Ap8802, 1a led step-down converter, Application information (cont.) – Diodes AP8802 User Manual
Page 12
AP8802
1A LED STEP-DOWN CONVERTER
AP8802
Document number: DS31766 Rev. 9 - 2
12 of 19
www.diodes.com
May 2012
© Diodes Incorporated
Application Information (cont.)
Soft-Start
An external capacitor from the CTRL pin to ground will provide a soft-start delay, by increasing the time taken for the voltage on this pin to
rise to the turn-on threshold and by slowing down the rate of rise of the control voltage at the input of the comparator. Adding capacitance
increases this delay by approximately 200µs/nF. The graph below shows the variation of soft-start time for different values of capacitor.
0
20
40
60
80
100
120
CAPACITANCE (nF)
Figure. 21 Soft-Start Time vs. Capacitance
from ADJ Pin to Ground
16
14
0
-2
12
10
4
2
8
6
S
O
F
T
-S
T
A
R
T
T
IME
(m
s
)
Thermal Considerations
The graph below in Figure 22, gives details for power derating. This assumes the device to be mounted on a 25x25mm PCB with 1oz copper
standing in still air.
AMBIENT TEMPERATURE ( C)
Maximum Power Dissipation
°
Figure. 22 A 8802 Derating Curves
P
2.6
0
25
50
75
100
125
SO-8
SO-8EP
U-DFN3030-10
P
O
WE
R
DI
SSI
P
A
T
IO
N (
W
)
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0