REV. 0

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a

ADP1147-3.3/ADP1147-5

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 781/329-4700

World Wide Web Site: http://www.analog.com

Fax: 781/326-8703

© Analog Devices, Inc., 1998

High Efficiency Step-Down

Switching Regulator Controllers

FUNCTIONAL BLOCK DIAGRAM

Q

R

S

SENSE(–)

SLEEP

1.25V

OFF-TIME

CONTROL

5pF

100k

13k

SENSE(+) SENSE(–)

ADP1147

10mV to 150mV

R

S

Q

1

2

C

V

G

S

T

B

REFERENCE

FEATURES

Greater Than 95% Efficiency

Current Mode Switching Architecture Provides

Superior Load and Line Transient Response

Wide Input Voltage Range 3.5 V* to 16 V

User Defined Current Limit

Short Circuit Protection

Shutdown Pin

Low Dropout Voltage

Low Standby Current 160

A typ

Low Cost

Available in 8-Lead PDIP or 8-Lead SOIC

APPLICATIONS

Portable Computers

Modems

Cellular Telephones

Portable Equipment

GPS Systems

Handheld Instruments

GENERAL DESCRIPTION

The ADP1147 is part of a family of High Efficiency Step-Down

Switching Regulators. These regulators offer superior load and

line transient response, a user defined current limit and an

automatic power savings mode. The automatic power savings

mode is used to maintain efficiency at lower output currents.

The ADP1147 incorporates a constant off-time, current mode

switching architecture to drive an external P-channel MOSFET

at frequencies up to 250 kHz. Constant off-time switching gen-

erates a constant ripple current in the external inductor. This

results in a wider input voltage operating range of 3.5 V* to

16 V, and a less complex circuit design.

*3.5 volt operation is for the ADP1147-3.3.

1000pF

SHUTDOWN

L

*

50 H

D1

30BQ040

1 F

0V = NORMAL

1.5V = SHUTDOWN

0.05

1k

3300pF

470pF

100 F

5V/2A

390 F

P-CHANNEL

IRF7204

SHUTDOWN

GND

P-DRIVE

SENSE(–)

ADP1147

SENSE(+)

+

+

+

*COILTRONICS CTX 50–2MP

**KRL SL-1-C1-0R050J

Figure 1. High Efficiency Step-Down Converter

(Typical Application)

A very low dropout voltage with excellent output regulation can

be obtained by minimizing the dc resistance of the Inductor, the

savings mode conserves power by reducing switching losses at

lower output currents. When the output load current falls below

the minimum required for the continuous mode the ADP1147

will automatically switch to the power savings mode. It will remain

in this mode until the inductor requires additional current or the

sleep mode is entered. In sleep mode with no load the standby

power consumption of the device is reduced to 2.0 mW typical

For designs requiring even greater efficiencies refer to the

ADP1148 data sheet.

LOAD CURRENT – mA

100

95

60

1

10k

10

100

1k

90

85

65

80

75

70

Figure 2. ADP1147-5 Typical Efficiency, Figure 1 Circuit