SR5650 Thermal Characteristics
© 2010 Advanced Micro Devices, Inc.
47062 SR5650 Databook 2.00
Proprietary
5-3
5.2.2
Thermal Diode Characteristics
The SR5650 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 junction temperature, can be derived from a differential voltage reading (
V). The equation relating the
temperature 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 errors. Measured values of diode ideality factor and series resistance for the diode circuit are
defined in
Thermal Design and Analysis Guidelines for SR5650/5670/5690
.
V
K
T
N
ln
q
--------------------------------------------
=