MPC8640DEC datasheet(120/140 Pages) FREESCALE

120 / 140 page

MPC8640 and MPC8640D Integrated Host Processor Hardware Specifications, Rev. 1

120

Freescale Semiconductor

Thermal

19.2.4

Temperature Diode

The MPC8640 has a temperature diode on the microprocessor that can be used in conjunction with other

system temperature monitoring devices (such as Analog Devices, ADT7461™). These devices use the

negative temperature coefficient of a diode operated at a constant current to determine the temperature of

the microprocessor and its environment. For proper operation, the monitoring device used should

auto-calibrate the device by canceling out the VBE variation of each MPC8640’s internal diode.

The following are the specifications of the MPC8640 on-board temperature diode:

Vf > 0.40 V

Vf < 0.90 V

Operating range 2–300

μA

Diode leakage < 10 nA @ 125

°C

Ideality factor over 5–150

μA at 60°C: n = 1.0275 ± 0.9%

Ideality factor is defined as the deviation from the ideal diode equation:

Another useful equation is:

Where:

Ifw = Forward current

Is = Saturation current

Vd = Voltage at diode

Vf = Voltage forward biased

VH = Diode voltage while IH is flowing

VL = Diode voltage while IL is flowing

IH = Larger diode bias current

IL = Smaller diode bias current

q = Charge of electron (1.6 x 10 –19 C)

n = Ideality factor (normally 1.0)

K = Boltzman’s constant (1.38 x 10–23 Joules/K)

T = Temperature (Kelvins)

Ifw = Is e

– 1

qVf

___

nKT

VH – VL = n

MPC8640DEC 데이터시트(PDF) 120 Page - Freescale Semiconductor, Inc