VIPER
Power and power management
Power and power management
Power supplies
The VIPER is designed to operate from a 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 12V to the PC/104 stack if
required. For details of the power connector please see the section
, page
There are four on board 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 of the +3.3V
supplies is dedicated for use with the CompactFLASH interface on PL5 and +3.3V flat
panels on PL3.
The +5V supply is monitored automatically on-board; if this supply falls below +4.63V
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 using the CompactFLASH socket and an LCD display, ensure the total current
requirement on 3.3V does not exceed 900mA! Please check the datasheets of
the devices you are using, as there is no on-board protection!
Battery backup
An external battery (CR2032 or similar) pro3.0V to +3.3V can be used as a
battery backup for the DS1307 RTC and the SRAM. The external battery supplies
power to the battery backup circuit only when there is no +5V supply to the board.
To use an external battery connect its + and - terminals across PL16 pins 3 (VBAT) and
2 (GND) respectively, see
, page
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
DS1307 RTC with Clock Out Off
0.3
0.5
DS1307 RTC with Clock Out On
0.48
0.8
Supply Supervisor
0.6
1
Total with RTC Clock Out Off
1.1
3.5
Total with RTC Clock Out On
1.28
3.8
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
DS1307 minimum voltages are 1.5V and 2V respectively. If the supply falls
below these points then the corresponding device may loose data. Please
check your battery datasheet for mAh and operating temperature specifications.
© 2004 Arcom Issue H
51
