ADSemiconductor®
ANMG04 (4-CH Auto Sensitivity Calibration Capacitive Touch Sensor)
8 ANMG04 Implementation
8.1 Typical current consumption
ANMG04 uses internal bias circuit, so internal clock frequency and current consumption is fixed and no
external bias circuit is needed. Internal clock frequency and calibration speed can be changed by I2C register
setting4. Faster calibration speed needs more current consumption than normal or slower calibration speed. Slow
calibration speed isn’t recommended if it has not problem of current consumption.
Internal bias circuit can make the circuit design simple and reduce external components.
8.2 CS implementation
ANMG04 has 256 step selections of sensitivity and internal surge protection resister. Sensitivity of each sensing
channel (CS) can be independently controlled on others. External components of CS pin such as series resistor
or parallel capacitor isn’t necessary. The parallel parasitic capacitance of CS pins caused by touch line, touch
pad and neighbor GND or other pattern may affect sensitivity. The sensitivity will be decreased when bigger
parallel parasitic capacitance of CS pin is added.
Parallel capacitor (CS1~S4) of CS pin is useful in case of detail sensitivity mediation is required such as for
complementation sensitivity difference between channels. Same as above parallel parasitic capacitance,
sensitivity will be decreased when a big value of parallel capacitor (CS1~S4) is used. Under 50pF capacitor can be
used as sensitivity meditation capacitor and a few pF is usually used. The RS, serial connection resistor of CS
pins, may be used to avoid mal-function from external surge and ESD. (It might be optional.) From 200Ω to
1kΩ is recommended for RS. Refer to below CS pins application figure.
RS4
CS4<<
Touch PAD4
CS4
RS1
Touch PAD1
CS1<<
CS1
The ANMG04 has eight independent touch sensor input from CS1 to CS4. The internal touch decision process
of each channel is separated from others. Therefore eight channel touch key board application can be designed
by using only one ANMG04 without coupling problems.
The size and shape of PAD might have influence on the sensitivity. The sensitivity will be optimal when the size
of PAD is approximately an half of the first knuckle (it’s about 10 ㎜ｘ 7 ㎜). The connection line of CS to
touch PAD is recommended to be routed as short as possible to prevent from abnormal touch detect caused by
connection line. The unused CS pin should not be connected with the ground.
4
Refer to 10.2.4. Clock control register.
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