Hardware Description

3.4Power 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.

ARM DUI 0224I

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ARM ARM DUI 0224I manual Power supply control