Compaq 21264, EV67 specifications Push-Pull Output Driver OPP, Push-Pull Output Clock Driver Oppclk

Power Supply Sequencing and Avoiding Potential Failure Mechanisms

Table 9–11 Push-Pull Output Driver (O_PP)

Parameter		Test
Symbol	Description	Conditions	Minimum	Maximum
VOL	Low-level output voltage	IOL = 40 mA	—	500 mV
VOH	High-level output voltage	IOL = –40 mA	VDD – 500 mV	—
IOZ	High-impedance output current	0 < V < VDD	—	150	μA
COD	Open-drain pin capacitance	Freq = 10 MHz	—	6.0 pF
				Note 6
Table 9–12 Push-Pull Output Clock Driver (O_PP_CLK)
Parameter		Test
Symbol	Description	Conditions	Minimum	Maximum
VOL	Low-level output voltage	Note 4	—	VDD/2 – 325 mV
VOH	High-level output voltage	Note 4	VDD/2 + 325 mV	—
IOZ	High-impedance output	0 < V < VDD	—	40 mA	1
	current

1Measured value includes current from onchip termination structures.

9.3Power Supply Sequencing and Avoiding Potential Failure Mech- anisms

Before the power-on sequencing can occur, systems should ensure that DCOK_H is deasserted and Reset_L is asserted. Then, systems ramp power to the 21264/EV67 PLL_VDD @ 3.3 V and the 21264/EV67 power planes (VDD @ 2.0 V, not to exceed

2.15V under any circumstances), with PLL_VDD leading VDD. Systems should supply differential clocks to the 21264/EV67 on ClkIn_H and ClkIn_L. The clocks should be running as power is supplied.

When enabling the power supply inputs in a system, three failure mechanisms must be avoided:

1.Bidirectional signal buses must not conflict during power-up. A conflict on these buses can generate high current conditions, which can compromise the reliability of the associated chips.

2.Similarly, input receivers should not see intermediate voltage levels that can also generate high current conditions, which can compromise the reliability of the receiving chip.

3.Finally, no CMOS chip should see an input voltage that is higher than its internal VDD. In such a condition, a reasonable level of charge can be injected into the bulk of the die. This condition can expose the chip to a positive-feedback latchup condition.

The 21264/EV67 addresses those three failure mechanisms by disabling all of its outputs and bidirectional pins (with three exceptions) until the assertion of DCOK_H. The three exceptions are Tdo_H, EV6Clk_L, and EV6Clk_H. Tdo_H is used only in

Alpha 21264/EV67 Hardware Reference Manual Electrical Data 9–5