Transformer Driver for
Isolated RS-485 Interface
VIN
5V
C1
0.1µF
6
4
SD
ON / OFF
VCC
1
D1
MAX253
3
FREQUENCY
SWITCH
FS
GND1
2
8
D2
GND2
7
*SEE TABLE 2
1CT:1.3CT* 1N5817
C3
0.1µF
5V @ 200mA
TP1 ISO OUTPUT
C2
22µF
1N5817
OPTIONAL 21kHz LOWPASS OUTPUT FILTER
L2
25µH
FILTER
OUTPUT
OUTPUT
C7
2.2µF
Figure 6. 5V to Isolated 5V Application Circuit
VIN
3.3V
C1
0.1µF
4
SD
ON / OFF
1
D1
MAX253
3
FREQUENCY
SWITCH
FS
GND1 GND2
2
7
8
D2
VCC
6
1N5817
*SEE TABLE 2
1CT:2.1CT* 1N5817
1N5817
1N5817
C4
0.1µF
C3
0.1µF
5V @ 100mA
TP1 ISO OUTPUT
C2
22µF
OPTIONAL 21kHz LOWPASS OUTPUT FILTER
L2
25µH
FILTER
OUTPUT
OUTPUT
C7
2.2µF
Figure 7. 3.3V to Isolated 5V Application Circuit
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