Datasheet LT1308 Datasheet (Linear Technology)

Final Electrical Specifications

FEATURES

LOAD CURRENT (mA)

1

EFFICIENCY (%)

95

90

85

80

75

70

65

10 100 1000

1308 F01a

VIN = 4.2V

VIN = 3.6V

VIN = 3V

LT1308

Single Cell High Current

Micropower 600kHz

Boost DC/DC Converter

January 1998

U

DESCRIPTION

■

5V at 1A from a Single Li-Ion Cell

■

3.3V at 300mA from a Single NiCd Cell

■

Low Quiescent Current: 100µA

■

Operates with VIN as Low as 1V

■

Fixed Frequency Operation: 600kHz

■

Current Mode PWM Delivers Low Output Ripple

■

Guaranteed Start-Up into Full Load

■

Low Shutdown Current: 3µA

■

Low-Battery Comparator

■

Automatic Burst ModeTM Operation at Light Load

■

Low V

Switch: 300mV at 2A

CESAT

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APPLICATIONS

■

GSM Terminals

■

Digital Cameras

■

Answer-Back Pagers

■

Cordless Telephones

■

DECT Phones

■

GPS Receivers

■

Battery Backup Supplies

The LT®1308 is a micropower, fixed frequency boost
DC/DC converter that operates from an input voltage as
low as 1V. Capable of delivering 5V at load current of 1A
from a single Li-Ion cell, the LT1308 also features power
saving Burst Mode operation at light loads. High efficiency
is maintained over a broad 1mA to 1A load range.

The device contains a low-battery detector with a 200mV
reference and shuts down to less than 5µA quiescent
current. No-load quiescent current is 100µA and the
internal NPN power switch handles a 2A current with a
voltage drop of just 300mV.

High frequency 600kHz switching allows the use of small,
surface mount components. The LT1308’s current mode
architecture provides fast response to load and line varia­tions. The device is available 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 APPLICATION

4.2V TO 3V

SHDN
LBI

Li-Ion
CELL

C1: CERAMIC
C2: AVX TPS SERIES
D1:INTERNATIONAL RECTIFIER 10BQ015
L1: COILTRONICS CTX5-1
 COILCRAFT DO3316-472


Figure 1. Single Li-Ion Cell to 5V/1A DC/DC Converter

C1
10µF

LBO

U

L1

V

IN

SW

LT1308

FB

V

C

GND



R

C

47k

C



C

22nF

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.

301k

R2
100k

4.7µH

R1

D1

5V
1A

+

C2
100µF

1308F01

Converter Efficiency

1

LT1308

WU

NUMBER

LT1308CS8
LT1308IS8

1308
1308I

A

W

O

LUTEXI T

S

A

WUW

ARB

U
G

I

S

VIN, SHDN, LBO Voltage ......................................... 10V

SW Voltage ............................................................. 30V

FB Voltage ....................................................... VIN + 1V

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

LBI Voltage ............................................ 0V ≤ V

LBI

≤ 1V

Current into FB Pin .............................................. ±1mA

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

Operating Temperature Range

Commercial (Note 1) ......................... –20°C to 70°C

PACKAGE

TOP VIEW

V

1



C

FB

2

SHDN

3

GND

4

S8 PACKAGE

8-LEAD PLASTIC SO

T

= 125°C, θJA = 80°C/W

JMAX

/

O

RDER I FOR ATIO

ORDER PART

LBO

8

LBI

7

V



6

IN

SW

5

S8 PART MARKING

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

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

Consult factory for Military grade parts.

