FMA1125DC-24N Fujitsu, FMA1125DC-24N Datasheet - Page 5

• Manufacturer Part Number: FMA1125DC-24N
• Description: IC, CONTROLLER, TOUCH SENSOR, 24QFN
• Manufacturer: Fujitsu

Specifications of FMA1125DC-24N

• Brief Features: Patented Fully Digital Architecture, Configurable Touch Input Channels, Host Interface Via I2C
• Supply Voltage Range: 2.3V To 5.5V
• Operating Temperature Range: -40°C To +90°C
• Ic Function: Touch Sensor Controller
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Operation Principles
Touch Detection
The FMA1125DC includes the Impedance Change Detection engine* within the device, which detects impedance differences between the
reference input and the sensor input.
As shown in Figure 1, if the pad is not touched, the impedance of the sensor input Zin should be kept less than the impedance of the
reference Zref. If the pad is touched, as shown in Figure 2, Zin is increased by Ztouch. When Ztouch, by touching, becomes greater than
the difference of Zin and Zref in the not touched state, i.e., if Zin in touched state becomes greater than Zref by a value higher than 0.1pF,
the ICD (Impedance Change Detection) engine within the chip generates the acknowledged output signal indicating it senses the touch.
Notice that a value of 0.1pF or higher is needed to maintain stable output against various noises. The sensor input impedance, Zin,
includes parasitic capacitance of the input line, tuning capacitance of the input pin and on-chip input impedance, while Zref includes on-
chip impedance, AIC control values and external tuning capacitance if necessary.
AIC
The AIC* function maintains consistent sensitivity against external environmental changes such as temperature, supply voltage/current,
humidity, and system-level variations. This helps users to develop their applications more conveniently by providing the actual impedance
value of each sensor input. For developers, a Tuning Viewer program is provided, which helps to optimize PCB design and to decide AIC
input parameters. More detailed information is available in the FMA1125DC Tuning Guide.
The ICD engine residing in the FMA1125DC controls reference impedance values for each sensor input pin by acquiring each input’s
impedance data. It periodically updates all reference values under the condition that all touch pads remain in no-touched status. This
auto-calibration function absorbs environmental changes and guarantees product stability.
APIS
When touch pads are arranged too closely to each other, it is sometimes difficult to identify which pad is touched. APIS
Pattern Interference Suppression) is a filtering function that identifies which pads are intentionally touched. If APIS mode is not defined,
all touch data without APIS filtering are transmitted to the MCU. For example, if the application is a numeric keypad, the user can use
APIS mode 1 to get the strongest output and filter out all other weakly touched inputs. Without APIS, the host may have to do this
filtering function thus APIS reduces the burden of the host’s computing time.
*Proprietary technology of ATLab, Inc.
IDC =
™
™
Touch Pad System Model
Zref
Figure 1: When a Pad is Not Touched.
1, if Zin – Zref > 0.1pF
0, otherwise
Zin
(Automatic Impedance Calibration)
Touch Pad
Touch Output
Impendance
Detection
Zin < Zref
Change
Impedance Status
Zin
Zref
Confidential
Touch Pad System Model
Zref
Zin
Touch Pad
Impendance
Figure 2: When a Pad is Touched.
Detection
Change
FMA1125DC
Fujitsu Microelectronics America, Inc.
Impedance Status
™
Zin
Zref
(Adjacent
Ztouch
Touch
Detected
3