45
0832F–HIREL–02/07
e2v semiconductors SAS 2007
PC7410
14.2
Power Supply Voltage Sequency
The notes in Table 6-1 on page 9 contain cautions about the sequencing of the external bus voltages
and core voltage of the PC7410 (when they are different). These cautions are necessary for the long
term reliability of the part. If they are violated, the electrostatic discharge (ESD) protection diodes will be
forward-biased and excessive current can flow through these diodes. If the system power supply design
does not control the voltage sequencing, one or both of the circuits of Figure 14-3 can be added to meet
these requirements. The MUR420 Schottky diodes of Figure 14-3 control the maximum potential differ-
ence between the external bus and core power supplies on power-up and the 1N5820 diodes regulate
the maximum potential difference on power-down.
Figure 14-3. Example Voltage Sequencing Circuits
14.3
Decoupling Recommendations
Due to the PC7410’s dynamic power management feature, large address and data buses and high oper-
ating frequencies, the PC7410 can generate transient power surges and high frequency noise in its
power supply, especially while driving large capacitive loads. This noise must be prevented from reach-
ing other components in the PC7410 system and the PC7410 itself requires a clean, tightly regulated
source of power. Therefore, it is recommended that the system designer place at least one decoupling
capacitor at each V
DD, OVDD, and L2OVDD pin of the PC7410. It is also recommended that these decou-
pling capacitors receive their power from separate V
DD, (L2)OVDD, and GND power planes in the PCB,
utilizing short traces to minimize inductance.
These capacitors should have a value of 0.01 µF or 0.1 µF. Only ceramic SMT (surface mount technol-
ogy) capacitors should be used to minimize lead inductance, preferably 0508 or 0603 orientations where
connections are made along the length of the part. Consistent with the recommendations of Dr. Howard
Johnson in High Speed Digital Design: A Handbook of Black Magic (Prentice Hall, 1993) and contrary to
previous recommendations for decoupling PowerPC microprocessors, multiple small capacitors of equal
value are recommended over using multiple values of capacitance.
In addition, it is recommended that there be several bulk storage capacitors distributed around the PCB,
feeding the V
DD, L2OVDD, and OVDD planes to enable quick recharging of the smaller chip capacitors.
These bulk capacitors should have a low ESR (equivalent series resistance) rating to ensure the quick
response time necessary. They should also be connected to the power and ground planes through two
vias to minimize inductance. Suggested bulk capacitors are 100 - 330 µF (AVX TPS tantalum or Sanyo
OSCON).
MUR420
MUR420
1N5820
1N5820
1.8V
2.5V
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