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

LECTRICAL C CHARA TERIST

E

Commercial Grade 0°C to 70°C. VIN = 1.1V, V

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

I

Q

VFBFeedback Voltage ● 1.20 1.22 1.24 V
I

B

g

m

A

V

f

OSC

Quiescent Current Not Switching ● 80 160 µA

FB Pin Bias Current (Note 2) VFB = V
Reference Line Regulation 1.1V ≤ VIN ≤ 2V (25°C, 0°C) 0.6 1.1 %/V

Minimum Input Voltage 0.92 1 V
Input Voltage Range ● 16V
Error Amp Transconductance ∆I = 5µA40µmhos
Error Amp Voltage Gain 25°C, 0°C 100 V/V

Switching Frequency ● 500 600 700 kHz
Maximum Duty Cycle ● 80 88 95 %
Switch Current Limit (Note 3) DC = 40% ● 2.0 2.5 A

Switch V

CESAT

Burst Mode Operation Switch Current Limit L = 3.3µH, V
Shutdown Pin Current V

LBI Threshold Voltage ● 180 200 220 mV
LBO Output Low I
LBO Leakage Current V
LBI Input Bias Current (Note 4) V

ICS

= VIN, TA = 25°C, unless otherwise noted.

SHDN

= 0V ● 13µA

V

SHDN

REF

1.1V ≤ V
2V ≤ V

70°C 80 V/V

DC = 80% 1.6 2 A
ISW = 2A (25°C, 0°C) 300 350 mV

I

SW

SHDN

V

SHDN

V

SHDN

SINK

LBI

LBI

≤ 2V (70°C) 1.5 %/V

IN

≤ 6V ● 0.3 0.8 %/V

IN

= 2A (70°C) 330 400 mV

= 3.3V, VIN = 1.2V 200 mA

OUT

= 1.1V ● 2.5 4.0 µA
= 6V 13 26 µA
= 0V ● –1.5 –2.5 µA

= 10µA ● 0.1 0.25 V

= 250mV, V
= 150mV ● 530nA

= 5V ● 0.01 0.1 µA

LBO

● 27 80 nA

U

2

LT1308

LECTRICAL C CHARA TERIST

E

Commercial Grade 0°C to 70°C. VIN = 1.1V, V

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

Low-Battery Detector Gain 1MΩ Load (25°C, 0°C) 1000 3000 V/V

Switch Leakage Current VSW = 5V ● 0.01 10 µA
Reverse Battery Current (Note 5) 750 mA

ICS

= VIN, TA = 25°C unless otherwise noted.

SHDN

1MΩ Load (70°C) 500 V/V

Commercial Grade TA = –20°C, VIN = 1.1V, V

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

I

V
g
A
f

Q

FB

m

V

OSC

Quiescent Current VFB = 1.3V, Not Switching 80 160 µA

Feedback Voltage 1.195 1.22 1.245 V
Error Amp Transconductance ∆I = 5µA35µmhos
Error Amp Voltage Gain 100 V/V
Switching Frequency 500 600 750 kHz
Maximum Duty Cycle 88 %
Switch V

CESAT

Shutdown Pin Current V

LBI Threshold Voltage 180 200 220 mV

Industrial Grade –40°C to 85°C. VIN = 1.2V, V

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

I

Q

VFBFeedback Voltage ● 1.195 1.22 1.245 V
I

B

g

m

A

V

f

OSC

Quiescent Current Not Switching ● 80 160 µA

FB Pin Bias Current (Note 2) VFB = V
Reference Line Regulation 1.1V ≤ VIN ≤ 2V (–40°C) 0.6 1.1 %/V

Minimum Input Voltage (–40°C) 1.2 V
Input Voltage Range ● 1.2 6 V
Error Amp Transconductance ∆I = 5µA40µmhos
Error Amp Voltage Gain –40°C 100 V/V

Switching Frequency VIN = 1.3V (–40°C) 500 600 750 kHz

Maximum Duty Cycle –40°C808895%

Switch Current Limit (Note 3) DC = 40% ● 2.0 2.5 A

Switch V

CESAT

Burst Mode Operation Switch Current Limit L = 3.3µH, V

= VIN, unless otherwise noted (Note 1).

SHDN

= 0V 1 3 µA

V

SHDN

ISW = 2A, VIN = 1.2V 300 350 mV

= V

SHDN

IN

= 0V –1.5 – 2.5 µA

V

SHDN

= VIN, TA = 25°C, unless otherwise noted.

