Thermal Design Power; Pull-Up And Pull-Down Resistor Values; Figure 99. Pull-Up Resistor Example - Intel 815EG Design Manual

R
13.2

Thermal Design Power

The Thermal Design power (TDP) is defined as the estimated maximum possible expected power
generated in a component by a realistic application. It is based on extrapolations in both hardware
and software technology over the life of the product. It does not represent the expected power
generated by a power virus.
The TDP of the GMCH component is 5.1W.
The TDP of the ICH2 is 1.5 W ±15%.
13.2.1

Pull-Up and Pull-Down Resistor Values

The pull-up and pull-down values are system dependent. The appropriate value for a system can be
determined from an AC/DC analysis of the pull-up voltage used, the current drive capability of the
output driver, the input leakage currents of all devices on the signal net, the pull-up voltage
tolerance, the pull-up/pull-down resistor tolerance, the input high-voltage/low-voltage
specifications, the input timing specifications (RC rise time), etc. Analysis should be performed to
determine the minimum/maximum values usable on an individual signal. Engineering judgment
should be used to determine the optimal value. This determination can include cost concerns,
commonality considerations, manufacturing issues, specifications, and other considerations.
A simplistic DC calculation for a pull-up value is:
R = (VCC
MAX
R = (VCC
MIN
Since I
LEAKAGE
determined by the maximum allowable rise time. The following calculation allows for t, the
maximum allowable rise time, and C, the total load capacitance in the circuit, including the input
capacitance of the devices to be driven, the output capacitance of the driver, and the line
capacitance. This calculation yields the largest pull-up resistor allowable to meet the rise time t.
R = -t / (C * In(1-(V
MAX

Figure 99. Pull-Up Resistor Example

I
Leakage
®
Intel 815EG Chipset Platform Design Guide
MIN - V MIN) / I
PU IH
MAX - V MAX) / I
PU IL
MAX is normally very small, R
MIN / VCC
IH
Vcc m in.
pu
R
m ax
m ax.
MAX
LEAKAGE
MAX
OL
may not be meaningful. R
MAX
MIN) ) )
PU
V m in. I m ax.
IH O L
Power Delivery
also is
MAX
Vcc m ax.
pu
R
m in
V m ax.
IL
PW R_Pullup_R es_815E_B0
167