1 - OVERVIEW

QT140/150 devices are burst mode digital charge-transfer

(QT) sensor ICs designed specifically for touch controls; they

include all hardware and signal processing functions

necessary to provide stable sensing under a wide variety of

conditions. Only a single low cost capacitor per channel is

required for operation.

Figures 1-6 and 1-7 show basic circuits for these devices.

See Table 1-1 for device pin listings.

The DIP and SOIC pinouts are not the same and serious

damage can occur if a part is miswired.

1.1 BASIC OPERATION

The devices employ bursts of charge-transfer cycles to

acquire signals. Burst mode permits low power operation,

dramatically reduces RF emissions, lowers susceptibility to

RF fields, and yet permits excellent speed. Internally, signals

are digitally processed to reject impulse noise using a

'consensus' filter that requires three consecutive

confirmations of detection. Each channel is measured in

sequence starting with Channel 1.

The QT switches and charge measurement hardware

functions are all internal to the device. A single-slope

switched capacitor ADC includes the QT charge and transfer

switches in a configuration that provides direct ADC

conversion; an external Cs capacitor accumulates the charge

from sense-plate Cx, which is then measured.

Larger values of Cx cause the charge transferred into Cs to

rise more rapidly, reducing available resolution; as a

minimum resolution is required for proper operation, this can

result in dramatically reduced gain. Conversely, larger values

of Cs reduce the rise of differential voltage across it,

increasing available resolution by permitting longer QT

bursts. The value of Cs can thus be increased to allow larger

values of Cx to be tolerated. The IC is responsive to both Cx

and Cs, and changes in Cs can result in substantial changes

in sensor gain.

2

QT140/150 1.01/1102

/RST

OSC_I

OSC_O

OPT2

OPT1

SYNC

NC

OUT4

OUT3

OUT1

AKS

OC

NC

Vss

Vdd

Vdd

SNS1A

SNS1B

SNS2A

SNS2B

Vss

OUT2

SNS3A

SNS3B

SNS4A

SNS4B

NC

Vss

SSOP

/RST

OSC_I

OSC_O

OPT2

OPT1

SYNC

NC

OUT4

OUT3

OUT1

AKS

OC

NC

Vdd

Vss

Vss

Vss

SNS1A

SNS1B

SNS2A

Vdd

OUT2

SNS2B

SNS3A

SNS3B

SNS4A

SNS4B

NC

DIP

Reset pin (active low input)

/RST

28

Reset pin (active low input)

/RST

28

Oscillator input

OSC_I

27

Oscillator input

OSC_I

27

Oscillator output

OSC_O

26

Oscillator output

OSC_O

26

Option Mode (Input pin - see Table 2-1)

OPT2

25

Option Mode (Input pin - see Table 2-1)

OPT2

25

Option Mode (Input pin - see Table 2-1)

OPT1

24

Option Mode (Input pin - see Table 2-1)

OPT1

24

Synchronization pin (I/O pin - pull high with 10K)

SYNC

23

Synchronization pin (I/O pin - pull high with 10K)

SYNC

23

Channel 5 output, o-d or p-p (n/c on QT140)

NC/OUT5

22

Channel 5 output, o-d or p-p (n/c on QT140)

NC/OUT5

22

Channel 4 output, o-d or p-p

OUT4

21

Channel 4 output, o-d or p-p

OUT4

21

Channel 3 output, o-d or p-p

OUT3

20

Channel 3 output, o-d or p-p

OUT3

20

Channel 2 output, o-d or p-p

OUT2

19

Channel 2 output, o-d or p-p

OUT2

19

Channel 1 output, o-d or p-p

OUT1

18

Channel 1 output, o-d or p-p

OUT1

18

Adjacent Key Suppression Opt. (input ; 1=AKS)

AKS

17

Adjacent Key Suppression Opt. (input; 1=AKS)

AKS

17

Output Option (input pin; 1= open drain)

OC

16

Output Option (input pin; 1= open drain)

OC

16

Sense pin (to Cs5) n/c on QT140

NC/SNS5B

15

Sense pin (to Cs5) n/c on QT140

NC/SNS5B

15

Sense pin (to Cs5, electrode) n/c on QT140

NC/SNS5A

14

Supply negative rail (ground)

Vss

14

Sense pin (to Cs4)

SNS4B

13

Sense pin (to Cs5, electrode) n/c on QT140

NC/SNS5A

13

Sense pin (to Cs4, electrode)

SNS4A

12

Sense pin (to Cs4)

SNS4B

12

Sense pin (to Cs3)

SNS3B

11

Sense pin (to Cs4, electrode)

SNS4A

11

Sense pin (to Cs3, electrode)

SNS3A

10

Sense pin (to Cs3)

SNS3B

10

Sense pin (to Cs2)

SNS2B

9

Sense pin (to Cs3, electrode)

SNS3A

9

Sense pin (to Cs2, electrode)

SNS2A

8

Sense pin (to Cs2)

SNS2B

8

Sense pin (to Cs1)

SNS1B

7

Sense pin (to Cs2, electrode)

SNS2A

7

Sense pin (to Cs1, electrode)

SNS1A

6

Sense pin (to Cs1)

SNS1B

6

Negative power (Ground)

Vss

5

Sense pin (to Cs1, electrode)

SNS1A

5

Negative power (Ground)

Vss

4

Positive power

Vdd

4

Negative power (Ground)

Vss

3

Positive power

Vdd

3

Positive power

Vdd

2

Negative power (Ground)

Vss

2

Positive power

Vdd

1

Negative power (Ground)

Vss

1

Description

Name

Pin

Description

Name

Pin

QT140 / QT150 DIP-28

QT140 / QT150 SSOP-28

Table 1-1 Pin Listing

Fig 1-1 QT140 Pinouts

NOTE: SSOP / DIP Pinouts are not the same!