TEXAS INSTRUMENTS ADS7845 Technical data

®

ADS7845

ADS7845

TOUCH SCREEN CONTROLLER

FEATURES

● 5-WIRE TOUCH SCREEN INTERFACE

● RATIOMETRIC CONVERSION

● SINGLE SUPPLY: 2V to 5V

● UP TO 125kHz CONVERSION RATE

● SERIAL INTERFACE

● PROGRAMMABLE 8- OR 12-BIT RESOLUTION

● AUXILIARY ANALOG INPUTS

● FULL POWER-DOWN CONTROL

APPLICATIONS

● PERSONAL DIGITAL ASSISTANTS

● PORTABLE INSTRUMENTS

● POINT-OF-SALES TERMINALS

● PAGERS

● TOUCH-SCREEN MONITORS

+V

GND

UR
LR

CC

DESCRIPTION

The ADS7845 is a 12-bit sampling analog-to-digital
converter (ADC) with a synchronous serial interface
and low on-resistance switches for driving touch
screens. Typical power dissipation is 750µW at a
125kHz throughput rate and a +2.7V supply. The
reference voltage (V
+VCC, providing a corresponding input voltage range
of 0V to V

. The device includes a shutdown mode

REF

which reduces typical power dissipation to under

0.5µW. The ADS7845 is guaranteed down to 2.7V
operation.

Low power, high speed, and on-board switches make
the ADS7845 ideal for battery-operated systems such
as personal digital assistants with resistive touch screens
and other portable equipment. The ADS7845 is avail­able in a 16-lead SSOP package and is guaranteed
over the –40°C to +85°C temperature range.

) can be varied between 1V and

REF

SBAS104

GND

Driver

+V

CC

UL
LL

+V

CC

GND

AUX IN
WIPER

PENIRQ

V

REF

International Airport Industrial Park • Mailing Address: PO Box 11400, Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 • Tel: [phone]

Twx: 910-952-1111 • Internet: http://www.burr-brown.com/ • Cable: BBRCORP • Telex: 066-6491 • FAX: [phone] • Immediate Product Info: [phone]

©

1998 Burr-Brown Corporation PDS-1497A Printed in U.S.A. December, 1998

MUX

CDAC

SAR

ADS7845

Comparator

Serial

Data

Interface

and

Control

DOUT

BUSY

CS

DCLK

DIN

SPECIFICATIONS

At TA = –40°C to +85°C, +VCC = +2.7V, V
otherwise noted.

PARAMETER CONDITIONS MIN TYP MAX UNITS
RESOLUTION 12 Bits

ANALOG INPUT

Full-Scale Input Span Positive Input - Negative Input 0 V
Absolute Input Range Positive Input –0.2 +V

Capacitance 25 pF
Leakage Current 0.1 µA

SYSTEM PERFORMANCE

No Missing Codes 11 Bits
Integral Linearity Error ±2 LSB
Offset Error ±6 LSB
Gain Error ±4 LSB
Noise 30 µVrms
Power Supply Rejection Ratio 70 dB

SAMPLING DYNAMICS

Conversion Time 12 Clk Cycles
Acquisition Time 3 Clk Cycles
Throughput Rate 125 kHz
Multiplexer Settling Time 500 ns
Aperture Delay 30 ns
Aperture Jitter 100 ps
Channel-to-Channel Isolation V

