© 1997 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
HIGH-EFFICIENCY STEP-UP
DC-DC CONVERTER
SC1628
January 30, 1998
Note:
(1) Add suffix ‘TR’ for tape and reel.
FEATURES
• 4V to 24V input voltage operation
• Adjustable output voltage
• Low quiescent current at 100µA
• Pulse-skipping and pulse-frequency modulation
maintain high efficiency (max. 95%)
• 90kHz to 250kHz oscillator frequency
• Power-saving shutdown mode (8µA typical)
• Push-pull driver output
DESCRIPTION
The SC1628 is a high performance step-up DC-DC
converter, designed to drive an external power switch
to generate programmable positive voltages. In the
particularly suitable LCD contrast bias and flash
memory programming power supply applications,
typical full load efficiencies are 85% to 95%. The 4V to
24V input operation range allows the SC1628 to be
powered directly by the battery pack in most batterypowered applications for greater efficiency. The output
voltage can be scaled to 40V or greater 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
100µA and can be reduced down to 8µA in shutdown
mode. With a switching frequency range of 90kHz to
250kHz, small size switching components may be
used, which is ideal for battery powered portable
equipment such as notebook and palmtop computers.
TEL:805-498-2111 FAX:805-498-3804 WEB:http://www.semtech.com
BLOCK DIAGRAM
APPLICATIONS
• Flash memory programming power supply
• Positive LCD contrast bias for notebook and palm-
top computers
• Step-up DC-DC converter module
• Telecom power supply
ORDERING INFORMATION
ABSOLUTE MAXIMUM RATINGS
Parameter Symbol Maximum Units
Supply Voltage V
IN
24 V
SHDN Voltage V
SHDN
15 V
Operating
Temperature Range
T
A
0 to 70 °C
Storage
Temperature Range
T
STG
-65 to 125 °C
PIN CONFIGURATION
DEVICE
(1)
PACKAGE
SC1628CS SO-8
© 1997 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
HIGH-EFFICIENCY STEP-UP
DC-DC CONVERTER
SC1628
January 30, 1998
TYPICAL APPLICATIONS
ELECTRICAL CHARACTERISTICS
Unless otherwise specified, TA = 25°C, VIN = 13V
Flash Memory Programming Supply
Color LCD Contrast Bias Supply
Parameter Conditions Min Typ Max Units
Input Voltage 4 24 V
Quiescent Current V
FB
= 1.5V 100 200 µA
Shutdown Mode Current V
SHDN
= 0V 8 20 µA
V
REF
Voltage I
SOURCE
= 250µA 1.16 1.22 1.28 V
V
REF
Source Current 250 µA
DLOW “ON Resistance” 15
Ω
DHI “ON Resistance” 10
Ω
CL Threshold V
IN
- V
CL
45 60 75 mV
Shutdown Threshold 0.8 1.5 2.4 V
Shutdown Input Leakage Current V
SHDN
< 15V 1 µA
,
,
© 1997 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
HIGH-EFFICIENCY STEP-UP
DC-DC CONVERTER
SC1628
January 30, 1998
TYPICAL APPLICATIONS (cont.)
2-Cells to +12V Flash Memory Programmer
,
4-Cells to +30V Low Power Supply
Telecom +5V Supply
© 1997 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
HIGH-EFFICIENCY STEP-UP
DC-DC CONVERTER
SC1628
January 30, 1998
DEVICE OUTLINE - SO-8
PIN DESCRIPTIONS
PIN 1: V
IN
4V to 24V input supply voltage.
PIN 5: GND
Power ground.
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 6: DLOW
Driver sinking output. Connected to
the gate of the external N-channel
MOSFET or the base of the NPN
bipolar transistor.
PIN 3: SHDN
Logical input to shutdown the chip:
>1.5V = normal operation,
GND = shutdown.
Cannot be floating or forced greater
than 15V. In shutdown mode DLOW
and DHI pins are low.
PIN 7: DHI
Driver sourcing output. Connected to
DLOW when using an external Nchannel MOSFET. When using an
external NPN bipolar transistor,
connect a base resistance R
B
from
this pin to DLOW. R
B
value depends
upon V
IN
, the inductor value and the
NPN current gain.
PIN 4: FB
Feedback signal input to comparator.
Connecting a resistance R1 to V
OUT
and a resistance R2 to GND yields
the output voltage:
(refer to typical application circuit).
PIN 8: CL
Current-limit input. The threshold
voltage is 60mV from V
IN
. This pin
clamps the switch peak current under
abnormal conditions.
REFOUT
V
2R
2R1R
V ×
+
=
PIN CONFIGURATION
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