Datasheet
© 2005 Microchip Technology Inc. DS21935A-page 15
TCN75A
4.3.4.6 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 num-
ber 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 deas-
serted (Comparator mode) or before another interrupt
is asserted (Interrupt mode).
4.3.4.7 ΣΔ ADC Resolution
The TCN75A provides access to select the ADC
resolution from 9-bit to 12-bit 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 2-4 shows accuracy versus resolution.
Table 4-1 shows the T
A
register conversion time for the
corresponding resolution.
TABLE 4-1: RESOLUTION AND
CONVERSION TIME
4.4 Summary of Power-up Condition
The TCN75A has an internal Power-on Reset (POR)
circuit. If the power supply voltage V
DD
glitches down
to the 1.7V (typ.) threshold, the device resets the
registers to the power-up default settings.
Table 4-2 shows the power-up default summary.
TABLE 4-2: POWER-UP DEFAULTS
At power-up, the TCN75A has an inherent 2 ms (typ.)
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
°C/bit (typ.)
t
CONV
(typ.)
9 0.5 30 ms
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