AT42QT1110-MU View Datasheet(PDF) - Atmel Corporation
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AT42QT1110-MU Datasheet PDF : 50 Pages
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3.5 Power Supply
3.5.1
General Considerations
See Section 8.2 on page 38 for the power supply range. If the power supply fluctuates slowly with temperature, the
device tracks and compensates for these changes automatically with only minor changes in sensitivity. If the supply
voltage drifts or shifts quickly, the drift compensation mechanism is not able to keep up, causing sensitivity
anomalies or false detections.
The usual power supply considerations with QT parts apply to the device. The power should be clean and come from
a separate regulator if possible. However, this device is designed to minimize the effects of unstable power, and,
except in extreme conditions, should not require a separate Low Dropout (LDO) regulator.
See underneath Figure 1.3 on page 4 for suggested regulator manufacturers.
Caution: A regulator IC shared with other logic can result in erratic operation and is not
advised.
A single ceramic 0.1 µF bypass capacitor, with short traces, should be placed very close to
the power pins of the IC. Failure to do so can result in device oscillation, high current
consumption, or erratic operation.
It is assumed that a larger bypass capacitor (like1 µF) is somewhere else in the power circuit; for example, near the
regulator.
3.5.2
Brownout Detection
The QT1110 includes a power supply monitoring circuit that detects if Vdd drops below a safe operating voltage.
When this occurs, the device goes into a Reset state, where no acquisition or processing is carried out. The device
remains in this state until Vdd returns to the specified voltage range.
Once a safe operating voltage is detected, the QT1110 behaves as per normal power-on/reset conditions; that is,
any saved settings are restored from EEPROM, the internal self-tests are run and all channels are calibrated.
The Brown-out detector threshold is 2.7 V ±10%.
3.6 QFN Package Restrictions
The central pad on the underside of the QFN chip should be connected to ground. Do not run any tracks underneath
the body of the chip, only ground. Figure 3-1 shows examples of good and bad tracking.
Figure 3-1. Examples of Good and Bad Tracking
Example of GOOD tracking
Example of BAD tracking
AT42QT1110-MU / AT42QT1110-AU [DATASHEET]
9
9520J–AT42–05/2013
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