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45732 AMD 780E Databook 3.10
© 2009 Advanced Micro Devices, Inc.
5-8
Proprietary
RS780E Thermal Characteristics
5.2.2
Thermal Diode Characteristics
The RS780E has an on-die thermal diode, with its positive and negative terminals connected to the THERMALDIODE_P
and THERMALDIODE_N pins respectively. Combined with a thermal sensor circuit, the diode temperature, and hence
the ASIC temperature, can be derived from a differential voltage reading (
V
). The equation relating
T
to
V
is given
below:
where:
V
= Difference of two base-to-emitter voltage readings, one using current = I and the other using current =
N x I
N
= Ratio of the two thermal diode currents (=10 when using an ADI thermal sensor, e.g. ADM 1020, 1030)
= Ideality factor of the diode
K
= Boltzman’s Constant
T
= Temperature in Kelvin
q
= Electron charge
The series resistance of the thermal diode (R
T
) must be taken into account as it introduces an error in the reading
(for every 1.0
, approximately 0.8
o
C is added to the reading). The sensor circuit should be calibrated to offset the
R
T
induced, plus any other known fixed error. Measured values of diode ideality factor and series resistance for the
diode circuit are defined in the
Thermal Design and Analysis Guidelines
f
or the RS780 Product Family
, order#
44638.
V
K
T
N
ln
q
--------------------------------------------
=