HCPL-7820 Datasheet, PDF (12/15 Pages) Agilent(Hewlett-Packard) – High CMR Analog Isolation Amplifiers

300
250
P_S, OUTPUT
200
P_S, INPUT
150
MAX. OPERATING
TEMP. IS 100 °C
100
50
0
0
50
100
150
200
T_A – TEMPERATURE – °C
Figure 22. Dependence of Safety-
Limiting Values on Temperature.
Applications Information
Functional Description
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
signal, which is filtered to obtain
the final output signal.
Application Circuit
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
(R_SENSE), is applied to the input of
VOLTAGE
REGULATOR
CLOCK
GENERATOR
ISO-AMP
INPUT
Σ∆
MODULATOR
ENCODER
ISOLATION
BOUNDARY
LED DRIVE
CIRCUIT
DETECTOR
CIRCUIT
Figure 23. HCPL-7820/7825 Block Diagram.
VOLTAGE
REGULATOR
DECODER
AND D/A
FILTER
ISO-AMP
OUTPUT
HV+
FLOATING
SUPPLY
GATE DRIVE
CIRCUIT
•••
C5
75 pF
MOTOR
•••
+–
R_SENSE
FLOATING
SUPPLY
U1
78L05
IN OUT
C1
C2
1
0.1
0.1
µF
µF
R5
2
39 Ω
C3
U2
0.01
µF
3
+5 V
8
C4
0.1 µF
7
R1
2.00 KΩ
6
R2
2.00 KΩ
4
5
HCPL-7820/7825
C6
75 pF
•••
R3
10.0 KΩ
+15 V
C8
0.1 µF
–
U3
+ _MC34081
C7
R4
10.0 KΩ
0.1 µF
-15 V
HV–
Figure 24. Recommended Application Circuit.
1-244
V_OUT