QT60326-AS Atmel, QT60326-AS Datasheet - Page 13

• Manufacturer Part Number: QT60326-AS
• Description: SENSOR IC MTRX TOUCH32KEY 44TQFP
• Manufacturer: Atmel
• Series: QMatrix™, QProx™r
• Type: Capacitiver

Specifications of QT60326-AS

• Rohs Status: RoHS non-compliant
• Number Of Inputs/keys: 32 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: *

5 Setups
The devices calibrate and process all signals using a
number of algorithms specifically designed to provide for
high survivability in the face of adverse environmental
challenges. They provide a large number of processing
options which can be user-selected to implement very
flexible, robust keypanel solutions.
User-defined Setups are employed to alter these
algorithms to suit each application. These setups are
loaded into the device in a block load over one of the serial
interfaces. The Setups are stored in an onboard eeprom
array. After a block load, the device should be reset to
allow the new Setups block to be shadowed in internal
Flash ROM and to allow all the new parameters to take
effect.
Refer to Section 6.2, page 17 for a table of all Setups.
Block length issues: The setups block is 247 bytes long
to accommodate 48 keys. This can be a burden on smaller
host controllers with limited memory. In larger quantities
the devices can be procured with the setups block
preprogrammed from Quantum. If the application only
requires a small number of keys (such as 16) then the
setups table can be compressed in the host by filling large
stretches of the Setups area with nulls.
Many setups employ lookup-table value translation. The
Setups Block Summary on page 19 shows all translation
values.
Default Values shown are factory defaults.
5.1 Negative Threshold - NTHR
The negative threshold value is established relative to a
key’s signal reference value. The threshold is used to
determine key touch when crossed by a negative-going
signal swing after having been filtered by the detection
integrator. Larger absolute values of threshold desensitize
keys since the signal must travel farther in order to cross
the threshold level. Conversely, lower thresholds make
keys more sensitive.
As Cx and Cs drift, the reference point drift-compensates
for these changes at a user-settable rate; the threshold
level is recomputed whenever the reference point moves,
and thus it also is drift compensated.
The amount of NTHR required depends on the amount of
signal swing that occurs when a key is touched. Thicker
panels or smaller key geometries reduce ‘key gain’, ie
signal swing from touch, thus requiring smaller NTHR
values to detect touch.
The negative threshold is programmed on a
per-key basis using the Setup process. See
table, page 19.
Typical values:
Default value:
5.2 Positive Threshold - PTHR
The positive threshold is used to provide a
mechanism for recalibration of the reference
point when a key's signal moves abruptly to the
lQ
Advanced information; subject to change
(7 to 12 counts of threshold; 4 is internally
added to NTHR to generate the threshold).
(10 counts of threshold)
3 to 8
6
Threshold
Hysteresis
Output
Figure 5-1 Thresholds and Drift Compensation
13
positive. This condition is not normal, and usually occurs
only after a recalibration when an object is touching the
key and is subsequently removed. The desire is normally
to recover from these events quickly.
Positive threshold levels are programmed in using the
Setup process on a per-key basis.
Typical values:
Default value:
5.3 Drift Compensation - NDRIFT, PDRIFT
Signals can drift because of changes in Cx and Cs over
time and temperature. It is crucial that such drift be
compensated, else false detections and sensitivity shifts
can occur.
Drift compensation (Figure 5-1) is performed by making the
reference level track the raw signal at a slow rate, but only
while there is no detection in effect. The rate of adjustment
must be performed slowly, otherwise legitimate detections
could be ignored. The devices drift compensate using a
slew-rate limited change to the reference level; the
threshold and hysteresis values are slaved to this
reference.
When a finger is sensed, the signal falls since the human
body acts to absorb charge from the cross-coupling
between X and Y lines. An isolated, untouched foreign
object (a coin, or a water film) will cause the signal to rise
very slightly due to an enhancement of coupling. This is
contrary to the way most capacitive sensors operate.
Once a finger is sensed, the drift compensation
mechanism ceases since the signal is legitimately
detecting an object. Drift compensation only works when
the signal in question has not crossed the negative
threshold level.
The drift compensation mechanism can be made
asymmetric if desired; the drift-compensation can be made
to occur in one direction faster than it does in the other
simply by changing the NDRIFT and PDRIFT Setups
parameters. This can be done on a per-key basis.
Specifically, drift compensation should be set to
compensate faster for increasing signals than for
decreasing signals. Decreasing signals should not be
compensated quickly, since an approaching finger could
be compensated for partially or entirely before even
touching the touch pad. However, an obstruction over the
(5 to 8 counts of threshold; 4 is internally added to
PTHR to generate the threshold)
(6 counts of threshold)
Signal
Reference
QT60486-AS 0.07/1103
1 to 4
2