HCPL-7860 View Datasheet(PDF) - HP => Agilent Technologies

Part Name

Description

Manufacturer

HCPL-7860

Optically Isolated Sigma-Delta (Σ−∆) Modulator

HP => Agilent Technologies 

Power Supplies and Bypassing

The recommended application

circuit is shown in Figure 17.

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 zener

diode (D1); the value of

resistor R1 should be chosen

to supply sufficient current

from the existing floating

supply. The voltage from the

current sensing resistor or

shunt (Rsense) is applied to

the input of the HCPL-7860/

HCPL-786J (U2) through an

RC anti-aliasing filter (R2 and

C2). And finally, the output

clock and data of the isolated

modulator are connected to

the digital interface IC.

Although the application

circuit is relatively simple, a

few recommendations should

be followed to ensure optimal

performance.

FLOATING

POSITIVE

SUPPLY

HV+

GATE DRIVE

CIRCUIT

The power supply for the

isolated modulator is most

often obtained from the same

supply used to power the

power transistor gate drive

circuit. If a dedicated supply

is required, in many cases it is

possible to add an additional

winding on an existing

transformer. Otherwise, some

sort of simple isolated supply

can be used, such as a line

powered transformer or a

high-frequency DC-DC

converter.

An inexpensive 78L05 three-

terminal regulator can also be

used to reduce the floating

supply voltage to 5 V. To help

attenuate high-frequency

power supply noise or ripple,

a resistor or inductor can be

used in series with the input

of the regulator to form a low-

pass filter with the regulator’s

input bypass capacitor.

As shown in Figure 17, 0.1 µF

bypass capacitors (C1 and C3)

should be located as close as

possible to the input and

output power-supply pins of

the isolated modulator (U2).

The bypass capacitors are

required because of the high-

speed digital nature of the

signals inside the isolated

modulator. A 0.01 µF bypass

capacitor (C2) is also

recommended at the input due

to the switched-capacitor

nature of the input circuit. The

input bypass capacitor also

forms part of the anti-aliasing

filter, which is recommended

to prevent high-frequency

noise from aliasing down to

lower frequencies and

interfering with the input

signal.

+5V

MOTOR

+-

R SENSE

R1

D1

5.1 V

R2 39 Ω

C1

0.1 µF

C2

0.01 µF

V DD1

V IN+

V IN-

GND1

V DD2

MCLK

MDAT

GND2

HCPL-7860/

HCPL-786J

HV-

Figure 17. Recommended Application Circuit.

C3

0.1 µF

CCLK

CLAT

CDAT

MCLK1

MDAT1

MCLK2

MDAT2

GND

V DD

CHAN

SCLK

SDAT

CS

THR1

OVR1

RESET

HCPL-0872

TO

CONTROL

CIRCUIT

14

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