ua78s40 ETC-unknow, ua78s40 Datasheet - Page 6

• Manufacturer Part Number: ua78s40
• Description: Switching Regulator Subsystem
• Manufacturer: ETC-unknow

V sat = Saturation voltage of the output switch. V F = Forward voltage drop of the ringback rectifier.
The following power supply characteristics must be chosen:
See Application Note AN920 for further information
V ripple(pp)
6
(t on + t off ) max
V out
f min
I out
V in
I pk(switch)
15V
V in
L (min)
Calculation
R SC
C O
t off
C T
– Nominal input voltage. If this voltage is not constant, then use V in(max) for step–down and V in(min) for step–up and inverting convertor.
– Desired output voltage: V out = 1.25
– Desired output current.
– Minimum desired output switching frequency at the selected values for V in and I O .
– Desired peak–to–peak output ripple voltage. In practice, the calculated value will need to be increased due to the capacitor’s equivalent series
–
t on
100
resistance and board layout. The ripple voltage should be kept to a low value since it will directly effect the line and load regulation.
18k
R2
1.5k
R1
+
8
9
Reference
1.25V
10
7
V in(min) – V sat – V out
C T
V in(min) – V sat – V out
I pk(switch) (t on + t off )
Oscilator
–
+
I pk(switch)
Comp.
8 V ripple(pp)
11
Step–Down
4 x 10 5 t on
2 I out(max)
6
V out + V F
I pk(switch)
1
0.33
f min
)
I pk
I
–
+
C T
R 2
R 1
Amp
Figure 7. Inverting Converter
Op
12
5
for step–down and step–up:
Design Formula Table
1800
pF
t on(max)
V CC
A78S40
13
4
R SC
0.30
S
R
14
3
2 I out(max)
V in(min) – V sat
Q
V out – V F V in(min)
I pk(switch)
V out
Step–Up
4 x 10 5 t on
V in(min) V sat
I out t on
100
V ripple
I pk(switch)
15
2
0.33
+
f min
I
170
1.25 R 2
t on – t off
D1
R 1
t off
MOTOROLA ANALOG IC DEVICE DATA
D45H8
t on(max)
16
1
270
for inverting.
50 H
1N5822
L
V in(min) – V sat
2 I out(max)
I pk(switch)
V in(min) – V sat
100 +
V out + V F
4 x 10 5 t on
Inverting
I out t on
V ripple
I pk(switch)
0.33
–15V/500mA
f min
C O
I
t on + t off
V out
t on(max)
t off