHz

OSCILLATOR

C3

–

Q3

1

SOFT START

V

1.24V

REF

U

OPERATIO

The LT1309 is a current limited, Burst Mode (gated
oscillator) type switching regulator that produces a 12V
output from a 3.3V or 5V input. Operation can best be
understood by referring to the Block Diagram. When the
voltage at the Sense pin (Pin 7) is less than 12V, compara­tor C1 enables the oscillator, turning switches Q1 and Q2
on. The switch turns off when current limit is reached or
when the oscillator maximum on-time is reached. When

5 3

GND

PGND

1309 BD

Q2 turns off, current built up in the inductor flows into the
output capacitor and load. This action occurs until the
output voltage reaches 12V. During start-up, the Sense pin
voltage is either 3.3V or 5V, depending on the input. The
VPP VALID signal remains high until the output voltage
reaches 12V, signaling correct voltage level to program
flash memory. Connecting a 1µF/0.1µF parallel RC to the
Soft Start pin limits inrush current during start-up.

5

LT13 09

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APPLICATIONS INFORMATION

Inductor Selection

The low inductance value required with the LT1309 (10µH)
allows the use of very small units such as the Murata-Erie
LQH3C100. Requirements for the inductor include low
DCR, ability to perform efficiently at 500kHz and a satura­tion current rating of 700mA to 900mA. Often inductor
manufacturers rate maximum current for a small inductor
based on self-heating considerations. For use in switching
regulators where the inductor current is not constant the
maximum specified DC current can be safely exceeded.

Capacitor Selection

The LT1309 needs very little input and output capacitance
to function. Output capacitance should be 1µF or 2µF for
acceptable output ripple voltage. Flash memory tolerates
higher ripple voltage than might be suitable for a low noise
system. The capacitor can be either a single high capaci­tance ceramic unit such as Tokin 1E105ZY5U-203 or
Murata-Erie GRM230Y5V105Z016, or can be distributed
as 10 to 20 0.1µF ceramic units. Lower ripple can be

obtained by increasing the capacitance to the 5µ F to 10µ F
level. 2µF to 5µF of tantalum (low-Q) capacitance is
recommended on the input side to reduce resonance
effects which can otherwise cause hundreds of millivolts
of ripple voltage at the input.

Diode Selection

The LT1309’s high switching speed demands a high speed
rectifier. Schottky diodes are preferred for their low for­ward drop and fast recovery. A suitable choice is the
Motorola MBR0520. This is a 0.5A, 20V Schottky in a very
small package that is 1.35mm high.

PC Board Layout

The component placement shown in Figure 1 is recom­mended for PC board layouts. The high speed current
paths are kept to a minimum distance and the switch node
copper is minimized to keep radiated noise low. Notice the
placement of the input decoupling capacitor next to the IC.
This is necessary for best performance.

R1

C3

1

C1

V

IN

L1

D1

V

OUT

Figure 1. LT1309 Recommended Layout

2

3

4

C2

GND

8

7

6

VPP VALID

5

ON/OFF

1309 F01

6

PACKAGE DESCRIPTION

U

Dimensions in inches (millimeters) unless otherwise noted.

S8 Package

8-Lead Plastic Small Outline (Narrow 0.150)

(LTC DWG # 05-08-1610)

0.189 – 0.197*
(4.801 – 5.004)

7

8

5

6

LT1309

0.010 – 0.020

(0.254 – 0.508)

0.008 – 0.010

(0.203 – 0.254)

*

DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH 


SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE

**

DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD 
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE



× 45°

0°– 8° TYP

0.016 – 0.050

0.406 – 1.270

0.228 – 0.244

(5.791 – 6.197)

0.053 – 0.069

(1.346 – 1.752)

0.014 – 0.019

(0.355 – 0.483)

0.150 – 0.157**
(3.810 – 3.988)

1

3

2

4

(1.270)

0.004 – 0.010

(0.101 – 0.254)

0.050

BSC

SO8 0695

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.

7

LT13 09

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up to 200mA

OUT

8

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

[phone]

●

FAX

: [phone]

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TELEX

: 499-3977

LT/GP 0896 7K • PRINTED IN THE USA

 LINEAR TECHNOLOGY CORPORATION 1995