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| MCP9805 Datasheet, PDF (14/34 Pages) Microchip Technology – Memory Module Digital Temperature Sensor | |||
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MCP9805
4.1.4 AMBIENT TEMPERATURE
REGISTER (TA)
The MCP9805 uses a band gap temperature sensor
circuit to output analog voltage proportional to absolute
temperature. An internal ÎΣ ADC is used to convert the
analog voltage to a digital word. The converter resolu-
tion is set to 0.25 °C/LSb + sign (11-bit data). The digital
word is loaded to a 16-bit read-only Ambient Tempera-
ture register (TA) that contains 11-bit temperature data
in twoâs complement format.
The TA register bits (bits 12 thru 0) are double-buffered.
Therefore, the user can access the register while, in the
background, the MCP9805 performs an analog-to-dig-
ital conversion of the band gap temperature sensor.
The temperature data from the ÎΣ ADC is loaded in
parallel to TA at tCONV refresh rate.
The TA magnitude in decimal to ambient temperature
conversion is shown in Equation 4-1:
EQUATION 4-1: DECIMAL CODE TO
TEMPERATURE
CONVERSION
TA = Code à 2â2
Where:
TA = Ambient Temperature (°C)
Code = MCP9805 output magnitude in
decimal
In addition, the TA register uses three bits (bits 15, 14
and 13) to reflect the Event pin state. This allows the
user to identify the cause of the Event output trigger
(see Section 4.2.3 âEvent Output Configurationâ);
bit 15 is set to â1â if TA is greater than or equal to TCRIT,
bit 14 is set to â1â if TA is greater than TUPPER and bit 13
is set to â1â if TA is less than TLOWER.
The TA register bit assignment and boundary
conditions are described in Register 4-5.
REGISTER 4-5: AMBIENT TEMPERATURE REGISTER (TA) â ADDRESS â0000 0101âb
Upper-Half:
R-0
TA Vs. TCRIT
bit 15
R-0
R-0
TA Vs. TUPPER TA Vs. TLOWER
R-0
SIGN
R-0
R-0
R-0
R-0
27 °C/LSb 26 °C/LSb 25 °C/LSb 24 °C/LSb
bit 8
Lower-Half:
R-0
R-0
23 °C/LSb 22 °C/LSb
bit 7
R-0
21 °C/LSb
R-0
R-0
R-0
20 °C/LSb 2-1 °C/LSb 2-2 °C/LSb
U-0
â(2)
U-0
â
bit 0
bit 15 TA vs. TCRIT(1) bit:
bit 14
0 = TA < TCRIT
1 = TA ⥠TCRIT
TA vs. TUPPER(1) bit:
bit 13
0 = TA ⤠TUPPER
1 = TA > TUPPER
TA vs. TLOWER(1) bit:
0 = TA ⥠TLOWER
1 = TA < TLOWER
bit 12 SIGN bit:
0 = TA ⥠0°C
1 = TA < 0°C
Note 1: Not affected by the status of the Event output configuration (bits 5 to 0 of CONFIG) and THYST = 0°C,
Register 4-3.
2: Bit 1 may remain set â1â for some devices indicating 2-3 °C/LSb or 0.125°C temperature resolution,
depending on the state of the device calibration code.
Legend:
R = Readable bit
-n = Value at POR
W = Writable bit
â1â = bit is set
U = Unimplemented bit, read as â0â
â0â = bit is cleared
x = bit is unknown
DS21977B-page 14
© 2005 Microchip Technology Inc.
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