High Sensitivity Capacitive Switch Controller with Superior Anti-Noise Characteristics: Easily add touch switch functionality for smart home appliances

ROHM has recently announced the development of a controller IC that makes it possible to configure a capacitive touch switch for replacing conventional mechanical ON/OFF switches in home appliances, office equipment, and numerous other applications.

The BU21079F is the latest addition to ROHM’s lineup of capacitive switch controller ICs (BU21072MUV, BU21078MUV), and features high sensitivity along with strong anti-noise characteristics. In addition, intermittent operation enables low power consumption, while a leaded surface-mount SOP16 package has been adopted for broad compatibility.

The control panels of electronic equipment are often comprised of multiple switches, including a mechanical ON/OFF switch. However, in recent years, touch operation stemming from smartphones has become increasingly popular, making capacitive switches the go-to choice in a variety of devices due to their superior reliability against breakdown compared with mechanical switches, which are susceptible to contact failure caused by abrasion and/or foreign particle intrusion. Plus they lend themselves to more streamlined, contemporary designs.

Based on these demands, ROHM has developed capacitive touchscreen and touch switch controller ICs that take advantage of unique user interface control technology to provide high sensitivity with high noise immunity. In addition, to meet the growing need for lower power consumption and reduced mounting load the BU21079F features intermittent operation, and is available in the industry-standard SOP16 surface mount package. This makes it possible to configure comparatively simple, easy-to-use control panels for printers, office equipment, electric ranges, IH cooking heaters, and other home appliances.

Normally, for capacitive switches, there is an inverse relationship between sensitivity and noise immunity. As the sensitivity increases the resistance to noise tends to decrease. To solve this problem, ROHM utilized proprietary analog technology and circuit optimization to achieve enhanced noise identification functionality – while maintaining high sensitivity. As a result, support for overlays up to 15mm thick is enables, along with wiring distances up to 1m – twice the distance of conventional products. This makes it possible to configure touch switch operation in sets that presented difficulties in the past, including devices with curved panels and larger equipment such as home appliances. Additional features include an integrated MCU and I²C I/F, broad supply voltage range (3.0-5.5V), a matrix switch expansion function, press and hold function, and compatibility with 8ch switches.

Pricing: 200yen (Samples)

Availability: Now (Samples), November 2013 (OEM Quantities)

Key Features

1. Industry-leading noise immunity

ROHM’s exclusive high sensitivity analog front end makes it possible to clear IEC61000-4-6 compliance testing, which represents the industry’s highest standard for noise immunity in capacitive switches. This eliminates the need for noise and EMI countermeasures, minimizing both mounting load and costs.

2. Compatible with overlays up to 15mm thick

Original high-speed sampling operation enables support for overlays up to 15mm thick, making the BU21079F ideal for applications where it was previously difficult to introduce touch switch functionality, such as sets with curved or rounded panels.

3. Reduced power consumption

Intermittent operation (fewer sensing operations – i.e. during standby) reduces power consumption significantly compared with conventional products.

4. Supports wiring distances up to 1m

High noise immunity enables wiring distances up to 1m – twice the distance vs. conventional models. This expands applicability to include larger devices, where it has been problematic to incorporate touch switch functionality.

Terminology
• Touch Switch Controller Compared with touchscreen controllers used in smartphones, a touch switch controller adds dedicated ON/OFF functionality, high response speed, and high noise immunity.
• Analog Front End (AFE) A processing block that makes it easy to convert analog signals that are weak or contain noise into a digital format. • Sampling The act of detecting analog signals within a specific interval for conversion to digital.
• IEC61000-4-6 Specifies immunity testing established IEC (International Electrotechnical Commission) against conducted disturbances induced by a radio-frequency electromagnetic field.
• EMI (Electromagnetic Interference) Noise generated by peripheral devices.