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QT320-D Datasheet Preview

QT320-D Datasheet

2-CHANNEL PROGAMMABLE ADVANCED SENSOR IC

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LQ
QPROXQT320
2-CHANNEL PROGAMMABLE ADVANCED SENSOR IC
Two channel digital advanced capacitive sensor IC
Projects two ‘touch buttons’ through any dielectric
Cloning for user-defined sensing behavior
100% autocal - no adjustments required
Only one external capacitor per channel
User-defined drift compensation, threshold levels
Variable gain via Cs capacitor change
Selectable output polarities
Toggle mode / normal mode outputs
HeartBeat™ health indicator on outputs (can be disabled)
1.8 ~ 5V supply, 60µA
APPLICATIONS
Light switches
Industrial panels
Appliance control
Security systems
Access systems
Pointing devices
Computer peripherals
Entertainment devices
The QT320 charge-transfer (“QT’”) touch sensor chip is a self-contained digital IC capable of detecting near-proximity or
touch on two sensing channels. It will project sense fields through almost any dielectric, like glass, plastic, stone, ceramic,
and most kinds of wood. It can also turn small metal-bearing objects into intrinsic sensors, making them respond to proximity
or touch. This capability coupled with its ability to self calibrate continuously can lead to entirely new product concepts.
It is designed specifically for human interfaces, like control panels, appliances, security systems, lighting controls, or
anywhere a mechanical switch or button may be found; it may also be used for some material sensing and control
applications provided that the presence duration of objects does not exceed the recalibration time-out interval.
The IC requires only a common inexpensive capacitor per channel in order to function.
Power consumption and speed can be traded off depending on the application; drain can be as low as 60µA, allowing
operation from batteries.
The IC’s RISC core employs signal processing techniques pioneered by Quantum; these are specifically designed to make
the device survive real-world challenges, such as ‘stuck sensor’ conditions and signal drift. Even sensitivity is digitally
determined. All key operating parameters can be set by the designer via the onboard eeprom which can be configured to alter
sensitivity, drift compensation rate, max on-duration, output polarity, and toggle mode independently on each channel.
No external switches, opamps, or other analog components aside from Cs are usually required.
The Quantum-pioneered HeartBeat™ signal is also included, allowing a host controller to monitor the health of the QT320
continuously if desired; this feature can be disabled via the cloning process.
By using the charge transfer principle, the IC delivers a level of performance clearly superior to older technologies in a highly
cost-effective package.
AVAILABLE OPTIONS
TA
00C to +700C
-400C to +850C
SOIC
-
QT320-IS
8-PIN DIP
QT320-D
-
LQ
Copyright © 2002 QRG Ltd
QT320/R1.03 08/02




Quantum

QT320-D Datasheet Preview

QT320-D Datasheet

2-CHANNEL PROGAMMABLE ADVANCED SENSOR IC

No Preview Available !

Table 1-1 Pin Descriptions
Pin Name
Function
1 OUT1 Detection output, Ch. 1
2 S2B
Sense Ch 2 pin B
3 S1A
Sense Ch 1 pin A
4
VSS
Negative supply (ground)
5 S1B
Sense Ch 1 pin B
6 S2A
Sense Ch 2 pin A
7 OUT2 Detection output, Ch. 2
8 VDD
Positive supply
which requires several consecutive confirmations of a
detection before an output is activated.
The two channels of sensing operate in a completely
independent fashion. A unique cloning process allows the
internal eeprom of the device to be programmed for each
channel, to permit unique combinations of sensing and
processing functions for each.
The two sensing channels operate in interleaved
time-sequence and thus cannot interfere with each other.
Alternate Pin Functions for Cloning
3 SCK
Serial clone data clock
6 SDO
Serial clone data out
7 SDI
Serial clone data in
1 - OVERVIEW
The QT320 is a 2 channel digital burst mode charge-transfer
(QT) sensor designed specifically for touch controls; it
includes all hardware and signal processing functions
necessary to provide stable sensing under a wide variety of
changing conditions. Only two low-cost, non-critical capacitors
are required for operation.
A unique aspect of the QT320 is the ability of the designer to
clonea wide range of user-defined setups into the parts
eeprom during development and in production. Cloned setups
can dramatically alter the behavior of each channel,
independently. For production, the parts can be cloned
in-circuit or can be procured from Quantum pre-cloned.
Figure 1-1 shows the basic QT320 circuit using the device,
with a conventional output drive and power supply
connections.
1.1 BASIC OPERATION
The QT320 employs bursts of variable-length charge-transfer
cycles to acquire its signal. Burst mode permits power
consumption in the microamp range, dramatically reduces RF
emissions, lowers susceptibility to EMI, and yet permits
excellent response time. Internally the signals are digitally
processed to reject impulse noise using a 'consensus' filter
Figure 1-1 Basic QT320 circuit
1.2 ELECTRODE DRIVE
1.2.1 SWITCHING OPERATION
The IC implements two channels of direct-to-digital
capacitance acquisition using the charge-transfer method, in
a process that is better understood as a capacitance-
to-digital converter (CDC). The QT switches and charge
measurement functions are all internal to the IC (Figure 1-2).
The CDC treats sampling capacitor Cs as a floating store of
accumulated charge which is switched between the sense
pins; as a result, the sense electrode can be connected to
either pin with no performance difference. In both cases the
rule Cs >> Cx must be observed for proper operation. The
polarity of the charge build-up across Cs during a burst is the
same in either case. Typical values of Cs range from 2nF to
100nF for touch operation.
Larger values of Cx cause charge to be transferred into Cs
more rapidly, reducing available resolution and resulting in
lower gain. Conversely, larger values of Cs reduce the rise of
differential voltage across it, increasing available resolution
and raising gain. The value of Cs can thus be increased to
allow larger values of Cx to be tolerated (Figures 5-1 to 5-4).
As Cx increases, the length of the burst decreases resulting in
lower signal numbers.
Figure 1-2 Internal Switching
It is possible to connect separate Cx and Cxloads to Sa and
Sb simultaneously, although the result is no different than if
the loads were connected together at Sa (or Sb). It is
important to limit the amount of stray Cx capacitance on both
terminals, especially if the load Cx is already large. This can
be accomplished by minimising trace lengths and widths.
lQ
2
QT320/R1.03 08/02


Part Number QT320-D
Description 2-CHANNEL PROGAMMABLE ADVANCED SENSOR IC
Maker Quantum
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QT320-D Datasheet PDF






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