AT42QT1244_14 Datasheet, PDF (15/61 Pages) ATMEL Corporation – 24-key QMatrix FMEA IEC/EN/UL60730 Touch Sensor

The sub-components that the QT1244 is able to verify internally are tested repeatedly during the normal running of
the device, with the various tests run in parallel. As each test ends the result is recorded and the test is restarted.
The real time that elapses from the start of each test to the start of the next iteration of the same test is called the
failure detect time, or hazard time, the maximum time for which an error could be undetected.
Each test is broken down into a number of smaller parts, each of which is processed in turn during each matrix scan.
Each test is therefore completed either after a number of matrix scans, as shown in Table 3-3.
Table 3-3. Test run times (expressed in matrix scans)
Test
FMEA
Other
Variable Memory
Firmware CRC
Setups CRC
Required Matrix Scans
to complete test
24
18
768
342
5
Table 3-4 shows matrix scan times for Setups that yield the shortest matrix scan time and a much longer scan time
resulting from the use of long dwell and low frequency settings.
Table 3-4. Matrix Scan Times
Setups Conditions
BL = 0 (16 pulses),
DWELL = 0 (0.13 µs),
FREQ0 = 1,
All keys enabled,
FHM = 0,
MSYNC = 0 (off),
SLEEP = 0 (sleep disabled),
DEBUG = 0 (off).
BL = 3 (64 pulses),
DWELL = 7 (4.5 µs),
FREQ0 = 25,
All keys enabled,
FHM = 0,
MSYNC = 0 (off),
SLEEP = 0 (sleep disabled),
DEBUG = 0(off).
Matrix Scan Time (ms)
7.5
38
Longer matrix scan times are possible than those shown in Table 3-4 by using even higher values for FREQ0 (lower
burst frequencies), but these are considered extreme settings.
QT1244 [PRELIMINARY DATASHEET]
15
9631EX–AT42–12/13