
Electrical Design Considerations
56F8323 Technical Data
Preliminary
127
The thermal characterization parameter is measured per JESD51-2 specification using a 40-gauge
type T thermocouple epoxied to the top center of the package case. The thermocouple should be
positioned so that the thermocouple junction rests on the package. A small amount of epoxy is
placed over the thermocouple junction and over about 1mm of wire extending from the junction.
The thermocouple wire is placed flat against the package case to avoid measurement errors caused
by cooling effects of the thermocouple wire.
When heat sink is used, the junction temperature is determined from a thermocouple inserted at the
interface between the case of the package and the interface material. A clearance slot or hole is
normally required in the heat sink. Minimizing the size of the clearance is important to minimize
the change in thermal performance caused by removing part of the thermal interface to the heat
sink. Because of the experimental difficulties with this technique, many engineers measure the heat
sink temperature and then back-calculate the case temperature using a separate measurement of the
thermal resistance of the interface. From this case temperature, the junction temperature is
determined from the junction-to-case thermal resistance.
12.2 Electrical Design Considerations
Use the following list of considerations to assure correct operation of the 56F8323:
Provide a low-impedance path from the board power supply to each V
DD
pin on the 56F8323, and
from the board ground to each V
SS
(GND) pin
The minimum bypass requirement is to place six 0.01–0.1
μ
F capacitors positioned as close as
possible to the package supply pins. The recommended bypass configuration is to place one bypass
capacitor on each of the V
DD
/V
SS
pairs, including V
DDA
/V
SSA.
Ceramic and tantalum capacitors
tend to provide better performance tolerances.
Ensure that capacitor leads and associated printed circuit traces that connect to the chip V
DD
and
V
SS
(GND)
pins are less than 0.5 inch per capacitor lead
Use at least a four-layer Printed Circuit Board (PCB) with two inner layers for V
DD
and V
SS
Bypass the V
DD
and V
SS
layers of the PCB with approximately 100
μ
F, preferably with a high-grade
capacitor such as a tantalum capacitor
Because the 56F8323 output signals have fast rise and fall times, PCB trace lengths should be
minimal
CAUTION
This device contains protective circuitry to guard
against damage due to high static voltage or electrical
fields. However, normal precautions are advised to
avoid application of any voltages higher than
maximum-rated voltages to this high-impedance circuit.
Reliability of operation is enhanced if unused inputs are
tied to an appropriate voltage level.
F
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
.