AN2504 Datasheet, PDF (1/14 Pages) STMicroelectronics – Using STMicroelectronics Voltage Detectors

AN2504
Application note
Using STMicroelectronics Voltage Detectors
1
Introduction
Voltage detectors are designed to monitor the system supply voltage and assert the output
signal, OUT, every time it goes below a defined voltage threshold.
The major advantages of these circuits are low current consumption and a precise
temperature-compensated voltage reference, V_REF (see Figure 1). STMicroelectronics
voltage detectors are also laser programmed to the desired voltage threshold over the range
of 1.6V to 6.0V in 100mV steps and they have a good transient immunity (see Figure 5).
Figure 1.
N-Channel Open Drain Output Block Diagram
VCC
R1
+
–
R2
VREF
VOUT
VSS
R3
AI10482b
Note that voltage detector output state simply indicates if the supply voltage is above or
below a specific threshold, which can be used for early power fail warning.
However microprocessors' inputs require some minimum input pulse width to register the
change of signal on the logical input. In this case we recommend using reset circuits, which
guarantee the minimum pulse width known as reset time-out period. Reset circuits have
some other advantages compared to voltage detectors (e.g. specification across
temperature, better voltage threshold accuracy, and lower temperature coefficient). On the
other hand voltage detectors are usually able to operate at higher voltages, have lower
current consumption, greater hysteresis and usually a lower price.
The qualities mentioned above cause voltage detectors to be preferentially used in the
following applications:
• Battery Monitoring
• Power-Supply Monitoring • Portable Medical Devices
• Power Fail Detection
• PDAs
• Notebook Computers
• Back-up Supply Switching • Portable/Battery-
Powered Electronics
• Cell Phones.
February 2007
Rev 1
1/14
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