IQS128EV04 S Azoteq, IQS128EV04 S Datasheet - Page 11

• Manufacturer Part Number: IQS128EV04 S
• Description: Touch Sensor Development Tools Long range IQS128 proximity kit
• Manufacturer: Azoteq

Specifications of IQS128EV04 S

• Tool Is For Evaluation Of: IQS128
• Interface Type: LED
• Operating Voltage: 2.95 V to 5.5 V

4
The charge transfer method of capacitive
sensing
IQS128/IQS128L.
principle is thoroughly described in the
application
Capacitive Sensing”.)
A
measurement of the capacitance of the
sense electrode (connected to Cx) relative to
ground.
charging Cx and discharging Cx to the
reference capacitor, at the charge transfer
frequency (FCX - refer to Section 10). The
number of the pulses required to reach a trip
voltage on the reference capacitor is referred
to
instantaneous capacitive measurement. The
CS value is used to determine if either a
physical contact or a proximity event has
occurred based on the change in CS
detected. The typical values of CS, without a
touch or a proximity condition range between
1344 and 1865, although higher and lower
CS can be used based on the application
Copyright © Azoteq (Pty) Ltd 2011
All Rights Reserved
Cx pin
charge
as
Cx pin
Measuring capacitance using the Charge Transfer method
It consists of a series of pulses
counts
is
cycle
note:
t
LP_CHARGE
Figure 4.2 Charge cycles as charged in LP modes (IQS128L only)
t
CHARGE
employed
1
1
(The
(CS)
is
“AZD004
t
SAMPLE
IQ Switch
used
Figure 4.1 Charge cycles as can be see on CX
charge
which
t
to
LP
-
on
®
ProxSense
2
take
is
transfer
Azoteq
IQS128 & IQS128LP Datasheet v2.4
the
the
a
®
Series
requirements. With CS larger than +/-1865
the gain of the system may become too high
causing unsteady CS.
The IQS128/IQS128L schedules a charge
cycle every t
regular samples for processing of results.
The duration of the charge cycle is defined
as t
required to reach the trip voltage.
activities, such as data streaming (if device is
in streaming mode), are completed between
charge cycles.
Please note: Attaching a probe to the Cx
pin will increase the capacitance of the
electrode and therefore the CS. This may
have an immediate influence on the CS
(decrease t
proximity or a touch event. After t
seconds
accommodate for this change. If the total
load on Cx, with the probe attached is still
lower than the maximum Cx load the system
will continue to function normally after t
seconds
2
CHARGE
3
the
and varies according to the CS
CHARGE
with
SAMPLE
system
– thus CS) and cause a
the
4
seconds to ensure
probe
will
adjust
Page 11 of 33
3
attached.
April 2013
Other
HALT
HALT
to