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| AN938 Datasheet, PDF (29/33 Pages) STMicroelectronics – The L4973 family is a 3.5 A monolithic DC-DC converter | |||
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AN938
Figure 39. Design example for 70 V input supply
Applications
CBOOT
VCC 50-70V
Q
R
CIN
7,8
17
CIN1
9
2,3
L4973
12
16 11
CZ DZ
CSS
CREF
RRE
CC
CO
D
5V
IO=3.5A
COUT
AM03521v1
4.3
Buck-boost converter
This topology is useful to stabilize an output voltage higher, equal or lower than the input
supply. Figure 40 shows the schematic diagram of a converter designed for 12 V, Iout = 3.5 Ã
(1-D), with an input supply ranging from 8 V to 55 V.
The 20 V Zener connected to the gate-source of the power MOSFET is for protection
purposes when the supply voltage is higher than 20 V.
Such a circuit, asymmetrical half-bridge, is fully protected from output short-circuit, by
turning off the on-board floating mos.
Figure 40. Up/down converter
220nF
8V<Vi<55V
1000μF
9
2,3
11
L4973
47K
4,5,6
12
1 17 13,14,15
11
1.2nF
1.2μF
Rcomp
Ccomp
150μH STPS5L60
Vo=12V/1.4A
12K
56nF
Dz
20V
4.7K
2.330μF
ESR
<50mΩ
AM03522v1
Doc ID 5410 Rev 10
29/33
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