Device Architecture
where
ITMSLO is the current when the Temperature Strobe is Low, typically 100 µA
ITMSHI is the current when the Temperature Strobe is High, typically 10 µA
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.
ΔV = VTMSLO – VTMSHI = 1.986 × 10–4nT
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.
VADC = ΔV × 12.5 = 2.5 mV ⁄ (K × T)
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.
210
2.56 V
----------------
1K = 2.5 mV ×
= 1 LSB
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.
Table 2-38 • Temperature Data Format
Digital Output
Temperature
–40°C
–20°C
0°C
Temperature (K)
(ADC 10-bit mode)
00 1110 1001
00 1111 1101
01 0001 0001
01 0001 0010
01 0001 1011
01 0010 1010
01 0100 0011
01 0110 0110
233
253
273
274
283
298
323
358
1°C
10 °C
25°C
50 °C
85 °C
2-98
Preliminary v1.7
ACTEL [ Actel Corporation ]
