Data Sheet

ADPA1105

Rev. 0 | Page 15 of 16

THERMAL MANAGEMENT

Proper thermal management is critical to achieve the specified

performance and rated operating life. Pulsed biasing is required

to limit the average power dissipated and maintain a safe channel

temperature. The channel (or die) temperature correlates

closely with the mean time to failure.

Consider a continuous bias case (see Figure 51). When bias is

through a turn on transient interval and eventually settles to a

(1)

where:

TIME

Figure 51. Continuous Bias

Next, consider a pulsed bias case at low duty cycle (see Figure 52).

as a series of exponentially rising and decaying pulses. The peak

channel temperature reached during consecutive pulses increases

during the turn on transient interval, and eventually settles to a

steady state condition where peak channel temperatures from

pulse to pulse stabilize.

POWER DISSIPATED

DURING THE PULSE

TIME

Figure 52. Pulsed Bias at Low Duty Cycle

Transient thermal measurements were performed on the

ADPA1105 amplifier at several different bias pulse widths and

duty cycles to obtain the thermal resistance values listed in Table 7.

Table 7. Pulse Settings and Thermal Resistance Values

Pulse Settings

Pulse Width (μs)

Duty Cycle (%)

100

10

2.11

200

20

2.82

300

30

3.54

Narrower pulse widths and/or lower duty cycles can result in

greater reliability.

The ADPA1105 amplifier is designed for low duty cycle pulsed

applications. However, there can be brief periods of time when

the device operates (perhaps accidently) under continuous

bias conditions. The thermal resistance increases to 6.5°C/W

under these conditions. Even at the nominal quiescent bias

dissipation results in a 130°C channel temperature rise above

the base temperature. Use extreme caution in this case to ensure

that the device does not exceed the device maximum reliable

channel temperature of 200°C.