4.0 PC Board Layout Considerations
Fusion 878A
4.3 Latchup Avoidance
PCI Video Decoder
4-4
Conexant
100600B
4.3 Latchup Avoidance
Latchup is possible with all CMOS devices. It is triggered when any signal pin
exceeds the voltage on the power pins associated with that pin by more than 0.5 V,
or falls below the ground pins associated with that pin by more than 0.5 V.
Latchup can also occur if the voltage on any power pin exceeds the voltage on any
other power pin by more than 0.5 V.
To avoid latchup of the Fusion 878A, follow these precautions:
•
Apply power to the device before or at the same time as you apply power to
the interface circuit.
•
Connect all VDD, VBB and VAA pins together through a low impedance
plane.
•
Connect all BGND and AGND pins together through a low impedance
plane.
•
If you are using a voltage regulator on the digital and/or analog power
planes, use protection diodes.
See
for an illustration of optional regulatory circuitry.
Figure 4-1. Optional Regulatory Circuitry
In
Out
Ground
GND
(+5 V)
(+5 V)
(+12 V)
System Power
System Power
VAA, VDD, VBB
Suggested part numbers:
Regulator Texas Instruments
µ
A78 MO5M
Diodes must handle the
current requirements of
the Fusion 878A and
the peripheral circuitry.
879A_048