SK-TSC-1127-SB Fujitsu, SK-TSC-1127-SB Datasheet - Page 15

• Manufacturer Part Number: SK-TSC-1127-SB
• Description: KIT, STARTER, TOUCH CNTRL, FMA1127
• Manufacturer: Fujitsu
• Type: Starter Kitr

Specifications of SK-TSC-1127-SB

• Mcu Supported Families: FMA1127
• Tool / Board Applications: Touch Sensor Controller
• Silicon Manufacturer: Fujitsu
• Kit Contents: SK-TSC-1127S-SB Touch Board, ADA-16FX-TSC-LCD, 10-pin Ribbon Cable, 3x FMA1127DC-30S Sample
• Features: 10-pin Connector For I2C And Interrupt Signals, Pin
• Rohs Compliant: No
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

SK-TSC-1127-SB User Guide
Typically, to start tuning a new application, first of all the Reference Delay and Alpha settings
need to be set. For this, the ‘mon2’ monitor mode can help to directly show the effect of
changed settings.
The Reference Delay is set by the ‘srd nn’ command, where ‘nn’ is the desired value from 0-
99. A warm reset command is issued automatically to activate the new setting. Typical
starting value will be ~50.
The Reference Delay value moves all of the bars (mon2 mode) to the left (higher RD value)
or to the right (lower RD value). Using the Reference Delay, the average (idle) impedance of
all touch sensors can be placed somewhere in the middle of the FMA1127 dynamic range,
indicated by the bars. Incrementing the Reference Delay by one step has a similar effect as
attaching an external capacitor of 0.078pF to the AREF pin of the TSC. So, in case the
reference delay maximum value of 99 is not sufficient, an additional capacitor of max. 10 pF
can be connected to the AREF pin to increase the reference impedance value.
If the variation of the different sensor idle impedances is too high, small tuning capacitors
have to be added (from the touch pads to ground), so that the idle capacitances of the
different channels are in the same range. However, a difference of 40-50 counts still is not
critical as long as there is enough room left to 0 and 99. Therefore, most typical applications
(including the SK-TSC-1127S-SB) will not require tuning capacitors.
After setting the Reference Delay, the Alpha of the channels can be set. Alpha is the
difference between measured impedance and the reference in idle (not touched) state. A
smaller value of Alpha makes the pad more sensitive, while increasing Alpha decreases
sensitivity. Typical values for a directly touched (only solder stop or thin foil between
electrode and finger) pad will be ~20 or higher. If some mm of plastic is used as front cover,
typical Alpha values will be in the range of 4-10.
The Alpha values are preset by the application in order to fit to the used PCB. Two settings
can be chosen by holding SW2 during reset and initialization; ‘P1’ can be used for the PCB
without front panel, while ‘P2’ is more sensitive in order to be used with a front plate, e.g.
plastic or glass.
NOTE:
When a front panel with high dielectric constant, such as glass, is pressed against the SK-
TSC-1127S-SB PCB during operation (no front panel present at power-up or reset), the
sudden increase in capacitance might be detected as touch. As the Automatic Impedance
Calibration is suspended as long as a touch is detected, a calibration should be forced (e.g.
by using the ‘wr’ command to issue a warm reset) after the front panel was added during
operation and when this was detected as touch. If the front panel is already present during
power-up or reset, the initial calibration will automatically adjust sensitivity.
Based on these Settings, the Alpha values can be set for the entire slider (‘sax’), for one
channel only (‘sa’), or it can be incremented / decremented for all channels (a+nn / a-nn).
The current values of Alpha and Reference Delay can be checked with the ‘sv’ command.
All remaining registers can be accessed by the ‘set’ and ‘setx’ commands using their
addresses. Please note that after writing to certain registers, a ‘warm reset’ has to be
performed e.g. using the ‘wr’ command.
Please refer to the application note ‘FMA1127_Init_Reg_Description’ for further register
description.
© Fujitsu Microelectronics Europe GmbH
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