Datasheet
14
LT1776
TYPICAL APPLICATIONS
U
Minimum Component Count Application
Figure 4a shows a basic “minimum component count”
application. The circuit produces 5V at up to 500mA I
OUT
with input voltages in the range of 10V to 40V. The typical
P
OUT
/P
IN
efficiency is shown in Figure 4b. As shown, the
SHDN and SYNC pins are unused, however either (or both)
can be optionally driven by external signals as desired.
User-Programmable Undervoltage Lockout
Figure 5 adds a resistor divider to the basic application.
This is a simple, cost-effective way to add a user-
programmable undervoltage lockout (UVLO) function.
Resistor R5 is chosen to have approximately 200µA
through it at the nominal SHDN pin lockout threshold of
1.25V. The somewhat arbitrary value of 200µA was
C1: PANASONIC HFQ
C2: AVX D CASE TPSD107M010R0080
C4, C5: X7R OR COG/NPO
D1: MOTOROLA 100V, 1A, SMD SCHOTTKY
L1: COILCRAFT DO3316P-104
C1
39µF
63V
1776 F04a
V
IN
10V TO
40V
+
C2
100µF
10V
+
D1
MBRS1100
R1
36.5k
1%
V
OUT
5V
0mA to 500mA
R2
12.1k
1%
R3
22k
5%
L1
100µH
C3
2200pF
X7R
C4
100pF
C5
100pF
FOR 3.3V V
OUT
VERSION:
R1: 24.3K, R2: 14.7k
L1: 68µH, DO3316P-683
I
OUT
: 0mA TO 500mA
V
IN
V
CC
V
SW
LT1776
FB
V
C
SHDN
SYNC
2
5
4
3
7
8
1
6
GND
Figure 4a. Minimum Component Count Application
I
LOAD
(mA)
1
60
EFFICIENCY (%)
70
80
90
10 100 1000
1776 F04b
50
40
30
20
V
IN
= 10V
V
IN
= 20V
V
IN
= 30V
V
IN
= 40V
Figure 4b. P
OUT
/P
IN
Efficiency