56F801_1 Datasheet, PDF (44/48 Pages) Freescale Semiconductor, Inc – 16-bit Digital Signal Controllers

• Measure the thermal resistance from the junction to where the leads are attached to the case. This definition
is approximately equal to a junction to board thermal resistance.
• Use the value obtained by the equation (T_J – T_T)/P_D where T_T is the temperature of the package case
determined by a thermocouple.
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.
5.2 Electrical Design Considerations
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.
Use the following list of considerations to assure correct operation:
• Provide a low-impedance path from the board power supply to each V_DD pin on the controller, and from the
board ground to each V_SS (GND) pin.
• The minimum bypass requirement is to place 0.1 μF 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 ten 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.
56F801 Technical Data, Rev. 17
44
Freescale Semiconductor