LT1173CS8PBF LINEAR TECH, LT1173CS8PBF Datasheet - Page 4

• Manufacturer Part Number: LT1173CS8PBF
• Manufacturer: LINEAR TECH

TYPICAL PERFOR
PI
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.
BLOCK
4
LT1 173
LIM
LIM
IN
REFERENCE
120
110
100
90
U
1.245V
(Pin 2): Input supply voltage.
(Pin 1): Connect this pin to V
–50
and V
GND
V
Quiescent Current vs Temperature
IN
FU
–25
SET
IN
U
. A 220 resistor will limit the switch current
IN
I D AGRA
0
FB
C
TEMPERATURE (°C)
.
TI
25
O
50
U
A2
GAIN BLOCK/
COMPARATOR
ERROR AMP
A1
S
LT1173
75
V = 3V
W
IN
W
LT1173 •TPC06
S
100
A
IN
OSCILLATOR
U
AO
125
for normal use. Where
CE
C
HARA TERISTICS
50
40
30
20
10
DRIVER
0
I
LIM
0
Supply Current vs Switch Current
LT1173 • BD01
200
C
SW1
SW2
SWITCH CURRENT (mA)
400
V = 5V
IN
GND (Pin 5): Ground.
AO (Pin 6): Auxiliary Gain Block (GB) output. Open collec-
tor, 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 LT1173 (adjustable) this pin
goes to the comparator input. On the LT1173-5 and
LT1173-12, this pin goes to the internal application resis-
tor that sets output voltage.
GND
REFERENCE
600
1.245V
V = 2V
V
IN
IN
800
LT1173 •TPC07
R1
SET
1000
753k
R2
GAIN BLOCK/
ERROR AMP
A2
COMPARATOR
LT1173-5, -12
26.0
25.5
25.0
24.5
24.0
23.5
23.0
22.5
22.0
SENSE
A1
Oscillator Frequency
0
5
LT1173-12:
OSCILLATOR
LT1173-5:
AO
10
V
IN
R1 = 250k
R1 = 87.4k
15
(V)
DRIVER
I
20
LIM
LT1173 • TPC08
LT1173 • BD02
25
SW1
SW2
30