QT60160 datasheet(7/26 Pages) ETC2

7 / 26 page

A single ceramic 0.1uF bypass capacitor, with short traces,

should be placed very close to supply pins 3, 4, 5 and 6 of the

IC. Failure to do so can result in device oscillation, high

current consumption, erratic operation etc. Pins 18, 20, and

21 do not require bypassing.

2.11 Startup / Calibration Times

The devices require initialization times of up t o 20ms. A

calibration takes one matrix scan.

Disabled keys are subtracted from the burst sequence and

thus the cal time is shortened. The scan time should be

measured on an oscilloscope.

2.12 Reset Input

The /RST pin can be used to reset the device to simulate a

power-down cycle, in order to bring the device up into a

known state should communications with the device be lost.

The pin is active low, and a low pulse lasting at least 10µs

must be applied to this pin to cause a reset.

The reset pin has an internal 30K

✡ - 60K✡ resistor. A 2.2µF

capacitor plus a diode to Vdd can be connected to this pin as

a traditional reset circuit, but this is not required.

If an external hardware reset is not used, the reset pin may

be connected to Vdd or left floating .

2.13 Spread Spectrum Acquisitions

QT60xx0 devices use spread-spectrum burst modulation.

This has the effect of drastically reducing the possibility of

EMI effects on the sensor keys, while simul taneously

spreading RF emissions. This feature is hard-wired into the

device and cannot be disabled or modified.

Spread spectrum is configured as a frequency chirp over a

wide range of frequencies for robust operation.

2.14 Detection Integrators

See also Section 6.5, page 18.

The devices feature a detection integration mechanism, which

acts to confirm a detection in a robust fashion. A per-key

counter is incremented each time the key has exceeded its

threshold and stayed there for a number of acquisitions.

When this counter reaches a preset limit the key is finally

declared to be touched.

For example, if the limit value is 10, then the device has to

exceed its threshold and stay there for 10 acquisitions in

succession without going below the threshold level, before

the key is declared to be touched. If on any acquisition the

signal is not seen to exceed the threshold level, the counter is

cleared and the process has to start from the beginning.

The QT60xx0 uses a two-tier confirmation mechanism having

two such counters for each key. These can be thought of as

‘inner loop’ and ‘outer loop’ confirmation counters.

The ‘inner’ counter is referred to as the ‘fast-DI’; this acts to

attempt to confirm a detection via rapid successive

acquisition bursts, at the expense of delaying the sampling of

the next key. Each key has its own fast-DI counter and limit

value; these limits can be changed via the Setups block on a

per-key basis.

The ‘outer’ counter is referred to as the ‘normal-DI’; this DI

counter increments whenever the fast-DI counter has reached

its limit value. If a fast-DI counter failed to reach its terminal

count, the corresponding normal-DI counter is also reset. The

normal-DI counter also has a limit value which is settable on

a per-key basis. If a normal-DI counter reaches its terminal

count, the corresponding key is declared to be touched and

becomes ‘active’. Note that the normal-DI can only be

incremented once per complete keyscan cycle, i .e. more

slowly, whereas the fast-DI is incremented ‘on the spot’

without interruption.

The net effect of this mechanism is a multiplication of the

inner and outer counters and hence a highly noise-resistance

sensing method. If the inner limit is set to 5, and the outer to

3, the net effect is 5x3=15 successive threshold crossings to

declare a key as active.

2.15 Sleep

The device will sleep whenever possible to conserve power.

Periodically, the part will wake automatically, scan the matrix,

and return to sleep unless there is activity which demands

further attention. The part will always return to sleep

automatically once all activity has ceased. The time for which

the part will sleep before automatically awakening can be

configured.

A new communication with the device while it is asleep will

cause it to wake up, service the communication and scan the

matrix. At least one full matrix scan is always performed after

waking up and before returning to sleep.

At the end of each matrix scan, the part will return to sleep

unless recent activity demands further attention. If there has

been recent activity, the part will perform another complete

matrix scan and then attempt to sleep once again. This

process is repeated indefinitely until the activity stops and the

part returns to sleep.

Key touch activity will prevent the part from sleeping. The part

will not sleep if any touch events were d etected at any key in

the most recent scan of the key matrix.

QT60240-ISG R8.06/0906

QT60160 Datasheet(PDF) 7 Page - List of Unclassifed Manufacturers

QT60160 Datasheet(HTML) 7 Page - List of Unclassifed Manufacturers

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

Datasheet Download

Link URL