MAXIM MXB7843 User Manual

General Description

The MXB7843 is an industry-standard 4-wire touch­screen controller. It contains a 12-bit sampling analog­to-digital converter (ADC) with a synchronous serial
interface and low on-resistance switches for driving
resistive touch screens. The MXB7843 uses an external
reference. The MXB7843 can make absolute or ratio­metric measurements. The MXB7843 has two auxiliary
ADC inputs. All analog inputs are fully ESD protected,
eliminating the need for external TransZorb™ devices.

The MXB7843 is guaranteed to operate with a single

2.375V to 5.25V supply voltage. In shutdown mode, the
typical power consumption is reduced to under 0.5µW,
while the typical power consumption at 125ksps
throughput and a 2.7V supply is 650µW.

Low-power operation makes the MXB7843 ideal for bat­tery-operated systems, such as personal digital assis­tants with resistive touch screens and other portable
equipment. The MXB7843 is available in 16-pin QSOP
and TSSOP packages, and is guaranteed over the

-40°C to +85°C temperature range.

Applications

Personal Digital Assistants

Portable Instruments

Point-of-Sales Terminals

Pagers

Touch-Screen Monitors

Cellular Phones

Features

♦ ESD-Protected ADC Inputs

±15kV IEC 61000-4-2 Air-Gap Discharge
±8kV IEC 61000-4-2 Contact Discharge

♦ Pin Compatible with MXB7846

♦ +2.375V to +5.25V Single Supply

♦ 4-Wire Touch-Screen Interface

♦ Ratiometric Conversion

♦ SPI™/QSPI™, 3-Wire Serial Interface

♦ Programmable 8-/12-Bit Resolution

♦ Two Auxiliary Analog Inputs

♦ Automatic Shutdown Between Conversions

♦ Low Power

270µA at 125ksps
115µA at 50ksps
25µA at 10ksps
5µA at 1ksps
2µA Shutdown Current

MXB7843

2.375V to 5.25V, 4-Wire Touch-Screen
Controller

________________________________________________________________ Maxim Integrated Products 1

16

15

14

13

12

11

10

9

1

2

3

4

5

6

7

8

V

DD

DCLK

CS

DIN

BUSY

DOUT

PENIRQ

V

DD

REF

TOP VIEW

MXB7843

QSOP/TSSOP

X+

Y+

GND

X-

Y-

IN3

IN4

Pin Configuration

Ordering Information

19-2435; Rev 1; 9/05

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

PART TEMP RANGE PIN-PACKAGE

MXB7843EEE -40°C to +85°C 16 QSOP

MXB7843EUE -40°C to +85°C 16 TSSOP

TransZorb is a trademark of Vishay Intertechnology, Inc.

SPI/QSPI are trademarks of Motorola, Inc.

Typical Application Circuit appears at end of data sheet.

MXB7843

2.375V to 5.25V, 4-Wire Touch-Screen
Controller

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.

VDD, DIN, CS, DCLK to GND ...................................-0.3V to +6V

Digital Outputs to GND...............................-0.3V to (V

DD

+ 0.3V)

V

REF

, X+, X-, Y+, Y-, IN3, IN4 to GND........-0.3V to (VDD+ 0.3V)

Maximum Current into Any Pin .........................................±50mA

Maximum ESD per IEC-61000-4-2 (per MIL STD-883 HBM)

X+, X-, Y+, Y-, IN3, IN4 ...........................................15kV (4kV)

All Other Pins ..........................................................2kV (500V)

Continuous Power Dissipation (T

A

= +70°C)

16-Pin QSOP (derate 8.30mW/°C above +70°C).........667mW

16-Pin TSSOP (derate 5.70mW/°C above +70°C) .......456mW

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

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

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

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

ELECTRICAL CHARACTERISTICS

(VDD= 2.7V to 3.6V, V

REF

= 2.5V, f

DCLK

= 2MHz (50% duty cycle), f

SAMPLE

= 125kHz, 12-bit mode, 0.1µF capacitor at REF, TA=

T

MIN

to T

MAX

, unless otherwise noted. Typical values are at TA= +25°C.)

