QT60486-AS Atmel, QT60486-AS Datasheet - Page 15

• 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

After the PRD interval has expired and the auto-
recalibration has taken place, the affected key will once
again function normally. PRD is set on a per-key basis.
PRD Typical values:
PRD Default value:
5.7 Burst Length - BL
The signal gain for each key is controlled by circuit
parameters as well as the burst length.
The burst length is simply the number of times the
charge-transfer (‘QT’) process is performed on a given key.
Each QT process is simply the pulsing of an X line once,
with a corresponding Y line enabled to capture the
resulting charge passed through the key’s capacitance Cx.
QT60xx6 devices use a fixed number of QT cycles which
are executed in burst mode. There can be up to 64 QT
cycles in a burst, in accordance with the list of permitted
values shown in Section 6.5.
Increasing burst length directly affects key sensitivity. This
occurs because the accumulation of charge in the charge
integrator is directly linked to the burst length. The burst
length of each key can be set individually, allowing for
direct digital control over the signal gains of each key
individually.
Apparent touch sensitivity is also controlled by the
Negative Threshold level (NTHR). Burst length and NTHR
interact; normally burst lengths should be kept as short as
possible to limit RF emissions, but NTHR should be kept
above 6 to reduce false detections due to external noise.
The detection integrator mechanism also helps to prevent
false detections.
BL Typical values:
BL Default value:
5.8 Adjacent Key Suppression - AKS
These devices incorporate adjacent key suppression
(‘AKS’ - patent pending) that can be selected on a per-key
basis. AKS permits the suppression of multiple key
presses based on relative signal strength. This feature
assists in solving the problem of surface moisture which
can bridge a key touch to an adjacent key, causing multiple
key presses. This feature is also useful for panels with
tightly spaced keys, where a fingertip might inadvertently
activate an adjacent key.
AKS works for keys that are AKS-enabled anywhere in the
matrix and is not restricted to physically adjacent keys; the
device has no knowledge of which keys are actually
physically adjacent. When enabled for a key, adjacent key
suppression causes detections on that key to be
suppressed if any other AKS-enabled key in the panel has
a more negative signal deviation from its reference.
This feature does not account for varying key gains (burst
length) but ignores the actual negative detection threshold
setting for the key. If AKS-enabled keys in a panel have
different sizes, it may be necessary to reduce the gains of
larger keys relative to smaller ones to equalize the effects
of AKS. The signal threshold of the larger keys can be
altered to compensate for this without causing problems
with key suppression.
lQ
Advanced information; subject to change
2, 3 (48, 64 pulses / burst)
2 (48 pulses / burst)
5 to 8 (0.7s to 2.0s)
6 (1 second)
15
Adjacent key suppression works to augment the natural
moisture suppression of narrow gated transfer switches
creating a more robust sensing method.
AKS Default value:
5.9 Oscilloscope Sync - SSYNC
Pin 43 (S_Sync) can output a positive pulse oscilloscope
sync that brackets the burst of a selected key. More than
one burst can output a sync pulse as determined by the
Setups parameter SSYNC for each key.
This feature is invaluable for diagnostics; without it,
observing signals clearly on an oscilloscope for a particular
burst is very difficult.
This function is supported in Quantum’s QmBtn PC
software via a checkbox.
SSYNC Default value:
5.10 Negative Hysteresis - NHYST
The devices employ programmable hysteresis levels of
6.25%, 12.5%, 25%, or 50%. The hysteresis is a
percentage of the distance from the threshold level back
towards the reference, and defines the point at which a
touch detection will drop out. A 12.5% hysteresis point is
closer to the threshold level than to the signal reference
level.
Hysteresis prevents chatter and works to make key
detection more robust. Hysteresis is used only once the
key has been declared to be in detection, in order to
determined when the key should drop out.
Excessively large amounts of hysteresis can result in
‘sticking key’ that do not release after touch, especially
when signal levels are small. Low amounts of hysteresis
can cause key chatter due to low level signal noise or
minor amounts of finger motion.
The hysteresis levels are set for all keys only; it is not
possible to set the hysteresis differently from key to key.
NHYST Typical values:
NHYST Default value:
5.11 Dwell Time - DWELL
The Dwell parameter in Setups causes the acquisition
pulses to have differing charge capture durations.
Generally, shorter durations provide for enhanced surface
moisture suppression, while longer durations are usually
more compatible with EMC requirements. Longer dwell
times permit the use of larger series resistors in the X and
Y lines to suppress RFI effects, without compromising key
gain.
This parameter lets the designer trade off one requirement
for with the other.
DWELL Typical value:
DWELL Default value:
5.12 Mains Sync - MSYNC
The MSync feature uses the WS pin. The Sleep and Sync
features can be used simultaneously; the part can be put
into Sleep mode, but awakened by a mains sync signal at
the desired time.
0, 1 (6.25%, 12.5%).
1 (12.5%)
1 (187.5ns)
1 (187.5ns)
QT60486-AS 0.07/1103
0 (Off)
0 (Off)