Power and power management, Power supplies, Power – Eurotech Appliances VIPER / VIPER-LITE PXA255 User Manual
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VIPER Technical Manual
Power and power management
© 2007 Eurotech Ltd Issue E
73
Power and power management
Power supplies
The VIPER is designed to operate from a single +5V ±5% (4.75V to +5.25V) supply.
The power connector PL16 has a +12V connection defined, but is not required for the
VIPER under normal operation. It can be used to supply +12V to the PC/104 stack if
required. For details of the power connector please see the section
There are four onboard supply voltages derived from the +5V supply. These are +1.06
to +1.3V (microprocessor Core), +1.8V (CPLD Core) and two +3.3V. One +3.3V supply
is dedicated for use with the CompactFLASH interface and +3.3V flat panels.
The +5V supply is monitored automatically on-board; if this supply falls below +4V the
board is reset. When the power supply rises above this threshold voltage the board
comes out of reset and reboots itself. The power supply monitor ensures that the board
does not hang if the supply voltage fails at any point.
If a CompactFLASH and an LCD display are used, ensure the total current
requirement on 3.3V does not exceed 900mA! Please check the datasheets of
the devices you are using, as this supply is not protected!
Battery backup
An onboard Lithium-Ion non-rechargeable battery (CR2032) provides battery backup
for the DS1338 RTC, SRAM and optional TPM security feature when there is no +5V
supply to the board. An external battery (CR2032 or similar) may also be fitted. To use
an external battery see
The table below shows the typical and maximum current load on the external battery:
Device load on battery
Typical (µA)
Maximum (µA)
SRAM 0.2
2
DS1338 RTC with Clock Out Off / On
0.3 / 0.48
0.82/ 1.05
TPM (Optional)
2
4
Supply Supervisor
0.6
1
Total with RTC Clock Out Off
1.1 ( 3.1 with TPM)
3.82 (7.82 with TPM)
Total with RTC Clock Out On
1.28 (3.28 with TPM) 4.05 (8.05 with TPM)
An onboard Schottky diode drops 13mV from VBAT at 25°C. At -40°C this may
increase to 170mV and at +85°C decrease below 10mV. The SRAM and
DS1338 minimum voltages are 1.5V and 1.3V respectively. Reliable operation
below these minimum voltages cannot be guaranteed.
The VIPER does not provide a battery charging circuit.