 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
SP703CP Datasheet(PDF) 12 Page - Sipex Corporation |
|
|
|||||||||||||||||||||||||||||
SP703CP Datasheet(HTML) 12 Page - Sipex Corporation |
|
|
12 / 16 page  SP703/704DS/07 SP703/704 Low Power Microprocessor Supervisory © Copyright 2000 Sipex Corporation 12 Allowable Backup Power-Source Batteries Lithium batteries work very well as backup batteries due to very low self-discharge rate and high energy density. Single lithium batteries with open-circuit voltages of 3.0V to 3.6V are ideal. Any battery with an open-circuit voltage less than the minimum reset threshold plus 0.3V can be connected directly to the V BATT input of this series with no additional circuitry; see Figure 8. However, batteries with open-circuit voltages that are greater than this value cannot be used for backup, as current is sourced into V OUT through the diode (D1 in Figure 9) when V CC is close to the reset threshold. Operation Without a Backup Power Source If a backup power source is not used, ground V BATT and connect VOUT to VCC. Since there is no need to switch over to any backup power source, V OUT does not need to be switched. A direct connection to V CC eliminates any voltage drops across the switch which may push V OUT below V CC. Replacing the Backup Battery The backup battery can be removed while V CC remains valid, without danger of triggering RESET/RESET. As long as V CC stays above the reset threshold, battery-backup mode cannot be entered. Adding Hysteresis to the Power-Fail Comparator Hysteresis adds a noise margin to the power-fail comparator and prevents repeated triggering of PFO when V IN is close to its trip point. Figure 14 shows how to add hysteresis to the power-fail comparator. Select the ratio of R 1 and R 2 such that PFI sees 1.25V when VIN falls to its trip point (V TRIP). R3 adds the hysteresis. It will typically be an order of magnitude greater (about 10 times) than R 1 or R2. The current through R 1 and R2 should be at least 1µA to ensure that the 25nA (max) PFI input current does not shift the trip point. R 3 should be larger than 10K Ω so it does not load down the PFO pin. Capacitor C1 adds additional noise rejection. Monitoring a Negative Voltage The power-fail comparator can be used to monitor a negative supply rail using the circuit of Figure 15. When the negative rail is valid, PFO is low. When the negative supply voltage drops, PFO goes high. This circuit's accuracy is affected by the PFI threshold tolerance, the V CC voltage, and the resistors, R1 and R2. Figure 14. Adding Hysteresis to the POWER-FAIL Comparator PFI PFO R3 *C1 R2 R1 VIN connect to µP VCC +5V GND PFO VIN +5V VL VH VTRIP 0V 0V *optional VTRIP = R2 R1 + R2 VH = R2 || R3 R1 + R2 || R3 1.25 R2 = VL - 1.25 R1 5.0 - 1.25 R3 + 1.25 1.25 |
|
|
Link URL |
| Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Contact us | Privacy Policy | Link to Datasheet | 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 |
British ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
