LT1108 Datasheet, PDF (1/12 Pages) Linear Technology – Micropower DC/DC Converter Adjustable and Fixed 5V, 12V

FEATURES
s _{Operates at Supply Voltages from 2V to 30V}
s _{Consumes Only 110µA Supply Current}
s _{Works in Step-Up or Step-Down Mode}
s _{Only Four External Components Required}
s _{Low Battery Detector Comparator On-Chip}
s _{User Adjustable Current Limit}
s _{Internal 1A Power Switch}
s _{Fixed or Adjustable Output Voltage Versions}
s _{Space Saving 8-Pin MiniDIP or S8 Package}
APPLICATI S
s _{Palmtop Computers}
s _{3V to 5V, 5V to 12V Converters}
s _{9V to 5V, 12V to 5V Converters}
s _{LCD Bias Generators}
s _{Peripherals and Add-On Cards}
s _{Battery Backup Supplies}
s _{Cellular Telephones}
s _{Portable Instruments}
LT1108
Micropower
DC/DC Converter
Adjustable and Fixed 5V, 12V
DESCRIPTIO
The LT1108 is a versatile micropower DC/DC converter.
The device requires only four external components to
deliver a fixed output of 5V or 12V. Supply voltage ranges
from 2V to 12V in step-up mode and to 30V in step-down
mode. The LT1108 functions equally well in step-up, step-
down, or inverting applications.
The LT1108 is pin-for-pin compatible with the LT1173, but
has a duty cycle of 70%, resulting in increased output
current in many applications. The LT1108 can deliver
150mA at 5V from a 2 AA cell input and 5V at 300mA from
9V in step-down mode. Quiescent current is just 110µA,
making the LT1108 ideal for power conscious battery-
operated systems.
Switch current limit can be programmed with a single
resistor. An auxiliary gain block can be configured as a low
battery detector, linear post regulator, undervoltage lock-
out circuit, or error amplifier.
TYPICAL APPLICATI
Palmtop Computer Logic Supply
L1*
100µH
1N5817
2 × AA
CELLS
+
100µF
47Ω
I_LIM
V_IN
SW1
LT1108-5
SENSE
GND
SW2
5V
150mA
+
AVX
TPS
330µF
6.3V
*L1 = GOWANDA GA20-103K
COILTRONICS CTX100-4
SUMIDA CD105-101K
LT1108 • TA01
Efficiency
84
82
V_IN = 3V
80
V_IN = 2.5V
78
V_IN = 2V
76
74
72
70
1
10
100
LOAD CURRENT (mA)
LT1108 • TA02
1