PARAMETER

SYM B O L

CONDITIONS

MIN

TYP

MAX

UNITS

DC ACCURACY (Note 1)

Resolution 12 Bits

No Missing Codes 11 12 Bits

Relative Accuracy INL (Note 2) ±1 ±2 LSB

Differential Nonlinearity DNL ±1 LSB

Offset Error ±6 LSB

Gain Error (Note 3) ±4 LSB

Noise 70

µV

RMS

CONVERSION RATE

Conversion Time t

CONV

12 clock cycles (Note 4) 6 µs

Track/Hold Acquisition Time t

ACQ

3 clock cycles 1.5 µs

Throughput Rate

16 clock conversion 125 kHz

Multiplexer Settling Time

ns

Aperture Delay 30 ns

Aperture Jitter

p s

Channel-to-Channel Isolation VIN = 2.5V

P-P

at 50kHz

dB

Serial Clock Frequency f

DCLK

0.1 2.0

MHz

Duty Cycle 40 60 %

ANALOG INPUT (X+, X-, Y+, Y-, IN3, IN4)

Input Voltage Range 0

V

Input Capacitance 25 pF

Input Leakage Current On/off-leakage, VIN = 0 to V

DD

±1 µA

SWITCH DRIVERS

Y+, X+ 7

On-Resistance (Note 5)

Y-, X- 9

Ω

f

SAMPLE

500

100

100

±0.1

V

REF

MXB7843

2.375V to 5.25V, 4-Wire Touch-Screen
Controller

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VDD= 2.7V to 3.6V, V

REF

= 2.5V, f

DCLK

= 2MHz (50% duty cycle), f

SAMPLE

= 125kHz, 12-bit mode, 0.1µF capacitor at REF, TA=

T

MIN

to T

MAX

, unless otherwise noted. Typical values are at TA= +25°C.)

PARAMETER

SYM B O L

CONDITIONS

MIN

TYP

MAX

UNITS

REFERENCE (Reference applied to REF)

Reference Input Voltage Range (Note 6) 1

V

Input Resistance 5GΩ

f

SAMPLE

= 125kHz 13 40

f

SAMPLE

= 12.5kHz 2.5

Input Current

f

DCLK

= 0 ±3

µA

DIGITAL INPUTS (DCLK, CS, DIN)

Input High Voltage V

IH

V

DD

V

Input Low Voltage V

IL

0.8 V

Input Hysteresis V

HYST

mV

Input Leakage Current I

IN

±1 µA

Input Capacitance C

IN

15 pF

DIGITAL OUTPUT (DOUT, BUSY)

Output Voltage Low V

OL

I

SINK

= 250µA 0.4 V

Output Voltage High V

OH

I

SOURCE

= 250µA

V

DD

-

0.5

V

PENIRQ Output Low Voltage V

OL

50kΩ pullup to V

DD

0.8 V

Three-State Leakage Current I

L

CS = V

DD

1

µA

Three-State Output Capacitance

C

OUT

CS = V

DD

15 pF

POWER REQUIREMENTS

Supply Voltage V

DD

V

f

SAMPLE

= 125ksps

650

f

SAMPLE

= 12.5ksps

Supply Current I

DD

f

SAMPLE

= 0

µA

Shutdown Supply Current I

SHDN

DCLK = CS = V

DD

3µA

Power-Supply Rejection Ratio PSRR VDD = 2.7V to 3.6V full scale 70 dB

✕

0.7

100

2.375 5.250

270

220

150

V

DD

±10

MXB7843

2.375V to 5.25V, 4-Wire Touch-Screen
Controller

4 _______________________________________________________________________________________

Note 1: Tested at VDD= +2.7V.
Note 2: Relative accuracy is the deviation of the analog value at any code from its theoretical value after the full-scale range has

been calibrated.

Note 3: Offset nulled.
Note 4: Conversion time is defined as the number of clock cycles multiplied by the clock period; clock has 50% duty cycle.
Note 5: Resistance measured from the source to drain of the switch.
Note 6: ADC performance is limited by the conversion noise floor, typically 300µV

P-P

. An external reference below 2.5V can com-

promise the ADC performance.

TIMING CHARACTERISTICS (Figure 1)

(VDD= 2.7V to 3.6V, V

REF

= 2.5V, f

DCLK

= 2MHz (50% duty cycle), f

SAMPLE

= 125kHz, 12-bit mode, 0.1µF capacitor at REF, TA=

T

MIN

to T

MAX

, unless otherwise noted. Typical values are at TA= +25°C.)

