QT110-IS Atmel, QT110-IS Datasheet - Page 4

• Manufacturer Part Number: QT110-IS
• Description: SENSOR IC TOUCH/PROXMTY 1CH8SOIC
• Manufacturer: Atmel
• Series: QTouch™r
• Type: Capacitiver

Specifications of QT110-IS

• Rohs Status: RoHS non-compliant
• Touch Panel Interface: 1, 2-Wire
• Number Of Inputs/keys: 1 Key
• Resolution (bits): 14 b
• Data Interface: Serial
• Voltage Reference: Internal
• Voltage - Supply: 2.5V, 3.3V, 5V
• Current - Supply: 20µA
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Output Type: Logic
• Interface: 2-Wire
• Input Type: Logic
• Other names: 427-1002

A ‘virtual capacitive ground’ can be created by connecting
the QT110’s own circuit ground to:
Free-floating ground planes such as metal foils should
maximize exposed surface area in a flat plane if possible. A
square of metal foil will have little effect if it is rolled up or
crumpled into a ball. Virtual ground planes are more
effective and can be made smaller if they are physically
bonded to other surfaces, for example a wall or floor.
1.3.4 F
The electrode can be prevented from sensing in undesired
directions with the assistance of metal shielding connected
to circuit ground (Figure 1-6). For example, on flat surfaces,
the field can spread laterally and create a larger touch area
than desired. To stop field spreading, it is only necessary to
surround the touch electrode on all sides with a ring of metal
connected to circuit ground; the ring can be on the same or
opposite side from the electrode. The ring will kill
field spreading from that point outwards.
If one side of the panel to which the electrode is
fixed has moving traffic near it, these objects can
cause inadvertent detections. This is called
‘walk-by’ and is caused by the fact that the fields
radiate from either surface of the electrode
equally well. Again, shielding in the form of a
metal sheet or foil connected to circuit ground
will prevent walk-by; putting a small air gap
between the grounded shield and the electrode
will keep the value of Cx lower and is
encouraged. In the case of the QT110, the
sensitivity is low enough that 'walk-by' should not
be a concern if the product has more than a few
(1) A nearby piece of metal or metallized housing;
(2) A floating conductive ground plane;
(3) A nail driven into a wall when used with small
(4) A larger electronic device (to which its output might be
Figure 1-6
Sen se
w ire
electrodes;
connected anyway).
IELD
U ns hielded
S
Electrod e
HAPING
Shielding Against Fringe Fields
Sens e
w ire
E lec trod e
S h ield ed
T hr es ho ld
O u tpu t
- 4 -
millimeters of internal air gap; if the product is very thin and
contact with the product's back is a concern, then some form
of rear shielding may be required.
1.3.5 S
The QT110 can be set for one of 3 gain levels using option
pin 5 (Table 1-1). If left open, the gain setting is high. The
sensitivity change is made by altering the numerical
threshold level required for a detection. It is also a function
of other things: electrode size, shape, and orientation, the
composition and aspect of the object to be sensed, the
thickness and composition of any overlaying panel material,
and the degree of ground coupling of both sensor and object
are all influences.
1.3.5.1 Increasing Sensitivity
In some cases it may be desirable to increase sensitivity
further, for example when using the sensor with very thick
panels having a low dielectric constant.
Sensitivity can often be increased by using a bigger
electrode, reducing panel thickness, or altering panel
composition. Increasing electrode size can have diminishing
returns, as high values of Cx will reduce sensor gain
(Figures 4-1 ~ 4-3). Also, increasing the electrode's surface
area will not substantially increase touch sensitivity if its
diameter is already much larger in surface area than the
object being detected. The panel or other intervening
material can be made thinner, but again there are
diminishing rewards for doing so. Panel material can also be
changed to one having a higher dielectric constant, which
will help propagate the field through to the front. Locally
adding some conductive material to the panel (conductive
materials essentially have an infinite dielectric constant) will
also help dramatically; for example, adding carbon or metal
fibers to a plastic panel will greatly increase frontal field
strength, even if the fiber density is too low to make the
plastic bulk-conductive.
1.3.5.2 Decreasing Sensitivity
In some cases the QT110 may be too sensitive, even on low
gain. In this case gain can be lowered further by any of a
Table 1-1 Gain Setting Strap Options
Figure 2-1 Drift Compensation
ENSITIVITY
Medium
Gain
High
S ign a l
Low
R e fe re nce
H yste resis
Tie Pin 5 to:
None
Pin 6
Pin 7