Datasheet

4
LT1301
PIN FUNCTIONS
UUU
GND (Pin 1): Signal Ground. Tie to PGND under the
package.
Sel (Pin 2): Output Select. When tied to V
IN
converter
regulates at 12V. When grounded or floating converter
regulates at 5V. May be driven under logic control.
SHDN (Pin 3): Shutdown. Pull high to shut down the
LT1301. Ground for normal operation.
Sense (Pin 4): “Output” Pin. Goes to internal resistive
divider. If operating at 5V output, a 0.1µF ceramic capaci-
tor is required from Sense to Ground.
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 .
V
IN
(Pin 6): Supply Pin. Must be bypassed with a large
value electrolytic to ground. Keep bypass within 0.2" of the
device.
SW (Pin 7): Switch Pin. Connect inductor and diode here.
Keep layout short and direct to minimize radio frequency
interference.
PGND (Pin 8): Power Ground. Tie to signal ground (pin 1)
under the package. Bypass capacitor from V
IN
should be
tied directly to PGND within 0.2" of the device.
Figure 2.
BLOCK DIAGRAM
W
OSCILLATOR
155kHZ
R2
730Ω
C2

SW
R1
3Ω
Q2
1×
Q1
160×
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
69.2k
97.5k
500k
C1
1
LT1301 F2