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ADS7846 Schematic ( PDF Datasheet ) - Burr-Brown Corporation

Teilenummer ADS7846
Beschreibung TOUCH-SCREEN CONTROLLER
Hersteller Burr-Brown Corporation
Logo Burr-Brown Corporation Logo 




Gesamt 17 Seiten
ADS7846 Datasheet, Funktion
® ADS7846
ADS7846
For most current data sheet and other product
information, visit www.burr-brown.com
TOUCH-SCREEN CONTROLLER
FEATURES
q SAME PINOUT AS ADS7843
q 2.2V TO 5.25V OPERATION
q INTERNAL 2.5V REFERENCE
q DIRECT BATTERY MEASUREMENT (0V to 6V)
q ON-CHIP TEMPERATURE MEASUREMENT
q TOUCH-PRESSURE MEASUREMENT
q QSPI/SPI 3-WIRE INTERFACE
q AUTO POWER DOWN
q TSSOP-16 AND SSOP-16 PACKAGES
APPLICATIONS
q PERSONAL DIGITAL ASSISTANTS
q PORTABLE INSTRUMENTS
q POINT-OF-SALES TERMINALS
q PAGERS
q TOUCH-SCREEN MONITORS
q CELLULAR PHONES
PENIRQ
DESCRIPTION
The ADS7846 is a next-generation version to the industry
standard ADS7843 4-wire touch-screen controller. The
ADS7846 is 100% pin-compatible with the existing
ADS7843, and will drop into the same socket. This allows
for easy upgrade of current applications to the new ver-
sion. Only software changes will be required to take
advantage of the added features of direct battery measure-
ment, temperature measurement, and touch-pressure mea-
surement. The ADS7846 also has an on-chip 2.5V refer-
ence that can be utilized for the auxiliary input, battery
monitor, and temperature measurement modes. The refer-
ence can also be powered down when not used to conserve
power. The internal reference will operate down to 2.7V
supply voltage while monitoring the battery voltage from
0V to 6V.
The low power consumption of < 0.5mW typ at 2.7V
(reference OFF), high speed (> 125kHz clock rate), and
on-chip drivers make the ADS7846 an ideal choice for
battery-operated systems such as Personal Digital Assis-
tants (PDAs) with resistive touch screens, pagers, cellu-
lar phones, and other portable equipment. The ADS7846
is available in the small TSSOP-16 and SSOP-16 pack-
ages and is guaranteed over the –40°C to +85°C tem-
perature range.
+VCC
X+
X–
Y+
Y–
VBAT
AUX
Temperature
Sensor
Battery
Monitor
6-Channel
MUX
SAR
ADS7846
CDAC
Comparator
Serial
Data
Out
DOUT
BUSY
CS
DCLK
DIN
VREF
Internal 2.5V
Reference
International Airport Industrial Park • Mailing Address: PO Box 11400, Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 • Tel: (520) 746-1111
Twx: 910-952-1111 • Internet: http://www.burr-brown.com/ • Cable: BBRCORP • Telex: 066-6491 • FAX: (520) 889-1510 • Immediate Product Info: (800) 548-6132
©1999 Burr-Brown Corporation
PDS-11545B
ADPrSint7ed8in4U6.S.A. June, 2000
®






