ACS8944 Semtech Corporation, ACS8944 Datasheet - Page 20

• Manufacturer Part Number: ACS8944
• Description: Jitter Attenuating, Multiplying Phase Locked Loop for Oc-12/stm-4
• 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.
The device includes a large thermal die paddle which
must be soldered to the PCB in addition to the pins for
improved thermal dissipation characteristics and to
strengthen the mechanical connection to the PCB.
Figure 16 Typical 48 Pin QFN PCB Footprint
Revision 3/November 2006 © Semtech Corp.
ADVANCED COMMUNICATIONS
FINAL
Page 20
Although not essential for the ACS8944, 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 0.33mm diameter.
These vias should be completely connected (flooded over)
to the thermal landing(s) as well as to internal ground
planes if using a multilayer PCB. 3 x 3 vias pitched at 1.27
mm between via centres would be more than sufficient for
the ACS8944 if this method were adopted.
ACS8944 JAM PLL
DATASHEET
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