ISL59920 Datasheet, PDF (15/16 Pages) Intersil Corporation – Triple Analog Video Delay Lines

ISL59920, ISL59921, ISL59922, ISL59923
Power Dissipation
As the delay setting increases, additional filter blocks turn on
and insert into the signal path. When the delay per channel
increments, V_SP current increases by 0.9mA while V_SM
does not change significantly. Under the extreme settings,
the positive supply current reaches 141mA and the negative
supply current can be 41mA. Operating at ±5V power supply,
the worst-case ISL5992x power dissipation is:
PD = 5 • 141mA + 5 • 41mA = 910mW
(EQ. 1)
The minimum θ_JA required for long term reliable operation of
the ISL5992x is calculated using Equation 2:
θ_JA = (T_J – T_A ) ⁄ PD = 55°C ⁄ W
(EQ. 2)
Where:
T_J is the maximum junction temperature (+135°C)
T_A is the maximum ambient temperature (+85°C)
For a 20 Ld package on a well laid-out PCB with good
connectivity between the QFN’s pad and the PCB copper
area, 31°C/W θ_JA thermal resistance can be achieved. This
yields a much higher power dissipation of 3.54W using
Equation 2 (see Figure 31). To disperse the heat, the bottom
heat spreader must be soldered to the PCB. Heat flows
through the heat spreader to the circuit board copper then
spreads and convects to air. Thus, the PCB copper plane
becomes the heatsink (see TB389). This has proven to be a
very effective technique. A separate application note, which
details the 20 Ld QFN PCB design considerations, is
available.
15
FN6826.2
August 31, 2010