Datasheet

ADT7470 Data Sheet
Rev. E | Page 14 of 40
TEMPERATURE READBACK BY THE HOST
The user cannot read the ADT7470 temperature register values
if the ADT7470 is in the process of a temperature measurement.
The user must wait until the data from all the TMP05s and
TMP06s in the chain are received by the ADT7470 before
reading these values. Otherwise, the temperature registers
may store an incorrect value. It is recommended to wait at
least 200 ms for each TMP05 and TMP06 in the chain. The
recommended procedure is as follows:
1. Set Register 40 Bit[7] = 1. This starts the temperature
measurements.
2. Wait 200 ms for each TMP05/TMP06 in the loop.
3. Set Register 40 Bit[7] = 0.
4. Read the temperature registers.
TEMPERATURE DATA FORMAT
Temperature data on the ADT7470 is stored in an 8-bit format,
with the 7 LSBs being the temperature, and the MSB acting as
the sign bit. Use the following formulae when reading back
from the temperature registers, o calculate the temperature:
Positive Temperature = ADC Code (decimal)
Negative Temperature = ADC (decimal) minus 256
For negative temperature readings, the MSB is always set to 1.
Example:
1. Temperature read back from register 0x20: 0xFF.
2. Convert into decimal format. 0xFF = 255 (decimal).
3. Check if MSB is set to 1. It is in this example. Therefore,
use negative temperature formula, ADC (d) minus 256.
4. Temperature = 255 − 256 = −1°C.
Table 8. Temperature Data Format
Temperature (°C) Digital Output (8 Bit)
−128 1000 0000
−125 1000 0011
−100 1001 1100
−75 1011 0101
−50 1100 1110
−25 1110 0111
−10 1111 0110
+0 0000 0000
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40ms
40ms 76ms
100ms
t
START
ADT7470
t
1 STOP
t
2 STOP
TMP_START
TMP_IN
ADT7470
TMP05 1
TEMP = 25°C
TMP05 2
TEMP = 120
°C
NOTES:
t
START
IS GENERATED BY THE ADT7470 AND IS THE START PULSE FOR TMP05 1.
t
1 STOP
IS GENERATED BY TMP05 1 AND IS THE START PULSE FOR TMP05 2.
t
2 STOP
IS GENERATED BY TMP05 2.
EACH START/STOP PULSE IS TYPICALLY 25µs.
TMP05s MUST BE IN DAISY-CHAIN MODE.
SEE THE TMP05 DATA SHEET FOR MORE INFORMATION.
t
2
t
1
t
1 LOW
t
1 HIGH
t
2 LOW
t
2 HIGH
04684-0-032
Figure 14. Typical Timing Diagram of ADT7470 with Two TMP05s Connected in Daisy-Chain Mode