Datenblatt-Suchmaschine für elektronische Bauteile |
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MAX807NCWE Datenblatt(PDF) 13 Page - Maxim Integrated Products |
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MAX807NCWE Datenblatt(HTML) 13 Page - Maxim Integrated Products |
13 / 16 page Battery-Backup Mode Battery backup preserves the contents of RAM in the event of a brownout or power failure. With a backup battery installed at BATT, the MAX807 automatically switches RAM to backup power when VCC falls. Two conditions are required for switchover to battery-back- up mode: 1) VCC must be below the reset threshold; 2) VCC must be below VBATT. Table 1 lists the status of inputs and outputs during battery-backup mode. Backup-Battery Input The BATT input is similar to VCC, except the PMOS switch is much smaller. This input is designed to con- duct up to 20mA to OUT during battery backup. The on-resistance of the PMOS switch is approximately 13 Ω. Figure 12 shows the two series pass elements between the BATT input and OUT that facilitate UL approval. VBATT can exceed VCC during normal opera- tion without causing a reset. Output Supply Voltage The output supply (OUT) transfers power from VCC or BATT to the µP, RAM, and other external circuitry. At the maximum source current of 250mA, VOUT will typi- cally be 260mV below VCC. Decouple this terminal with a 0.1µF capacitor. BATT ON Output The battery on (BATT ON) output indicates the status of the internal battery switchover comparator, which con- trols the internal VCC and BATT switches. For VCC greater than VBATT (ignoring the small hysteresis effect), BATT ON typically sinks 3.2mA at 0.4V. In bat- tery-backup mode, this output sources approximately 5mA. Use BATT ON to indicate battery switchover sta- tus, or to supply gate or base drive for an external pass transistor for higher current applications (see the Typical Operating Circuit). Full-Featured µP Supervisory Circuit with ±1.5% Reset Accuracy ______________________________________________________________________________________ 13 Figure 12. VCC and BATT-to-OUT Switch MAX807 P PP OUT VCC BATT 0.1 µF CONTROL CIRCUITRY Table 1. Input and Output Status in Battery-Backup Mode The power-fail comparator remains active in battery-backup mode for VCC ≥ 4V. Below 4V, PFO is forced low. PFO 2 WDI is ignored and goes high impedance WDI 4 Battery switchover comparator monitors VCC for active switchover. VCC 3 MR is ignored MR 6 Logic high; the open-circuit output voltage is equal to VCC. RESET 8 Logic low LOW LINE 7 Ground—0V reference for all signals GND 5 Logic high. The open-circuit output voltage is equal to VCC. WDO 10 High impedance CE IN 12 Logic high. The open-circuit output voltage is equal to VBATT. CE OUT 11 Supply current is 1µA maximum for VBATT ≤ 2.8V. BATT 14 PIN OUT is connected to BATT through two internal PMOS switches in series. OUT 16 The power-fail comparator remains active in battery-backup mode for VCC ≥ 4V. PFI 1 FUNCTION NAME Logic high when VBATT exceeds 2.285V. Valid for VCC ≥ 4V. Below 4V, BATT OK is forced low. BATT OK 15 Logic high. The open-circuit output voltage is equal to VBATT. BATT ON 13 Logic low RESET 9 |
Ähnliche Teilenummer - MAX807NCWE |
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Ähnliche Beschreibung - MAX807NCWE |
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