1 Overvie
1.1
Differences With QT110
1
The QT1103 is a general replacement device for the highly
popular QT1101. It has all of the same features as the older
device but differs in the following ways:
• Rs resistors on each channel eliminated
• Up to 4x more sensitive for a given value of Cs
• Shorter burst lengths, less power for a given value of
Cs
• ‘Burst A and B’ only mode for up to eight keys, with
less power
• ‘Burst B’ only mode for up to four keys, with less
power than ‘Burst A and B’ mode
• Requires an external reset signal
The QT1103 should be used instead of the QT1101 for new
designs due to a simpler circuit, lower power and lower cost.
1.2 Parameters
1.2.1 Introduction
The QT1103 is an easy to use, ten touch-key sensor IC
based on Quantum’s patented charge-transfer (‘QT’)
principles for robust operation and ease of design. This
device has many advanced features which provide for
reliable, trouble-free operation over the life of the product.
1.2.2 Burst Operation
The device operates in ‘burst mode’. Each key is acquired
using a burst of charge-transfer sensing pulses whose count
varies depending on the value of the reference capacitor Cs
and the load capacitance Cx. In LP mode, the device sleeps
in an ultra-low current state between bursts to conserve
power. The keys signals are acquired using three successive
bursts of pulses:
Burst A: Keys 0, 1, 4, 5
Burst B: Keys 2, 3, 6, 7
Burst C: Keys 8, 9
Bursts always operate in C-A-B sequence.
1.2.3 Self-calibration
On power-up, all ten keys are self-calibrated within 300ms
(typical) to provide reliable operation under almost any
conditions.
1.2.4 Autorecalibration
The device can time out and recalibrate each key
independently after a fixed interval of continuous touch
detection, so that the keys can never become ‘stuck on’ due
to foreign objects or other sudden influences. After
recalibration the key will continue to function normally. The
delay is selectable to be either 10s, 60s, or infinite (disabled).
The device also autorecalibrates a key when its signal
reflects a sufficient decrease in capacitance. In this case the
device recalibrates after ~2 seconds so as to recover normal
operation quickly.
1.2.5 Drift Compensation
Drift compensation operates to correct the reference level of
each key slowly but automatically over time, to suppress
false detections caused by changes in temperature, humidity,
dirt and other environmental effects.
1.2.6 Detection Integrator Confirmation
Detection Integrator (DI) confirmation reduces the effects of
noise on the QT1103. The DI mechanism requires
consecutive detections over a number of measurement
bursts for a touch to be confirmed and indicated on the
outputs. In a like manner, the end of a touch (loss of signal)
has to be confirmed over a number of measurement bursts.
This process acts as a type of ‘debounce’ against noise.
A per-key counter is incremented each time the key has
exceeded its threshold and stayed there for a number of
measurement bursts. When this counter reaches a preset
limit the key is finally declared to be touched.
For example, if the limit value is six, then the device has to
exceed its threshold and stay there for six measurement
bursts in succession without going below the threshold level,
before the key is declared to be touched. If on any
measurement burst the signal is not seen to exceed the
threshold level, the counter is cleared and the process has to
start from the beginning.
In normal operation, the start of a touch must be confirmed
for six measurement bursts and the end of a touch for three.
In a special ‘Fast Detect‘ mode (available via jumper
resistors) (Tables 1.2 and 1.6), confirmation of the start of a
touch requires only three and the end of a touch requires two
measurement bursts.
Fast detect is only available when AKS is disabled.
1.2.7 Spread-spectrum Operation
The bursts operate over a spread of frequencies, so that
external fields will have minimal effect on key operation and
emissions are very weak. Spread spectrum operation works
with the DI mechanism to dramatically reduce the probability
of false detection due to noise.
1.2.8 Sync Mode
The QT1103 features a Sync mode to allow the device to
slave to an external signal source, such as a mains signal
(50/60Hz), to limit interference effects. This is performed
using the SYNC/LP pin. Sync mode operates by triggering
three sequential acquire bursts, in sequence C-A-B from the
Sync signal. Thus, each Sync pulse causes all ten keys to be
acquired (see Section 2.5.2, page 8).
1.2.9 Low Power (LP) Mode
The device features an LP mode for microamp levels of
current drain with a slower response time, to allow use in
battery operated devices. On detection of touch, the device
automatically reverts to its normal mode and asserts the
DETECT pin active to wake up a host controller. The device
remains in normal, full acquire speed mode until another
pulse is seen on its SYNC/LP pin, upon which it goes back to
LP mode (see Optimization of LP Mode, page 9).
When eight or fewer keys are required, current drain in LP
mode can be further reduced by choosing appropriate
channels on the QT1103 (see the end of Section 2.5.3,
page 8).
Lq
3 QT1103_3R0.03_0607
