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Linear Technology Electronic Components Datasheet

LT1108 Datasheet

Micropower DC/DC Converter Adjustable and Fixed 5V/ 12V

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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
47
ILIM VIN
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
VIN = 3V
80 VIN = 2.5V
78 VIN = 2V
76
74
72
70
1
10 100
LOAD CURRENT (mA)
LT1108 • TA02
1


Linear Technology Electronic Components Datasheet

LT1108 Datasheet

Micropower DC/DC Converter Adjustable and Fixed 5V/ 12V

No Preview Available !

LT1108
ABSOLUTE AXI U RATI GS
Supply Voltage (VIN) ............................................... 36V
SW1 Pin Voltage (VSW1) ......................................... 50V
SW2 Pin Voltage (VSW2) ............................ – 0.5V to VIN
Feedback Pin Voltage (LT1108) ............................. 5.5V
Sense Pin Voltage (LT1108, -5, -12) ...................... 36V
Maximum Power Dissipation ............................ 500mW
Maximum Switch Current ...................................... 1.5A
Operating Temperature Range .................... 0°C to 70°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
PACKAGE/ORDER I FOR ATIO
TOP VIEW
ILIM 1
VIN 2
SW1 3
SW2 4
8 FB (SENSE*)
7 SET
6 A0
5 GND
N8 PACKAGE
8-LEAD PLASTIC DIP
*FIXED VERSIONS
TJMAX = 90°C, θJA = 130°C/W
ORDER PART
NUMBER
LT1108CN8
LT1108CN8-5
LT1108CN8-12
TOP VIEW
ILIM 1
VIN 2
SW1 3
SW2 4
8 FB (SENSE*)
7 SET
6 A0
5 GND
S8 PACKAGE
8-LEAD PLASTIC SOIC
*FIXED VERSIONS
TJMAX = 90°C, θJA = 150°C/W
ORDER PART
NUMBER
LT1108CS8
LT1108CS8-5
LT1108CS8-12
S8 PART MARKING
1108
10805
10812
ELECTRICAL CHARACTERISTICS TA = 25°C, VIN = 3V, unless otherwise noted.
SYMBOL
IQ
PARAMETER
Quiescent Current
Quiescent Current, Boost Mode Configuration
VIN Input Voltage
Comparator Trip Point Voltage
VOUT Output Sense Voltage
Comparator Hysteresis
Output Hysteresis
fOSC Oscillator Frequency
Duty Cycle
tON Switch-ON Time
Feedback Pin Bias Current
Set Pin Bias Current
VOL Gain Block Output Low
Reference Line Regulation
VSAT SWSAT Voltage, Step-Up Mode
CONDITIONS
Switch OFF
No Load
LT1108-5
LT1108-12
Step-Up Mode
Step-Down Mode
LT1108 (Note 1)
LT1108-5 (Note 2)
LT1108-12 (Note 2)
LT1108
LT1108-5
LT1108-12
Full Load, Step-Up Mode
ILIM Tied to VIN, Step-Up Mode
LT1108, VFB = 0V
VSET = VREF
ISINK = 100µA, VSET = 1V
2V VIN 5V
5V VIN 30V
VIN = 3V, ISW = 650mA
VIN = 5V, ISW = 1A
MIN
q
q2
q
q 1.2
q 4.75
q 11.4
q
q
q
q 14
q 63
q 28
q
q
q
q
q
q
TYP
110
135
250
1.245
5
12
5
20
50
19
70
36
10
20
0.15
0.20
0.02
0.5
0.8
MAX
150
12.6
30.0
1.3
5.25
12.6
10
40
100
25
78
48
50
100
0.4
0.400
0.075
0.65
1.00
UNITS
µA
µA
µA
V
V
V
V
V
mV
mV
mV
kHz
%
µs
nA
nA
V
%/ V
%/ V
V
V
2


Part Number LT1108
Description Micropower DC/DC Converter Adjustable and Fixed 5V/ 12V
Maker Linear Technology
Total Page 12 Pages
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