SHDN

= 0V ● 13µA

V

SHDN

REF

1.1V ≤ V
2V ≤ V

85°C 80 V/V

V

85°C75%

DC = 80% 1.6 2 A
ISW = 2A (–40°C) 300 350 mV

I

SW

≤ 2V (85°C) 1.5 %/V

IN

≤ 6V ● 0.3 0.8 %/V

IN

= 1.3V (85°C) 500 600 750 kHz

IN

= 2A (85°C) 330 400 mV

= 3.3V 200 mA

OUT

2.5 4.0 µA

● 27 80 nA

3

LT1308

LECTRICAL C CHARA TERIST

E

ICS

Industrial Grade –40°C to 85°C. VIN = 1.2V, V

= VIN, TA = 25°C, unless otherwise noted.

SHDN

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

Shutdown Pin Current V

= 1.2V ● 2.5 4.0 µA

SHDN

V

= 6V ● 13 26 µA

SHDN

= 0V ● –1.5 –2.5 µA

V

SHDN

LBI Threshold Voltage ● 180 200 220 mV
LBO Output Low I
LBO Leakage Current V
LBI Input Bias Current (Note 4) V

= 10µA ● 0.1 0.25 V

SINK

= 250mV, V

LBI

= 150mV ● 530nA

LBI

= 5V ● 0.01 0.1 µA

LBO

Low-Battery Detector Gain 1MΩ Load (–40°C) 1000 3000 V/V

1MΩ Load (85°C) 300 V/V

Switch Leakage Current VSW = 5V ● 0.01 10 µA

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

Note 1: C grade device specifications are guaranteed over the 0°C to 70°C
temperature range. In addition, C grade device specifications are assured
over the –40°C to 85°C temperature range by design or correlation, but
are not production tested.

Note 3: Switch current limit guaranteed by design and/or correlation to
static tests. Duty cycle affects current limit due to ramp generator (see
Block Diagram).

Note 4: Bias current flows out of LBI pin.
Note 5: The LT1308 will withstand continuous application of 1.6V applied

to GND pin while VIN and SW are grounded.

Note 2: Bias current flows into FB pin.

UW

TYPICAL PERFORMANCE CHARACTERISTICS

Switch Saturation Voltage vs

90

VIN = 1.2V

85

80

75

70

65

EFFICIENCY (%)

60

55

50

= 3.3V

V

OUT

= 169k

R1

1 100 1000

10

LOAD CURRENT (mA)

1308 G01

V

OUT

200mV/DIV

AC COUPLED

100mA

I

LOAD

5mA

Transient Response

V

IN =

V

OUT

C2
R

C

L = 4.7µH

500µs/DIV

1.2V

= 5V

= 22µF

, CC = 47k, 6.8nF

1308 G02

CurrentEfficiency

500

400

(mV)

300

CESAT

200

SWITCH V

100

0

0

25°C

0.5

1.0

SWITCH CURRENT (A)

85°C

–40°C

1.5

1308 G03

2.0

UUU

PIN FUNCTIONS

VC (Pin 1): Compensation Pin for Error Amplifier. Con­nect a series RC from this pin to ground. Typical values
are 47kΩ and 22nF. Minimize trace area at VC.

FB (Pin 2): Feedback Pin. Reference voltage is 1.22V.
Connect resistive divider tap here. Minimize trace area at
FB. Set V

according to: V

OUT

= 1.22V(1 + R1/R2).

OUT

4

SHDN (Pin 3): Shutdown. Ground this pin to turn off
switcher. Must be tied to VIN (or higher voltage) to enable
switcher. Do not float the SHDN pin.

GND (Pin 4): Ground. Connect directly to local ground
plane. Ground plane should enclose all components
associated with the LT1308.

PIN FUNCTIONS

LT1308

UUU

SW (Pin 5): Switch Pin. Connect inductor/diode here.
Minimize trace area at this pin to keep EMI down.

