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THS4031, THS4032
100-MHz LOW-NOISE HIGH-SPEED AMPLIFIERS
SLOS224C – JULY 1999 – REVISED APRIL 2000
31
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
APPLICATION INFORMATION
general PowerPAD
design considerations (continued)
The next thing to be considered is 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 57 to Figure 60 shows
this effect, along with the quiescent heat, with an ambient air temperature of 50
°
C. When using V
CC
=
±
5 V, heat
is generally not a problem, even with SOIC packages. But, when using V
CC
=
±
15 V, the SOIC package is
severely limited in the amount of heat it can dissipate. The other key factor when looking at these graphs is how
the devices are mounted on the PCB. The PowerPAD
devices are 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,
θ
JA
decreases and the heat dissipation capability
increases. The currents and voltages shown in these graphs are for the total package. For the dual amplifier
package (THS4032), the sum of the RMS output currents and voltages should be used to choose the proper
package.
Figure 57
Package With
θ
JA < = 120
°
C/W
SO-8 Package
θ
JA = 167
°
C/W
Low-K Test PCB
VCC =
±
5 V
TJ = 150
°
C
TA = 50
°
C
100
80
40
0
0
1
| VO | – RMS Output Voltage – V
2
3
–
I
|
140
180
200
4
5
160
120
60
20
|
Maximum Output
Current Limit Line
THS4031
MAXIMUM RMS OUTPUT CURRENT
vs
RMS OUTPUT VOLTAGE DUE TO THERMAL LIMITS
Safe Operating
Area
Figure 58
100
10
0
3
| VO | – RMS Output Voltage – V
6
9
1000
12
15
Maximum Output
Current Limit Line
SO-8 Package
θ
JA = 167
°
C/W
Low-K Test PCB
SO-8 Package
θ
JA = 98
°
C/W
High-K Test PCB
TJ = 150
°
C
TA = 50
°
C
–
IO
|
|
VCC =
±
15 V
DGN Package
θ
JA = 58.4
°
C/W
THS4031
MAXIMUM RMS OUTPUT CURRENT
vs
RMS OUTPUT VOLTAGE DUE TO THERMAL LIMITS
Safe Operating
Area