Datasheet

ADC128D818
www.ti.com SNAS483E –FEBRUARY 2010–REVISED MARCH 2013
(Non-Linear Scale for Clarity)
Figure 33. 9-bit Temperature-to-Digital Transfer Function
Digital Output (D
OUT
)
Temp
Binary [MSb...LSb] Decimal Hex
+125°C 0 _1111_1010 250 0_FA
+25°C 0_0011_0010 50 0_32
+0.5°C 0_0000_0001 1 0_01
+0°C 0_0000_0000 0 0_00
−0.5°C 1_1111_1111 511 1_FF
−25°C 1_1100_1110 462 1_CE
−40°C 1_1011_0000 432 1_B0
In general, the easiest way to calculate the temperature (°C) is to use the following formulas:
If D
OUT
[MSb] = 0: +Temp(°C) = D
OUT
(dec) / 2 (3)
If D
OUT
[MSb] = 1: –Temp(°C) = [2
9
- D
OUT
(dec)] / 2 (4)
Temperature Limits
One of the ADC128D818 features is monitoring the temperature reading. This monitoring is accomplished by
setting a temperature limit to the Temperature High Limit Register (T
hot
, address 38h) and Temperature
Hysteresis Limit Register (T
hot_hyst
, address 39h). When the temperature reading > T
hot
, an interrupt occurs. How
this interrupt occurs will be explained in the Temperature Interrupt section.
Each temperature limit is represented by an 8-bit, two's complement word with an LSb (Least Significant bit)
equal to 1°C. The table below shows some sample temperatures that can be programmed to the Temperature
Limit Registers.
In general, use the following equations to calculate the digital code that represents the desired temperature limit:
If Temp Limit (°C) >= 0: Digital Code (dec) = Temp Limit(°C) (5)
If Temp Limit (°C) < 0: Digital Code (dec) = 2
8
- |Temp Limit(°C)| (6)
Digital Code
Temp Limit
Binary [MSb...LSb] Decimal Hex
+125°C 0111_1101 125 7D
+25°C 0001_1001 25 19
+1.0°C 0000_0001 1 01
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