HCPL-7820 datasheet(12/15 Pages) HP

12 / 15 page

1-244

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

(RSENSE), is applied to the input of

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

Figure 22. Dependence of Safety-

Limiting Values on Temperature.

VOLTAGE

REGULATOR

CLOCK

GENERATOR

Σ∆

MODULATOR

ENCODER

LED DRIVE

CIRCUIT

DETECTOR

CIRCUIT

DECODER

AND D/A

FILTER

ISO-AMP

OUTPUT

VOLTAGE

REGULATOR

ISO-AMP

INPUT

ISOLATION

BOUNDARY

Figure 24. Recommended Application Circuit.

Figure 23. HCPL-7820/7825 Block Diagram.

0.1 µF

+5 V

VOUT

2.00 K

Ω

+15 V

0.1 µF

-15 V

–

MC34081

10.0 K

Ω

HCPL-7820/7825

10.0 K

Ω

75 pF

78L05

IN OUT

0.01

µF

Ω

FLOATING

SUPPLY

GATE DRIVE

CIRCUIT

FLOATING

SUPPLY

• • •

HV+

• • •

HV–

• • •

–

RSENSE

MOTOR

75 pF

0.1

µF

0.1

µF

2.00 K

Ω

TA – TEMPERATURE – °C

150

100

300

100

150

MAX. OPERATING

TEMP. IS 100 °C

200

PS, OUTPUT

250

200

PS, INPUT

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