Datasheet

16
LT1776
TYPICAL APPLICATIONS
U
(a)
C1: PANASONIC HFQ 39µF AT 63V
C2: AVX D CASE 100µF 10V
TPSD107M010R0080
C3: 2200pF, X7R
C1
1776 F06a
V
IN
10V TO
40V
+
C2
+
D1
R1
36.5k
1%
V
OUT
5V
0mA to 400mA
R2
12.1k
1%
R3
22k
5%
L1
68µH
C3
C4
C5
C4, C5: 100pF, X7R OR COG/NPO
D1: MOTOROLA 100V, 1A, SMD SCHOTTKY
MBRS1100 (T3)
L1: COILCRAFT DO1608C-683
FOR 3.3V V
OUT
VERSION:
I
OUT
: 0mA TO 500mA
L1: 47µH, DO1608C-473
R1: 24.3K, R2: 14.7k
V
IN
V
CC
V
SW
LT1776
FB
V
C
SHDN
SYNC
2
5
4
3
7
8
1
6
GND
LOAD CURRENT (mA)
1
60
EFFICIENCY (%)
70
80
90
10 100 1000
1776 F06b
50
40
30
20
V
IN
= 10V
V
IN
= 20V
V
IN
= 30V
V
IN
= 40V
(b)
Figure 6. Minimum Inductor Size Application
“bang-bang” digital manner, via comparator U2, an
LTC1440. Resistor divider R3/R4 provides a scaled ver-
sion of the output voltage, which is compared against U2’s
internal reference. Intentional hysteresis is set by the R5/
R6 divider. As the output voltage falls below the regulation
range, the LT1776 is turned on. The output voltage rises,
and as it climbs above the regulation range, the LT1776 is
turned off. Efficiency is maximized, as the LT1776 is only
powered up while it is providing heavy output current.
Burst Mode Operation Configuration
Figure 4b demonstrates that power supply efficiency de-
grades with lower output load current. This is not surpris-
ing, as the LT1776 itself represents a fixed power overhead.
A possible way to improve light load efficiency is in Burst
Mode operation.
Figure 7 shows the LT1776 configured for Burst Mode
operation. Output voltage regulation is now provided in a