SWITCH DRIVERS

On-Resistance

UL, UR 7 Ω
LL, LR 7 Ω

REFERENCE INPUT

Range 1.0 +V
Resistance CS = GND or +V
Input Current 13 40 µA

DIGITAL INPUT/OUTPUT

Logic Family CMOS
Logic Levels, Except PENIRQ

V

IH

V

IL

V

OH

V

OL

PENIRQ

V

OL

Data Format Straight Binary

POWER SUPPLY REQUIREMENTS

+V

CC

Quiescent Current 280 650 µA

Power Dissipation +VCC = +2.7V 1.8 mW

TEMPERATURE RANGE

Specified Performance –40 +85 °C

NOTE: (1) LSB means Least Significant Bit. With V

= +2.5V, f

REF

SAMPLE

= 125kHz, f

CLK

= 16 • f

= 2MHz, 12-bit mode, and digital inputs = GND or +VCC, unless

SAMPLE

ADS7845E

Negative Input –0.2 +0.2 V

= 2.5Vp-p at 50kHz 100 dB

IN

CC

= 12.5kHz 2.5 µA

f

SAMPLE

CS = +V

CC

| I

| ≤ +5µA+V

IH

| I

| ≤ +5µA –0.3 +0.8 V

IL

IOH = –250µA+V

IOL = 250µA 0.4 V

• 0.7 +VCC +0.3

CC

• 0.8 V

CC

5GΩ

0.001 3 µA

TA = 0°C to +85°C, 100kΩ Pull-Up 0.8 V

Specified Performance

= 12.5kHz 220 µA

f

SAMPLE

Shutdown Mode with 3 µA

DCLK = DIN = +V

equal to +2.5V, one LSB is 610µV. (2) ADS7845 will operate down to 2.0V.

REF

(2)

CC

2.7 5.5 V

REF

+0.2 V

CC

CC

V

(1)

V

The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes
no responsibility for the use of this information, and all use of such information shall be entirely at the user’s own risk. Prices and specifications are subject to change
without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant
any BURR-BROWN product for use in life support devices and/or systems.

®

ADS7845

2

PIN CONFIGURATION

Top View SSOP

+V

1

CC

2

UL

3

UR

4

LR

GND

WIPER

AUXIN

LL

5
6
7
8

ADS7845

ABSOLUTE MAXIMUM RATINGS

+V

to GND ........................................................................ –0.3V to +6V

CC

Analog Inputs to GND ............................................ –0.3V to +V

Digital Inputs to GND .............................................–0.3V to +V

Power Dissipation .......................................................................... 250mW

Maximum Junction Temperature................................................... +150°C

Operating Temperature Range ........................................–40°C to +85°C

Storage Temperature Range ......................................... –65°C to +150°C

Lead Temperature (soldering, 10s) ............................................... +300°C

NOTE: (1) Stresses above those listed under “Absolute Maximum Ratings”
may cause permanent damage to the device. Exposure to absolute maximum
conditions for extended periods may affect device reliability.

(1)

16
15
14
13
12
11
10

9

DCLK
CS
DIN
BUSY
DOUT
PENIRQ
+V

CC

V

REF

+ 0.3V

CC

+ 0.3V

CC

PIN DESCRIPTION

PIN NAME DESCRIPTION

1+V
2 UL Upper Left Panel Driver (V
3 UR Upper Right Panel Driver (switch between V

4 LL Lower Left Panel Driver (switch between GND

5 LR Lower Right Panel Driver (GND ON/OFF)
6 GND Ground
7 WIPER Panel Input
8 AUXIN Auxiliary Input

9V
10 +V
11 PENIRQ Pen Interrupt. Open anode output (requires 10kΩ

12 DOUT Serial Data Output. Data is shifted on the falling

13 BUSY Busy Output. This output is high impedance when

14 DIN Serial Data Input. If CS is LOW, data is latched on

15 CS Chip Select Input. Controls conversion timing and

16 DCLK External Clock Input. This clock runs the SAR con-

CC

REF

CC

Power Supply, 2.0V to 5V.

ON/OFF)

CC

and GND)

)

and V

CC

Voltage Reference Input
Power Supply, 2.0V to 5V.

to 100kΩ pull-up resistor externally).

edge of DCLK. This output is high impedance
when CS is HIGH.

CS is HIGH.

rising edge of DCLK.

enables the serial input/output register.

version process and synchronizes serial data I/O.

CC

ELECTROSTATIC
DISCHARGE SENSITIVITY

This integrated circuit can be damaged by ESD. Burr-Brown
recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling and
installation procedures can cause damage.

ESD damage can range from subtle performance degradation to
complete device failure. Precision integrated circuits may be
more susceptible to damage because very small parametric
changes could cause the device not to meet its published specifi­cations.

