TCN75A
5.3.4.6
Fault Queue
5.4
Summary of Power-up Condition
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 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, TA must be greater than
TSET for six consecutive conversions before ALERT is
asserted as a comparator or an interrupt output.
The TCN75A has an internal Power-on Reset (POR)
circuit. If the power supply voltage VDD glitches down
to the 1.7V (typ.) threshold, the device resets the
registers to the power-up default settings.
Table 5-2 shows the power-up default summary.
TABLE 5-2:
Register
POWER-UP DEFAULTS
Data
Power-up Defaults
(Hex)
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 deas-
serted (Comparator mode) or before another interrupt
is asserted (Interrupt mode).
TA
0000
A000
9600
00
0°C
80°C
TSET
THYST
Pointer
75°C
Temperature register
5.3.4.7
ΣΔ ADC Resolution
Continuous Conversion
Comparator mode
Active-low Output
Fault Queue 1
The TCN75A 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.
CONFIG
00
9-bit Resolution
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 tCONV for the TCN75A to
update the TA register with valid temperature data.
Table 5-1 shows the TA register conversion time for the
corresponding resolution.
TABLE 5-1:
RESOLUTION AND
CONVERSION TIME
Bits
Resolution
tCONV (typ.)
9
0.5
0.25
30 ms
60 ms
10
11
12
0.125
0.0625
120 ms
240 ms
DS21935C-page 22
© 2006 Microchip Technology Inc.
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