Fairchild RC5050, RC5051 Output Ripple and Noise, Efficiency, Processor Voltage Identification

AN50APPLICATION 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	2.5 ±5%
150Mhz		11.2	26.7
180Mhz		12.5	29.7
200Mhz		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 ±13mV 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 maximum output current and greater than 40% at low current draw.

Processor Voltage Identification

There are four voltage identification Pins, VID3-VID0, on the Pentium Pro processor package which can be used to support automatic selection of the power supply voltage. These pins are internally unconnected or are shorted to ground (VSS). The logic status of the VID pins defines the voltage required by the processor. In order to address future low voltage microprocessors, the RC5050 and RC5051 include a VID4 input bit to extend the output voltage range as low as 1.3V. The output voltage programming codes are presented in Table 3. A “1” refers to an open pin and a ‘0’ refers to a short to ground.

Table 3. Output Voltage Programming Codes

VID4	VID3	VID2	VID1	VID0	VOUT to CPU
0	1	1	1	1	1.30V
0	1	1	1	0	1.35V
0	1	1	0	1	1.40V
0	1	1	0	0	1.45V
0	1	0	1	1	1.50V
0	1	0	1	0	1.55V

Table 3. Output Voltage Programming

Codes (continued)

VID4	VID3	VID2	VID1	VID0	VOUT to CPU
0	1	0	0	1	1.60V
0	1	0	0	0	1.65V
0	0	1	1	1	1.70V
0	0	1	1	0	1.75V
0	0	1	0	1	1.80V
0	0	1	0	0	1.85V
0	0	0	1	1	1.90V
0	0	0	1	0	1.95V
0	0	0	0	1	2.00V
0	0	0	0	0	2.05V
1	1	1	1	1	No CPU
1	1	1	1	0	2.1V
1	1	1	0	1	2.2V
1	1	1	0	0	2.3V
1	1	0	1	1	2.4V
1	1	0	1	0	2.5V
1	1	0	0	1	2.6V
1	1	0	0	0	2.7V
1	0	1	1	1	2.8V
1	0	1	1	0	2.9V
1	0	1	0	1	3.0V
1	0	1	0	0	3.1V
1	0	0	1	1	3.2V
1	0	0	1	0	3.3V
1	0	0	0	1	3.4V
1	0	0	0	0	3.5V

Note:

1.0 = processor pin is tied to GND

1 = processor pin is open.

2