Datasheet

AFE031
SBOS531D –AUGUST 2010–REVISED MAY 2012 www.ti.com
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. 1SMB59xxB
(1)
D2, D3 Schottky diode Diodes, Inc. 1N5819HW
TVS Transient voltage suppressor Diodec Semiconductor P6SMBJxxC
(2)
MOV Varistor LittleFuse TMOV20RP140E
HV Cap High-voltage capacitor Illinois Capacitor, Inc 474MKP275KA
(3)
240 VAC, 50 Hz
COMPONENT DESCRIPTION MANUFACTURER MFR PART NO (OR EQUIVALENT)
D1 Zener diode Diodes, Inc. 1SMB59xxB
(1)
D2, D3 Schottky diode Diodes, Inc. 1N5819HW
TVS Transient voltage suppressor Diodec Semiconductor P6SMBJxxC
(2)
MOV Varistor LittleFuse TMOV20RP300E
HV Cap High-voltage capacitor Illinois Capacitor, Inc 474MKP275KA
(3)
(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 ● PA_V
S
).
(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.
The AFE031 is assembled into a 7-mm
2
x 7-mm
2
, 48-lead, QFN package. As Figure 52 shows, this QFN
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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