NE5562D Philipss, NE5562D Datasheet - Page 20

• Manufacturer Part Number: NE5562D
• Description: Switched-mode power supply control circuit
• Manufacturer: Philipss

Philips Semiconductors
CALCULATING THE DELAY CAPACITOR
Actual delay time for a given capacitor value at Pin 16 may be
estimated using the graphs in Figure 33 for OC1 and OC2. By first
determining the allowable overcurrent time product for a particular
power converter, a capacitor delay value may be calculated.
Note that the OC1 charge pump is typically 13 A while OC2 pumps
550 A into the capacitor. If the exact value is to be calculated for a
particular delay requirement, use the following procedure:
1. Determine the level of overcurrent—OC1 or OC2.
2. Find the maximum delay time which the supply may safely sus-
1994 Aug 31
Switched-mode power supply control circuit
tain for this continuous overcurrent condition. Note that OC1 may
be activated on every cycle if OC2 is not reached, causing con-
tinuous charging of C-Delay. However, OC2 overcurrent detec-
tion causes the supply to go into slow-start shutdown (hiccup
3.86V
0.00V
3.66V
0.00V
Figure 33. Overcurrent Shutdown Function
10
1 F
0.1 F
OC2 DELAY TIME (MILLISECONDS)
OC1 DELAY TIME (MILLISECONDS)
20
(neglecting recycle dfelay)
C
C
DELAY
100
DELAY
30
5 F
0.5 F
40
1 F
10 F
50
200
60
70
300
80
SL00420
20
For a continuous OC1 overcurrent:
For a continuous OC2 overcurrent:
Some downward adjustment of the OC2 capacitor value may be
necessary to compensate for the 1-2 A of discharge current at Pin
16 during the delay cycles.
Example: A maximum of 100 OC2 current fault cycles is allowed.
Example: OC2/C
Find number of OC1 cycles before shutdown with 0.036 F C
C
C
C
mode), on the first such pulse. OC2 delays are based on an
DLY
DLY
f
DLY
SW
interrupted charging cycle with total cycle time determined by the
external slow-start delay capacitor duty cycle maximum
divider—time constant.
=0.036 F
=400kHz, find C
(13X10
(550X10
(550X10
Figure 34. OC1 Ramp and Shutdown Delay
DLY
6
)(Delay time
6
6
)(Delay cycles x 1 f
)(100 x 1 4 x 105)
DLY
3.86V
3.86V
3.86V
sec)
SW
(1)
(2)
NE/SE5562
)
Product specification
SL00421
DLY
.