LMH6580, LMH6581

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SNOSAY4C – AUGUST 2007 – REVISED MAY 2013

THERMAL MANAGEMENT

The LMH6580/LMH6581 are high performance devices that produce a significant amount of heat. With ±5V

supplies, the LMH6580/LMH6581 will dissipate approximately 0.5 W of idling power with all outputs enabled.

Idling power is calculated based on the typical supply current of 50 mA and a 10V supply voltage. This power

dissipation will vary within the range of 0.4 W to 0.6 W due to process variations. In addition, each equivalent

video load (150

Ω) connected to the outputs should be budgeted 30 mW of power. For a typical application with

one video load for each output this would be a total power of 0.62 W. With a

θJA of 44 °C/W this will result in the

silicon being 27°C over the ambient temperature. A more aggressive application would be two video loads per

output which would result in 0.74 W of power dissipation. This would result in a 33°C temperature rise. For

heavier loading, the TQFP package thermal performance can be significantly enhanced with an external heat

sink and by providing for moving air ventilation. Also, be sure to calculate the increase in ambient temperature

from all devices operating in the system case. Because of the high power output of this device, thermal

management should be considered very early in the design process. Generous passive venting and vertical

board orientation may avoid the need for fan cooling or heat sinks. Also, the LMH6580/LMH6581 can be

operated with a ±3.3V power supply. This will cut power dissipation substantially while only reducing bandwidth

by about 10% (2 VPP output). The LMH6580/LMH6581 are fully characterized and factory tested at the ±3.3V

power supply condition for applications where reduced power is desired.

PRINTED CIRCUIT LAYOUT

Generally, a good high frequency layout will keep power supply and ground traces away from the input and

output pins. Parasitic capacitances on these nodes to ground will cause frequency response peaking and

possible circuit oscillations (see Application Note OA-15 for more information). If digital control lines must cross

analog signal lines (particularly inputs) it is best if they cross perpendicularly. Texas Instruments suggests the

following evaluation boards as a guide for high frequency layout and as an aid in device testing and

characterization:

Device

Package

Evaluation Board Part Number

LMH6580

48–Pin

LMH730164EF

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