19-2435; Rev 1; 9/05
2.375V to 5.25V, 4-Wire Touch-Screen
Controller
General Description
The MXB7843 is an industry-standard 4-wire touch-
screen controller. It contains a 12-bit sampling analog-
to-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 ratio-
metric 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 bat-
tery-operated systems, such as personal digital assis-
tants 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.
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
Applications
Personal Digital Assistants
Portable Instruments
Point-of-Sales Terminals
Pagers
Touch-Screen Monitors
Cellular Phones
Ordering Information
PART
MXB7843EEE
MXB7843EUE
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
16 QSOP
16 TSSOP
Typical Application Circuit appears at end of data sheet.
TransZorb is a trademark of Vishay Intertechnology, Inc.
SPI/QSPI are trademarks of Motorola, Inc.
TOP VIEW
V
DD
1
X+ 2
Y+ 3
X- 4
Y- 5
GND 6
IN3 7
IN4 8
16 DCLK
15 CS
14 DIN
Pin Configuration
MXB7843
13 BUSY
12 DOUT
11 PENIRQ
10 V
DD
9
REF
QSOP/TSSOP
________________________________________________________________
Maxim Integrated Products
1
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.
2.375V to 5.25V, 4-Wire Touch-Screen
Controller
MXB7843
ABSOLUTE MAXIMUM RATINGS
V
DD
, 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 (V
DD
+ 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
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.
ELECTRICAL CHARACTERISTICS
(V
DD
= 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, T
A
=
T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
DC ACCURACY
(Note 1)
Resolution
No Missing Codes
Relative Accuracy
Differential Nonlinearity
Offset Error
Gain Error
Noise
CONVERSION RATE
Conversion Time
Track/Hold Acquisition Time
Throughput Rate
Multiplexer Settling Time
Aperture Delay
Aperture Jitter
Channel-to-Channel Isolation
Serial Clock Frequency
Duty Cycle
ANALOG INPUT (X+, X-, Y+, Y-, IN3, IN4)
Input Voltage Range
Input Capacitance
Input Leakage Current
SWITCH DRIVERS
On-Resistance (Note 5)
Y+, X+
Y-, X-
7
9
Ω
On/off-leakage, V
IN
= 0 to V
DD
0
25
±0.1
±1
V
REF
V
pF
µA
f
DCLK
V
IN
= 2.5V
P-P
at 50kHz
0.1
40
t
CONV
t
ACQ
f
SAMPLE
12 clock cycles (Note 4)
3 clock cycles
16 clock conversion
500
30
100
100
2.0
60
1.5
125
6
µs
µs
kHz
ns
ns
ps
dB
MHz
%
(Note 3)
70
INL
DNL
(Note 2)
11
12
±1
±1
±6
±4
±2
12
Bits
Bits
LSB
LSB
LSB
LSB
µV
RMS
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
2
_______________________________________________________________________________________
2.375V to 5.25V, 4-Wire Touch-Screen
Controller
ELECTRICAL CHARACTERISTICS (continued)
(V
DD
= 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, T
A
=
T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
Reference Input Voltage Range
Input Resistance
f
SAMPLE
= 125kHz
Input Current
DIGITAL INPUTS (DCLK,
CS,
DIN)
Input High Voltage
Input Low Voltage
Input Hysteresis
Input Leakage Current
Input Capacitance
DIGITAL OUTPUT (DOUT, BUSY)
Output Voltage Low
Output Voltage High
PENIRQ
Output Low Voltage
Three-State Leakage Current
Three-State Output Capacitance
POWER REQUIREMENTS
Supply Voltage
Supply Current
Shutdown Supply Current
Power-Supply Rejection Ratio
V
DD
f
SAMPLE
= 125ksps
I
DD
I
SHDN
PSRR
f
SAMPLE
