Design Tips
Figure 13. Buffered Circuit for the Reference Voltage
4. Design Tips
The application of the supply voltage supervisors of the series TL77xx is not complicated. However it
should be noticed, that this circuit is an analog circuit, whose function and performance - e.g. the stability
of the reference voltage - may be negatively influenced by noise in the neighboring circuits. Therefore the
voltage monitor should be placed on the printed circuit board, where there are no neighboring circuits in
the which switch high currents (like bus interface circuits and power switches). When laying out the layout
of the printed circuit board special care should taken with the interconnects which carry analog signals.
Beside the SENSE input these are the C and Vref terminals. Noise coupled into the C input will lead to a
t
t
reduction of the output pulse width. Noise coupled into the V input or into the filter capacitor at this input
ref
may lead to undesired triggering of the circuit and by this to an undesired RESET pulse. Practice shows,
that this malfunction when high currents flow over the interconnects of these capacitors to the GND
terminal of the voltage monitor. To avoid these effects, the GND terminals of these capacitors must be
connected by the shortest way to the GND terminal of the voltage monitor in so that no currents caused by
other circuits flow over these wires. Figure14 show a layout proposal for the printed circuit board.
Furthermore the resistors of the voltage divider at the SENSE input of the TL7702 (R and R3 in figure 14)
2
have to be placed in so, that no noise may be coupled into this circuit.
Supply voltage Supervisor TL77xx Series
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TI [ TEXAS INSTRUMENTS ]
