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UM822JCE Datasheet(PDF) 9 Page - Union Semiconductor, Inc. |
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UM822JCE Datasheet(HTML) 9 Page - Union Semiconductor, Inc. |
9 / 17 page ________________________________________________________________________ http://www.union-ic.com Rev.01 Jan.2015 9/17 UM807/821/822 assert reset to prevent code execution errors during power-up, power-down, or brownout conditions. RESET _____________ is guaranteed to be a logic low for VCC > 1V. Once VCC exceeds the reset threshold, an internal timer keeps RESET _____________ low for the reset timeout period; after this interval, RESET _____________ goes high. If a brownout condition occurs (VCC dips below the reset threshold), RESET _____________ goes low. Any time VCC goes below the reset threshold, the internal timer resets to zero, and RESET _____________ goes low. The internal timer starts after VCC returns above the reset threshold, and RESET _____________ remains low for the reset timeout period. The manual reset input (MR _______ ) can also initiate a reset. See the Manual Reset Input section. The UM822 has an active-high RESET output that is the inverse of the UM807/821’s RESET _____________ output. The UM807 uses an open-drain output, and the UM821/822 have a push-pull output stage. Connect a pull-up resistor on the UM807’s RESET _____________ output to any supply between 0 and 6V. Manual Reset Input Each device in the UM807/821/822 family includes one manual reset input, which must be held logic-low for an extended setup period (tMR) before the RESET _____________ output asserts. When valid manual reset input conditions/setup periods are met, the RESET _____________ output is one-shot pulse asserted low for a fixed reset pulse width (140ms min). Existing front-panel pushbutton switches (i.e., power on/off, channel up/down, or mode select) can be used to drive the manual reset inputs. The extended manual reset setup period prevents nuisance system resets during normal front-panel usage or resulting from inadvertent short-term pushbutton closure. This input has an internal 20kΩ pull-up resistor, so it can be left open if it is not used. MR _______ can be driven with TTL or CMOS-logic levels, or with open-drain/collector outputs. Connect a normally open momentary switch from MR _______ to GND to create a manual-reset function; external debounce circuitry is not required. If MR _______ is driven from long cables or if the device is used in a noisy environment, connecting a 0.1μF capacitor from MR _______ to ground provides additional noise immunity. Reset Threshold Accuracy The UM807/821/822 are ideal for systems using a 5V±5% or 3V±5% power supply with ICs specified for 5V±10% or 3V±10%, respectively. They are designed to meet worst-case specifications over temperature. The reset is guaranteed to assert after the power supply falls out of regulation, but before power drops below the minimum specified operating voltage range for the system ICs. The thresholds are pre-trimmed and exhibit tight distribution, reducing the range over which an undesirable reset may occur. |
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