QT102-ISG View Datasheet(PDF) - Quantum Research Group

Part Name

Description

Manufacturer

QT102-ISG

QTOUCH™ TOGGLE-MODE CHARGE-TRANSFER IC WITH POWER MANAGEMENT FUNCTIONS

Quantum Research Group 

3 Operation

3.1 Acquisition Modes

3.1.1 Introduction

The OUT pin of the QT102 can be configured to be active

high or active low (see Section 3.3).

• If active high then

Š ‘on’ is high

Š ‘off’ is low

• If active low then

Š ‘on’ is low

Š ‘off’ is high

The acquisition mode depends on the state of the OUT pin

(on or off) and whether a touch is detected. In the following

text ‘on’ is when the output is in its active state.

The DI can also be viewed as a 'consensus' filter, that

requires four successive detections to create an output.

3.2.2 Detect Threshold

The device detects a touch when the signal has crossed a

threshold level. The threshold level is fixed at 10 counts.

3.3 Output Polarity Selection

The output (OUT pin) of the QT102 can be configured to have

an active high or active low output by means of the output

configuration resistor Rop. The resistor is connected between

the output and either Vss or VDD (see Figure 3.3 and

Table 3.1). A typical value for Rop is 100k.

Figure 3.3 Output Polarity

SENSE

ELECTRODE

3.1.2 OUT Pin ‘On’ (Fast Mode)

The QT102 runs in Fast mode when the OUT pin is on. In this

mode the device runs at maximum speed at the expense of

increased current consumption. The delay between bursts in

Fast mode is approximately 2.6ms, as shown in Figure 3.1.

Figure 3.1 Fast Mode Bursts

(Output in On condition)

SNSK

QT102

~2.6ms

VDD

5

RS

VDD

3 SNSK

CS

4 SNS

OUT 1

TIME 6

Rm

VSS

2

Rop

Vop

3.1.3 OUT Pin ‘Off’ (Low Power Mode)

The QT102 runs in Low Power (LP) mode if the OUT pin is off.

In this mode it sleeps for approximately 85ms at the end of

each burst, saving power but slowing response. On detecting

a possible key touch, it temporarily switches to Fast mode

until either the key touch is confirmed or found to be spurious

(via the detect integration process). If the touch is confirmed

the QT102 will switch to Fast mode as shown in Figure 3.2. If

a touch is denied the device will revert to normal LP mode

operation automatically.

Figure 3.2 Low Power Mode/Touch Detection

Table 3.1 Output Configuration

Name

Function

(Vop) (Output polarity)

Vss

Active high

VDD

Active low

Note that some devices such as Digital Transistors have an

internal biasing network that will naturally pull the OUT pin to

its inactive state. If these are being used then the resistor Rop

is not required (see Figure 3.4).

Figure 3.4 Output Connected to Digital Transistor

SNSK

QT102

~85ms

sleep

sleep

fast detect

integrator

SENSE

ELECTRODE

OUT

3.2 Signal Processing

3.2.1 Detect Integrator

It is desirable to suppress detections generated by electrical

noise or from quick brushes with an object. To accomplish

this, the QT102 incorporates a ‘detect integration’ (DI) counter

that increments with each detection until a limit is reached,

after which the output is activated. If no detection is sensed

prior to the final count, the counter is reset immediately to

zero. In the QT102, the required count is four.

VDD

5

RS

VDD

3 SNSK

CS

4 SNS

OUT 1

TIME 6

Rm

VSS

2

Load

lQ

7

QT102_2R3.04_0807

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