Eurotech Appliances PXA255 Power and power management, Power supplies, Typical (µA), Maximum (µA), 1.1 ( 3.1 with TPM), 3.82 (7.82 with TPM), 1.28 (3.28 with TPM), 4.05 (8.05 with TPM)

VIPER Technical Manual	Power and power management

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 PL16 379H– Power connector , page 95 380H.

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 PL16 381H– Power connector , page 95 382Hfor connections.

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.