1
LT1108
Micropower
DC/DC Converter
Adjustable and Fixed 5V, 12V
D
U
ESCRIPTIO
S
F
EA
T
U
RE
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.
■
Operates at Supply Voltages from 2V to 30V
■
Consumes Only 110µA Supply Current
■
Works in Step-Up or Step-Down Mode
■
Only Four External Components Required
■
Low Battery Detector Comparator On-Chip
■
User Adjustable Current Limit
■
Internal 1A Power Switch
■
Fixed or Adjustable Output Voltage Versions
■
Space Saving 8-Pin MiniDIP or S8 Package
U
S
A
O
PP
L
IC
AT
I
■
Palmtop Computers
■
3V to 5V, 5V to 12V Converters
■
9V to 5V, 12V to 5V Converters
■
LCD Bias Generators
■
Peripherals and Add-On Cards
■
Battery Backup Supplies
■
Cellular Telephones
■
Portable Instruments
U
A
O
PP
L
IC
AT
ITY
P
I
CA
L
LOAD CURRENT (mA)
1
78
EFFICIENCY (%)
80
82
84
10 100
LT1108 • TA02
76
74
72
70
V
IN
= 3V
V
IN
= 2.5V
V
IN
= 2V
AVX
TPS
330µF
6.3V
L1*
100µH
LT1108 • TA01
1N5817
5V
150mA
GND SW2
SW1
I
LIM
V
IN
LT1108-5
SENSE
100µF
+
*L1 =
+
2 × AA
CELLS
GOWANDA GA20-103K
COILTRONICS CTX100-4
SUMIDA CD105-101K
47Ω
EfficiencyPalmtop Computer Logic Supply