LT1108-12 Linear Technology, LT1108-12 Datasheet - Page 4

• Manufacturer Part Number: LT1108-12
• Description: Micropower DC/DC Converter Adjustable and Fixed 5V/ 12V
• Manufacturer: Linear Technology

LT1108
TYPICAL PERFOR
I
lower current limit is desired, connect a resistor between
I
to approximately 400mA.
V
SW1 (Pin 3): Collector of power transistor. For step-up
mode connect to inductor/diode. For step-down mode
connect to V
SW2 (Pin 4): Emitter of power transistor. For step-up
mode connect to ground. For step-down mode connect to
inductor/diode. This pin must never be allowed to go more
than a Schottky diode drop below ground.
4
PI
LIM
LIM
IN
22
21
20
19
18
17
15
16
14
13
U
28
26
24
22
16
14
12
10
20
18
(Pin 2): Input supply voltage.
–50
0
(Pin 1): Connect this pin to V
and V
25
Oscillator Frequency
Minimum/Maximum Frequency
vs ON-Time
FU
–25
IN
30
U
. A 220 resistor will limit the switch current
IN
TEMPERATURE (°C)
C
.
0
TI
ON-TIME ( s)
35
O
25
U
40
S
50
W
LT1108 • TPC07
45
75
LT1108 • TPC10
A
IN
U
100
50
for normal use. Where
CE
C
HARA TERISTICS
80
75
70
65
60
55
50
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
–50
–50
Duty Cycle
Switch Saturation Voltage
Step-Up Mode
I
SW
–25
–25
= 650mA
C
TEMPERATURE (°C)
TEMPERATURE (°C)
0
0
25
25
GND (Pin 5): Ground.
AO (Pin 6): Auxiliary gain block (GB) output. Open collector,
can sink 100 A.
SET (Pin 7): GB input. GB is an op amp with positive input
connected to SET pin and negative input connected to
1.245V reference.
FB/SENSE (Pin 8): On the LT1108 (adjustable) this pin
goes to the comparator input. On the LT1108-5 and
LT1108-12, this pin goes to the internal application resistor
that sets output voltage.
50
50
LT1108 • TPC08
75
LT1108 • TPC11
75
100
100
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1.0
0.8
0.9
30
44
42
40
38
36
34
32
–50
–50
Switch-ON Time
Switch Saturation Voltage
Step-Down Mode
I
SW
–25
–25
= 650mA
TEMPERATURE (°C)
TEMPERATURE (˚C)
0
0
25
25
50
50
LT1108 • TPC12
LT1108 • TPC09
75
75
100
100