= 12.5ksps
f
SAMPLE
= 0
DCLK =
CS
= V
DD
V
DD
= 2.7V to 3.6V full scale
70
2.375
270
220
150
3
µA
dB
5.250
650
µA
V
V
IH
V
IL
V
HYST
I
IN
C
IN
V
OL
V
OH
V
OL
I
L
C
OUT
I
SINK
= 250µA
I
SOURCE
= 250µA
50kΩ pullup to V
DD
CS
= V
DD
CS
= V
DD
1
15
V
DD
-
0.5
0.8
±10
15
0.4
100
±1
✕
MXB7843
SYMBOL
(Note 6)
CONDITIONS
MIN
1
TYP
MAX
V
DD
UNITS
V
GΩ
REFERENCE
(Reference applied to REF)
5
13
2.5
±3
V
DD
0.7
0.8
40
µA
f
SAMPLE
= 12.5kHz
f
DCLK
= 0
V
V
mV
µA
pF
V
V
V
µA
pF
_______________________________________________________________________________________
3
2.375V to 5.25V, 4-Wire Touch-Screen
Controller
MXB7843
TIMING CHARACTERISTICS (Figure 1)
(V
DD
= 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, T
A
=
T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
Acquisition Time
DCLK Clock Period
DCLK Pulse Width High
DCLK Pulse Width Low
DIN-to-DCLK Setup Time
DIN-to-DCLK Hold Time
CS
Fall-to-DCLK Rise Setup Time
CS
Rise-to-DCLK Rise Ignore
DCLK Falling-to-DOUT Valid
CS
Rise-to-DOUT Disable
CS
Fall-to-DOUT Enable
DCLK Falling-to-BUSY Rising
CS
Falling-to-BUSY Enable
CS
Rise-to-BUSY Disable
SYMBOL
t
ACQ
t
CP
t
CH
t
CL
t
DS
t
DH
t
CSS
t
CSH
t
DO
t
TR
t
DV
t
BD
t
BDV
t
BTR
C
LOAD
= 50pF
C
LOAD
= 50pF
C
LOAD
= 50pF
CONDITIONS
MIN
1.5
500
200
200
100
0
100
0
200
200
200
200
200
200
TYP
MAX
UNITS
µs
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
TIMING CHARACTERISTICS
(Figure 1)
Note 1:
Tested at V
DD
= +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.
4
_______________________________________________________________________________________
2.375V to 5.25V, 4-Wire Touch-Screen
Controller
MXB7843
Typical Operating Characteristics
(V
DD
= 2.7V, V
REF
= 2.5V, f
DCLK
= 2MHz, f
SAMPLE
= 125kHz, C
LOAD
= 50pF, 0.1µF capacitor at REF, T
A
= +25°C, unless otherwise
noted.)
INTEGRAL NONLINEARITY
vs. DIGITAL OUTPUT CODE
MXB7843 toc01
DIFFERENTIAL NONLINEARITY
vs. DIGITAL OUTPUT CODE
MXB7843 toc02
CHANGE IN OFFSET ERROR
vs. SUPPLY VOLTAGE
1.5
OFFSET ERROR (LSB)
1.0
0.5
0
-0.5
-1.0
-1.5
-2.0
MXB7843 toc04
0.5
0.4
0.3
0.2
0.1
0
-0.1
-0.2
-0.3
-0.4
0
INL (LSB)
1.0
0.8
0.6
0.4
DNL (LSB)
0.2
0
-0.2
-0.4
-0.6
-0.8
-1.0
2.0
500 1000 1500 2000 2500 3000 3500 4000
OUTPUT CODE
0
500 1000 1500 2000 2500 3000 3500 4000
OUTPUT CODE
2.5
3.0
3.5
4.0
4.5
5.0
5.5
SUPPLY VOLTAGE (V)
CHANGE IN OFFSET ERROR
vs. TEMPERATURE
MXB7843 toc05
CHANGE IN GAIN ERROR
vs. SUPPLY VOLTAGE
MXB7843 toc07
CHANGE IN GAIN ERROR
vs. TEMPERATURE
MXB7843 toc08
1.0
OFFSET ERROR FROM +25°C (LSB)
3
2
GAIN ERROR (LSB)
1
0
-1
-2
1.0
GAIN ERROR FROM +25°C (LSB)
0.5
0
-0.5
-1.0
-1.5
-2.0
0.5
0
-0.5
-1.0
-40 -25
-10
5
20
35
50
65
80
TEMPERATURE (°C)
-3
2.5
3.0
3.5
4.0
4.5
5.0
5.5
SUPPLY VOLTAGE (V)
-40 -25 -10
5
20
35
50
65
80
TEMPERATURE (°C)
SWITCH ON-RESISTANCE vs. SUPPLY VOLTAGE
(X+, Y+ : + V
DD
TO PIN; X-, Y- : TO GND)
MXB7843 toc03
SWITCH ON-RESISTANCE vs. TEMPERATURE
(X+, Y+ : + V
DD
TO PIN; X-, Y- : PIN TO GND)
11
10
9
8
7
6
5
4
3
2
1
0
X-
X+
Y-
Y+
MXB7843 toc06
14
12
X-
10
R
ON
(Ω)
12
Y-
6
4
2
0
2.5
3.0
3.5
X+
Y+
4.0
4.5
5.0
5.5
R
ON
(Ω)
8
-40 -25
-10
5
20
35
50
65
80
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
_______________________________________________________________________________________
5
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