 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
MAX705CUA Datasheet(PDF) 7 Page - Maxim Integrated Products |
|
||||||||||||||||||||||||||||||
MAX705CUA Datasheet(HTML) 7 Page - Maxim Integrated Products |
|
|
7 / 12 page  Low-Cost, µP Supervisory Circuits 7 Maxim Integrated MAX705–MAX708/MAX813L Power-Fail Comparator The power-fail comparator can be used for various pur- poses because its output and noninverting input are not internally connected. The inverting input is internal- ly connected to a 1.25V reference. To build an early-warning circuit for power failure, con- nect the PFI pin to a voltage divider (see Typical Operating Circuit). Choose the voltage divider ratio so that the voltage at PFI falls below 1.25V just before the +5V regulator drops out. Use PFO to interrupt the µP so it can prepare for an orderly power-down. __________Applications Information Ensuring a Valid RESET Output Down to VCC = 0V When VCC falls below 1V, the MAX705-MAX708 RESET output no longer sinks current—it becomes an open cir- cuit. High-impedance CMOS logic inputs can drift to undetermined voltages if left undriven. If a pull-down resistor is added to the RESET pin as shown in Figure 5, any stray charge or leakage currents will be drained to ground, holding RESET low. Resistor value (R1) is not critical. It should be about 100k Ω, large enough not to load RESET and small enough to pull RESET to ground. Monitoring Voltages Other Than the Unregulated DC Input Monitor voltages other than the unregulated DC by connecting a voltage divider to PFI and adjusting the ratio appropriately. If required, add hysteresis by con- necting a resistor (with a value approximately 10 times the sum of the two resistors in the potential divider net- work) between PFI and PFO. A capacitor between PFI and GND will reduce the power-fail circuit’s sensitivity to high-frequency noise on the line being monitored. RESET can be asserted on other voltages in addition to the +5V VCC line. Connect PFO to MR to initiate a RESET pulse when PFI drops below 1.25V. Figure 6 shows the MAX705-MAX708 configured to assert RESET when the +5V supply falls below the reset threshold, or when the +12V supply falls below approximately 11V. Monitoring a Negative Voltage The power-fail comparator can also monitor a negative supply rail (Figure 7). When the negative rail is good (a negative voltage of large magnitude), PFO is low, and when the negative rail is degraded (a negative voltage of lesser magnitude), PFO is high. By adding the resis- tors and transistor as shown, a high PFO triggers reset. As long as PFO remains high, the MAX705- MAX708/MAX813L will keep reset asserted (RESET = low, RESET = high). Note that this circuit’s accuracy depends on the PFI threshold tolerance, the VCC line, and the resistors. tWP tWD tWD tWD +5V 0V WDI +5V 0V WDO +5V 0V RESET +5V 0V (RESET) tRS ( ) ARE FOR MAX813L ONLY. RESET EXTERNALLY TRIGGERED BY MR Figure 3. MAX705/MAX706/MAX813L Watchdog Timing Figure 4. MAX705/MAX706 RESET, MR, and WDO Timing with WDI Three-Stated. The MAX707/MAX708/MAX813L RESET output is the inverse of RESET shown. tRS tRS +5V 0V RESET WDO +5V 0V MR tMR MR EXTERNALLY DRIVEN LOW +5V 0V VCC VRT VRT tMD |
Similar Part No. - MAX705CUA |
|
Similar Description - MAX705CUA |
|
|
|
Link URL |
| Privacy Policy |
| ALLDATASHEET.COM |
| Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
| Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
|
Family Site : ic2ic.com |
icmetro.com |
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
