ISL59424 Datasheet, PDF (11/13 Pages) Intersil Corporation – 1GHz Triple Multiplexing Amplifiers

ISL59424, ISL59445
The QFN Package Requires Additional PCB Layout
Rules for the Thermal Pad
The thermal pad is electrically connected to V- supply
through the high resistance IC substrate. Its primary function
is to provide heat sinking for the IC. However, because of the
connection to the V- supply through the substrate, the
thermal pad must be tied to the V- supply to prevent
unwanted current flow to the thermal pad. Do not tie this pin
to GND. Connecting this pin to GND could result in large
back biased currents flowing between GND and V-. The
ISL59445 uses the package with pad dimensions of
D2 = 2.48mm and E2 = 3.4mm.
Maximum AC performance is achieved if the thermal pad is
attached to a dedicated de-coupled layer in a multi-layered
PC board. In cases where a dedicated layer is not possible,
AC performance may be reduced at upper frequencies.
The thermal pad requirements are proportional to power
dissipation and ambient temperature. A dedicated layer
eliminates the need for individual thermal pad area. When a
dedicated layer is not possible a 1” x 1” pad area is sufficient
for the ISL59445 that is dissipating 0.5W in +50°C ambient.
Pad area requirements should be evaluated on a case by
case basis.
11
FN7456.2
September 8, 2005