MCP9800A0-MSLASHMS datasheet(25/42 Pages) MICROCHIP

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 2010 Microchip Technology Inc.

DS21909C-page 25

MCP9800/1/2/3

5.3.4.6

Fault Queue

The fault queue feature can be used as a filter to lessen

the probability of spurious activation of the ALERT pin.

TA must remain above TSET for the consecutive

number of conversion cycles selected using the Fault

Queue bits. Bit 3 and bit 4 of CONFIG can be used to

select up to six fault queue cycles. For example, if six

fault queues are selected, TA must be greater than

TSET for six consecutive conversions before ALERT is

asserted as a comparator or an interrupt output.

This queue setting also applies for THYST. If six fault

queues are selected, TA must remain below THYST for

six consecutive conversions before ALERT is

deasserted (Comparator mode) or before another

interrupt is asserted (Interrupt mode).

5.3.4.7

 ADC Resolution

The MCP9800/1/2/3 provides access to select the ADC

resolution from 9-bit to 12-bit (0.5°C to 0.0625°C

resolution) using bit 6 and bit 5 of the CONFIG register.

The user can gain better insight into the trends and

characteristics of the ambient temperature by using a

finer resolution. Increasing the resolution also reduces

the quantization error. Figure 2-3 shows accuracy

versus resolution.

Table 5-3 shows the TA register conversion time for the

corresponding resolution.

TABLE 5-3:

RESOLUTION AND

CONVERSION TIME

5.4

Summary of Power-up Condition

The MCP9800/1/2/3 has an internal Power-on Reset

(POR) circuit. If the power supply voltage VDD glitches

down to the 1.7V (typical) threshold, the device resets

the registers to the power-up default settings.

Table 5-4 shows the power-up default summary.

TABLE 5-4:

POWER-UP DEFAULTS

At power-up, the MCP9800/1/2/3 has an inherent 2 ms

(typical) power-up delay before updating the registers

with default values and start a conversion cycle. This

delay reduces register corruption due to unsettled

power. After power-up, it takes tCONV for the TCN75A

to update the TA register with valid temperature data.

Bits

Resolution

tCONV (typical)

90.5

30 ms

0.25

60 ms

0.125

120 ms

0.0625

240 ms

Data

(Hex)

Power-up Defaults

0000

0°C

TSET

A000

80°C

THYST

9600

75°C

Pointer

Temperature register

CONFIG

Continuous Conversion

Comparator mode

Active-low Output

Fault Queue 1

9-bit Resolution

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