at42qt1481 ATMEL Corporation, at42qt1481 Datasheet - Page 16

• Manufacturer Part Number: at42qt1481
• Description: 48-key Qmatrix Ic
• Manufacturer: ATMEL Corporation

2.16
2.17
16
Sleep
FMEA Tests
AT42QT1481
The QT1481 can be configured for automatic sleep using the Sleep Drift Compensation (SDC)
setup, and woken with a low pulse applied to the WS pin.
If the sleep feature is enabled using SDC (see
command (0x16) has been issued, the QT1481 sleeps whenever possible to conserve power.
Periodically, it should be woken by the host using the WS pin. Upon being woken, the matrix is
scanned and the QT1481 returns to sleep unless there is activity which demands further
attention. The QT1481 returns to sleep automatically after a period of inactivity, the duration of
which is defined by the AWAKE feature.
At least one full matrix scan is always performed after waking up and before returning to sleep.
At the end of each matrix scan, the part returns to sleep unless recent activity, such as a touch
event, demands further attention. If there has been recent activity, the part performs another
complete matrix scan before attempting to sleep once again. This process is repeated
indefinitely until the activity stops and the part returns to sleep.
Key touch activity forces the matrix scanning into free run whereby each matrix scan is not
interleaved with sleep. The part will not sleep while any key is calibrating or if any touch events
are detected at any key in the most recent scan of the key matrix. If the sleep feature is disabled
in the setups, the QT1481 never sleeps.
Sleep should be used with extreme caution if the QT1481 is being used in an FMEA or EN60730
compliant design because all operations are stopped within the QT1481 while the part is asleep
and the host will have difficulty distinguishing between faulty operation and EN60730 counters
appearing to run slow because the part is intermittently sleeping. Also see
MSYNC”
Failure Modes and Effects Analysis (FMEA) is a tool used to determine critical failure problems
in control systems. FMEA analysis is being applied increasingly to a wide variety of applications
including domestic appliances. To survive FMEA testing the control board must survive any
single problem in a way that the overall product can either continue to operate in a safe way, or
shut down.
The most common FMEA requirements regard opens and shorts analysis of adjacent pins on
components and connectors. However, other criteria must usually be taken into account, for
example complete QT1481 failure, and the use of redundant signaling paths.
The QT1481 incorporates special self-test features which allow products to pass such FMEA
tests easily. These tests are performed during a dummy timeslot after the last enabled key.
The sequence of tests are performed repeatedly during normal running once all initialization,
include the burst spacing optimization in auto mode, is complete. During initialization, all FMEA
error flags are cleared. Any FMEA errors are reported as the tests are performed for the first
time.
The FMEA testing is done on all enabled keys in the matrix, and results are reported via the
serial interface. Disabled keys are not tested.
Assuming no detect events occur, the real time that elapses from the start of one sequence of
FMEA tests to the start of the next, or the FMEA sequence time, never exceeds 2s.
,
Section 5.14 on page
46.
Section 5.16 on page
47), and the sleep
“Mains Sync –
9621B–AT42–06/11