QT320-IS Atmel, QT320-IS Datasheet - Page 10

• Manufacturer Part Number: QT320-IS
• Description: SENSOR IC TOUCH PROG 2CH 8-SOIC
• Manufacturer: Atmel
• Series: QProx™r
• Type: Capacitiver

Specifications of QT320-IS

• Rohs Status: RoHS non-compliant
• Touch Panel Interface: 2, 2-Wire
• Number Of Inputs/keys: 2 Key
• Resolution (bits): 16 b
• Data Interface: Serial
• Voltage Reference: Internal
• Voltage - Supply: 1.8 V ~ 5.25 V
• Current - Supply: 600µA
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SMD (300 mil)
• Output Type: *
• Interface: *
• Input Type: *
• Other names: 427-1031

2.7.3 H
Both OUT pins have HeartBeat™ ‘health’ indicator pulses
superimposed on them. Heartbeat floats both 'OUT' pins for
approximately 15µs once before Channel 2’s burst.
These pulses can be used to determine that the sensor is
operating properly. The pulses are evident on an OUT line
that is low, and appear as positive pulses.
They are not evident on an OUT pin that is high.
Heartbeat indication can be used to determine if the chip is
operating properly. The frequency of the pulses can be used
to determine if the IC is operating within desired limits.
It is not possible to disable these pulses.
Heartbeat pulses can be easily filtered by placing a suitable
capacitor from an OUT pin to Vss, to prevent the OUT line
from rising substantially within the 15µs pulse. For example,
with a 10K pullup resistor, the capacitor can be 0.015µF of
virtually any type.
2.7.4 O
The outputs can sink up to 2mA of non-inductive current. If an
inductive load is used, such as a small relay, the load should
be diode-clamped to prevent damage. The current must be
limited to 2mA max to prevent detection side effects from
occurring, which happens when the load current creates
voltage drops on the die and bonding wires; these small shifts
can materially influence the signal level to cause detection
instability.
3 CIRCUIT GUIDELINES
3.1 SAMPLE CAPACITORS
Cs capacitors can be virtually any plastic film or low to
medium-K ceramic capacitor. The normal usable Cs range is
from 1nF ~ 200nF depending on the sensitivity required;
larger values of Cs require higher stability to ensure reliable
sensing. Acceptable capacitor types include NPO or C0G
ceramic, PPS film, Y5E and X7R ceramic in that order.
If the design requires sensitivity matching between channels,
it is strongly advised to use tight tolerance capacitors and to
trim the relative sensitivities as described in Section 1.4.4.
lQ
OUT1
OUT2
EART
UTPUT
Figure 3-1 ESD/EMC protection resistors
RE3
RE4
B
EAT
D
RIVE
™ O
1
7
C
OUT1
OUT2
APABILITY
UTPUT
4
8
VDD
VSS
Vdd
S1A
S1B
S2A
S2B
3
5
6
2
CS1
CS2
RE1
RE2
SENSOR 1
SENSOR 2
10
3.2 POWER SUPPLY
3.2.1 S
The QT320 derives its internal references from the power
supply. Sensitivity shifts and timing changes will occur with
changes in Vdd, as often happens when additional power
supply loads are switched on or off via one of the Out pins.
These supply shifts can induce detection ‘cycling’, whereby
an object is detected, the load is turned on, the supply sags,
the detection is no longer sensed, the load is turned off, the
supply rises and the object is reacquired, ad infinitum.
Detection ‘stiction’, the opposite effect, can occur if a load is
shed when an output is active and the signal swings are
small: the Out pin can remain stuck even if the detected
object is no longer near the electrode.
3.2.2 S
Vdd can range from 1.8 to 5.25 volts during operation, and
2.2 to 5.25 during eeprom Setups configuration. Current drain
will vary depending on Vdd, the chosen sleep cycles, and the
burst lengths. Increasing Cx values will decrease power drain
since increasing Cx loads decrease burst length (Figures 5-1,
5-4).
If the power supply is shared with another electronic system,
care should be taken to assure that the supply is free of
spikes, sags, and surges. The QT320 will track slow changes
in Vdd if drift compensation is enabled, but it can be adversely
affected by rapid voltage steps and spikes at the millivolt
level.
If desired, the supply can be regulated using a conventional
low current regulator, for example CMOS LDO regulators with
low quiescent currents, or standard 78Lxx-series 3-terminal
regulators.
For proper operation a 100nF (0.1uF) ceramic bypass
capacitor should be used between Vdd and Vss; the bypass
cap should be placed very close to the Vdd and Vss pins.
3.3 PCB LAYOUT
3.3.1 G
The use of ground planes around the device is encouraged
for noise reasons, but ground should not be coupled too close
to the four sense pins in order to reduce Cx load. Likewise,
the traces leading from the sense pins to the electrode should
not be placed directly over a ground plane; rather, the ground
plane should be relieved by at least 3 times the width of the
sense traces directly under it, with periodic thin bridges over
the gap to provide ground continuity.
3.3.2 C
If a cloning connector is used, place this close to the QT320
(Figure 4-1). Placing the cloning connector far from the
QT320 will increase the load capacitance Cx of the sensor
and decrease sensitivity, as some of the cloning lines are
sense lines. Long distances on these lines can also make the
clone process more susceptible to communication errors from
ringing and interference.
Cloning can be designed for production by using pads (SMT
or through-hole) on the solder side which are connected to a
fixture via spring loaded ATE-style ‘pogo-pins’. This eliminates
the need for an actual connector to save cost.
LONE
ROUND
TABILITY
UPPLY
P
R
ORT
P
EQUIREMENTS
LANES
C
ONNECTOR
QT320/R1.03 08/02