MSAN-107 Zarlink Semiconductor, Inc., MSAN-107 Datasheet - Page 13

• Manufacturer Part Number: MSAN-107
• Description: Understanding and Eliminating Latch-Up in CMOS Applications
• Manufacturer: Zarlink Semiconductor, Inc.

Application Note
However, performance constraints on the port may
be such that the current-limiting resistors chosen are
too small to protect against severe faults such as
accidental connection of the AC mains supply.
Protection against such faults can be provided by
connection of external clamping diodes in the
manner outlined for ribbon cables. Again, Schottky
diodes may be required.
If fault conditions are likely to be very severe, it may
be necessary to reference external clamping diodes
to voltages inset by 0.7V from the power supply (Fig.
21).
output structures of the device on the port whenever
These diodes will conduct before the input/
Figure 21 - Inset Supply Voltages for External Clamping
Figure 20 - External Clamping Diodes
an over-voltage condition exists. Thus, no current
will flow to trigger latch-up. The reference voltages
are inset by 0.7V to allow the use of regular, low-cost
diodes. Due to the potentially large currents flowing
through the protection diodes, a clamping circuit
similar to the one in Fig. 18 is not feasible. The
output resistance in this case needs to be
substantially lower
Digital and Analog Devices in Same System
I
powered by different supply voltages, there is the
n systems which have digital and analog devices
.
MSAN-107
A-43