ACS8946 Semtech Corporation, ACS8946 Datasheet - Page 37

• Manufacturer Part Number: ACS8946
• Description: Jitter Attenuating, Multiplying Phase Locked Loop, with Protection Switch, for Oc-12/stm-4 and GbE
• Manufacturer: Semtech Corporation

Thermal Conditions
The device is rated for full temperature range when this
package is used with a 4-layer or more PCB. Copper
coverage must exceed 50%. All pins must be soldered to
the PCB. Maximum operating temperature must be
reduced when the device is used with a PCB with less than
these requirements.
As the device includes a large thermal die paddle ground
connection which must be soldered to the PCB in addition
to the pins, giving improved pull-off strength and thermal
dissipation characteristics as well as the necessary
grounding.
Figure 22 Typical 48 Pin QFN PCB Footprint
Revision 3/November 2006 © Semtech Corp.
ADVANCED COMMUNICATIONS
FINAL
Page 37
Although not essential for the ACS8946, one technique
that may be used to improve heat dissipation from
through the large centre pad is to include a thermal
landing the same size as the centre pad on the
component side of the board (and one on the opposite
side of the PCB) connected to analog ground using a
number of thermal vias, approximately 0.33 mm
diameter. These vias should be completely connected
(flooded over) to the thermal landing(s) as well as to
internal ground planes if using a multi-layer PCB. 3 x 3
vias pitched at 1.27 mm between via centres would be
more than sufficient for the ACS8946 if this method were
adopted.
ACS8946 JAM PLL
DATASHEET
www.semtech.com