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M40ZVCCMH1E Arkusz danych(PDF) 11 Page - STMicroelectronics |
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M40ZVCCMH1E Arkusz danych(HTML) 11 Page - STMicroelectronics |
11 / 25 page M40Z300, M40Z300W Operation 11/25 battery capacity for the SNAPHAT® of your choice can then be divided by this current to determine the amount of data retention available (see Table 13 on page 23). Caution: Take care to avoid inadvertent discharge through VOUT and E1CON - E4CON after battery has been attached. For a further more detailed review of lifetime calculations, please see Application Note AN1012. 2.3 Power-on reset output All microprocessors have a reset input which forces them to a known state when starting. The M40Z300/W has a reset output (RST) pin which is guaranteed to be low within tWPT of VPFD (see Table 7). This signal is an open drain configuration. An appropriate pull-up resistor should be chosen to control the rise time. This signal will be valid for all voltage conditions, even when VCC equals VSS. Once VCC exceeds the power failure detect voltage VPFD, an internal timer keeps RST low for tREC to allow the power supply to stabilize. 2.4 Battery low pin The M40Z300/W automatically performs battery voltage monitoring upon power-up, and at factory-programmed time intervals of at least 24 hours. The Battery Low (BL) pin will be asserted if the battery voltage is found to be less than approximately 2.5V. The BL pin will remain asserted until completion of battery replacement and subsequent battery low monitoring tests, either during the next power-up sequence or the next scheduled 24-hour interval. If a battery low is generated during a power-up sequence, this indicates that the battery is below 2.5V and may not be able to maintain data integrity in the SRAM. Data should be considered suspect, and verified as correct. A fresh battery should be installed. If a battery low indication is generated during the 24-hour interval check, this indicates that the battery is near end of life. However, data is not compromised due to the fact that a nominal VCC is supplied. In order to insure data integrity during subsequent periods of battery back-up mode, the battery should be replaced. The SNAPHAT® top should be replaced with valid VCC applied to the device. The M40Z300/W only monitors the battery when a nominal VCC is applied to the device. Thus appli-cations which require extensive durations in the battery back-up mode should be powered-up periodically (at least once every few months) in order for this technique to be beneficial. Additionally, if a battery low is indicated, data integrity should be verified upon power-up via a checksum or other technique. The BL pin is an open drain output and an appropriate pull-up resistor to VCC should be chosen to control the rise time. 2.5 VCC noise and negative going transients ICC transients, including those produced by output switching, can produce voltage fluctuations, resulting in spikes on the VCC bus. These transients can be reduced if capacitors are used to store energy which stabilizes the VCC bus. The energy stored in the bypass capacitors will be released as low going spikes are generated or energy will be |
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