Datasheet SC1652CSTR Datasheet (Semtech Corporation)

© 1997 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

MICROPOWER INVERTING
DC-DC CONVERTER

SC1652

January 29, 1998

Note:
(1) Add suffix ‘TR’ for tape and reel.

PIN CONFIGURATION

FEATURES

• 2.4V to 7V input voltage operation

• Adjustable output voltage up to -40V

• Low quiescent current at 80µA

• Pulse frequency modulation maintains high

efficiency (max 87%)

• 70kHz to 160kHz switching frequency

• Power-saving shutdown mode (0.7µA typical)

• High efficiency with low cost external PNP bipolar

transistor

DESCRIPTION

The SC1652 is a high performance inverting DC-DC
converter, designed to drive an external power switch
to generate programmable negative voltages. In the
particularly suitable LCD bias contrast application,
efficiency of 87% can be achieved with low cost PNP
bipolar transistor drivers. The output voltage can be
scaled to -40V by two external resistors. A pulse
frequency modulation scheme is employed to maintain
high efficiency conversion under wide input voltage
ranges. Quiescent current is about 80µA and can be
reduced to 0.7µA in shutdown mode. With a switching
frequency range of 70kHz to 160kHz, small size
switching components may be used, which is ideal for
battery powered portable equipment such as notebook
and palmtop computers.

TEL:[phone] FAX:[phone] WEB:http://www.semtech.com

APPLICATIONS

• Negative LCD Contrast Bias for

1. Notebook & palmtop computers

2. Pen-based data systems

3. Portable data collection terminals

4. Personal digital assistants

• Negative voltage supplies

DEVICE

(1)

V

OUT

PACKAGE

SC1652CS Adj SO-8

ORDERING INFORMATION

ABSOLUTE MAXIMUM RATINGS

Parameter Symbol Maximum Units

Supply Voltage

V

+

7.0 V

Operating
Temperature Range

T

A

0 to 70 °C

Storage Temperature
Range

T

STG

-65 to 125 °C

BLOCK DIAGRAM

© 1997 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

MICROPOWER INVERTING
DC-DC CONVERTER

SC1652

January 29, 1998

ELECTRICAL CHARACTERISTICS

Unless otherwise specified, TA = 25°C, V+ = 5V

Test Conditions Test Limits

Parameter Min Typ Max Units

Input Voltage 2.4 7 V
Switch Off Current 80 150 µA
Shutdown Mode Current 0.7 2 µA
V

REF

Voltage I

SOURCE

=250µA 1.16 1.22 1.28 V

V

REF

Source Current 250 µA

DLOW “ON Resistance” 5

Ω

DHI “ON Resisance” 7

Ω

CL Threshold 45 60 75 mV
Shutdown Threshold 0.8 1.5 2.4 V

TYPICAL PERFORMANCE CHARACTERISTICS

TYPICAL APPLICATION CIRCUIT

to

.

.

to

© 1997 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

MICROPOWER INVERTING
DC-DC CONVERTER

SC1652

January 29, 1998

TYPICAL APPLICATION INFORMATION

The typical application circuit generates an adjustable negative voltage for
contrast bias of LCD displays. Efficiency and output power can be opti­mized by using the appropriate inductor and switch. The following formulas
provide a guideline for determining the optimal component values:

()

()

.OhminR

,HinL,AmpereinI

,VoltinV,VoltinV:unitswhere,8.0VL3R

10and

V

I

200IatV4.0V

V

I

200I

VVV:PNP

VI

V

V15.01.11L

B

OUT

OUTB

OUT

C)SAT(CE

OUT

)MAX(C

OUTCEO

OUTOUT

µ

−××≅

=β×=<

×≥

+>

×

××−=

++

+

+

+

+

+

© 1997 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

MICROPOWER INVERTING
DC-DC CONVERTER

SC1652

January 29, 1998

PIN CONFIGURATION

PIN DESCRIPTIONS

PIN 1: V

+

2.4V to 7V input supply voltage.

PIN 2: V

REF

1.22V reference output. Bypass with a

0.047µF capacitor to GND. Sourcing
capability is guaranteed to be greater
than 250µA.

PIN 3: SHDN Logic input to shutdown the chip.

>1.5V = normal operation,
GND = shutdown.
In shutdown mode DLOW and DHI
pins are high.

PIN 4: FB Feedback signal input to comparator.

Connecting a resistance R1 to V

OUT

and a resistance R2 to V

REF

yields the

output voltage:

PIN 5: GND Power ground.
PIN 6: DLOW Driver sinking output. Connected to

DHI when using an external P-channel
MOSFET. When using an external
PNP bipolar transistor, connect a
resistor R

B

from this pin to DHI. R

B

value depends upon V+, inductor value
and the PNP bipolar transistor. By
adjusting the R

B

value, efficiency can

be optimized.

PIN 7: DHI Driver sourcing output. Connect to the

gate of the external P-channel
MOSFET or base of the PNP bipolar
transistor.

PIN 8: CL Current-limit input. This pin clamps the

switch peak current under abnormal
conditions.

REFOUT

V

R2

R1

- V ×=

OUTLINE DRAWING SO-8