HCPL-7800 Datasheet, PDF (14/17 Pages) Agilent(Hewlett-Packard) – High CMR Isolation Amplifiers

FLOATING
POSITIVE
SUPPLY
HV+
GATE DRIVE
CIRCUIT
MOTOR
+
-
R _SENSE
IN
U1
78L05
C1
0.1 µF
OUT
R5
39 Ω
C2
0.1 µF
C3
0.01 µF
1
8
2
U2
7
3 ^HCPL-7800 6
4
5
+5 V
C4
0.1 µF
R1
2.00 KΩ
R2
2.00 KΩ
C6
75 pF
HV-
Figure 26. Recommended Application Circuit.
C5
75 pF
R3
10.0 KΩ
+15 V
C8
0.1 µF
-
U3
+
MC34081
C7
0.1 µF
R4
10.0 KΩ
-15 V
V_OUT
400
OUTPUT POWER, P_S
INPUT POWER, P_S
300
200
100
0
0 20 40 60 80 100 120 140 160 180
175
T_A – TEMPERATURE – °C
Figure 27. Dependence of Safety-
Limiting Parameters on Ambient
Temperature.
Applications Information
Functional Description
Figure 28 shows the primary
functional blocks of the HCPL-
7800. In operation, the sigma-
delta analog-to-digital converter
converts the analog input signal
into a high-speed serial bit
stream, the time average of which
is directly proportional to the
input signal. This high speed
stream of digital data is encoded
and optically transmitted to the
detector circuit. The detected
signal is decoded and converted
into accurate analog voltage
levels, which are then filtered to
produce the final output signal.
To help maintain device accuracy
over time and temperature,
internal amplifiers are chopper-
stabilized. Additionally, the
encoder circuit eliminates the
effects of pulse-width distortion of
the optically transmitted data by
generating one pulse for every
edge (both rising and falling) of
the converter data to be
transmitted, essentially converting
the widths of the sigma-delta
output pulses into the positions
of the encoder output pulses. A
significant benefit of this coding
scheme is that any non-ideal
characteristics of the LED (such
as non-linearity and drift over
time and temperature) have little,
if any, effect on the performance
of the HCPL-7800.
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