User's Manual

Intel
®
820 Chipset Design Guide 2-71
Layout/Routing Guidelines
2.20.7 VBIAS DC Voltage and Noise Measurements
•
Steady state VBIAS will be a DC voltage of about 0.38V ±0.06V.
•
VBIAS will be “kicked” when the battery is inserted to about 0.7–1.0V, but it will come back
to its DC value within a few ms.
•
Noise on VBIAS must be kept to a minimum, 200 mV or less.
•
VBIAS is very sensitive and cannot be directly probed; it can be probed through a 0.01 uF
capacitor.
•
Excess noise on VBIAS can cause the ICH internal oscillator to misbehave or even stop
completely.
•
To minimize noise of VBIAS, it is necessary to implement the routing guidelines described
above and the required external RTC circuitry.