FSB Design Guidelines
R
Intel
®
855PM Chipset Platform Design Guide
67
Figure 31. Intel 855PM MCH HVREF[4:0] Reference Voltage Generation Circuit
R1
Ω
1%
R2
Ω
1%
C1
200 pF
C2
200 pF
+VCCP
AB16
AB12
AA9
M7
P8
Intel
855PM
MCH
HVREF
HVREF
HVREF
HVREF
HVREF
C3
1 uF
MCH_GTLREF
A recommended layout for the MCH_GTLREF generation circuit is shown in Figure 32. The
MCH_GTLREF generation circuit components are located on the secondary side to minimize
motherboard space usage and optimize robustness of the connection. Each of the AB16, AB12, and P8
HVREF pins has a decoupling capacitor (C1, C2, and C3) next to them. GND side of the C1, C2, and
C3 capacitors is connected to the GND flood on the secondary side and stitched with vias to internal
GND planes. R1 is placed next to pin AB16 and R2 is placed next to pin P8. Layer 3 of the motherboard
shorts the two clusters of HVREF pins P8, M7, AB16, AB12, and AA9. The two clusters are further
shorted on the primary side layer.