QT118H-S ETC, QT118H-S Datasheet - Page 9

• Manufacturer Part Number: QT118H-S
• Description: CHARGE-TRANSFER TOUCH SENSOR
• Manufacturer: ETC

The circuit is remarkably immune to HF RFI provided that
certain design rules be adhered to:
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1. Use SMT components.
2. Always use a ground plane under the circuit.
3. Use a 0.1uF bypass cap very close to the supply pins.
4. If ESD diodes are used, always use Re1, Re2, and Cf.
5. Keep all ESD components close to the IC.
6. Do not route the sense wire near other traces or wires
Make Re1 / Re2 as large as possible without
compromising gain (depends on Cf and Cx).
Cf acts to shunt aside RF from entering the two diodes, thus
preventing their conduction due to RF currents. This form of
conduction will lead to false or erratic operation. Cf also acts
to lower sensitivity, and in many cases Cs will need to be
increased to compensate for this loss.
7. The sense electrode should be kept away from other
8. If the ESD diodes are not used, use Re1 in the electrode
conductors, even ground, which can re-radiate in RF
currents.
trace anyway, with a value as large as possible without
compromising gain.
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