Analog Devices ADP1108 Datasheet

Micropower DC-DC Converter

a

Adjustable and Fixed 3.3 V, 5 V, 12 V

FEATURES
Operates at Supply Voltages From 2.0 V to 30 V
Consumes Only 110 mA Supply Current
Step-Up or Step-Down Mode Operation
Minimum External Components Required
Low Battery Detector Comparator On-Chip
User-Adjustable Current Limit
Internal 1 A Power Switch
Fixed or Adjustable Output Voltage Versions
8-Pin DIP or SO-8 Package

APPLICATIONS
Notebook/Palm Top Computers
3 V to 5 V, 5 V to 12 V Converters
9 V to 5 V, 12 V to 5 V Converters
LCD Bias Generators
Peripherals and Add-On Cards
Battery Backup Supplies
Cellular Telephones
Portable Instruments

GENERAL DESCRIPTION

The ADP1108 is a highly versatile micropower switch-mode
dc-dc converter that operates from an input voltage supply as
low as 2.0 V and typically starts up from 1.8 V.

The ADP1108 can be programmed into a step-up or step-down
dc-to-dc converter with only three external components. The
fixed outputs are 3.3 V, 5 V and 12 V. An adjustable version is
also available. In step-up mode, supply voltage range is 2.0 V to
12 V, and 30 V in step-down mode. The ADP1108 can deliver
150 mA at 5 V from a 2 AA cell input and 300 mA at 5 V from
a 9 V input in step-down mode. Switch current limit can be
programmed with a single resistor.

For battery operated and power conscious applications, the
ADP1108 offers a very low power consumption of less than
110 µA.

The auxiliary gain block available in ADP1108 can be used
as a low battery detector, linear post regulator, under voltage
lockout circuit or error amplifier.

V

V

IN

IN

ADP1108

FUNCTIONAL BLOCK DIAGRAMS

SET

ADP1108

A2

GAIN BLOCK/
ERROR AMP

1.245V

REFERENCE

1.245V

REFERENCE

R1

FBGND

SET

A1

COMPARATOR

A2

GAIN BLOCK/
ERROR AMP

A1

COMPARATOR

R2

753kΩ

SENSEGND

OSCILLATOR

ADP1108-3.3
ADP1108-5
ADP1108-12

OSCILLATOR

ADP1108-3.3: R1 = 456kΩ
ADP1108-5: R1 = 250kΩ
ADP1108-12: R1 = 87.4kΩ

DRIVER

DRIVER

SW2

AO

I

LIM

SW1

AO
I

LIM

SW1

SW2

REV. 0

Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: [phone] World Wide Web Site: http://www.analog.com
Fax: [phone] © Analog Devices, Inc., 1997

ADP1108–SPECIFICA TIONS

(08C to +708C, V

= 3.0 V unless otherwise noted)

