
Device Architecture
2- 98
Pr el iminar y v1 .7
where
ITMSLO is the current when the Temperature Strobe is Low, typically 100 A
ITMSHI is the current when the Temperature Strobe is High, typically 10 A
VTMSLO is diode voltage while Temperature Strobe is Low
VTMSHI is diode voltage while Temperature Strobe is High
n is the non-ideality factor of the diode-connected transistor. It is typically 1.004 for the Actel-
recommended transistor type 2N3904.
K = 1.3806 x 10-23 J/K is the Boltzman constant
Q = 1.602 x 10-19 C is the charge of a proton
When ITMSLO / ITMSHI = 10, the equation can be simplified as shown in EQ 2-8. EQ 2-8
In the Fusion TMB, the ideality factor n for 2N3904 is 1.004 and
ΔV is amplified 12.5 times by an
internal amplifier; hence the voltage before entering the ADC is as given in
EQ 2-9.
EQ 2-9
This means the temperature to voltage relationship is 2.5 mV per degree Kelvin. The unique design
of Fusion has made the Temperature Monitor System simple for the user. When the 10-bit mode
ADC is used, each LSB represents 1 degree Kelvin, as shown in
EQ 2-10. That is, e. 25°C is equal to
293°K and is represented by decimal 293 counts from the ADC.
EQ 2-10
If 8-bit mode is used for the ADC resolution, each LSB represents 4 degrees Kelvin; however, the
resolution remains as 1 degree Kelvin per LSB, even for 12-bit mode, due to the Temperature
Monitor design. An example of the temperature data format for 10-bit mode is shown in
Table 2-38 Temperature Data Format
Temperature
Temperature (K)
Digital Output
(ADC 10-bit mode)
–40°C
233
00 1110 1001
–20°C
253
00 1111 1101
0°C
273
01 0001 0001
1°C
274
01 0001 0010
10 °C
283
01 0001 1011
25°C
298
01 0010 1010
50 °C
323
01 0100 0011
85 °C
358
01 0110 0110
ΔVV
TMSLO
V
TMSHI
–
1.986
10
4
–
×
nT
==
V
ADC
ΔV 12.5
×
2.5 mV
KT
×
()
==
1K
2.5 mV
2
10
2.56 V
-----------------
×
1 LSB
==