Datasheet

4
LT1300
PIN FUNCTIONS
UUU
GND (Pin 1): Signal Ground.
Sel (Pin 2): Output Select. When tied to V
IN
or V
OUT
converter regulates at 5V. When grounded converter
regulates at 3.3V.
SHDN (Pin 3): Shutdown. Pull high to effect shutdown. Tie
to ground for normal operation.
Sense (Pin 4): “Output” Pin.
I
LIM
(Pin 5): Float for 1A switch current limit. Tie to ground
for approximately 400mA. A resistor between I
LIM
and
ground sets peak current to some intermediate value (see
Figure 5).
V
IN
(Pin 6): Supply Pin. Must be bypassed with a large
value electrolytic to ground. A 0.1µF ceramic capacitor
close to the pin may be needed in some cases.
SW (Pin 7): Switch Pin. Connect inductor and diode here.
Keep layout short and direct to minimize electronic radia-
tion.
PGND (Pin 8): Power Ground. Tie to signal ground (pin 1)
under the package. Bypass capacitor from V
IN
should be
tied directly to the pin.
Figure 1.
BLOCK DIAGRAM
W
OSCILLATOR
155kHZ
R2
730Ω
C2

SW
R1
3Ω
Q2
1x
Q1
160x
18mV
OFF
V
IN
V
IN
I
LIM
PGND
V
OUT
ENABLE
A1
COMPARATOR
–
+
+
+
–
+
1.25V
REFERENCE

L1
D1
7
2
4
SENSE
A2 CURRENT 
COMPARATOR
A3 DRIVER
BIAS
Q3
8.5k
58
SHUTDOWN
3
SELECT
2
GND
161k
144k
500k
C1
1
LT1300 F1