MAXIM MXB7846 Technical data
MXB7846
2.375V to 5.25V, 4-Wire Touch-Screen Controller
with Internal Reference and Temperature Sensor
________________________________________________________________
Maxim Integrated Products
1
Pin Configuration
19-2436; Rev 2; 1/08
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.
General Description
The MXB7846 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 MXB7846 uses an internal
+2.5V reference or an external reference. The
MXB7846 can make absolute or ratiometric measurements. In addition, this device has an on-chip temperature 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 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 MXB7846 ideal for battery-operated systems, such as personal digital assistants 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.
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 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
Ordering Information
TRANSZORB is a trademark of Vishay Intertechnology, Inc.
SPI/QSPI are trademarks of Motorola, Inc.
Typical Application Circuit appears at end of data sheet.
PART TEMP RANGE
MXB7846EEE -40°C to +85°C 16 QSOP E16-6
MXB7846EUE -40°C to +85°C 16 TSSOP U16-1
PINPACKAGE
PKG
CODE
TOP VIEW
V
GND
BAT
AUX
DD
1
X+
2
Y+
3
4
X-
Y-
5
6
7
8
16
DCLK
15
CS
14
DIN
MXB7846
QSOP/TSSOP
13
BUSY
12
DOUT
PENIRQ
11
10
V
DD
REF
9
MXB7846
2.375V to 5.25V, 4-Wire Touch-Screen Controller
with Internal Reference and Temperature Sensor
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, 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 (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-, 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
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.)
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 Including internal reference 70 µV
CONVERSION RATE
Conversion Time t
Track/Hold Acquisition Time t
Throughput Rate f
Multiplexer Settling Time 500 ns
Aperture Delay 30 ns
Aperture Jitter 100 p s
Channel-to-Channel Isolation VIN = 2.5V
Serial Clock Frequency f
Duty Cycle 40 60 %
ANALOG INPUT (X+, X-, Y+, Y-, AUX)
Input Voltage Range 0V
Input Capacitance 25 pF
Input Leakage Current On/off leakage, VIN = 0 to V
SWITCH DRIVERS
On-Resistance (Note 5)
INTERNAL REFERENCE
Reference Output Voltage V
REF Output Tempco TCV
REF Short-Circuit Current 18 mA
REF Output Impedance 250 Ω
PARAMETER SYM B O L CONDITIONS MIN TYP MAX UNITS
CONV
ACQ
SAMPLE
DCLK
REF
12 clock cycles (Note 4) 6 µs
3 clock cycles 1.5 µs
16 clock conversion 125 kHz
Y+, X+ 7
Y-, X- 9
VDD = 2.7V to 5.25V, TA = +25°C 2.45 2.50 2.55 V
REF
at 50kHz 100 dB
P-P
DD
0.1 2.0 MHz
REF
±0.1 ±1 µA
50 ppm°/C
RMS
V
Ω
MXB7846
2.375V to 5.25V, 4-Wire Touch-Screen Controller
with Internal Reference and Temperature Sensor
_______________________________________________________________________________________ 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
EXTERNAL REFERENCE (Internal reference disabled, reference applied to REF)
Reference Input Voltage Range (Note 7) 1 V
DD
V
Input Resistance 1GΩ
Input Current
f
f
f
= 125kHz 13 40
SAMPLE
= 12.5kHz 2.5
SAMPLE
= 0 ±3
DCLK
µA
BATTERY MONITOR (BAT)
Input Voltage Range 06V
Input Resistance During acquisition 10 kΩ
V
= 2.5V ±2
Accuracy
REF
Internal reference ±3
%
TEMPERATURE MEASUREMENT
Resolution
Accuracy
Differential method (Note 8) 1.6 °C
Single-conversion method 0.3 °C
Differential method (Note 8) ±2°C
Single-conversion method ±3°C
DIGITAL INPUTS (DCLK, CS, DIN)
Input High Voltage V
Input Low Voltage V
Input Hysteresis V
Input Leakage Current I
Input Capacitance C
IH
IL
HYST
IN
IN
✕
V
0.7 V
DD
100 mV
15 pF
0.8 V
±1 µA
DIGITAL OUTPUT (DOUT, BUSY)
Output Voltage Low V
Output Voltage High V
PENIRQ Output Low Voltage V
Three-State Leakage Current I
Three-State Output Capacitance C
OUT
OL
OH
OL
L
I
= 250µA 0.4 V
SINK
I
50kΩ pullup to V
CS = V
CS = V
= 250µA V
SOURCE
DD
DD
DD
0.5 V
DD -
1 ±10 µA
15 pF
0.8 V
POWER REQUIREMENTS
Supply Voltage V
Supply Current I
Shutdown Supply Current I
Power-Supply Rejection Ratio P
DD
DD
SHDN
SRR
External reference 2.375 5.250
Internal reference 2.70 5.25
External
reference
Internal
reference
DCLK = CS = V
f
f
f
f
f
f
DD
= 125ksps 270 650
SAMPLE
= 12.5ksps 220
SAMPLE
= 0 150
SAMPLE
= 125ksps 780 950
SAMPLE
= 12.5ksps 720
SAMPLE
= 0 650
SAMPLE
3µA
VDD = 2.7V to 3.6V full scale 70 dB
V
µA
µA
MXB7846
2.375V to 5.25V, 4-Wire Touch-Screen Controller
with Internal Reference and Temperature Sensor
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: 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.
