17
LT1777
TYPICAL APPLICATIONS
U
Basic 5V Output Application
Figure 8 shows a basic application that produces 5V at up
to 500mA I
OUT
. Efficiency and Internal Power Dissipation
graphs are shown in Figure 9 for input voltages of 12V,
24V and 36V, and for sense inductor values of 0µH, 1µH
and 2.2µH. Be aware that continuous operation at the
combination of high input voltage, large sense inductor
and high output current may not be possible due to
thermal constraints. (Brief transients in input voltage or
output current should not present a problem, though.) As
shown, the SHDN and SYNC pins are unused, however
either (or both) can be optionally driven by external signals
as desired.
The data as shown were performed using an off-the-shelf
Coilcraft DO3316-224 as the main inductor. This is a
cost-effective inductor using an open style of construc-
tion. For a toroidal style inductor, the Coiltronics
CTX250-4 or similar may be substituted.
+
V
IN
V
CC
V
SW
LT1777
V
D
SHDN
SYNC
4
10
7
6
D1
L1
0µH TO 2.2µH
(SEE BELOW)
L2
220µH
C2
100µF
10V
R1
36.5k
1%
1777 F08
V
OUT
5V
R2
12.1k
1%
5
3
V
IN
10V TO 40V
12
14
13
V
C
FB
SGND
+
C1
39µF
63V
R3
12k
C3
2200pF
C4
100pF
C1: PANASONIC HFQ ELECTROLYTIC
C2: AVX D CASE TPSD107M010R0080
C3, C4, C5: NPO OR X7R
C6, C7: Z5U
D1: MOTOROLA 100V, 1A SMD SCHOTTKY
MBRS1100
L1: SENSE INDUCTOR CAN VARY FROM 0µH TO 2.2µH
AS PER APPLICATION. GRAPHICAL DATA TAKEN WITH:
1µH = D01608C-102, COILCRAFT OR SIMILAR
2.2µH = D01608C-222, COILCRAFT OR SIMILAR (SEE TEXT)
L2: COILCRAFT D03316-224 OR SIMILAR (SEE TEXT)
C5
100pF
C6
0.1µF
C7
0.1µF
Figure 8. Basic 5V Output Application
