SEMTECH SC1628

HIGH-EFFICIENCY STEP-UP
DC-DC CONVERTER
January 30, 1998
SC1628
TEL:805-498-2111 FAX:805-498-3804 WEB:http://www.semtech.com
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.
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
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
(1)
DEVICE
SC1628CS
Note:
(1) Add suffix ‘TR’ for tape and reel.
PIN CONFIGURATION
© 1997 SEMTECH CORP.
PACKAGE
SO-8
ABSOLUTE MAXIMUM RATINGS
Parameter
Symbol
Maximum
Units
Supply Voltage
VIN
24
V
SHDN Voltage
VSHDN
15
V
Operating
Temperature Range
TA
0 to 70
°C
Storage
Temperature Range
TSTG
-65 to 125
°C
652 MITCHELL ROAD NEWBURY PARK CA 91320
HIGH-EFFICIENCY STEP-UP
DC-DC CONVERTER
SC1628
January 30, 1998
ELECTRICAL CHARACTERISTICS
Unless otherwise specified, TA = 25°C, VIN = 13V
Parameter
Conditions
Min
Input Voltage
Typ
4
Max
Units
24
V
Quiescent Current
VFB = 1.5V
100
200
µA
Shutdown Mode Current
VSHDN = 0V
8
20
µA
1.22
1.28
V
VREF Voltage
ISOURCE = 250µA
1.16
VREF Source Current
250
µA
DLOW “ON Resistance”
15
Ω
DHI “ON Resistance”
10
Ω
CL Threshold
VIN - VCL
Shutdown Threshold
Shutdown Input Leakage Current
VSHDN < 15V
45
60
75
mV
0.8
1.5
2.4
V
1
µA
TYPICAL APPLICATIONS
Color LCD Contrast Bias Supply
,
Flash Memory Programming Supply
,
© 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:
VIN
4V to 24V input supply voltage.
PIN 5: GND
PIN 2:
VREF
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 4:
FB
Feedback signal input to comparator.
Connecting a resistance R1 to VOUT
and a resistance R2 to GND yields
the output voltage:
VOUT =
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 RB from
this pin to DLOW. RB value depends
upon VIN, the inductor value and the
NPN current gain.
PIN 8: CL
Current-limit input. The threshold
voltage is 60mV from VIN. This pin
clamps the switch peak current under
abnormal conditions.
R1+ R 2
× VREF
R2
(refer to typical application circuit).
© 1997 SEMTECH CORP.
Power ground.
PIN CONFIGURATION
652 MITCHELL ROAD NEWBURY PARK CA 91320