Applications Information
Functional Description
signal, which is filtered to obtain
the final output signal.
300
250
200
150
100
Figure 23 shows the primary
functional blocks of the HCPL-
7820/7825. In operation, the
sigma-delta modulator converts
the analog input signal into a
high-speed serial bit stream. The
time average of this bit stream is
directly proportional to the input
signal. This stream of digital data
is encoded and optically trans-
mitted to the detector circuit. The
detected signal is decoded and
converted back into an analog
Application Circuit
P , OUTPUT
S
The recommended application
circuit is shown in Figure 24. A
floating power supply (which in
many applications could be the
same supply that is used to drive
the high-side power transistor) is
regulated to 5 V using a simple
three-terminal voltage regulator
(U1). The voltage from the cur-
rent sensing resistor, or shunt
(RSENSE), is applied to the input of
P , INPUT
S
MAX. OPERATING
TEMP. IS 100 °C
50
0
0
50
100
150
200
T
– TEMPERATURE – °C
A
Figure 22. Dependence of Safety-
Limiting Values on Temperature.
VOLTAGE
CLOCK
VOLTAGE
REGULATOR
GENERATOR
REGULATOR
ISOLATION
BOUNDARY
Σ∆
LED DRIVE
CIRCUIT
DETECTOR
CIRCUIT
DECODER
AND D/A
ISO-AMP
OUTPUT
ISO-AMP
INPUT
ENCODER
FILTER
MODULATOR
Figure 23. HCPL-7820/7825 Block Diagram.
FLOATING
SUPPLY
HV+
C5
75 pF
GATE DRIVE
CIRCUIT
• • •
R3
FLOATING
SUPPLY
10.0 KΩ
U1
78L05
+5 V
+15 V
C8
0.1 µF
IN OUT
C1
C2
1
2
8
7
C4
0.1
µF
0.1
µF
0.1 µF
R5
39 Ω
R1
–
2.00 KΩ
C3
V
U3
U2
OUT
0.01
µF
R2
+
6
5
3
4
MC34081
2.00 KΩ
MOTOR
+
–
C7
• • •
R
SENSE
C6
75 pF
R4
10.0 KΩ
0.1 µF
HCPL-7820/7825
-15 V
• • •
HV–
Figure 24. Recommended Application Circuit.
1-244
HP [ HEWLETT-PACKARD ]
