THS4081, THS4082

175MHz LOW POWER HIGHSPEED AMPLIFIERS

SLOS274D − DECEMBER 1999 − REVISED JUNE 2001

19

POST OFFICE BOX 655303

APPLICATION INFORMATION

general PowerPAD

 design considerations (continued)

The next consideration is the package constraints. The two sources of heat within an amplifier are quiescent

power and output power. The designer should never forget about the quiescent heat generated within the

device, especially multiamplifier devices. Because these devices have linear output stages (Class A-B), most

of the heat dissipation is at low output voltages with high output currents. Figure 47 to Figure 50 show this effect,

along with the quiescent heat, with an ambient air temperature of 50

°C. Obviously, as the ambient temperature

increases, the limit lines shown will drop accordingly. The area under each respective limit line is considered

the safe operating area. Any condition above this line will exceed the amplifier’s limits and failure may result.

when looking at these graphs is how the devices are mounted on the PCB. The PowerPAD

extremely useful for heat dissipation. But, the device should always be soldered to a copper plane to fully use

the heat dissipation properties of the PowerPAD

. The SOIC package, on the other hand, is highly dependent

on how it is mounted on the PCB. As more trace and copper area is placed around the device,

and the heat dissipation capability increases. The currents and voltages shown in these graphs are for the total

package. For the dual amplifier package (THS4082), the sum of the RMS output currents and voltages should

be used to choose the proper package. The graphs shown assume that both amplifier’s outputs are identical.

Figure 47

Package With

θJA < = 127°C/W

SO-8 Package

θJA = 167°C/W

Low-K Test PCB

VCC = ± 5 V

TJ = 150°C

TA = 50°C

100

80

40

0

01

2

3

140

180

200

45

160

120

60

20

| VO | − RMS Output Voltage − V

Maximum Output

Current Limit Line

THS4081

MAXIMUM RMS OUTPUT CURRENT

vs

RMS OUTPUT VOLTAGE DUE TO THERMAL LIMITS

Safe Operating

Area

Figure 48

100

10

03

6

9

1000

12

15

Maximum Output

Current Limit Line

SO-8 Package

θJA = 167°C/W

Low-K Test PCB

SO-8 Package

θJA = 98°C/W

High-K Test PCB

TJ = 150°C

TA = 50°C

| VO | − RMS Output Voltage − V

VCC = ± 15 V

DGN Package

θJA = 58.4°C/W

THS4081

MAXIMUM RMS OUTPUT CURRENT

vs

RMS OUTPUT VOLTAGE DUE TO THERMAL LIMITS

Safe Operating

Area