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PDF ADS7846 Data sheet ( Hoja de datos )
| Número de pieza | ADS7846 | |
| Descripción | TOUCH-SCREEN CONTROLLER | |
| Fabricantes | Burr-Brown Corporation | |
| Logotipo |  |
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® 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
®
1 page  
TYPICAL PERFORMANCE CURVES
At TA = +25°C, +VCC = +2.7V, VREF = External +2.5V, fSAMPLE = 125kHz, and fCLK = 16 • fSAMPLE = 2MHz, unless otherwise noted.
SUPPLY CURRENT vs TEMPERATURE
400
350
300
250
200
150
100
–40
–20
0 20 40 60
Temperature (˚C)
80 100
POWER DOWN SUPPLY CURRENT
vs TEMPERATURE
140
120
100
80
60
40
20
–40
–20
0 20 40 60
Temperature (˚C)
80 100
SUPPLY CURRENT vs +VCC
390
370
fSAMPLE = 12.5kHz
350
330
310
290
270
250
2
2.5
3 3.5 4
+VCC (V)
4.5
5
MAXIMUM SAMPLE RATE vs +VCC
1M
100k
10k
1k
2 2.5 3 3.5 4 4.5 5
+VCC (V)
CHANGE IN GAIN vs TEMPERATURE
0.15
0.10
0.05
0.00
–0.05
–0.10
–0.15
–40
–20
0 20 40 60
Temperature (˚C)
80 100
CHANGE IN OFFSET vs TEMPERATURE
0.6
0.4
0.2
0.0
–0.2
–0.4
–0.6
–40
–20
0 20 40 60
Temperature (˚C)
80 100
®
5 ADS7846
5 Page 
ADS7846; see Figure 9). This will work for both the single-
ended and the differential modes. Option 2 is to operate the
ADS7846 in the differential mode only for the touch-screen,
and command the ADS7846 to remain ON (touch-screen
drivers ON) and not go into power-down (PD0 = PD1 = 1).
Several conversions will be required depending on the
settling time required and ADS7846 data rate. Once the
required number of conversions have been made, the proces-
sor will command the ADS7846 into its power-down state
on the last measurement. This process would be required for
X-position, Y-position, and Z-position. Option 3 is to oper-
ate in the 15-Clock per Conversion mode which overlaps
ADCs and maintains the touch-screen drivers ON until it is
commanded to stop by the processor.
TEMPERATURE MEASUREMENT
In some applications, such as battery recharging, a measure-
ment of ambient temperature is required. The temperature
measurement technique used in the ADS7846 relies on the
characteristics of a semiconductor junction operation at a
fixed current level. The forward diode voltage (VBE) has a
well-defined characteristic versus temperature. The ambient
temperature can be predicted in applications by knowing the
25°C value of the VBE voltage and then monitoring the delta
of that voltage as the temperature changes. The ADS7846
offers two modes of operation. The first mode requires
calibration at a known temperature, but only requires a
single reading to predict the ambient temperature. The
PENIRQ diode is used (turned ON) during this measurement
cycle and the voltage across the diode is connected through
the MUX for digitizing the forward bias voltage by the ADC
with an address of A2 = 0, A1 = 0, and A0 = 0 (see Table I
and Figure 6 for details). This voltage is typically 600mV at
+25°C, with a 20µA current through it. The absolute value
of this diode voltage can vary a few millivolts, however, the
TC of this voltage is very consistent at –2.1mV/°C. During
the final test of the end product, the diode voltage would be
stored at a known room temperature, in memory, for calibra-
tion purposes by the user. The result is an equivalent tem-
perature measurement resolution of 0.3°C/LSB.
VCC
PENIRQ
External
Pull-Up
X+
MUX
A/D
Converter
TEMP 0 TEMP 1
Temperature Select
The second mode does not require a test temperature
calibration, but uses a two-measurement method to elimi-
nate the need for absolute temperature calibration and for
achieving 2°C/LSB accuracy. This mode requires a second
conversion with an address of A2 = 1, A1 = 1, and A0 = 1,
with an 82 times larger current. The voltage difference
between the first and second conversion using 82 times the
bias current will be represented by kT/q • 1n (N),
where N is the current ratio = 82, k = Boltzmann’s constant
(1.38054 • 10–23 electrons volts/degrees Kelvin), q = the
electron charge (1.602189 • 10–19 °C), and T = the tem-
perature in degrees Kelvin. This method can provide much
improved absolute temperature measurement, but less reso-
lution of 2°C/LSB. The resultant equation for solving for
°K is:
°K = q • ∆V/(k • 1n (N))
(1)
where,
∆V = V (I82) – V (I1) (in mV)
∴ °K = 2.68 ∆V °K/mV
°C = 2.63 • ∆V(mV) – 273°K
NOTE: The bias current for each diode temperature mea-
surement is only turned ON for 3 clock cycles (during the
acquisition mode) and, therefore, does not add any notice-
able increase in power, especially if the temperature mea-
surement only occurs occasionally.
BATTERY MEASUREMENT
An added feature of the ADS7846 is the ability to monitor
the battery voltage on the other side of the voltage regulator
(DC/DC converter), as shown in Figure 7. The battery
voltage can vary from 0.5V to 6V, while maintaining the
voltage to the ADS7846 at 2.7V, 3.3V, etc. The input
voltage (VBAT) is divided down by 4 so that a 6.0V battery
voltage is represented as 1.5V to the ADC. This simplifies
Battery
0.5V +
to
6.0V
DC/DC
Converter
2.7V
VCC
VBAT
0.125V to 1.5V
7.5kΩ
2.5kΩ
FIGURE 6. Functional Block Diagram of Temperature
Measurement Mode.
FIGURE 7. Battery Measurement Functional Block Diagram.
®
11 ADS7846
11 Page | ||
| Páginas | Total 17 Páginas | |
| PDF Descargar | [ Datasheet ADS7846.PDF ] | |
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