Voltage Regulator-Down (VRD) 10.1 Design Guide

Vtt Requirements (REQUIRED)
R
Design Guide
37
3 Vtt Requirements (REQUIRED)
The Vtt regulator provides power to the processor VID, the chipset - processor front side bus, and
miscellaneous buffer signals. This rail must settle to the voltage defined in Table 3-1 and assert an
active-high VIDPWRGD output when in regulation (see section 9.2). The Vtt regulator controller
does not include an enable signal; valid output voltage of Table 3-1 must be guaranteed by the
timing protocol defined in Figure 4-1.
3.1 Electrical Specifications
A linear regulator is recommended for the Vtt supply with adequate decoupling capacitors to
ensure the sum of AC bus noise and DC tolerance satisfy limits identified in Table 3-1. The
processor and chipset Vtt supply must be maintained within these tolerance limits across full
operational thermal limits, part-to-part component variation, age degradation, and regulator
accuracy. Full bandwidth bus noise amplitude must be guaranteed across all Vcc/Vss land pairs
defined in Table 4-1.
Future generation processors may require lower Vtt voltages. To support multiple processor
generations with different values, the Vtt regulator design must have the capability to identify the
necessary voltage setting and configure the Vtt regulation voltage to the correct value. The
processor communicates the required Vtt value to the regulator via the VTT_SELECT land. Table
3-2 lists each configuration with accompanying electrical requirements. At this time,
775_Vtt_CONFIG_B is PROPOSED and the electrical properties may change at any time.
The Vtt supply must be unconditionally stable under all DC and transient conditions across the
voltage and current ranges defined in Table 3-1. The Vtt supply must also operate in a no-load
condition: i.e., with no processor installed.
Table 3-1. Vtt Specifications
Processor
Vtt
Min
Vtt
Typ
Vtt
Max
Itt
Min
Itt
Max
Itt
TDC
Vtt_SELECT
1.140 V 1.200 V 1.260 V 0.15 A 5 A 2.6 A 1
775_Vtt_CONFIG_1
1.045 V 1.100 V 1.155 V 0.15 A 5 A 2.6 A 0
1.140 V 1.200 V 1.260 V 0.15 A 6.2 A 3.8 A 1
775_Vtt_CONFIG_2
1.045 V 1.100 V 1.155 V 0.15 A 6.2 A 3.8 A 0
All LGA775
Configurations
1.140V 1.200V 1.260V 0.15A 3.4A 5.25A
NOTES:
1. This configuration is PROPOSED and may be changed at a later date.
2. See Section 3.2 for details regarding Vtt support for the Intel
®
Pentium
®
4 processor Extreme Edition
Supporting Hyper-Threading Technology on 0.13 micron process.
3. Combined DC and Transient voltage tolerance is 5%, with a maximum 2% DC tolerance.