IN

Parameter Symbol Conditions Min Typ Max Units

QUIESCENT CURRENT I
QUIESCENT CURRENT, I

Q

Q

Switch Off 90 150 µA
No Load, TA = +25°C

BOOST MODE CONFIGURATION ADP1108-3.3 90 µA

ADP1108-5 90 µA
ADP1108-12 90 µA

INPUT VOLTAGE V

IN

Step-Up Mode 2.0 12.6 V

Step-Down Mode 30 V
COMPARATOR TRIP POINT VOLTAGE ADP1108
OUTPUT SENSE VOLTAGE V

OUT

ADP1108-3.3

ADP1108-5

ADP1108-12

1

2

2

2

1.20 1.245 1.30 V

3.13 3.3 3.46 V

4.75 5.00 5.25 V

11.4 12.0 12.6 V
COMPARATOR HYSTERESIS ADP1108 5 12 mV
OUTPUT HYSTERESIS ADP1108-3.3 13 30 mV

ADP1108-5 20 55 mV

ADP1108-12 50 100 mV
OSCILLATOR FREQUENCY 14 19 25 kHz
DUTY CYCLE Full Load 55 70 78 %
SWITCH ON TIME t

ON

I

Tied to V

LIM

IN

25 36 48 µs
FEEDBACK PIN BIAS CURRENT VFB = 0 V 25 200 nA
SET PIN BIAS CURRENT V
GAIN BLOCK OUTPUT LOW V

OL

REFERENCE LINE REGULATION 2.0 V ≤ V

= V

SET

I

= 100 µA, V

SINK

REF

= 1.00 V 0.15 0.4 V

SET

≤ 5 V 0.2 0.4 %/V

IN

60 130 nA

5 V ≤ VIN ≤ 30 V 0.02 0.075 %/V

SW

VOLTAGE, STEP-UP MODE V

SAT

SAT

V

= 3.0 V, ISW = 650 mA 0.5 0.75 V

IN

V

= 5.0 V, ISW = 1 A, 0.8 1.00 V

IN

TA = +25°CV

SW

VOLTAGE,

SAT

SAT

V

= 12 V, ISW = 650 mA,

IN

T

= +25°C 1.1 1.5 V

A

STEP-DOWN MODE 1.7 V
GAIN BLOCK GAIN A

V

RL = 100K

CURRENT LIMIT 220 Ω from I

3

LIM

400 1000 V/V

to VIN,

TA = +25°C 500 mA

CURRENT LIMIT TEMPERATURE

COEFFICIENT –0.3 %/°C

SWITCH OFF LEAKAGE CURRENT Measured at SW1 Pin,

TA = +25°C110µA

MAXIMUM EXCURSION BELOW GND V

SW2

1

≤ 10 µA, Switch Off

SW1

TA = +25°C –400 –350 mV

NOTES

1

This specification guarantees that both the high and low trip points of the comparator fall within the 1.20 V to 1.30 V range.

2

The output voltage waveform will exhibit a sawtooth shape due to the comparator hysteresis. The output voltage on the fixed output versions will always be within the
specified range.

3

100 kΩ resistor connected between a 5 V source and the AO pin.

All limits at temperature extremes are guaranteed via correlation using standard Quality Control methods.
Specifications subject to change without notice.

–2–

REV. 0

ADP1108

WARNING!

ESD SENSITIVE DEVICE

ABSOLUTE MAXIMUM RATINGS*

Supply Voltage (VIN) . . . . . . . . . . . . . . . . . . . . . . . . . . . +36 V

SW1 Pin Voltage (V
SW2 Pin Voltage (V

) . . . . . . . . . . . . . . . . . . . . . . . . +50 V

SW1

) . . . . . . . . . . . . . . . . . . –0.5 V to V

SW2

IN

Feedback Pin Voltage (ADP1108) . . . . . . . . . . . . . . . . +5.5 V

Sense Pin Voltage (ADP1108, 3.3, 5, 12) . . . . . . . . . . . +36 V

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

Maximum Switch Current . . . . . . . . . . . . . . . . . . . . . . . .1.5 A

Operating Temperature Range . . . . . . . . . . . . . 0°C to 170°C

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

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

*Stresses above those listed under Absolute Maximum Ratings may cause perma-

nent damage to the device. This is a stress rating only; functional operation of the
device at these or any other conditions above those listed in the operational
sections of this specification is not implied. Exposure to absolute maximum rating
conditions for extended periods may affect device reliability.

ORDERING GUIDE

Model Output Voltage Package*

ADP1108AN ADJ N-8
ADP1108AR ADJ SO-8
ADP1108AN-3.3 3.3 V N-8
ADP1108AR-3.3 3.3 V SO-8
ADP1108AN-5 5 V N-8
ADP1108AR-5 5 V SO-8
ADP1108AN-12 12 V N-8
ADP1108AR-12 12 V SO-8

*N = Plastic DIP, SO = Small Outline Package.

