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HCPL-7560

Optically Isolated Sigma-Delta (Σ-∆) Modulator

Avago Technologies 

Product Description

The HCPL-7560 Isolated Modulator (optocoupler) uses

sigma-delta modulation to convert an analog input

signal into a high-speed (10 MHz) single-bit digital data

stream; the time average of the modulator’s single-bit

data is directly proportional to the input signal. The

isolated modulator’s other main function is to provide

galvanic isolation between the analog input and the

digital output. An internal voltage reference determines

the full-scale analog input range of the modulator (ap-

proximately ± 320 mV); an input range of ± 200 mV is

recommended to achieve optimal performance.

HCPL-7560 can be used together with HCPL-0872,

Digital Interface IC or a digital filter. The primary func-

tions of the HCPL-0872 Digital Interface IC are to derive

a multi-bit output signal by averaging the single-bit

modulator data, as well as to provide a direct micro-

controller interface. The effective resolution of the

multi-bit output signal is a function of the length of

time (measured in modulator clock cycles) over which

the average is taken; averaging over longer periods of

time results in higher resolution. The Digital Interface

IC can be configured for five conversion modes, which

have different combinations of speed and resolution

to achieve the desired level of performance. Other

functions of the HCPL-0872 Digital Interface IC include

a Phase Locked Loop based pre-trigger circuit that

can either give more precise control of the effective

sampling time or reduce conversion time to less than

1µs, a fast over-range detection circuit that rapidly indi-

cates when the magnitude of the input signal is beyond

full-scale, an adjustable threshold detection circuit

that indicates when the magnitude of the input signal

is above a user adjustable threshold level, an offset

calibration circuit, and a second multiplexed input that

allows a second Isolated Modulator to be used with a

single Digital Interface IC.

The digital output format of the Isolated A/D Converter

is 15 bits of unsigned binary data. The input full-scale

range and code assignment is shown in Table 1 below.

Although the output contains 15 bits of data, the effec-

tive resolution is lower and is determined by selected

conversion mode as shown in Table 2 below.

Table 1. Input Full-Scale Range and Code Assignment.

Analog Input

Full Scale Range

Minimum Step Size

+Full Scale

Zero

-Full Scale

Voltage Input

640 mV

20 µV

+320 mV

0 mV

-320 mV

Digital Output

32768 LSBs

1 LSB

111111111111111

100000000000000

000000000000000

Table 2. Isolated A/D Converter Typical Performance Characteristics.

Conversion

Mode

1

2

Signal-to-Noise

Ratio (dB)

83

79

Effective

Resolution

(bits)

13.5

12.8

Conversion Time (µs)

Pre-Trigger Mode

0

1

2

205 102

103 51

3

73

11.9

39

19

0.2

4

66

5

53

10.7

20

10

8.5

10

5

Signal

Delay(µs)

102

51

19

10

5

Signal Bandwidth

(kHz)

3.4

6.9

22

45

90

Notes: Bold italic type indicates Default values.

13

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