CAT8710 Datasheet, PDF (5/7 Pages) ON Semiconductor – Quad Voltage Supervisor

CAT8710
Detailed Description
The CAT8710 is a space-saving, low-power, quad voltage
microprocessor supervisory circuit designed to monitor 4
voltage supplies. The CAT8710 has 2 factory preset
thresholds for monitoring standard power supply voltages of
3.3 V, 3.0 V, 2.5 V, or 1.8 V, and 2 adjustable thresholds for
monitoring voltages as low as 0.62 V.
Each internal voltage comparator has a typical hysteresis
of 0.3% with respect to its reset threshold, which improves
immunity to ambient noise without significantly reducing
threshold accuracy. CAT8710 is designed to ignore short
transients.
Applications Information
Reset Output
CAT8710 provides an extended reset signal 120 ms (typ)
in duration. The output is open drain and requires an external
pull-up resistor to an external power supply. This supply can
be less than or greater than VDD, but should not exceed
5.5 V. When the external pull−up voltage is greater than
VDD reverse current flow from the external pull−up voltage
to VDD is prevented by CAT8710’s internal circuitry.
The CAT8710 is powered by VDD, which is also a
monitored voltage. When any supply drops below its
threshold, the reset output asserts low and remains low as
long as VDD is above 1.0 V.
Figure 9. RESET Output Timing Diagram
3.3 V
CAT8710
V1MON
V2/VDD
RESET
V3
V4MON
GND
5V
mP
RESET
Adjustable Thresholds
CAT8710 allows users to create 2 custom voltage
thresholds. The threshold voltage at each adjustable input is
typically 0.62 V. Monitoring of voltages greater than 0.62 V
requires a resistor-divider network to be connected to the
circuit (Figure 11).
VIN + 0.62 V
(R1 ) R2)
R2
or, written in terms of R1:
ǒ Ǔ R1 + R2
VIN
0.62 V
*
1
Because the CAT8710 has a guaranteed input current of
less than 50 nA on the adjustable inputs, resistor values up
to 1000 kW can be used for R2 with < 1% error.
Unused Inputs
Connect 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.
Adding Manual Reset Capability
Figure 12 illustrates how to add manual reset to the
CAT8710. Depressing the pushbutton switch short−circuits
the analog input to ground and initiates a RESET pulse. This
technique can be used on either the V1 or V4 inputs. The
switch must be open for at least 120 ms in order to deassert
the RESET output. No external switch debounce is required.
A small capacitor across R₂ will improve noise immunity
when using long leads from the pushbutton switch to the
adjustable input.
POR
Applying power to the CAT8710 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, 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
All monitored inputs are immune to short supply
transients. For applications where higher immunity is
required, connect a 0.1 mF bypass capacitor from each input
pin to ground very close to CAT8710’s package.
Figure 10. Interfacing to Different Logic−Supply
Voltage
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