2 Device Operation

2.1 Start-up Time

After a reset or power-up event, the device requires 350ms

to initialize, calibrate, and start operating normally. Keys will

work properly once all keys have been calibrated after reset.

2.2 Option Resistors

The option resistors are read on power-up only. There are

two primary option mode configurations: full, and simplified.

In full options mode, eight 1M

✡ option resistors are required

as shown in Figure 1.1. All eight resistors are mandatory.

To obtain simplified mode, a 1M

✡ resistor should be

connected from SNS6K to SNS7. In simplified mode, only

one additional 1M

✡ option resistor is required for the AKS

feature (Figure 1.2).

Note that the presence and connection of option resistors

will affect the required values of Cs; this effect will be

especially noticeable if the Cs values are under 22nF. Cs

values should be adjusted for optimal sensitivity after the

option resistors are connected.

2.3 OUT Pins - Direct Mode

Direct output mode is selected via option resistors, as shown

in Table 1.4.

In this mode, there is one output for each key; each is active

when a touch is confirmed on the corresponding electrode.

Unused OUT pins should be left open.

If AKS is off, it is possible for all OUT pins to be active at the

same time.

Circuit of Figure 1.1: OUT polarity and drive are governed

by the resistor connections to Vdd or Vss according to

Table 1.4. The drive can be either push-pull or open-drain,

active low or high.

Circuit of Figure 1.2: In this simplified circuit, the OUT pins

are active high, push-pull only.

2.4 OUT Pins - Binary Coded Mode

Binary code mode is selected via option resistors, as shown

in Table 1.4.

In this mode, a key detection is registered as a binary code

on pins OUT_2, OUT_1 and OUT_0, with possible values

from 000 to 111. In practice, four lines are required to read

the code, unless key 0 is not implemented ; the output code

000 can mean either ‘nothing detecting’ or ‘key 0 is

detecting’. The fourth required line (if all eight keys are

implemented) is the DETECT signal, which is active-high

when any key is active.

The first key touched always wins and shows its output.

Keys that come afterwards are hidden until the currently

reported key has stopped detecting, in which case the code

will change to the latent key.

This mode is useful to reduce the number of connections to

a host controller, at the expense of being able to only report

one active key at a time. Note that in global AKS mode

(Section 2.7), only one key can report active at a time

anyway.

Circuit of Figure 1.1: OUT polarity and drive can only be

push-pull and active high.

Circuit of Figure 1.2: Binary coded not available.

2.5 DETECT Pin

DETECT represents the functional logical-OR of all eight

keys. DETECT can be used to wake up a battery-operated

product upon human touch.

DETECT is also required to indicate to a host when the

binary coded output pins (in that mode) are showing an

active key. While DETECT is active, the binary coded

outputs should be read at least twice along with DETECT to

make sure that the code was not transition ing between

states, to prevent a false reading.

The output polarity and drive of DETECT are governed

according to Table 1.4.

2.6 SYNC/LP Pin

The SYNC / LP pin function is configured according to the

SL_0 and SL_1 resistor connections to either Vdd or Vss,

according to Table 1.5.

Sync mode: Sync allows the designer to synchronize

acquire bursts to an external signal source, such as mains

frequency (50/60 Hz) to suppress interference. It can also be

used to synchronize two QT parts which operate near each

other, so that they will not cross-interfere if two or more of

the keys (or associated wiring) of the two parts are near

each other.

The SYNC input of the QT1080 is positive pulse triggered. If

the SYNC input does not change, the device will free-run at

its own rate after ~150ms.

A trigger pulse on SYNC will cause the device to fire two

acquire bursts in A-B sequence:

Burst A: Keys 0, 1, 4, 5

Burst B: Keys 2, 3, 6, 7

Low Power LP Mode: This allows the device to enter a Low

Power mode with very low power consumption, in one of

three response time settings : 110ms, 200ms, and 360ms

nominal.

LP mode is entered by a positive >150µs trigger pulse on the

SYNC/LP pin. Once the LP pulse is detected , the device will

enter and remain in this microamp mode until it senses and

confirms a touch. Then it will switch back to normal (full

speed) mode on its own, with a response time of 30ms

typical (burst length dependent). The device will go back to

LP mode again if SYNC/LP is held high, or after another LP

pulse is received.

The response time setting is determined by option resistors

SL_1 and SL_0; see Table 1.5. Slower response times result

in lower power drain.

The SYNC/LP pulse should be >150µs in duration.

If the SYNC/LP pin is held high permanently, the device will

go into normal mode during a key touch, and return to

low-current mode when the detection ceases.

If the SYNC/LP pin is held low constantly, the device will

remain in normal mode (25ms typical response time)

continuously.

7

QT1080 R11.06/0806