QT60486-AS Atmel, QT60486-AS Datasheet - Page 3

• Manufacturer Part Number: QT60486-AS
• Description: SENSOR IC MTRX TOUCH48KEY 44TQFP
• Manufacturer: Atmel
• Series: QMatrix™, QProx™r
• Type: Capacitiver

Specifications of QT60486-AS

• Rohs Status: RoHS non-compliant
• Number Of Inputs/keys: 48 Key
• Resolution (bits): 9, 11 b
• Data Interface: Serial, SPI™, UART
• Voltage - Supply: 4.75 V ~ 5.25 V
• Current - Supply: 25mA
• Operating Temperature: -40°C ~ 105°C
• Mounting Type: Surface Mount
• Package / Case: 44-TQFP, 44-VQFP
• Output Type: *
• Interface: *
• Input Type: *
• For Use With: 427-1088 - BOARD EVAL QT60486-AS QMATRIX

The signal swing from the smallest finger touch should
preferably exceed 10 counts, with 15 being a reasonable
target. The signal threshold setting (NTHR) should be set to a
value guaranteed to be less than the signal swing caused by
the smallest touch.
Increasing the burst length (BL) parameter will increase the
signal strengths as will increasing the Rs values.
2.6 Matrix Series Resistors
The X and Y matrix scan lines should use series 1K resistors
or higher. X drive lines require them in most cases to reduce
edge rates and thus RF emissions. Y lines need them to
reduce EMC susceptibility problems and in some cases, ESD
effects.
1K is a good starting point, but in fact the value can be much
higher in most cases. The end limit is reached when the
signal level and hence key sensitivity is clearly being affected
by the resistance. Too high a value on the X lines will limit the
charge coupling across the key. Too high a value on the Y
lines will reduce the amount of charge captured by the
sampling capacitor.
End limits can vary depending on key geometry and stray
capacitance, but often are found to be in the region of 20K ~
50K ohms.
2.7 Key Design & Layouts
Keys can be constructed out of a variety of materials
including flex circuits, FR4, and even inexpensive
single-sided CEM-1. It is best to place the chip near the keys
on the same PCB so as to reduce trace lengths, thereby
reducing the chances for EMC problems.
Please refer to the latest Quantum application note on how to
create PCB layouts for keys.
lQ
Advanced information; subject to change
3
2.8 Startup / Calibration Times
The devices require initialization times as follows:
Keys that cannot calibrate for some reason require 5 cal
cycles before they report as errors. However, the device can
report back during this interval that the key(s) affected are still
in calibration via status function bits.
2.9 Reset Input
The /RST pin can be used to reset the device to simulate a
power down cycle, in order to bring the part up into a known
state should communications with the part be lost. The pin is
active low, and a low pulse lasting at least 10µs must be
applied to this pin to cause a reset.
To provide for proper operation during power transitions the
devices have an internal brown-out detector set to 4 volts.
A Force Reset command, 0x04 is also provided which
generates an equivalent hardware reset.
If an external reset is not used, this pin may be connected to
Vdd.
1. From very first powerup to ability to communicate:
2. Normal cold start to ability to communicate:
3. Calibration time per key vs. burst spacings:
2,000ms (One time event to initialize all of eeprom)
70ms (Normal initialization from any reset)
spacing = 250µs: 425ms
spacing = 300µs: 510ms
spacing = 400µs: 680ms
spacing = 500µs: 850ms
spacing = 1ms: 1,700ms
spacing = 2ms: 3,400ms
To the above, add 2,000ms or 70ms from (1) or (2) for
the total elapsed time from reset to ability to report key
detections.
QT60486-AS 0.07/1103