19-2436; Rev 2; 1/08
2.375V to 5.25V, 4-Wire Touch-Screen Controller
with Internal Reference and Temperature Sensor
General Description
The MXB7846 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 MXB7846 uses an internal
+2.5V reference or an external reference. The
MXB7846 can make absolute or ratiometric measure-
ments. In addition, this device has an on-chip tempera-
ture sensor, a battery-monitoring channel, and has the
ability to perform touch-pressure measurements without
external components. The MXB7846 has one auxiliary
ADC input. All analog inputs are fully ESD protected,
eliminating the need for external TransZorb™ devices.
The MXB7846 is guaranteed to operate with a supply
voltage down to +2.375V when used with an external
reference or +2.7V with an internal reference. In shut-
down 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 MXB7846 ideal for bat-
tery-operated systems, such as personal digital assis-
tants with resistive touch screens and other portable
equipment. The MXB7846 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 MXB7843
♦
+2.375V to +5.25V Single Supply
♦
Internal +2.5V Reference
♦
Direct Battery Measurement (0 to 6V)
♦
On-Chip Temperature Measurement
♦
Touch-Pressure Measurement
♦
4-Wire Touch-Screen Interface
♦
Ratiometric Conversion
♦
SPI™/QSPI™, 3-Wire Serial Interface
♦
Programmable 8-/12-Bit Resolution
♦
Auxiliary Analog Input
♦
Automatic Shutdown Between Conversions
♦
Low Power (External Reference)
270µA at 125ksps
115µA at 50ksps
25µA at 10ksps
5µA at 1ksps
2µA Shutdown Current
MXB7846
Applications
Personal Digital Assistants
Portable Instruments
Point-of-Sales Terminals
Pagers
Touch-Screen Monitors
Cellular Phones
Typical Application Circuit appears at end of data sheet.
TRANSZORB is a trademark of Vishay Intertechnology, Inc.
SPI/QSPI are trademarks of Motorola, Inc.
PART
MXB7846EEE
MXB7846EUE
Ordering Information
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
PIN-
PACKAGE
16 QSOP
16 TSSOP
PKG
CODE
E16-6
U16-1
Pin Configuration
TOP VIEW
V
DD
1
X+ 2
Y+ 3
X- 4
Y- 5
GND 6
BAT 7
AUX 8
16 DCLK
15 CS
14 DIN
MXB7846
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 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
with Internal Reference and Temperature Sensor
MXB7846
ABSOLUTE MAXIMUM RATINGS
V
DD
, VBAT, 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-, AUX 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-, VBAT, AUX ......................................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-, AUX)
Input Voltage Range
Input Capacitance
Input Leakage Current
SWITCH DRIVERS
On-Resistance (Note 5)
INTERNAL REFERENCE
Reference Output Voltage
REF Output Tempco
REF Short-Circuit Current
REF Output Impedance
V
REF
TCV
REF
V
DD
= 2.7V to 5.25V, T
A
= +25°C
2.45
2.50
50
18
250
2.55
V
ppm°/C
mA
Ω
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)
Including internal reference
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
with Internal Reference and Temperature Sensor
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
BATTERY MONITOR (BAT)
Input Voltage Range
Input Resistance
Accuracy
TEMPERATURE MEASUREMENT
Resolution
Accuracy
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
V
DD
External reference
Internal reference
External
reference
Supply Current
I
DD
Internal
reference
Shutdown Supply Current
Power-Supply Rejection Ratio
I
SHDN
P
SRR
f
SAMPLE
= 125ksps
f
SAMPLE
= 12.5ksps
f
SAMPLE
= 0
f
SAMPLE
= 125ksps
f
SAMPLE
= 12.5ksps
f
SAMPLE
= 0
DCLK =
CS
= V
DD
V
DD
= 2.7V to 3.6V full scale
70
2.375
2.70
270
220
150
780
720
650
3
µA
dB
950
µA
5.250
5.25
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
V
DD
✕
0.7
0.8
V
V
mV
µA
pF
V
V
V
µA
pF
Differential method (Note 8)
Single-conversion method
Differential method (Note 8)
Single-conversion method
1.6
0.3
±2
±3
°C
°C
°C
°C
During acquisition
V
REF
= 2.5V
Internal reference
0
10
±2
±3
6
V
kΩ
%
f
SAMPLE
= 12.5kHz
f
DCLK
= 0
SYMBOL
(Note 7)
CONDITIONS
MIN
1
1
13
2.5
±3
40
TYP
MAX
V
DD
UNITS
V
GΩ
µA
MXB7846
EXTERNAL REFERENCE
(Internal reference disabled, reference applied to REF)
_______________________________________________________________________________________
3
2.375V to 5.25V, 4-Wire Touch-Screen Controller
with Internal Reference and Temperature Sensor
MXB7846
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:
External load should not change during conversion for specified accuracy.
Note 7:
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.
Note 8:
Difference between Temp0 and Temp1. No calibration necessary.
4
_______________________________________________________________________________________
2.375V to 5.25V, 4-Wire Touch-Screen Controller
with Internal Reference and Temperature Sensor
Typical Operating Characteristics
(V
DD
= 2.7V, V
REF
= 2.5V
EXTERNAL
, 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
MXB7846 toc01
MXB7846
DIFFERENTIAL NONLINEARITY
vs. DIGITAL OUTPUT CODE
MXB7846 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
MXB7846 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
MXB7846 toc05
CHANGE IN GAIN ERROR
vs. SUPPLY VOLTAGE
MXB7846 toc07
CHANGE IN GAIN ERROR
vs. TEMPERATURE
MXB7846 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)
MXB7846 toc03
SWITCH ON-RESISTANCE vs. TEMPERATURE
(X+, Y+ : +V
DD
TO PIN; X-, Y- : PIN TO GND)
MXB7846 toc06
INTERNAL REFERENCE
vs. SUPPLY VOLTAGE
C
L
= 0.1μf
2.5
INTERNAL REFERENCE (V)
2.4
2.3
2.2
2.1
2.0
MXB7846 toc09
14
12
X-
10
R
ON
(Ω)
12
11
10
9
8
7
6
5
4
3
2
1
0
-40 -25
-10
5
20
35
50
65
80
TEMPERATURE (°C)
X-
X+
Y-
Y+
2.6
Y-
6
4
2
0
2.5
3.0
3.5
X+
Y+
R
ON
(Ω)
8
4.0
4.5
5.0
5.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
_______________________________________________________________________________________
5
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