PARAMETER

CONDITIONS

UNITS

TIMING CHARACTERISTICS (Figure 1)

Acquisition Time t

ACQ

1.5 µs

DCLK Clock Period t

CP

500 ns

DCLK Pulse Width High t

CH

200 ns

DCLK Pulse Width Low t

CL

200 ns

DIN-to-DCLK Setup Time t

DS

100 ns

DIN-to-DCLK Hold Time t

DH

0ns

t

CSS

100 ns

CS Rise-to-DCLK Rise Ignore t

CSH

0ns

DCLK Falling-to-DOUT Valid t

DO

C

LOAD

= 50pF 200 ns

CS Rise-to-DOUT Disable t

TR

C

LOAD

= 50pF 200 ns

CS Fall-to-DOUT Enable t

DV

C

LOAD

= 50pF 200 ns

DCLK Falling-to-BUSY Rising t

BD

200 ns

CS Falling-to-BUSY Enable t

BDV

200 ns

CS Rise-to-BUSY Disable t

BTR

200 ns

SYM B O L

CS Fall-to-DCLK Rise Setup Time

MIN TYP MAX

MXB7843

2.375V to 5.25V, 4-Wire Touch-Screen
Controller

_______________________________________________________________________________________ 5

INTEGRAL NONLINEARITY

vs. DIGITAL OUTPUT CODE

MXB7843 toc01

OUTPUT CODE

INL (LSB)

350030002000 25001000 1500500

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

-0.4
04000

DIFFERENTIAL NONLINEARITY

vs. DIGITAL OUTPUT CODE

MXB7843 toc02

OUTPUT CODE

DNL (LSB)

350030002000 25001000 1500500

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1.0

-1.0

-0.8

0 4000

CHANGE IN OFFSET ERROR

vs. SUPPLY VOLTAGE

MXB7843 toc04

SUPPLY VOLTAGE (V)

OFFSET ERROR (LSB)

5.04.53.0 3.5 4.0

-1.5

-1.0

-0.5

0

0.5

1.0

1.5

2.0

-2.0

2.5 5.5

CHANGE IN OFFSET ERROR

vs. TEMPERATURE

MXB7843 toc05

TEMPERATURE (°C)

OFFSET ERROR FROM

+

25°C (LSB)

655035205-10-25

-0.5

0

0.5

1.0

-1.0

-40 80

CHANGE IN GAIN ERROR

vs. SUPPLY VOLTAGE

MXB7843 toc07

SUPPLY VOLTAGE (V)

GAIN ERROR (LSB)

5.04.54.03.53.0

-2

-1

0

1

2

3

-3

2.5 5.5

CHANGE IN GAIN ERROR

vs. TEMPERATURE

MXB7843 toc08

TEMPERATURE (°C)

GAIN ERROR FROM

+

25°C (LSB)

655035205-10-25

-1.5

-1.0

-0.5

0

0.5

1.0

-2.0

-40 80

SWITCH ON-RESISTANCE vs. SUPPLY VOLTAGE

(X+, Y+ : + V

DD

TO PIN; X-, Y- : TO GND)

MXB7843 toc03

SUPPLY VOLTAGE (V)

R

ON

(Ω)

5.04.54.03.53.0

2

4

6

8

10

12

14

0

2.5 5.5

X-

Y-

X+

Y+

SWITCH ON-RESISTANCE vs. TEMPERATURE

(X+, Y+ : + V

DD

TO PIN; X-, Y- : PIN TO GND)

MXB7843 toc06

TEMPERATURE (°C)

R

ON

(Ω)

35205-10-25

2
1

3

7

6
5

4

8

9

10

11

12

0

-40 50 65 80

Y+

X+

X-

Y-

Typical Operating Characteristics

(VDD= 2.7V, V

REF

= 2.5V, f

DCLK

= 2MHz, f

SAMPLE

= 125kHz, C

LOAD

= 50pF, 0.1µF capacitor at REF, TA= +25°C, unless otherwise

noted.)

MXB7843

2.375V to 5.25V, 4-Wire Touch-Screen
Controller

6 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(VDD= 2.7V, V

REF

= 2.5V, f

DCLK

= 2MHz, f

SAMPLE

= 125kHz, C

LOAD

= 50pF, 0.1µF capacitor at REF, TA= +25°C, unless otherwise

noted.)