PACKAGE/ORDERING INFORMATION

MAXIMUM

INTEGRAL PACKAGE SPECIFICATION

PRODUCT ERROR (LSB) PACKAGE NUMBER

LINEARITY DRAWING TEMPERATURE ORDERING TRANSPORT

ADS7845E ±2 16-Lead SSOP 322 –40°C to +85°C ADS7845E Rails

"" """ADS7845E/2K5 Tape and Reel

NOTES: (1) For detailed drawing and dimension table, please see end of data sheet, or Appendix C of Burr-Brown IC Data Book. (2) Models with a slash (/) are
available only in Tape and Reel in the quantities indicated (e.g., /2K5 indicates 2500 devices per reel). Ordering 2500 pieces of “ADS7845E/2K5” will get a single
2500-piece Tape and Reel. For detailed Tape and Reel mechanical information, refer to Appendix B of Burr-Brown IC Data Book.

(1)

3

RANGE NUMBER

ADS7845

(2)

MEDIA

®

TYPICAL PERFORMANCE CURVES

At TA = +25°C, +VCC = +2.7V, V

SUPPLY CURRENT vs TEMPERATURE

400

= +2.5V, f

REF

= 125kHz, and f

SAMPLE

CLK

= 16 • f

SAMPLE

= 2MHz, unless otherwise noted.

POWER-DOWN SUPPLY CURRENT

vs TEMPERATURE

140

350

300

250

200

Supply Current (µA)

150

100

20–40 100–20 0 40

60 80

Temperature (°C)

SUPPLY CURRENT vs +V

CC

400

350

f

= 200kHz

CLOCK

300

V

= +VCC

250

REF

120

100

80

60

Supply Current (nA)

40

20

1M

8-Bit Mode

100k

20–40 100–20 0 40

60 80

Temperature (°C)

MAXIMUM SAMPLE RATE vs +V

12-Bit Mode

CC

200

10k

150

Supply Current (µA)

100

50

4.53

+V

(V)

CC

3.51.5 2 52.5 4

Sample Rate (Hz)

1k

+V

3.51.5 2 52.5 4

(V)

CC

V

REF

= +VCC

4.53

0.15

0.10

0.05

0.00

–0.05

Delta from +25°C (LSB)

–0.10

–0.15

CHANGE IN GAIN vs TEMPERATURE

20–40 100–20 0 40

Temperature (°C)

®

ADS7845

60 80

0.6

CHANGE IN OFFSET vs TEMPERATURE

0.4

0.2

0.0

–0.2

Delta from +25°C (LSB)

–0.4

–0.6

20–40 100–20 0 40

60 80

Temperature (°C)

4

TYPICAL PERFORMANCE CURVES (CONT)

REFERENCE CURRENT vs TEMPERATURE

20–40 100–20 0 40

Temperature (°C)

Reference Current (µA)

18

16

14

12

10

8

6

60 80

SWITCH ON RESISTANCE vs TEMPERATURE

(X+, Y+: +V

CC

to Pin; X–, Y–: Pin to GND)

20–40 100–20

UL

LL

40

Temperature (°C)

R

ON

(Ω)

16

14

12

10

8

6

4

2

60 800

UR

LR

At TA = +25°C, +VCC = +2.7V, V

= +2.5V, f

REF

= 125kHz, and f

SAMPLE

CLK

= 16 • f

= 2MHz, unless otherwise noted.

SAMPLE

14

REFERENCE CURRENT vs SAMPLE RATE

12

10

8

6

4

Reference Current (µA)

2

0

750 12525 50 100

Sample Rate (kHz)

SWITCH ON RESISTANCE vs +V

(X+, Y+: +VCC to Pin; X–, Y–: Pin to GND)

CC

16

14

LL LR

12

10

(Ω)

ON

8

R

6

UL

UR

4

2

+V

3.5252.5

CC

4

4.53

(V)

1.8

1.6

1.4

2

MAXIMUM SAMPLING RATE vs R

INL: R = 2kΩ
INL: R = 500Ω
DNL: R = 2kΩ
DNL: R = 500Ω

IN

1.2
1

LSB Error

0.8

0.6

0.4

0.2
0

20 40 60 80 100 120 140 160 180 200

Sampling Rate (kHz)

5

®

ADS7845