PIN CONFIGURATIONS

8-Lead Plastic DIP 8-Lead SOIC
(N-8) (SO-8)

1

I

LIM

2

V

IN

3

SW1

(Not to Scale)

4

SW2

* FIXED VERSIONS

ADP1108

TOP VIEW

8

FB (SENSE)*

7

SET

6

AO

5

GND

1

I

LIM

2

V

IN

3

SW1

(Not to Scale)

4

SW2

* FIXED VERSIONS

ADP1108

TOP VIEW

8

FB (SENSE)*

7

SET

6

AO

5

GND

PIN FUNCTION DESCRIPTIONS

Mnemonic Function

I

LIM

For normal conditions this pin is connected to
V

. When lower current is required, a resistor

IN

should be connected between I

and VIN.

LIM

Limiting the switch current to 400 mA is
achieved by connecting a 220 Ω resistor.

V

IN

Input Voltage.

SW1 Collector of Power Transistor. For step-down

configuration, connect to V

. For step-up

IN

configuration, connect to an inductor/diode.

SW2 Emitter of Power Transistor. For step-down

configuration, connect to inductor/diode. For
step-up configuration, connect to ground. Do
not allow this pin to go more than a diode

drop below ground.
GND Ground.
AO Auxiliary Gain (GB) Output. The open

collector can sink 100 µA.
SET Gain Amplifier Input. The amplifier has

positive input connected to SET pin and

negative input connected to 1.245 V reference.
FB/SENSE On the ADP1108 (adjustable) version this pin

is connected to the comparator input. On the

ADP1108-3.3, ADP1108-5 and ADP1108-12,

the pin goes directly to the internal application

resistor that set output voltage.

CAUTION

ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection.
Although the ADP1108 features proprietary ESD protection circuitry, permanent damage may
occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD
precautions are recommended to avoid performance degradation or loss of functionality.

REV. 0

–3–

ADP1108

–Typical Performance Characteristics

1.2

1

0.8

– Volts

0.6

(SAT)
CC

0.4

V

0.2

0

0.1 0.2 1.20.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1

VIN = 3.0V

VIN = 2.0V

VIN = 5.0V

SWITCH CURRENT – Amps

Figure 1. Saturation Voltage vs. I
Current in Step-Up Mode

1100

VIN = 24V WITH L = 500µH @ V

1000

900
800
700
600
500
400

SWITCH CURRENT – mA

VIN = 12V WITH L = 250µH @ V

300
200
100

10 1k

100

R

– Ω

LIM

OUT

OUT

= 5V

SWITCH

= 5V

1.6

1.4

1.2

1

0.8

0.6

0.4

SWITCH ON VOLTAGE – Volts

0.2

0

0.05

V

CE (SAT)

0.25 0.35 0.45 0.55 0.65

0.15 0.75
SWITCH CURRENT – Amps

Figure 2. Switch ON Voltage vs.
Switch Current In Step-Down Mode

100

90
80
70
60
50
40
30

SUPPLY CURRENT – mA

20
10

0

200 300 400 600 700 800500

0 100 900

SWITCH CURRENT – mA

VIN = 5V

VIN = 2V

1100
1000

900
800
700

2V < VIN < 5V

600
500
400

SWITCH CURRENT – mA

300
200
100

10 100 1k

R

– Ω

LIM

Figure 3. Maximum Switch Current
vs. R

In Step-Up Mode

LIM

120

110

100

90

80

70

60

QUIESCENT CURRENT – µA

50

40

–40 0 85

25 70

TEMPERATURE – °C

Figure 4. Maximum Switch Current
vs. R

In Step-Down Mode

LIM

22
21
20
19
18
17
16
15

OSCILLATOR FREQUENCY – kHz

14
13

–40 0 85

25 70

TEMPERATURE – °C

Figure 7. Oscillator Frequency vs.
Temperature

Figure 5. Supply Current vs. Switch
Current

67
66
65
64
63
62
61

DUTY CYCLE – %

60
59
58
57

–40 0 85

25 70

TEMPERATURE – °C

Figure 8. Duty Cycle vs. Temperature

Figure 6. Quiescent Current vs.
Temperature

35

34.5
34

33.5
33

32.5
32

31.5

SWITCH ON TIME – µs

31

30.5
30

–40 0 85

25 70

TEMPERATURE – °C

Figure 9. Switch ON Time vs.
Temperature

–4–

REV. 0