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ZEUS Technical Manual Power and power management
© 2007 Eurotech Ltd Issue D 65
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
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.