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.)
TIMING CHARACTERISTICS (Figure 1)
Acquisition Time t
DCLK Clock Period t
DCLK Pulse Width High t
DCLK Pulse Width Low t
DIN-to-DCLK Setup Time t
DIN-to-DCLK Hold Time t
CS Fall-to-DCLK Rise Setup Time t
CS Rise-to-DCLK Rise Ignore t
DCLK Falling-to-DOUT Valid t
CS Rise-to-DOUT Disable t
CS Fall-to-DOUT Enable t
DCLK Falling-to-BUSY Rising t
CS Falling-to-BUSY Enable t
CS Rise-to-BUSY Disable t
PARAMETER SYM B O L CONDITIONS MIN TYP MAX UNITS
ACQ
CP
CH
CL
DS
DH
CSS
CSH
DO
TR
DV
BD
BDV
BTR
C
C
C
LOAD
LOAD
LOAD
= 50pF 200 ns
= 50pF 200 ns
= 50pF 200 ns
1.5 µs
500 ns
200 ns
200 ns
100 ns
0ns
100 ns
0ns
200 ns
200 ns
200 ns
Typical Operating Characteristics
(VDD= 2.7V, V
REF
= 2.5V
EXTERNAL
, f
DCLK
= 2MHz, f
SAMPLE
= 125kHz, C
LOAD
= 50pF, 0.1µF capacitor at REF, TA= +25°C, unless
otherwise noted.)
MXB7846
2.375V to 5.25V, 4-Wire Touch-Screen Controller
with Internal Reference and Temperature Sensor
_______________________________________________________________________________________
5
INTEGRAL NONLINEARITY
vs. DIGITAL OUTPUT CODE
0.5
0.4
0.3
0.2
0.1
0
INL (LSB)
-0.1
-0.2
-0.3
-0.4
0 4000
CHANGE IN OFFSET ERROR
1.0
0.5
OUTPUT CODE
vs. TEMPERATURE
350030002000 25001000 1500500
1.0
0.8
MXB7846 toc01
0.6
0.4
0.2
DNL (LSB)
-0.2
-0.4
-0.6
-0.8
-1.0
MXB7846 toc05
DIFFERENTIAL NONLINEARITY
vs. DIGITAL OUTPUT CODE
0
0 4000
OUTPUT CODE
CHANGE IN GAIN ERROR
vs. SUPPLY VOLTAGE
3
2
1
350030002000 25001000 1500500
MXB7846 toc02
OFFSET ERROR (LSB)
MXB7846 toc07
CHANGE IN OFFSET ERROR
vs. SUPPLY VOLTAGE
2.0
1.5
1.0
0.5
0
-0.5
-1.0
-1.5
-2.0
2.5 5.5
SUPPLY VOLTAGE (V)
CHANGE IN GAIN ERROR
vs. TEMPERATURE
1.0
0.5
0
MXB7846 toc04
5.04.53.0 3.5 4.0
MXB7846 toc08
0
-0.5
OFFSET ERROR FROM +25°C (LSB)
-1.0
-40 80
655035205-10-25
°
SWITCH ON-RESISTANCE vs. SUPPLY VOLTAGE
(X+, Y+ : +V
14
12
10
8
(Ω)
ON
R
6
4
2
0
2.5 5.5
TO PIN; X-, Y- : TO GND)
DD
X-
Y-
X+
Y+
SUPPLY VOLTAGE (V)
5.04.54.03.53.0
GAIN ERROR (LSB)
MXB7846 toc03
(Ω)
ON
R
0
-1
-2
-3
2.5 5.5
SUPPLY VOLTAGE (V)
5.04.54.03.53.0
SWITCH ON-RESISTANCE vs. TEMPERATURE
(X+, Y+ : +V
12
11
10
9
8
7
6
5
4
3
2
1
0
-40 50 65 80
TO PIN; X-, Y- : PIN TO GND)
DD
X-
X+
Y-
Y+
35205-10-25
TEMPERATURE (°C)
-0.5
-1.0
GAIN ERROR FROM +25°C (LSB)
-1.5
-2.0
2.6
2.5
MXB7846 toc06
2.4
2.3
2.2
INTERNAL REFERENCE (V)
