MCP9805T-BESLASHST datasheet(14/34 Pages) MICROCHIP

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MCP9805

DS21977B-page 14

4.1.4

AMBIENT TEMPERATURE

The MCP9805 uses a band gap temperature sensor

circuit to output analog voltage proportional to absolute

temperature. An internal

ΔΣ 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 two’s 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

ΔΣ 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

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 “Event Output Configuration”);

bit 15 is set to ‘1’ if TA is greater than or equal to TCRIT,

bit 14 is set to ‘1’ if TA is greater than TUPPER and bit 13

is set to ‘1’ if TA is less than TLOWER.

The

TA register bit assignment and boundary

conditions are described in Register 4-5.

Code

–

Where:

TA = Ambient Temperature (°C)

Code = MCP9805 output magnitude in

decimal

AMBIENT TEMPERATURE REGISTER (TA) → ADDRESS ‘0000 0101’b

bit 15

TA vs. TCRIT

(1) bit:

=TA < TCRIT

=TA ≥ TCRIT

bit 14

TA vs. TUPPER

(1) bit:

=TA ≤ TUPPER

=TA > TUPPER

bit 13

TA vs. TLOWER

(1) bit:

=TA ≥ TLOWER

=TA < TLOWER

bit 12

SIGN bit:

=TA ≥ 0°C

=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,

2: Bit 1 may remain set ‘1’ for some devices indicating 2-3 °C/LSb or 0.125°C temperature resolution,

depending on the state of the device calibration code.

Upper-Half:

R-0

TA Vs. TCRIT

TA Vs. TUPPER TA Vs. TLOWER

SIGN

27 °C/LSb

26 °C/LSb 25 °C/LSb

24 °C/LSb

bit 15

bit 8

Lower-Half:

R-0

U-0

23 °C/LSb

22 °C/LSb

21 °C/LSb

20 °C/LSb

2-1 °C/LSb 2-2 °C/LSb

—(2)

—

bit 7

bit 0

Legend:

R = Readable bit

W = Writable bit

U = Unimplemented bit, read as ‘0’

-n = Value at POR

‘1’ = bit is set

‘0’ = bit is cleared

x = bit is unknown

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