Fairchild RC5042 Output Ripple and Noise, Efficiency, Processor Voltage Identification, Data Bits

AN42			APPLICATION NOTE
Table 2. Intel Pentium Pro and OverDrive Processor Power Specifications
	Voltage	Maximum	Maximum Thermal
	Specification	Current	Design Power1
CPU Model & Features	VCCP (VDC)	ICCP (A)	(W)
150MHz – 256K L2 Cache	3.1 ± 5%	9.9	29.2
166MHz – 512K L2 Cache	3.3 ± 5%	11.2	35.0
180MHz – 256K L2 Cache	3.3 ± 5%	10.1	31.7
200MHz – 256K L2 Cache	3.3 ± 5%	11.2	35.0
200MHz – 512K L2 Cache	3.3 ± 5%	12.4	37.9
OverDrive Processors
150 MHz	2.5 ± 5%	11.2	26.7
180 MHz		12.5	29.7
200 MHz		13.9	32.9
Flexible Motherboard2	2.4-3.5 ± 5%	14.5	45.0

Notes:

1.Maximum power values are measured at typical VCCP to take into account the thermal time constant of the CPU package.

2.Flexible motherboard specifications are recommendations only. Actual specifications are subject to change.

Output Ripple and Noise

Ripple and noise are defined as periodic or random signals over the frequency band of 20MHz at the output pins. Output ripple and noise requirements of ±1.0% must be met throughout the full load range and under all specified input voltage conditions.

Efficiency

The efficiency of the DC-DC converter must be greater than 80% at high current draw and greater than 40% at low current draw.

Processor Voltage Identification

The Pentium Pro package has four voltage identification pins, VID3–VID0, that can be used for automatic selection of the power supply voltage. These pins are internally uncon- nected or are shorted to ground (VSS). The logic status of the pins defines the voltage required by the processor. The VID codes have been implemented to support voltage specifica- tion variations on future Pentium Pro processors. These codes are presented in Table 3. A ‘1’ refers to an open pin and a ‘0’ refers to a short to ground. The VCCP power supply should supply the voltage that is requested or disable itself.

Table 3. Voltage Identification Codes for Pentium Pro

	Data Bits			VCCP
VID3	VID2	VID1	VID0	(VDC)
1	1	1	1	No CPU
1	1	1	0	2.1
1	1	0	1	2.2
1	1	0	0	2.3
1	0	1	1	2.4
1	0	1	0	2.5
1	0	0	1	2.6
1	0	0	0	2.7
0	1	1	1	2.8
0	1	1	0	2.9
0	1	0	1	3.0
0	1	0	0	3.1
0	0	1	1	3.2
0	0	1	0	3.3
0	0	0	1	3.4
0	0	0	0	3.5

I/O Controls

In addition to the voltage identification pins, several signals exist to control the DC-DC converter or to provide feedback from the converter to the CPU. These are Power-Good (PWRGD), Output Enable (OUTEN), and Upgrade Present (UP). These signals are discussed later.

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