2.1
2.0
-40 80
655035205-10-25
°
INTERNAL REFERENCE
vs. SUPPLY VOLTAGE
CL = 0.1μf
2.0 5.5
SUPPLY VOLTAGE (V)
5.04.54.03.53.02.5
MXB7846 toc09
Typical Operating Characteristics (continued)
(VDD= 2.7V, V
REF
= 2.5V
EXTERNAL
, f
DCLK
= 2MHz, f
SAMPLE
= 125kHz, C
LOAD
= 50pF, 0.1µF capacitor at REF, TA= +25°C, unless
otherwise noted.)
MXB7846
2.375V to 5.25V, 4-Wire Touch-Screen Controller
with Internal Reference and Temperature Sensor
6 _______________________________________________________________________________________
2.6
INTERNAL REFERENCE VOLTAGE
vs. TEMPERATURE
2.5
INTERNAL VOLTAGE REFERENCE
vs. TURN-ON TIME
INTERNAL VOLTAGE REFERENCE
vs. TURN-ON TIME
3.0
2.5
2.4
2.3
2.2
INTERNAL REFERENCE VOLTAGE (V)
2.1
VDD = 2.7V
= 0.1μF
C
L
2.0
-40
TEMPERATURE (°C)
REFERENCE CURRENT
vs. SUPPLY VOLTAGE
8.3
CL = 0.1μF
= 125kHz
f
SAMPLE
8.2
EXTERNAL REFERENCE
8.1
8.0
7.9
REFERENCE CURRENT (μA)
7.8
7.7
2.5 5.5
SUPPLY VOLTAGE (V)
TEMP DIODE VOLTAGE
vs. TEMPERATURE
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
TEMP DIODE VOLTAGE (V)
0.2
0.1
0
-40
TEMP2
TEMPERATURE (°C)
TEMP1
MXB7846 toc10
2.0
1.5
1.0
0.5
INTERNAL VOLTAGE REFERENCE (V)
80655035205-10-25
0
0
(1060μs) 12-BIT SETTLING
TURN-ON TIME (μs)
CL = 1μF
12001000800600400200
REFERENCE CURRENT vs. TEMPERATURE
8.3
8.2
MXB7846 toc12
8.1
8.0
7.9
REFERENCE CURRENT (μA)
VDD = 2.7V
= 0.1μF
C
L
7.8
5.04.54.03.53.0
7.7
= 125kHz
f
SAMPLE
EXTERNAL REFERENCE
-40 80
TEMPERATURE (°C)
655035205-10-25
TEMP0 DIODE VOLTAGE
vs. SUPPLY VOLTAGE
590
MXB7846 toc15
589
TEMP0
588
587
TEMP0 DIODE VOLTAGE (mV)
586
585
806535 50-10 5 20-25
2.7
SUPPLY VOLTAGE (V)
5.24.74.23.73.2
2.5
MXB7846 toc11a
2.0
1.5
1.0
INTERNAL VOLTAGE REFERENCE (V)
0.5
0
040
REFERENCE CURRENT vs. SAMPLE RATE
10
EXTERNAL REFERENCE
9
MXB7846 toc13
MXB7846 toc16
8
7
6
5
4
3
REFERENCE CURRENT (μA)
2
1
0
0 125
705
704
703
702
701
700
TEMP1 DIODE VOLTAGE (mV)
699
698
2.7
NO CAPACITOR
(30μs) 12-BIT SETTLING
TURN-ON TIME (μs)
SAMPLE RATE (kHz)
TEMP1 DIODE VOLTAGE
vs. SUPPLY VOLTAGE
TEMP1
SUPPLY VOLTAGE (V)
MXB7846 toc11b
3530252015105
MXB7846 toc14
100755025
MXB7846 toc17
5.24.74.23.73.2
Typical Operating Characteristics (continued)
(VDD= 2.7V, V
REF
= 2.5V
EXTERNAL
, f
DCLK
= 2MHz, f
SAMPLE
= 125kHz, C
LOAD
= 50pF, 0.1µF capacitor at REF, TA= +25°C, unless
otherwise noted.)