REFERENCE CURRENT
vs. SUPPLY VOLTAGE

MXB7843 toc12

SUPPLY VOLTAGE (V)

REFERENCE CURRENT (µA)

5.04.54.03.53.0

7.8

7.9

8.0

8.1

8.2

8.3

7.7

2.5 5.5

CL = 0.1µF
f

SAMPLE

= 125kHz

REFERENCE CURRENT vs. TEMPERATURE

MXB7843 toc13

TEMPERATURE (°C)

REFERENCE CURRENT (µA)

655035205-10-25

7.8

7.9

8.0

8.1

8.2

8.3

7.7

-40 80

VDD = 2.7V
C

L

= 0.1µF

f

SAMPLE

= 125kHz

REFERENCE CURRENT vs. SAMPLE RATE

MXB7843 toc14

SAMPLE RATE (kHz)

REFERENCE CURRENT (µA)

100755025

1

2

3

4

5

6

7

8

9

10

0

0125

SUPPLY CURRENT

vs. SUPPLY VOLTAGE

MXB7843 toc18

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (µA)

5.04.54.03.53.02.5

175

200

225

250

150

2.0 5.5

f

SAMPLE

= 12.5kHz

SUPPLY CURRENT vs. TEMPERATURE

MXB7843 toc19

TEMPERATURE (°C)

SUPPLY CURRENT (µA)

6550-25 -10 5 20 35

255

260

265

270

275

280

285

290

250

-40 80

f

SAMPLE

= 125kHz

V

DD

= 2.7V

SUPPLY CURRENT vs. SAMPLE RATE

MXB7843 toc20

SAMPLE RATE (kHz)

SUPPLY CURRENT (µA)

100755025

125

150

175

200

225

250

100

0 125

VDD = 2.7V
V

REF

= 2.5V

SHUTDOWN CURRENT
vs. SUPPLY VOLTAGE

MXB7843 toc21

SUPPLY VOLTAGE (V)

SHUTDOWN CURRENT (nA)

4.74.23.73.2

100

150

200

250

300

50

2.7 5.2

DLCK = CS = V

DD

SHUTDOWN CURRENT vs. TEMPERATURE

MXB7843 toc22

TEMPERATURE (°C)

SHUTDOWN CURRENT (nA)

655035205-10-25

60

70

80

90

100

110

120

50

-40 80

DCLK = CS = V

DD

MAXIMUM SAMPLE RATE

vs. SUPPLY VOLTAGE

MXB7843 toc23

SUPPLY VOLTAGE (V)

SAMPLE RATE (kHz)

5.04.54.03.53.02.5

10

100

1000

1

2.0 5.5

MXB7843

2.375V to 5.25V, 4-Wire Touch-Screen
Controller

_______________________________________________________________________________________ 7

Pin Description

PIN NAME FUNCTION

1VDDPositive Supply Voltage. Connect to pin 10.

2X+X+ Position Input, ADC Input Channel 1

3Y+Y+ Position Input, ADC Input Channel 2

4X-X- Position Input

5Y-Y- Position Input

6 GND Ground

7 IN3 Auxiliary Input to ADC; ADC Input Channel 3

8 IN4 Auxiliary Input to ADC; ADC Input Channel 4

9 REF

Voltage Reference Input. Reference voltage for analog-to-digital conversion. Apply a reference
voltage between 1V and V

DD

. Bypass REF to GND with a 0.1µF capacitor.

10 V

DD

Positive Supply Voltage, +2.375V to +5.25V. Bypass with a 1µF capacitor. Connect to pin 1.

11 PENIRQ Pen Interrupt Output. Open anode output. 10kΩ to 100kΩ pullup resistor required to VDD.

12 DOUT

Serial Data Output. Data changes state on the falling edge of DCLK. High impedance when CS is
HIGH.

13 BUSY

Busy Output. BUSY pulses high for one clock period before the MSB decision. High impedance when
CS is HIGH.

14 DIN Serial Data Input. Data clocked in on the rising edge of DCLK.

15 CS

Active-Low Chip Select. Data is only clocked into DIN when CS is low. When CS is high, DOUT and
BUSY are high impedance.

16 DCLK

Serial Clock Input. Clocks data in and out of the serial interface and sets the conversion speed (duty
cycle must be 40% to 60%).