THS3096PWPR datasheet(22/34 Pages) TI

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DIE

Side View (a)

DIE

End View (b)

Thermal

Pad

Bottom View (c)

PowerPAD™ DESIGN CONSIDERATIONS

0.140

0.060

0.010

vias

Top View

0.035

0.080

0.050

0.176

0.030

0.026

0.010

0.035

0.100

0.300

Pin 1

THS3092

THS3096

SLOS428A – DECEMBER 2003 – REVISED FEBRUARY 2004

•

Connections to other wideband devices on the

leadframe upon which the die is mounted [see

board may be made with short direct traces or

Figure 66(a) and Figure 66(b)]. This arrangement

through onboard transmission lines. For short

results in the lead frame being exposed as a thermal

connections, consider the trace and the input to

pad on the underside of the package [see Fig-

the next device as a lumped capacitive load.

ure 66(c)]. Because this thermal pad has direct

Relatively wide traces (50 mils to 100 mils)

thermal contact with the die, excellent thermal per-

should be used, preferably with ground and

formance can be achieved by providing a good

power planes opened up around them. Estimate

thermal path away from the thermal pad. Note that

the total capacitive load and determine if isolation

devices such as the THS3092/6 have no electrical

resistors on the outputs are necessary. Low

connection between the PowerPAD and the die.

parasitic capacitive loads (< 4 pF) may not need

The PowerPAD package allows for both assembly

an RS since the THS3092/6 are nominally com-

and thermal management in one manufacturing oper-

pensated to operate with a 2-pF parasitic load.

ation. During the surface-mount solder operation

Higher parasitic capacitive loads without an RS

(when the leads are being soldered), the thermal pad

are

allowed

the

signal

gain

increases

can also be soldered to a copper area underneath the

(increasing the unloaded phase margin). If a long

package. Through the use of thermal paths within this

trace is required, and the 6-dB signal loss intrin-

copper area, heat can be conducted away from the

sic to a doubly-terminated transmission line is

package into either a ground plane or other heat

acceptable, implement a matched impedance

dissipating device.

transmission line using microstrip or stripline

techniques (consult an ECL design handbook for

The PowerPAD package represents a breakthrough

microstrip and stripline layout techniques). A

in combining the small area and ease of assembly of

50-

Ω environment is not necessary onboard, and

surface

mount

with

the,

heretofore,

awkward

in fact, a higher impedance environment im-

mechanical methods of heatsinking.

proves distortion as shown in the distortion ver-

sus load plots. With a characteristic board trace

impedance based on board material and trace

dimensions, a matching series resistor into the

trace from the output of the THS3092/6 is used

as well as a terminating shunt resistor at the input

of the destination device. Remember also that the

terminating impedance is the parallel combination

of the shunt resistor and the input impedance of

Figure 66. Views of Thermal Enhanced Package

the destination device: this total effective im-

pedance should be set to match the trace im-

Although there are many ways to properly heatsink

pedance. If the 6-dB attenuation of a doubly

the PowerPAD package, the following steps illustrate

terminated transmission line is unacceptable, a

the recommended approach.

long trace can be series-terminated at the source

end only. Treat the trace as a capacitive load in

this case. This does not preserve signal integrity

as well as a doubly-terminated line. If the input

impedance of the destination device is low, there

is some signal attenuation due to the voltage

divider formed by the series output into the

terminating impedance.

•

Socketing a high speed part like the THS3092/6

are not recommended. The additional lead length

and pin-to-pin capacitance introduced by the

socket can create an extremely troublesome

parasitic network which can make it almost im-

possible to achieve a smooth, stable frequency

response. Best results are obtained by soldering

the THS3092/6 parts directly onto the board.

The

THS3092/6

are

available

Figure 67. DDA PowerPAD PCB Etch and Via

thermally-enhanced PowerPAD family of packages.

Pattern

These packages are constructed using a downset

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