ZEUS Technical Manual | Power and power management |
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Battery backup
An on-board non-rechargeable coin cell battery (CR2032) provides a 3V battery backup supply for the ISL1208 RTC, external SRAM and the supply supervisor, when there is no +5V supply to the board. The ZEUS is normally shipped with battery disconnected. See JP2 – Battery disconnect, page 93, for details.
The table below shows the typical and maximum current load on the backup battery:
| Device load on battery | Typical (µA) | Maximum (µA) |
SRAM | 0.3 | 3 |
ISL1208 RTC (with Clock Out Off) | 0.4 | 0.95 |
Supply Supervisor | 0.5 | 0.5 |
| Total | 1.2 | 1.45 |
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An onboard Schottky diode drops 13mV from VBAT at +25°C (+77°F). At -40°C (-40°F) this may increase to 170mV and at +85°C (+185°F) it may decrease below 10mV. The SRAM and ISL1208 minimum voltages are 1.5V and 1.8V respectively. Reliable operation below these minimum voltages cannot be guaranteed.
© 2007 Eurotech Ltd Issue D | 65 |
