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http://www.union-ic.com Rev.01 Jan.2015

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UM803

allows either device to assert reset (Figure 2).

Figure 2. Interfacing to μPs with Bidirectional Reset I/O

UM803 Open-Drain RESET

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Output Allows Use with Multiple Supplies

Generally, the pull-up connected to the UM803 will connect to the supply voltage that is being

from the monitored supply to reset circuitry powered by some other supply (Figure 3). Note that as

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. Also, with

any pull-up, RESET

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depends on the pull-up resistor value and the voltage to which it is connected.

Figure 3. UM803 Open-Drain RESET

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Output Allows Use with

Multiple Supplies

Benefits of Highly Accurate Reset Threshold

Most µP supervisor circuits have reset threshold voltages between 5% and 10% below the value of

nominal supply voltages. This ensures a reset will not occur within 5% of the nominal supply, but

will occur when the supply is 10% below nominal.

When using ICs rated at only the nominal supply ±5%, this leaves a zone of uncertainty where the

supply is between 5% and 10% low, and where the reset may or may not be asserted.

The UM803L_/T_/Z_ use highly accurate circuitry to ensure that reset is asserted close to the 5%

limit, and long before the supply has declined to 10% below nominal.

UM803

UM803