Electronic Components Datasheet Search |
|
LTC1235 Datasheet(PDF) 10 Page - Linear Technology |
|
LTC1235 Datasheet(HTML) 10 Page - Linear Technology |
10 / 16 page 10 LTC1235 S APPLICATI I FOR ATIO Replacing the Backup Battery with Power On When changing the backup battery with system power on, spurious resets can occur while battery is removed due to battery standby current. Although battery standby current is only a tiny leakage current, it can still charge up the stray capacitance on the VBATT pin. The oscillation cycle is as follows: When VBATT reaches within 50mV of VCC, the LTC1235 switches to battery backup or battery saving mode. In either case, the battery supply current pulls VBATT low and the device goes back to normal operation. The leakage current then charges up the VBATT pin again and the cycle repeats. If spurious resets during battery replacement pose no problems, then no action is required. Otherwise, two methods can be used to eliminate this problem. First, a capacitor from VBATT to GND will allow time for battery replacement by slowing the charge rate. For example, the battery standby current is 1 µA maximum over tempera- ture and the external capacitor required to slow the charge rate is: where TREQ'D is the maximum time required to replace the backup battery. With VCC = 4.5V, VBATT = 3V and TREQ'D = 3 sec, the value for external capacitor is 2 µF. Second, a resistor from VBATT to GND will hold the pin low while changing the battery. For example, the battery standby current is 1 µA maximum over temperature and the exter- nal resistor required to hold VBATT below VCC is: With VCC = 4.5V, a 4.3MΩ resistor will work. With a 3V battery, this resistor will draw only 0.7 µA from the battery, which is negligible in most cases. If the battery connections are made with long wires or PC traces, inductive spikes can be generated during battery replacement. Even if a resistor is used to prevent spurious resets as described above, these spikes can take the VBATT pin below GND violating the LTC1235 absolute maximum ratings. A 0.1 µF capacitor from VBATT to GND is recom- mended to eliminate these potential spikes when battery replacement is made through long wires. Figure 5. Charging External Battery Through VOUT The operating voltage at the VBATT pin ranges from 2.0V to 4.25V. High value capacitors, such as electrolytic or farad- size double layer capacitors, can be used for short term memory backup instead of a battery. For capacitor backup, see Typical Applications. The charging resistor for re- charging rechargeable batteries should be connected to VOUT through a diode since this eliminates the discharge path that exists when VCCcollapses and RAM is not backed up (Figure 5). Figure 4. Conditional Battery Backup Operation +5V +3V 0.1µF 0.1µF VBATT VCC LTC1235 VOUT GND 4 LTC1235 F05 VOUT – VBATT – VD R I = R BACKUP I/O LINE µP RAM 1N4148 VOUT IN BATTERY SAVING MODE LOGIC LOW BACKUP VCC RESET VOLTAGE THRESHOLD VOUT Hi-Z VBATT VOUT IN BATTERY BACKUP MODE LOGIC HIGH RESET VOLTAGE THRESHOLD VBATT BACKUP VCC VOUT VOUT = VBATT LTC1235 F04 CT 1A V– V EXT REQ'D CC BATT ≥ µ R V – 50mV 1A CC ≤ µ |
Similar Part No. - LTC1235 |
|
Similar Description - LTC1235 |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.NET |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | 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 |