MXB7846
2.375V to 5.25V, 4-Wire Touch-Screen Controller
with Internal Reference and Temperature Sensor
_______________________________________________________________________________________
7
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
250
f
= 12.5kHz
SAMPLE
225
200
SUPPLY CURRENT (μA)
175
150
2.0 5.5
SUPPLY VOLTAGE (V)
SHUTDOWN CURRENT
vs. SUPPLY VOLTAGE
300
DCLK = CS = V
250
200
DD
5.04.54.03.53.02.5
MXB7846 toc18
SUPPLY CURRENT (μA)
MXB7846 toc21
290
285
280
275
270
265
260
255
250
-40 80
SHUTDOWN CURRENT vs. TEMPERATURE
120
110
100
90
SUPPLY CURRENT vs. TEMPERATURE
f
= 125kHz
SAMPLE
= 2.7V
V
DD
6550-25 -10 5 20 35
TEMPERATURE (°C)
DCLK = CS = VDD = 3V
MXB7846 toc19
MXB7846 toc22
SUPPLY CURRENT vs. SAMPLE RATE
250
VDD = 2.7V
= 2.5V
V
REF
225
200
175
150
SUPPLY CURRENT (μA)
125
100
0 125
SAMPLE RATE (kHz)
MAXIMUM SAMPLE RATE
vs. SUPPLY VOLTAGE
1000
100
MXB7846 toc20
100755025
MXB7846 toc23
150
SHUTDOWN CURRENT (nA)
100
50
2.7 5.2
SUPPLY VOLTAGE (V)
80
SAMPLE RATE (kHz)
70
SHUTDOWN CURRENT (nA)
60
4.74.23.73.2
50
-40 80
TEMPERATURE (°C)
655035205-10-25
10
1
2.0 5.5
SUPPLY VOLTAGE (V)
5.04.54.03.53.02.5
Pin Description
MXB7846
2.375V to 5.25V, 4-Wire Touch-Screen Controller
with Internal Reference and Temperature Sensor
8 _______________________________________________________________________________________
Figure 1. Detailed Serial Interface Timing
PIN NAME FUNCTION
1VDDPositive Supply Voltage. Connect to pin 10.
2 X+ X+ Position Input, ADC Input Channel 1
3 Y+ Y+ Position Input, ADC Input Channel 2
4 X- X- Position Input
5 Y- Y- Position Input
6 GND Ground
7 BAT Battery Monitoring Inputs; ADC Input Channel 3
8 AUX Auxiliary Input to ADC; ADC Input Channel 4
Voltage Reference Output/Input. Reference voltage for analog-to-digital conversion. In internal
9 REF
10 V
DD
reference mode, the reference buffer provides a 2.50V nominal output. In external reference mode,
apply a reference voltage between 1V and V
. Bypass REF to GND with a 0.1µF capacitor.
DD
Positive Supply Voltage, +2.375V (2.70V) to +5.25V. External (internal) reference. 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
13 BUSY
Serial Data Output. Data changes state on the falling edge of DCLK. High impedance when CS is
HIGH.
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
16 DCLK
Active-Low Chip Select. Data is only clocked into DIN when CS is low. When CS is HIGH, DOUT and
BUSY are high impedance.
Serial Clock Input. Clocks data in and out of the serial interface and sets the conversion speed (duty
cycle must be 40% to 60%).
CS
t
DCLK
DIN
DOUT
BUSY
t
CSS
t
DS
t
DH
t
DV
t
BDV
CH
t
CL
t
CP
t
DO
t
BD
t
CSH
t
TR
t
BTR
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