Filter
Top Products
Hardware Description
ARM DUI 0224F Copyright © 2003-2007 ARM Limited. All rights reserved. 3-33
3.4 Power supply control
If the PB926EJ-S is powered from the brick power supply, a nominal 12V level
(VSMP) is supplied to the 5V and 3V regulators. If VSMP, drops too low, shutdown
signals nPOWERFAIL, nSHDN1, and nSHDN2 become active and power is switched
off. The shutdown circuitry is shown in Figure 3-16 on page 3-34. The power supply
can be toggled on and off by pressing the Power/Standby pushbutton.
If the PB926EJ-S is powered from the PCI backplane or the screw terminals, the VSMP
voltage is not present. Therefore:
• the 5VSB standby voltage is not present
• nSHDN1 is held LOW
• nSHDN2 is held HIGH (this enables the 5V analog regulator)
• the Power/Standby pushbutton has no effect and you must use the external power
source to turn the system on or off.