ADS7846 Datasheet, Funktion
TYPICAL PERFORMANCE CURVES (Cont.)
At TA = +25°C, +VCC = +2.7V, VREF = External +2.5V, fSAMPLE = 125kHz, and fCLK = 16 • fSAMPLE = 2MHz, unless otherwise noted.
14
12
10
8
6
4
2
0
0
REFERENCE CURRENT vs SAMPLE RATE
25 50 75 100
Sample Rate (kHz)
125
REFERENCE CURRENT vs TEMPERATURE
18
16
14
12
10
8
6
–40
–20
0 20 40 60
Temperature (˚C)
80 100
SWITCH ON RESISTANCE vs +VCC
(X+, Y+: +VCC to Pin; X–, Y–: Pin to GND)
8
7
6
Y–
5
X–
4
Y+ X+
3
2
1
2 2.5 3 3.5 4 4.5 5
+VCC (V)
SWITCH ON RESISTANCE vs TEMPERATURE
(X+, Y+: +VCC to Pin; X–, Y–: Pin to GND)
8
7
X– Y–
6
5
X+ Y+
4
3
2
1
–40
–20
0 20 40 60
Temperature (˚C)
80 100
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
20
MAXIMUM SAMPLING RATE vs RIN
INL: R = 2k
INL: R = 500
DNL: R = 2k
DNL: R = 500
40 60 80 100 120 140 160 180 200
Sampling Rate (kHz)
2.4920
2.4915
2.4910
2.4905
2.4900
2.4895
2.4890
2.4885
2.4880
2.4875
INTERNAL VREF vs TEMPERATURE
Temperature (°C)
®
ADS7846
6

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ADS7846 pdf, datenblatt
the multiplexer and control logic. In order to minimize the
power consumption, the divider is only ON during the
sampling of DIN to A2 = 0, A1 = 1, and A0 = 0. Tables I and
II show the relationship between the control bits and con-
figuration of the ADS7846.
PRESSURE MEASUREMENT
Measuring touch pressure can also be done with the
ADS7846. To determine pen or finger touch, the pressure of
the “touch” needs to be determined. Generally, it is not
necessary to have very high performance for this test,
therefore, the 8-bit resolution mode is recommended (how-
ever, calculations will be shown with the 12-bit resolution
mode). There are several different ways of performing this
measurement. The ADS7846 supports two methods. The
first method requires knowing the X-plate resistance, mea-
surement of the X-Position, and two additional cross panel
measurements (Z2 and Z1) of the touch screen (see Figure 8).
Using Equation 2 will calculate the touch resistance:
R TOUCH
=
RX
plate •
X
– Position
4096

Z2
Z1
– 1
(2)
The second method requires knowing both the X-plate and
Y-plate resistance, measurement of X-Position and Y-Posi-
tion, and Z1. Using Equation 3 will also calculate the touch
resistance:
R TOUCH
=
RX
plate • X
4096
Position

4096
Z1
– 1
RY
plate
Y
Position
4096
(3)
X+
Touch
X-Position
X–
Measure X-Position
Y+
Y–
Measure Z1-Position
X+ Y+
Touch
Z1-Position
X– Y–
X+ Y+
Touch
Z2-Position
X– Y–
Measure Z2-Position
FIGURE 8. Pressure Measurement Block Diagrams.
DIGITAL INTERFACE
Figure 9 shows the typical operation of the ADS7846’s digital
interface. This diagram assumes that the source of the digital
signals is a microcontroller or digital signal processor with a
basic serial interface. Each communication between the proces-
sor and the converter, such as SPI/SSI or micro-wire synchro-
CS
DCLK
DIN
BUSY
tACQ
18
S A2
(START)
A1
A0
MODE
SER/
DFR
PD1 PD0
Idle Acquire
1
81
Conversion
8
Idle
DOUT
DRIVERS 1 AND 2(1)
(SER/DFR HIGH)
DRIVERS 1 AND 2(1, 2)
(SER/DFR LOW)
OFF
OFF
11 10 9 8 7 6 5
(MSB)
4
3210
Zero Filled...
(LSB)
ON OFF
ON OFF
NOTES: (1) For Y-Position, Driver 1 is ON, X+ is selected, and Driver 2 is OFF. For X-Position, Driver 1 is OFF, Y+ is selected, and
Driver 2 is ON. Y– will turn ON when power-down mode is entered and PD1, PD0 = 00B. (2) Drivers will remain ON if power-down
mode is 11B (no power down) until selected input channel, reference mode, or power-down mode is changed, or CS is HIGH.
FIGURE 9. Conversion Timing, 24-Clocks per Conversion, 8-bit Bus Interface. No DCLK delay required with dedicated
serial port.
®
ADS7846
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