VIN (Pin 6): Supply Pin. Must have local bypass capacitor
right at the pin, connected directly to ground.

LBI (Pin 7): Low-Battery Detector Input. 200mV refer­ence. Voltage on LBI must stay between ground and

W

BLOCK DIAGRAM

V

IN

R6
40k

Q2
×10

R3
30k

R4
140k

V

IN

+

g

m

–

ERROR

AMPLIFIER

RAMP

GENERATOR

600kHz

OSCILLATOR

Σ

V

OUT

R1
(EXTERNAL)

R2
(EXTERNAL)

6

R5
40k

FB

FB

Q1

2

700mV. Low-battery detector does not function with
SHDN pin grounded. If not used, float LBI pin.

LBO (Pin 8): Low-Battery Detector Output. Open collec­tor, can sink 10µ A. A 1MΩ pullup is recommended. LBO
is high impedance when SHDN is grounded.

SHDN

3

LBO

8

SW

5

Q3

+

0.03Ω

–

4

1308 BD

GND

BIAS

+

+

V

C

1

+



–

A1

COMPARATOR

–

+

A2

ENABLE

200mV

R

SHUTDOWN

LBI

7

+

–

A4

FF

Q

S

DRIVER

A = 3

U

WUU

APPLICATIONS INFORMATION

LAYOUT HINTS

The LT1308 switches current at high speed, mandating
careful attention to layout for proper performance.

not get advertised performance with careless layouts.

Figure 2 shows recommended component placement.
Follow this closely in your PC layout. Note the direct path
of the switching loops. Input capacitor CIN

must

close (<5mm) to the IC package. As little as 10mm of wire
or PC trace from CIN to VIN will cause problems such as
inability to regulate or oscillation. A 10µF ceramic bypass
capacitor is the only input capacitance required

the battery has a low inductance path to the circuit

battery itself provides the bulk capacitance the device
requires for proper operation. If the battery is located some

You will

be placed

provided

. The

GROUND PLANE

MULTIPLE

VIAs

1

2

3

4

GND

LT1308

C

IN

8

7

1308 F02

V

IN

6

5

L

D

C

OUT

V

OUT

Figure 2. Recommended Component Placement. Traces
Carrying High Current Are Direct. Trace Area at FB Pin and V

C

Pin is Kept Low. Lead Length to Battery Should Be Kept Short.
Ground Plane Should Be Placed Under All Components

5

LT1308

LBO

LBI

TO PROCESSOR

R1

1M

R2
100k

V

IN

V

BAT

LT1308

1308 F04

3.3V

GND

200mV
INTERNAL
REFERENCE

–

+

R1 =

V

LB

– 200mV

2µA

U

WUU

APPLICATIONS INFORMATION

distance from the circuit, an additional input capacitor may
be required. A 220µ F aluminum electrolytic unit works well
in these cases. This capacitor need not have low ESR.

OPERATION FROM A LABORATORY POWER SUPPLY

If a lab supply is used, the leads used to connect the circuit
to the supply can have significant inductance at the
LT1308’s switching frequency. As in the previous situa­tion, an electrolytic capacitor may be required at the circuit
in order to reduce the AC impedance of the input suffi­ciently. An alternative solution is to attach the circuit
directly to the power supply at the supply terminals,
without the use of leads. The power supply’s output
capacitance will then provide the bulk capacitance the
LT1308 circuit requires.

SHUTDOWN PIN

tive input of the gain stage is tied internally to a 200mV
reference. The positive input is the LBI pin. Arrangement
as a low-battery detector is straightforward. Figure 4
details hookup. R1 and R2 need only be low enough in
value so that the bias current of the LBI pin doesn’t cause
large errors. For R2, 100k is adequate. The 200mV refer­ence can also be accessed as shown in Figure 5.

The LT1308 has a shutdown pin (SHDN) that must be
grounded to shut the device down or tied to a voltage equal

Figure 4. Setting Low-Battery Detector Trip Point

or greater than VIN to operate. The shutdown circuit is
shown in Figure 3.

