CAT884 Datasheet, PDF (6/8 Pages) ON Semiconductor – Quad Voltage Supervisor

CAT884
Adjustable Thresholds
CAT884 allows users to create 4 custom voltage
thresholds. The threshold voltage at each adjustable input is
typically 0.635 V. Monitoring of voltages greater than
0.635 V requires a resistor−divider network to be connected
to the circuit (Figure 9).
V_IN + 0.635 V
(R1 ) R2)
R2
or, written in terms of R1:
ǒǒ Ǔ Ǔ R1 + R2
V_IN
0.635 V
*1
Because the CAT884 has a guaranteed input current of less
than 50 nA on the monitoring inputs, resistor values up to
1,000 kW can be used for R2 with < 1% error.
Each of the 4 monitor inputs is also equipped with a glitch
canceling circuit which filters out noise spikes and transients
30 ms or shorter in duration. For applications where greater
noise immunity is required, connect a capacitor between
each input pin and ground (in parallel with R2), placing the
capacitor and resistor very close to CAT884’s package.
Unused Inputs
Connect any unused monitor inputs to a supply voltage
greater in magnitude than their specified threshold voltages;
use V_DD for normal operation (device power−supply pin).
Do not connect unused monitor inputs to ground or allow
them to float.
POR
Applying power to the CAT884 activates a POR circuit
which activates the reset output (active LOW). At power−up
POR prevents the system microprocessor from starting to
operate with insufficient voltage and prior to stabilization of
the clock oscillator. It ensures that operation is precluded
until internal registers are properly loaded and FPGA’s have
downloaded their configuration data. The reset signal
remains active until all monitored power supplies have risen
above their minimum preset voltage levels.
Power−Supply Bypassing
While not required for proper operation it is good practice
to bypass CAT884’s power supply with a 0.1 mF capacitor
placed close to the VDD pin.
V_IN
R1
CAT884
−
R2
+
VREF
+
−
Figure 9. Setting Monitor Voltage
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