Voltage Regulator Module (VRM) 10.2L Design Guidelines

Voltage Regulator Module (VRM) 10.2L Design Guidelines 17
3 Control Signals
3.1 Output Enable (OUTEN) - REQUIRED
The VRM should accept an input signal to enable its output voltage. When disabled, the regulator’s
output should go to a high impedance state and should not sink or source current. When OUTEN is
pulled low during the shutdown process, the VRM should not exceed the previous voltage level
regardless of the VID setting during the shutdown process. Once operating after power-up, it
should respond to a deasserted OUTEN within 500 ms. The circuitry driving OUTEN is an open-
collector/drain signal. It is EXPECTED that the pull-up resistor will be located on the baseboard
and will not be integrated into the PWM controller chip or VRM.
3.2 Voltage Identification (VID [5:0]) - REQUIRED
The VRM must accept six lines to set the nominal voltage as defined by Table 3-3. When the VID
[4:0] inputs are all high (in this case VID5 is a don’t care), such as when no processor is installed,
the regulator should disable its output voltage. If this disable code appears during previously
normal operation, the regulator should turn off its output within 500 ms.
The circuitry driving VID [5:0] is an open-collector/drain signal. These signals should be pulled-up
to the front side bus (FSB) Vtt voltage. It is EXPECTED that the pull-up resistors will be located
on the baseboard and will not be integrated into the PWM controller chip or VRM. Other platform
components may use VID inputs and may require tighter limits than specified in Table 3-2.
A normal no-processor VID [5:0] code for a Vcc regulator will be X11111, where X is defined as
logic 1 or 0, disabling the VRM.
NOTE:
1. Other platform components may use VID inputs and may require tighter limits.
Table 3-1. OUTEN Specifications
Symbol Parameter Min Max Units
VIH Input Voltage High 0.8 3.465 V
VIL Input Voltage Low 0 0.4 V
Table 3-2. VID [5:0] Specifications
Symbol Parameter Min Max Units Notes
V
IH
Input High Voltage 0.8 FSB Vtt Voltage V 1
V
IL
Input Low Voltage 0 0.4 V 1