Note that allowing SHDN to float turns on both the start­up current (Q2) and the shutdown current (Q3) for VIN >
2VBE. The LT1308 doesn’t know what to do in this situation
and behaves erratically. SHDN voltage above VIN is al­lowed. This merely reverse-biases Q3’s base emitter junc-

200k

V

BAT

2N3906

V

REF

200mV



10k

+

10µF

LBO

LBI

V

IN

LT1308

GND

1308 F05

tion, a benign condition.

V

IN

Q3

R2

SHDN

LOW-BATTERY DETECTOR

The LT1308’s low-battery detector is a simple PNP input

Figure 3. Shutdown Circuit

400k

400k

Q1

SHUTDOWN
CURRENT

START-UP
CURRENT

Q2

1308 F03

gain stage with an open collector NPN output. The nega-

6

GSM PHONES

The LT1308 is suitable for converting a single Li-Ion cell
to 5V for powering GSM RF power stages. Figure 6 details
a Li-Ion to 5V converter circuit using frequency compen­sation optimized for a typical GSM pulsed load. Figure 7
details transient response of Figure 6’s circuit with a
100mA to 1A pulsed load. A slower time sweep is used to
show several transmit pulses in Figure 8. At a VIN of 2.7V,
additional output capacitance is recommended to help
minimize V
voltage of 2.7V. Figure 10 expands the horizontal sweep
speed to 500µs/division to show detail of one transmit
pulse.

Figure 5. Accessing 200mV Reference

droop. Figure 9 shows V

OUT

with an input

OUT

LT1308

U

WUU

APPLICATIONS INFORMATION

DECT PHONES

The DECT standard specifies a transmit pulse 416µs in
duration. The LT1308 is capable of delivering a 400mA
pulse load from a 1.2V input with output capacitance of
100µF. Figure 11 depicts V
Figure 6’s circuit, configured for a 3.3V output by chang­ing resistor R1 to 169k. Figure 12 shows detail of one
transmit pulse at a higher sweep speed.

SHDN

NiCd
OR
Li-Ion
CELL

L1: TOKO 636CY4R7M
COILTRONICS CTX5-1
FOR V
FOR V

C1
10µF
CERAMIC

= 5V: R1 = 309k

OUT

= 3.3V: R1 = 169k

OUT

Figure 6. DC/DC Converter for GSM/DECT Application

LBI

LBO

V

C

LT1308

47k

33nF

transient response of

OUT

L1

4.7µH

V

IN

SW

R1

FB

GND

100k

+

D1
MBRS120

5V/1A OR

3.3V/300mA

C2
100µF

1308F06

= 2.7V

V

IN

V

OUT

200mV/DIV

AC COUPLED

1A

I

LOAD

100mA

1ms/DIV

Figure 9. GSM Load Transient Response.
At Low VIN, Large Output Capacitor (2200µF)

V

OUT

200mV/DIV

AC COUPLED

I

, 1A/DIV

L

I

LOAD

100mA

Serves to Hold up V

VIN = 2.7V

1A

500µs/DIV 1308 F10

OUT

Figure 10. GSM Load Transient Response.
Faster Sweep Speed (500µs/DIV) Details V
and Inductor Current of One Transmit Pulse

1308 F09

OUT

V

200mV/DIV

AC COUPLED

I

, 1A/DIV

L

I

LOAD

100mA

OUT

1A

= 3.6V

V

IN

100µs/DIV 1308 F07

Figure 7. GSM Load Transient Response.
100mA to 1A Transient Response for Figure 6’s Circuit.
Pulse Width = 577µs

