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MAX6363PUT46 Datasheet(PDF) 6 Page - Maxim Integrated Products |
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MAX6363PUT46 Datasheet(HTML) 6 Page - Maxim Integrated Products |
6 / 8 page Backup-Battery Switchover In a brownout or power failure, it may be necessary to preserve the contents of the RAM. With a backup bat- tery installed at BATT, the MAX6361/MAX6363/ MAX6364 automatically switch the RAM to backup power when VCC falls. The MAX6363 has a BATT ON output that goes high when in battery-backup mode. These devices require two conditions before switching to battery-backup mode: 1) VCC must be below the reset threshold. 2) VCC must be below VBATT. Table 2 lists the status of the inputs and outputs in battery-backup mode. The device will not power up if the only voltage source is on BATT. OUT will only power up from VCC at startup. Manual Reset Input (MAX6361 only) Many µP-based products require manual reset capabili- ty, allowing the operator, a test technician, or external logic circuitry to initiate a reset. For the MAX6361, a logic low on MR asserts reset. Reset remains asserted while MR is low, and for a minimum of 150ms (tRP) after it returns high. MR has an internal 20k Ω pull-up resistor. This input can be driven with TTL/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 the device is used in a noisy environment, connect a 0.1µF capaci- tor from MR to GND to provide additional noise immunity. Reset In (MAX6364 only) RESET IN is compared to an internal 1.235V reference. If the voltage at RESET IN is less than 1.235V, reset is asserted. The RESET IN comparator may be used as an undervoltage detector to signal a failing power sup- ply. It can also be used as a secondary power-supply reset monitor. Reset Output A µP’s reset input starts the µP in a known state. The MAX6361/MAX6363/MAX6364 µP supervisory circuits assert a reset to prevent code-execution errors during power-up, power-down, and brownout conditions. RESET is guaranteed to be a logic low or high depend- ing on the device chosen (see Ordering Information). RESET or RESET asserts when VCC is below the reset threshold and for at least 150ms (tRP) after VCC rises above the reset threshold. RESET or RESET also asserts when MR is low (MAX6361) and when RESET IN is less than 1.235V (MAX6364). Applications Information Operation Without a Backup Power Source The MAX6361/MAX6363/MAX6364 were designed for battery-backed applications. If a backup battery is not used, connect VCC to OUT and connect BATT to GND. Replacing the Backup Battery If BATT is decoupled with a 0.1µF capacitor to ground, the backup power source can be removed while VCC remains valid without danger of triggering a reset pulse. The device does not enter battery-backup mode when VCC stays above the reset threshold voltage. Negative-Going VCC Transients These supervisors are relatively immune to short-dura- tion, negative-going VCC transients. Resetting the µP when VCC experiences only small glitches is usually not desirable. The Typical Operating Characteristics section shows a graph of Maximum Transient Duration vs. Reset Threshold Overdrive for which reset is not asserted. The graph was produced using negative-going VCC pulses, starting at VCC and ending below the reset threshold by the magnitude indicated (reset threshold overdrive). The graph shows the maximum pulse width SOT23, Low-Power µP Supervisory Circuits with Battery Backup 6 _______________________________________________________________________________________ PIN STATUS VCC Disconnected from OUT OUT Connected to BATT BATT Connected to OUT. Current drawn from the battery is less than 1µA (at VBATT = 2.8V, excluding IOUT) when VCC = 0. RESET/RESET Asserted BATT ON High state MR, RESET IN Inputs ignored Table 2. Input and Output Status in Battery-Backup Mode SUFFIX 46 4.50 4.63 44 4.25 4.38 31 3.00 3.08 4.75 4.50 3.15 23 2.25 29 2.85 2.93 2.32 26 2.55 2.63 2.38 3.00 2.70 RESET THRESHOLD RANGES (V) Table 1. Reset Threshold Ranges MIN MAX TYP |
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