UA78S40 View Datasheet(PDF) - Motorola => Freescale
Part Name
Description
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UA78S40 Datasheet PDF : 8 Pages
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µA78S40
Vin
15V
+
100
9
Figure 7. Inverting Converter
RSC
0.30
CT
1800
pF
D45H8
1N5822
Vout
–15V/500mA
100
50µH L
270
100 + CO
10
11
12
13
14
15
16
VCC
CT
Ipk
Oscilator
1.25V
Reference
R1
8
7
1.5k
R2
18k
–
Comp.
+
– Op
+Amp
6
5
SQ
R
170
D1
4
3
2
1
Design Formula Table
Calculation
ton
toff
(ton + toff) max
CT
Ipk(switch)
Step–Down
Vout + VF
Vin(min) – Vsat – Vout
I
fmin
4 x 10 5 ton
2 Iout(max)
Step–Up
Vout – VF Vin(min)
Vin(min) Vsat
I
fmin
4 x 10 5 ton
2 Iout(max)
ton – toff
toff
RSC
0.33
Ipk(switch)
0.33
Ipk(switch)
L(min)
Vin(min) – Vsat – Vout
Ipk(switch)
ton(max)
Vin(min) – Vsat ton(max)
Ipk(switch)
CO
Ipk(switch) (ton + toff)
≈ Iout ton
8 Vripple(pp)
Vripple
Vsat = Saturation voltage of the output switch. VF = Forward voltage drop of the ringback rectifier.
Inverting
Vout + VF
Vin(min) – Vsat
I
fmin
4 x 10 5 ton
2 Iout(max)
ton + toff
toff
0.33
Ipk(switch)
Vin(min) – Vsat
Ipk(switch)
ton(max)
≈ Iout ton
Vripple
The following power supply characteristics must be chosen:
ǒ ) Ǔ + Vin – Nominal input voltage. If this voltage is not constant, then use Vin(max) for step–down and Vin(min) for step–up and inverting convertor.
Vout – Desired output voltage: Vout = 1.25 1
R2
R1
for step–down and step–up: Vout
1.25 R2 for inverting.
R1
Iout – Desired output current.
fmin – Minimum desired output switching frequency at the selected values for Vin and IO.
Vripple(pp) – Desired peak–to–peak output ripple voltage. In practice, the calculated value will need to be increased due to the capacitor’s equivalent series
– resistance and board layout. The ripple voltage should be kept to a low value since it will directly effect the line and load regulation.
See Application Note AN920 for further information
6
MOTOROLA ANALOG IC DEVICE DATA
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