TLC770X Datasheet, PDF (24/27 Pages) Texas Instruments – BiCMOS SUPPLY VOLTAGE SUPERVISORS

When switching the outputs, for some nanoseconds both transistors at the output will be momentarily conducting,
and - as is usual with digital CMOS circuits having push-pull outputs-current peaks of several mA will be generated
on the supply line (see Figure 22.).
7
∆ ICC
15
6
CONTROL
10
5
5
0
4
-5
3
-10
2
-15
1
-20
0
-25
-1
-30
0 15 30 45 60 75 90 105 120 135 150 165 180 195
t [ns]
Figure 22. Current peaks on the supply line when switching the RESET output
To prevent these current peaks causing malfunction of the circuit, a blocking capacitor having a value of 0.1 µF
should be connected between the supply line and Ground. This will ensure that the switching currents which arise do
not generate unacceptable disturbances on the supply line.
When laying out the circuit board for a monitoring circuit, care must be taken that no currents resulting from other
nearby circuits can flow in the lines leading to the monitor section. An additional critical point in the layout is the
connections to the blocking capacitor C_B, through which flow the current peaks mentioned above. A good solution to
this is the use of a star-shaped connection of all connections to Ground, which will reduce undesirable coupling to a
minimum.
Figure 23. shows a suggested layout for the connection of the capacitors C_t and C_B, and of the external voltage
divider R₁/R₂. The connections are taken directly to the corresponding connecting pins on the package, in order to
avoid the above mentioned undesirable influences.
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