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LT1108CS8-5#PBF

P1-P3P4-P6P7-P9P10-P12
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
2
LT1108
A
U
G
W
A
W
U
W
ARB
S
O
LU
T
EXI T
I
S
Supply Voltage (V
IN
)............................................... 36V
SW1 Pin Voltage (V
SW1
) ......................................... 50V
SW2 Pin Voltage (V
SW2
) ............................ –0.5V to V
IN
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
WU
U
PACKAGE
/
O
RDER I FOR ATIO
ORDER PART
NUMBER
LT1108CS8
LT1108CS8-5
LT1108CS8-12
S8 PART MARKING
ORDER PART
NUMBER
LT1108CN8
LT1108CN8-5
LT1108CN8-12
T
JMAX
= 90°C, θ
JA
= 150°C/W
T
JMAX
= 90°C, θ
JA
= 130°C/W
1
2
3
4
8
7
6
5
TOP VIEW
I
LIM
V
IN
SW1
SW2
FB (SENSE*)
SET
A0
GND
N8 PACKAGE
8-LEAD PLASTIC DIP
*FIXED VERSIONS
1
2
3
4
8
7
6
5
TOP VIEW
I
LIM
V
IN
SW1
SW2
FB (SENSE*)
SET
A0
GND
S8 PACKAGE
8-LEAD PLASTIC SOIC
*FIXED VERSIONS
E
LECTR
IC
AL C CHARA TERIST
ICS
T
A
= 25°C, V
IN
= 3V, unless otherwise noted.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
I
Q
Quiescent Current Switch OFF ● 110 150 µA
Quiescent Current, Boost Mode Configuration No Load LT1108-5 135 µA
LT1108-12 250 µA
V
IN
Input Voltage Step-Up Mode ● 2 12.6 V
Step-Down Mode ● 30.0 V
Comparator Trip Point Voltage LT1108 (Note 1) ● 1.2 1.245 1.3 V
V
OUT
Output Sense Voltage LT1108-5 (Note 2) ● 4.75 5 5.25 V
LT1108-12 (Note 2) ● 11.4 12 12.6 V
Comparator Hysteresis LT1108 ● 510 mV
Output Hysteresis LT1108-5 ● 20 40 mV
LT1108-12
● 50 100 mV
f
OSC
Oscillator Frequency ● 14 19 25 kHz
Duty Cycle Full Load, Step-Up Mode ● 63 70 78 %
t
ON
Switch-ON Time I
LIM
Tied to V
IN
, Step-Up Mode ● 28 36 48 µs
Feedback Pin Bias Current LT1108, V
FB
= 0V ● 10 50 nA
Set Pin Bias Current V
SET
= V
REF
● 20 100 nA
V
OL
Gain Block Output Low I
SINK
= 100µA, V
SET
= 1V ● 0.15 0.4 V
Reference Line Regulation 2V ≤ V
IN
≤ 5V ● 0.20 0.400 %/V
5V ≤ V
IN
≤ 30V ● 0.02 0.075 %/V
V
SAT
SW
SAT
Voltage, Step-Up Mode V
IN
= 3V, I
SW
= 650mA ● 0.5 0.65 V
V
IN
= 5V, I
SW
= 1A 0.8 1.00 V
1108
10805
10812
3
LT1108
T
A
= 25°C, V
IN
= 3V, unless otherwise noted.
E
LECTR
IC
AL C CHARA TERIST
ICS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V
SAT
SW
SAT
Voltage, Step-Down Mode V
IN
= 12V, I
SW
= 650mA 1.1 1.5 V
● 1.7 V
A
V
Gain Block Gain R
L
= 100k (Note 3) ● 400 1000 V/V
Current Limit 220Ω from I
LIM
to V
IN
400 mA
Current Limit Temperature Coefficient ● –0.3 %/°C
Switch OFF Leakage Current Measured at SW1 Pin 1 10 µA
V
SW2
Maximum Excursion Below GND I
SW1
≤ 10µA, Switch OFF –400 –350 mV
Note 2: The output voltage waveform will exhibit a sawtooth shape due to
the comparator hysteresis. The output voltage on the fixed output versions
will always be within the specified range.
Note 3: 100k resistor connected between a 5V source and the A0 pin.
The
● denotes specifications which apply over the full operating
temperature range.
Note 1: This specification guarantees that both the high and low trip points
of the comparator fall within the 1.2V to 1.3V range.
CCHARA TERIST
ICS
UW
AT
Y
P
I
CA
LPER
F
O
R
C
E
R
LIM
(Ω)
10
SWITCH CURRENT (mA)
100 1000
LT1108 • TPC03
1000
1200
1100
900
800
700
600
500
400
300
200
100
2V ≤ V
IN
≤ 5V
Saturation Voltage Step-Up Mode
(SW2 Pin Grounded)
Switch ON Voltage
Step-Down Mode
(SW1 Pin Connected to V
IN
)
Maximum Switch Current
vs R
LIM
Saturation Voltage Step-Up Mode
(SW2 Pin Grounded)
R
LIM
(Ω)
100
0
SWITCH CURRENT (mA)
200
400
600
800
1000
LT1108 • TPC04
100
300
500
700
900
1000
V
OUT
= 5V
V
IN
= 24V
L = 500µH
V
IN
= 12V
L = 250µH
Supply Current vs Switch Current Quiescent Current
TEMPERATURE (°C)
–50
QUIESCENT CURRENT (µA)
95
100
105
25
75
LT1108 • TPC06
90
85
80
–25 0 50
110
115
120
100
SWITCH CURRENT (A)
0
0
V
CESAT
(V)
0.2
0.4
0.6
0.8
1.2
0.2
0.4 0.6 0.8
LT1108 • TPC01
1.0 1.2
1.0
V
IN
= 2V
V
IN
= 5V
V
IN
= 3V
SWITCH CURRENT (A)
0
SWITCH ON VOLTAGE (V)
1.1
1.2
1.3
0.6
LT1108 • TPC02
1.0
0.9
0.2 0.4 0.8
0.8
0.7
1.4
0.5
0.1 0.3 0.7
SWITCH CURRENT (mA)
0
SUPPLY CURRENT (mA)
30
40
50
800
LTC1108 • TPC05
20
10
0
200
400
600
1000
V
IN
= 5V
V
IN
= 2V
P1-P3P4-P6P7-P9P10-P12

LT1108CS8-5#PBF

Mfr. #:
Buy LT1108CS8-5#PBF
Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Voltage Regulators Micropower DC/DC Converter Adjustable and Fixed 5V, 12V
Lifecycle:
New from this manufacturer.
Delivery:
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