AFE031

SBOS531D – AUGUST 2010 – REVISED MAY 2012

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Table 19 lists several recommended transient protection components.

Table 19. Recommended Transient Protection Devices

120 VAC, 60 Hz

COMPONENT

DESCRIPTION

MANUFACTURER

MFR PART NO (OR EQUIVALENT)

D1

Zener diode

Diodes, Inc.

D2, D3

Schottky diode

Diodes, Inc.

1N5819HW

TVS

Transient voltage suppressor

Diodec Semiconductor

MOV

Varistor

LittleFuse

TMOV20RP140E

HV Cap

High-voltage capacitor

Illinois Capacitor, Inc

240 VAC, 50 Hz

COMPONENT

DESCRIPTION

MANUFACTURER

MFR PART NO (OR EQUIVALENT)

D1

Zener diode

Diodes, Inc.

D2, D3

Schottky diode

Diodes, Inc.

1N5819HW

TVS

Transient voltage suppressor

Diodec Semiconductor

MOV

Varistor

LittleFuse

TMOV20RP300E

HV Cap

High-voltage capacitor

Illinois Capacitor, Inc

(1)

Select the Zener breakdown voltage at the lowest available rating beyond the normal power-supply operating range.

(2)

Select the TVS breakdown voltage at or slightly greater than (0.5

(3)

A common value for the high-voltage capacitor is 470 nF. Other values may be substituted depending on the requirements of the

application. Note that when making a substitution, it is important in terms of reliability that the capacitor be selected from the same

familiy or equivalent family of capacitors rated to withstand high-voltage surges.

THERMAL CONSIDERATIONS

In a typical powerline communications application, the AFE031 dissipates 2 W of power when transmitting into

the low impedance of the ac line. This amount of power dissipation can increase the junction temperature, which

in turn can lead to a thermal overload that results in signal transmission interruptions if the proper thermal design

of the PCB has not been performed. Proper management of heat flow from the AFE031 as well as good PCB

design and construction are required to ensure proper device temperature, maximize performance, and extend

device operating life.

package has a large area exposed thermal pad on the underside that is used to conduct heat away from the

AFE031 and into the underlying PCB.

Figure 52. QFN Package with Large Area Exposed Thermal Pad

Some heat is conducted from the silicon die surface through the plastic packaging material and is transferred into

the ambient environment. Because plastic is a relatively poor conductor of heat, however, this route is not the

primary thermal path for heat flow. Heat also flows across the silicon die surface to the bond pads, through the

wire bonds, into the package leads, and finally into the top layer of the PCB. While both of these paths for heat

flow are important, the majority (nearly 80%) of the heat flows downward, through the silicon die, into the

thermally-conductive die attach epoxy, and into the exposed thermal pad on the underside of the package (see

Figure 53). Minimizing the thermal resistance of this downward path to the ambient environment maximizes the

life and performance of the device.

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