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AT42QT2100 Datasheet(PDF) 16 Page - ATMEL Corporation |
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AT42QT2100 Datasheet(HTML) 16 Page - ATMEL Corporation |
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16 / 44 page  16 AT42QT2100 [DATASHEET] 9554E–AT42–01/13 4.4 Operating Modes 4.4.1 Introduction Four basic operating modes are possible: Free Run, Low Power (LP), Sleep and Sync. Sleep is a special case of LP mode, where the sleep time is infinite. Sync is a special case of LP mode where the timing of host communications is used as the timing basis for the QT2100 acquisition cycle. In the absence of host communications, the device operates in its most power-efficient low power mode, LP Mode 4. See below for further details. 4.4.2 Free Run Mode In this mode the device operates continuously with short intervals between burst groups; there are three bursts, one burst for each electrode group. DRDY goes high for approximately 500 µs between bursts and stays high during signal processing. In this mode, the acquisition bursts are unsynchronized, making this mode unsuitable if synchronization to mains frequency is needed. 4.4.3 Low Power Mode LP mode is designed to allow low power operation while still retaining full operation but at a slower speed. This mode is useful for devices that must use the touch keys to wake up a product, yet minimize power consumption. Several LP timings allow the user to trade power versus response time: the slower the response time, the lower the power consumed. In LP mode, the device spends a portion of the time sleeping between bursts; it wakes periodically to measure all channels with a set of three acquisition bursts, then goes back to sleep. If a touch is detected, the device operates as in Free Run mode and attempts to perform the Detect Integrator (DI) noise filter function to completion; if the DI filter fails to confirm a detection the device goes back to sleep and resumes LP mode. During the DI function the LPS bit will be cleared. If a key is found to be in detection the CHANGE pin will go high and the part will remain in Free Run mode. To go back into LP mode the host has to request LP mode again with an SPI communications exchange after the touch detection has been cleared by removal of touch or recalibration. CHANGE Pin in LP Mode: During the sleep portion of LP mode, CHANGE is held low. If however a change of key state is confirmed, CHANGE goes high and the part runs from then on in Free Run mode until the host reads the key state and puts the device back into LP mode or some other mode. MISO in LP Mode: During the sleep portion of LP mode, MISO floats. DRDY during LP Mode: DRDY remains high while the QT2100 is sleeping, to indicate to the host that SPI communications are possible. During an actual acquire burst, DRDY is held low. Command During LP Mode: The device can be woken from sleep by the SS pin being pulled low. Note that the SS pin must be pulled high in order for the device to enter its lowest power sleep mode. If SS is held low, the device enters a higher power sleep mode to enable SPI communications. The host may perform a normal SPI transfer as shown in Figure 4-3 on page 17. |
Similar Part No. - AT42QT2100_14 |
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Similar Description - AT42QT2100_14 |
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