Datasheet

Figure 35 : P.C. Board and Component Layout of the Circuit of fig. 34 (1:1 scale)
SELECTION OF COMPONENT VALUES (see fig. 34)
Component
Recommended
Value
Purpose
Allowed Rage
Notes
Min. Max.
R1
R2
–
100 k
Ω
Set Input Voltage
Threshold for Reset.
–
220k
Ω
R1/R2
V
i min
5
−
1
If output voltage is sensed R1 and
R2 may be limited and pin 12
connected to pin 10.
R3 4.3 k
Ω
Sets Switching Frequency 1 k
Ω
100k
Ω
R4 10 k
Ω
Pull-down Resistor 22k
Ω
May be omitted and pin 6 grounded
if inhibit not used.
R5 15 k
Ω
Frequency Compensation 10k
Ω
R6 Collector Load For Reset
Output
V
O
0.05A
Omitted if reset function not used.
R7
R8
–
4.7 k
Ω
Divider to Set Output
Voltage
–
–
–
1k
Ω
R7/R8 =
V
O
−
V
REF
V
REF
-
R
iim
– Sets Current Limit Level 7.5k
Ω
If R
iim
is omitted and pin 4 left open
the current limit is internally fixed.
C1 10
µ
F Stability 2.2
µ
F
C2 2.2
µ
F Sets Reset Delay – – Omitted if reset function not used.
C3 2.2 nF Sets Switching Frequency 1 nF 3.3nF
C4 2.2
µ
F Soft Start 1
µ
F – Also determines average short
circuit current.
C5 33 nF Frequency Compensation
C6 390 pF High Frequency
Compensation
– – Not required for 5 V operation.
C7, C8
L1
100
µ
F
300
µ
H
Output Filter –
100
µ
H
–
Q1 Crowbar Protection The SCR must be able to withstand
the peak discharge current of the
output capacitor and the short
circuit current of the device.
D1 Recirculation Diode 7A Schottky or 35 ns t
rr
Diode.
L296 - L296P
15/22