dsp56371 Freescale Semiconductor, Inc, dsp56371 Datasheet - Page 64

• Manufacturer Part Number: dsp56371
• Description: Dsp56371 Data Sheet
• Manufacturer: Freescale Semiconductor, Inc

Electrical Design Considerations
As noted above, the junction-to-case thermal resistances quoted in this data sheet are determined using the
first definition. From a practical standpoint, that value is also suitable for determining the junction
temperature from a case thermocouple reading in forced convection environments. In natural convection,
using the junction-to-case thermal resistance to estimate junction temperature from a thermocouple
reading on the case of the package will estimate a junction temperature slightly hotter than actual
temperature. Hence, the new thermal metric, thermal characterization parameter or Ψ
to be (T
when using the surface temperature of the package. Remember that surface temperature readings of
packages are subject to significant errors caused by inadequate attachment of the sensor to the surface and
to errors caused by heat loss to the sensor. The recommended technique is to attach a 40-gauge
thermocouple wire and bead to the top center of the package with thermally conductive epoxy.
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Use the following list of recommendations to assure correct DSP operation:
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This device contains circuitry protecting against damage due to high static voltage or
electrical fields. However, normal precautions should be taken to avoid exceeding
maximum voltage ratings. Reliability of operation is enhanced if unused inputs are tied to
an appropriate logic voltage level (for example, either GND or V
for a pull-up or pull-down resistor is 10 k ohm.
Provide a low-impedance path from the board power supply to each V
the board ground to each GND pin.
Use at least six 0.01–0.1 µF bypass capacitors positioned as close as possible to the four sides of
the package to connect the V
Ensure that capacitor leads and associated printed circuit traces that connect to the chip V
GND pins are less than 1.2 cm (0.5 inch) per capacitor lead.
Route the DVDD pin carefully to minimize noise.
Use at least a four-layer PCB with two inner layers for V
Because the DSP output signals have fast rise and fall times, PCB trace lengths should be
minimal. This recommendation particularly applies to the IRQA, IRQB, IRQC, and IRQD pins.
Maximum PCB trace lengths on the order of 15 cm (6 inches) are recommended.
Consider all device loads as well as parasitic capacitance due to PCB traces when calculating
capacitance. This is especially critical in systems with higher capacitive loads that could create
higher transient currents in the V
Take special care to minimize noise levels on the V
If multiple DSP56371 devices are on the same board, check for cross-talk or excessive spikes on
the supplies due to synchronous operation of the devices.
RESET must be asserted when the chip is powered up. A stable EXTAL signal must be supplied
before deassertion of RESET.
J
– T
Electrical Design Considerations
T
)/P
D
. This value gives a better estimate of the junction temperature in natural convection
CC
DSP56371 Data Sheet, Rev. 4.1
power source to GND.
CC
and GND circuits.
CAUTION
CCP
and GND
CC
and GND.
CC
P
). The suggested value
pins.
CC
pin on the DSP and from
Freescale Semiconductor
JT
, has been defined
CC
and