Datasheet
DD2.X
Preliminary
PowerPC 750CL Microprocessor
Figure 5-4. Interpolating Chip Junction Temperature Using Thermal Calibration Registers and User Voltage
Measurement
Voltage
TDCL
mV Low
TDCH
mV Elev
User’s (mV)
Set Point
Low
Temp.
Elevated
Temp.
Temp.
User’s
Maximum Temp.
5.7 Output Buffer DC Impedance
The 750CL 60x drivers were characterized over various process, voltage, and temperature conditions. To
measure driver impedance, an external resistor is connected to the chip pad, either to OV or GND. Then
DD
the value of the resistor is varied until the pad voltage is OV /2 (see Figure 5-5, Driver Impedance Measure-
DD
ment, on page 50).
The output impedance is actually the average of two resistances: the resistance of the pullup device and the
resistance of pulldown device. When Data is held high, SW1 is closed (SW2 is open), and R is trimmed until
N
Pad = OV /2; R then becomes the resistance of the pullup devices. When Data is held low, SW2 is closed
DD
N
(SW1 is open), and R is trimmed until Pad = OV /2; R then becomes the resistance of the pulldown
P
DD
P
devices. With a properly designed driver, R and R are close to each other in value; then driver impedance
P
N
equals (R + R )/2.
P
N
Version 2.5
December 2, 2008
System Design Information
Page 49 of 70
IBM [ IBM ]
