LT1777 Linear Technology, LT1777 Datasheet - Page 17

• Manufacturer Part Number: LT1777
• Description: Low Noise Step-Down Switching Regulator
• Manufacturer: Linear Technology

TYPICAL APPLICATIONS
Basic 5V Output Application
Figure 8 shows a basic application that produces 5V at up
to 500mA I
graphs are shown in Figure 9 for input voltages of 12V,
24V and 36V, and for sense inductor values of 0 H, 1 H
and 2.2 H. 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
OUT
10V TO 40V
. Efficiency and Internal Power Dissipation
V
IN
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
+
C1
39 F
63V
U
C4
100pF
C6
0.1 F
R3
12k
C5
100pF
C3
2200pF
Figure 8. Basic 5V Output Application
12
14
3
SHDN
SYNC
V
C
LT1777
SGND
L1: SENSE INDUCTOR CAN VARY FROM 0 H TO 2.2 H
L2: COILCRAFT D03316-224 OR SIMILAR (SEE TEXT)
V
IN
10
7
AS PER APPLICATION. GRAPHICAL DATA TAKEN WITH:
1 H = D01608C-102, COILCRAFT OR SIMILAR
2.2 H = D01608C-222, COILCRAFT OR SIMILAR (SEE TEXT)
V
V
SW
V
FB
CC
D
4
6
5
13
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.
0 H TO 2.2 H
(SEE BELOW)
L1
D1
220 H
L2
+
C2
100 F
10V
C7
0.1 F
R1
36.5k
1%
R2
12.1k
1%
1777 F08
V
5V
OUT
LT1777
17