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 TransZorbTM 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 0.5W,
while the typical power consumption at 125ksps
throughput and a 2.7V supply is 650W.
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
-40C to +85C temperature range.
Applications
Personal Digital Assistants
Portable Instruments
Point-of-Sales Terminals
Pagers
Touch-Screen Monitors
Cellular Phones
Features
o ESD-Protected ADC Inputs
15kV IEC 61000-4-2 Air-Gap Discharge
8kV IEC 61000-4-2 Contact Discharge
o Pin Compatible with MXB7846
o +2.375V to +5.25V Single Supply
o 4-Wire Touch-Screen Interface
o Ratiometric Conversion
o SPITM/QSPITM, 3-Wire Serial Interface
o Programmable 8-/12-Bit Resolution
o Two Auxiliary Analog Inputs
o Automatic Shutdown Between Conversions
o Low Power
270A at 125ksps
115A at 50ksps
25A at 10ksps
5A at 1ksps
2A 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 0; 4/02
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 +85C
16 QSOP
MXB7843EUE
-40
C to +85C
16 TSSOP
TransZorb is a trademark of General Semiconductor Industries,
Inc.
SPI/QSPI are trademarks of National Semiconductor Corp.
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.
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
= +70C)
16-Pin QSOP (derate 8.30mW/C above +70C).........667mW
16-Pin TSSOP (derate 5.70mW/C above +70C) .......456mW
Operating Temperature Range ...........................-40C to +85C
Junction Temperature ......................................................+150C
Storage Temperature Range .............................-65C to +150C
Lead Temperature (soldering, 10s) .................................+300C
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, 0.1F capacitor at REF, T
A
=
T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25C.)
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
V
RMS
CONVERSION RATE
Conversion Time
t
CONV
12 clock cycles (Note 4)
6
s
Track/Hold Acquisition Time
t
ACQ
3 clock cycles
1.5
s
Throughput Rate
f
SAMPLE
16 clock conversion
125
kHz
Multiplexer Settling Time
500
ns
Aperture Delay
30
ns
Aperture Jitter
100
p s
Channel-to-Channel Isolation
V
IN
= 2.5V
P-P
at 50kHz
100
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
REF
V
Input Capacitance
25
pF
Input Leakage Current
On/off-leakage, V
IN
= 0 to V
DD
0.1
1
A
SWITCH DRIVERS
Y+, X+
7
On-Resistance (Note 5)
Y-, X-
9
MXB7843
2.375V to 5.25V, 4-Wire Touch-Screen
Controller
_______________________________________________________________________________________
3
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, 0.1F capacitor at REF, T
A
=
T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25C.)
PARAMETER
SYM B O L CONDITIONS
MIN
TYP
MAX
UNITS
REFERENCE (Reference applied to REF)
Reference Input Voltage Range
(Note 6)
1
V
DD
V
Input Resistance
5
G
f
SAMPLE
= 125kHz
13
40
f
SAMPLE
= 12.5kHz
2.5
Input Current
f
DCLK
= 0
3
A
DIGITAL INPUTS (DCLK, CS, DIN)
Input High Voltage
V
IH
V
DD
0.7
V
Input Low Voltage
V
IL
0.8
V
Input Hysteresis
V
HYST
100
mV
Input Leakage Current
I
IN
1
A
Input Capacitance
C
IN
15
pF
DIGITAL OUTPUT (DOUT, BUSY)
Output Voltage Low
V
OL
I
SINK
= 250A
0.4
V
Output Voltage High
V
OH
I
SOURCE
= 250A
V
DD
-
0.5
V
PENIRQ Output Low Voltage
V
OL
50k
pullup to V
DD
0.8
V
Three-State Leakage Current
I
L
CS = V
DD
1
10
A
Three-State Output Capacitance
C
OUT
CS = V
DD
15
pF
POWER REQUIREMENTS
Supply Voltage
V
DD
2.375
5.250
V
f
SAMPLE
= 125ksps
270
650
f
SAMPLE
= 12.5ksps
220
Supply Current
I
DD
f
SAMPLE
= 0
150
A
Shutdown Supply Current
I
SHDN
DCLK = CS = V
DD
3
A
Power-Supply Rejection Ratio
PSRR
V
DD
= 2.7V to 3.6V full scale
70
dB
MXB7843
2.375V to 5.25V, 4-Wire Touch-Screen
Controller
4
_______________________________________________________________________________________
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 300V
P-P
. An external reference below 2.5V can com-
promise the ADC performance.
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, 0.1F capacitor at REF, T
A
=
T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25C.)
PARAMETER
SYM B O L CONDITIONS
MIN
TYP
MAX
UNITS
TIMING CHARACTERISTICS (Figure 1)
Acquisition Time
t
ACQ
1.5
s
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
0
ns
CS Fall-to-DCLK Rise Setup Time
t
CSS
100
ns
CS Rise-to-DCLK Rise Ignore
t
CSH
0
ns
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
MXB7843
2.375V to 5.25V, 4-Wire Touch-Screen
Controller
_______________________________________________________________________________________
5
INTEGRAL NONLINEARITY
vs. DIGITAL OUTPUT CODE
MXB7843 toc01
OUTPUT CODE
INL (LSB)
3500
3000
2000 2500
1000 1500
500
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
-0.4
0
4000
DIFFERENTIAL NONLINEARITY
vs. DIGITAL OUTPUT CODE
MXB7843 toc02
OUTPUT CODE
DNL (LSB)
3500
3000
2000 2500
1000 1500
500
-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)
5.0
4.5
3.0
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)
65
50
35
20
5
-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)
5.0
4.5
4.0
3.5
3.0
-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)
65
50
35
20
5
-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
(
)
5.0
4.5
4.0
3.5
3.0
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
(
)
35
20
5
-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
(V
DD
= 2.7V, V
REF
= 2.5V, f
DCLK
= 2MHz, f
SAMPLE
= 125kHz, C
LOAD
= 50pF, 0.1F capacitor at REF, T
A
= +25C, unless otherwise
noted.)
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