Datasheet
2010 Microchip Technology Inc. DS21909D-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.
T
A
must remain above T
SET
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, T
A
must be greater than
T
SET
for six consecutive conversions before ALERT is
asserted as a comparator or an interrupt output.
This queue setting also applies for T
HYST
. If six fault
queues are selected, T
A
must remain below T
HYST
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 T
A
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 V
DD
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 t
CONV
for the TCN75A
to update the T
A
register with valid temperature data.
Bits Resolution t
CONV
(typical)
90.5 30ms
10 0.25 60 ms
11 0.125 120 ms
12 0.0625 240 ms
Register
Data
(Hex)
Power-up Defaults
T
A
0000 0°C
T
SET
A000 80°C
T
HYST
9600 75°C
Pointer 00 Temperature register
CONFIG 00
Continuous Conversion
Comparator mode
Active-low Output
Fault Queue 1
9-bit Resolution