V

= 3.6V

IN

V

OUT

200mV/DIV

AC COUPLED

1A

I

LOAD

100mA

1ms/DIV 1308 F08

Figure 8. GSM Load Transient Response. Slower
Sweep Speed (1ms/DIV) Shows V

over Several

OUT

Transmit Pulses

VIN = 1.2V

V

OUT

200mV/DIV

AC COUPLED

400mA

I

LOAD

50mA

2ms/DIV 1308 F11

Figure 11. DECT Load Transient Response.
With a Single NiCd Cell the LT1308 Provides 3.3V
with 400mA Pulsed Load. Pulse Width = 416µs

V

V

= 1.2V

OUT

200mV/DIV

AC COUPLED

, 1A/DIV

I

L

400mA

I

LOAD

IN

50mA

100µs/DIV 1308 F09

Figure 12. DECT Load Transient Response.
Faster Sweep Speed (100µs/DIV) Details V
Inductor Current of Single DECT Transmit Pulse

OUT

and

7

LT1308

TYPICAL APPLICATION

2-4 Cell to 3.3V/175mA, 5V/175mA, 18V/10mA, –10V/10mA

U

Digital Camera Power Supply

L1A

N = 1

V

1.6V

TO 6V

100µF

IN

C1

+

C8

1nF

C1, C2, C3 = AVX TPS
C4, C5 = AVX TAJ
C6 = CERAMIC


R4
47k

C7
22nF

10µH

V

IN

SHDN

LT1308

V

C

GND

D1, D2 = IR10BQ015
D3, D4 = BAT-85
L1 = COILTRONICS CTX02-13973

PACKAGE DESCRIPTION

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°

0.016 – 0.050

0.406 – 1.270

0.053 – 0.069

(1.346 – 1.752)

0°– 8° TYP

C6

10µF

18

SW

2

3

L1C

3

N = 0.3

100k

340k

R1

2.08M

FB

L1B
N = 0.7

R3

4

R2

100µF

D1

D2

5V
175mA

3.3V
175mA

+

+

C2

C3
100µF

D3

7

L1D
N = 3.5

6

6

L1E
N = 2

5

D4

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)

8

0.004 – 0.010

(0.101 – 0.254)

0.228 – 0.244

0.014 – 0.019

(0.355 – 0.483)

0.050

(1.270)

BSC

(5.791 – 6.197)

1

CCD BIAS
18V
10mA

+

C4
10µF

+

C5
10µF

CCD BIAS
–10V

1308 TA01

10mA

7

2

5

6

0.150 – 0.157**
(3.810 – 3.988)

3

4

SO8 0695

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LTC®1163 Triple High Side Driver for 2-Cell Inputs 1.8V Minimum Input, Drives N-Channel MOSFETs
LTC1174 Micropower Step-Down DC/DC Converter 94% Efficiency, 130µA IQ, 9V to 5V at 300mA
LT1302 High Output Current Micropower DC/DC Converter 5V/600mA from 2V, 2A Internal Switch, 200µA I
LT1304 2-Cell Micropower DC/DC Converter Low-Battery Detector Active in Shutdown, 5V at 200mA for 2 Cells
LT1307 Single Cell Micropower 600kHz PWM DC/DC Converter 3.3V at 75mA from 1 Cell, MSOP Package
LT1316 Micropower DC/DC Converter with Programmable Peak Works with High Source Impedance, 1.5V Minimum Input, Low-Battery

Current Limit Detector Active in Shutdown, 33µA I

, MSOP Package

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LTC1440/1/2 Ultralow Power Single/Dual Comparators with Reference 2.8µA IQ, Adjustable Hysteresis
LTC1516 2-Cell to 5V Regulated Charge Pump 12µA IQ, No Inductors, 5V at 50mA from 3V Input
LT1521 Micropower Low Dropout Linear Regulator 500mV Dropout, 300mA Current, 12µA I

Linear Technology Corporation

8

1630 McCarthy Blvd., Milpitas, CA 95035-7417 ● [phone]
FAX: [phone]

●

TELEX: 499-3977 ● www.linear-tech.com

 LINEAR TECHNOLOGY CORPORATION 1998

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1308i LT/TP 0198 4K • PRINTED IN USA