Resistive touchscreen controller detects proximity, pressure with no additional components

Semtech Corp.'s 4-D Touch resistive touchscreen controllers integrate proximity sensing and haptic control for driving motors in handheld applications.

The SX8654/55/56/57/58 low-power 4/5-wire resistive touchscreen controllers are also equipped with on-chip ±15kV ESD protection, making them well-suited for mobile phones, tablets, DSCs, handheld GPS, automotive center consoles, and POS terminals.  

The SX865X controllers support a proximity detection distance of more than 5 cm using any standard 4/5-wire resistive panel, enabling various power-saving features such as automatic backlight activation or system wake-up. They feature a 12-bit ADC for coordinates and touch-pressure measurement with current consumption of 30µA at 8kSPS rate. The SX8654 family enters a low power state between conversions to save power consumption. 

The devices also incorporate a haptics motor driver for controlling Linear Resonant Actuator (LRA) and Eccentric Rotating Mass (ERM) micro motors (up to 250mA), while acknowledging touch events, emulating the tactile feedback similar to mechanical keys . The haptics waveform can be input via the I²C interface or with an external PWM signal.

Key highlights:

• Low-power operation

Ø  2.3V to 3.6V

Ø  30uA @ 2.3V 8ksps

Ø  0.4uA shut-down current

• 4/5-wire touchscreen interface with programmable digital filtering/averaging
• Fully programmable proximity sensing (SX8654/56)

Ø  5cm detection distance

Ø  No additional components required

• Built-in haptics driver for LRA and ERM (SX8654/55)

Ø  Up to 250 mA drive capability

Ø  Short circuit and over temperature protection

• On-chip ESD protection up to ±15kV
• Ultra small footprint: 4mm x 4mm 20-QFN and 2.07mm x 2.07mm 19-WLCSP
• Dedicated hardware reset pin
• 400kHz I²C interface

Pricing and Availability

The SX8654 (order code: SX8654IWLTRT), SX8655 (order code: SX8654IWLTRT) and SX8655 (order code: SX8656IWLTRT) are available in production quantities and are priced at $1.44, $0.84 and $1.08 respectively in 1,000-piece lots for the QFN package. The 1,000-piece price for the Immersion certified devices SX8657 (order code: SX8657IWLTRT) and SX8658 (order code: SX8658IWLTRT) are $1.44 and $0.84 respectively. All these devices are also available in the space-saving WLCSP. 

Datasheets:  SX8654; SX8655; SX8656; SX8657; SX8658

For more on haptics technology, see design article: Haptics technology: picking up good vibrations