CAT34TS00
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11
Register Data Format
The values used in the temperature data register and the 3
temperature trip point registers are expressed in two’s
complement format. The measured temperature value is
expressed with 12−bit resolution, while the 3 trip
temperature limits are set with 10−bit resolution. The total
temperature range is arbitrarily defined as 256°C, thus
yielding an LSB of 0.0625°C for the measured temperature
and 0.25°C for the 3 limit values. Bit B12 in all temperature
registers represents the sign, with a ‘0’ indicating a positive,
and a ‘1’ a negative value. In two’s complement format,
negative values are obtained by complementing their
positive counterpart and adding a ‘1’, so that the sum of
opposite signed numbers, but of equal absolute value, adds
up to zero.
Note that trailing ‘0’ bits, are ‘0’ irrespective of polarity.
Therefore the “don’t care” bits (B1 and B0) in the 10−bit
resolution temperature limit registers, are always ‘0’.
Table 14. 12−BIT TEMPERATURE DATA FORMAT
Binary (B12 to B0) Hex Temperature
1 1100 1001 0000 1C90 −55°C
1 1100 1110 0000 1CE0 −50°C
1 1110 0111 0000 1E70 −25°C
1 1111 1111 1111 1FFF −0.0625°C
0 0000 0000 0000 000 0°C
0 0000 0000 0001 001 +0.0625°C
0 0001 1001 0000 190 +25°C
0 0011 0010 0000 320 +50°C
0 0111 1101 0000 7D0 +125°C
Event Pin Functionality
The EVENT
output reacts to temperature changes as
illustrated in Figure 9, and according to the operating mode
defined by the Configuration register.
In Interrupt Mode, the (enabled) EVENT
output will be
asserted every time the temperature crosses one of the alarm
window limits, and can be de−asserted by writing a ‘1’ to the
clear event bit (B5) in the configuration register. Once the
temperature exceeds the critical limit, the EVENT
remains
asserted as long as the temperature stays above the critical
limit and cannot be cleared. A clear request sent to the
CAT34TS00 while the temperature is above the critical limit
will be acknowledged, but will be executed only after the
temperature drops below the critical limit.
In Comparator Mode, the EVENT
output is asserted
outside the alarm window limits, while in Critical
Temperature Mode, EVENT
is asserted only above the
critical limit. Clear requests are ignored in this mode. The
exact trip limits are determined by the 3 temperature limit
settings and the hysteresis offsets, as illustrated in Figure 10.
Following a TS shut−down request, the converter is
stopped and the most recently recorded temperature value
present in the TDR is frozen; the EVENT
output will continue
to reflect the state immediately preceding the shut−down
command. Therefore, if the state of the EVENT
output
creates an undesirable bus condition, appropriate action must
be taken either before or after shutting down the TS. This may
require clearing the event, disabling the EVENT output or
perhaps changing the EVENT
output polarity.
In normal use, events are triggered by a change in
recorded temperature, but the CAT34TS00 will also respond
to limit register changes. Whereas recorded temperature
values are updated at sampling rate frequency, limits can be
modified at any time. The enabled EVENT
output will react
to limit changes as soon as the respective registers are
updated. This feature may be useful during testing.
