MCP9844 datasheet(22/44 Pages) MICROCHIP

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MCP9844

DS20005192A-page 22

 2013 Microchip Technology Inc.

5.1.4

AMBIENT TEMPERATURE

The MCP9844 device uses a band gap temperature

sensor circuit to output analog voltage proportional to

absolute temperature. An internal

 ADC is used to

convert the analog voltage to a digital word. The con-

verter resolution is set to 0.25°C + sign (11-bit data).

The digital word is loaded to a 16-bit read-only Ambient

Temperature register

(TA) that contains 11-bit

temperature data in two’s complement format.

The TA register bits (bits 12 through 0) are double-buff-

ered. Therefore, the user can access the register while,

in the background, the MCP9844 performs an analog-

to-digital conversion. The temperature data from the



ADC is loaded in parallel to the TA register at tCONV

refresh rate.

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 5.2.3 “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 5-5.

AMBIENT TEMPERATURE REGISTER (TA)  ADDRESS ‘0000 0101’b (Note 1)

R-0

TA vs. TCRIT TA vs. TUPPER TA vs. TLOWER

SIGN

27 °C

26 °C

25 °C

24 °C

bit 15

bit 8

R-0

23 °C

22 °C

21 °C

20 °C

2-1 °C

2-2 °C

2-3 °C

2-4 °C

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

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

bit 11-0

Ambient Temperature (TA) Bits: (Note 2)

12-bit Ambient Temperature data in two’s complement format.

Note 1:

Bits 15, 14 and 13 are not affected by the status of the event output configuration (bits 5 to 0 of CONFIG)

(Register 5-3).

Bits 2, 1, and 0 may remain clear ‘0’ depending on the status of the resolution register. The power-up

default is 0.25°C/bit, bits 1 and 0 remain clear ‘0’.

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