AD7873 Fast Delivery |IC PHOENIX CO.,LIMITED

AD7873 ,Touch Screen Digitizer with Direct Battery and Touch-Pressure MeasurementSPECIFICATIONS +85C, unless otherwise noted.)1 1Parameter AD7873A AD7873B Unit Test Conditions/Com ..
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AD7873
Touch Screen Digitizer with Direct Battery and Touch-Pressure Measurement
REV.B
FUNCTIONAL BLOCK DIAGRAM
FEATURES
4-Wire Touch Screen Interface
On-Chip Temperature Sensor: –40�C to +85�C
On-Chip 2.5 V Reference
Direct Battery Measurement (0 V to 6 V)
Touch-Pressure Measurement
Specified Throughput Rate of 125 kSPS
Single Supply, VCC of 2.2V to 5.25 V
Ratiometric Conversion
High-Speed Serial Interface
Programmable 8- or 12-Bit Resolution
One Auxiliary Analog Input
Shutdown Mode: 1 �A Max
16-Lead QSOP, TSSOP, and LFCSP Packages
APPLICATIONS
Personal Digital Assistants
Smart Hand-Held Devices
Touch Screen Monitors
Point-of-Sale Terminals
Pagers
GENERAL DESCRIPTION
The AD7873 is a 12-bit successive-approximation ADC with a
synchronous serial interface and low on resistance switches for
driving touch screens. The AD7873 operates from a single 2.2V
to 5.25 V power supply and features throughput rates greater
than 125 kSPS.
The AD7873 features direct battery measurement, temperature
measurement, and touch-pressure measurement. The AD7873
also has an on-board reference of 2.5 V which can be used for
the auxiliary input, battery monitor, and temperature measure-
ment modes. When not in use, the internal reference can be
shut down to conserve power. An external reference can also be
applied and can be varied from 1 V to VCC, while the analog
input range is from 0 V to VREF. The device includes a shutdown
mode that reduces the current consumption to less than 1µA.
The AD7873 features on-board switches. This, coupled with low
power and high-speed operation, makes the device ideal for
battery-powered systems such as personal digital assistants with
resistive touch screens and other portable equipment. The part is
available in a 16-lead 0.15" Quarter Size Outline (QSOP) pack-
age, a 16-lead Thin Shrink Small Outline (TSSOP) package, and
a 16-lead Lead Frame Chip Scale (LFCSP) package.
Touch Screen Digitizer
PRODUCT HIGHLIGHTSRatiometric conversion mode available, eliminating errors
due to on-board switch resistancesOn-board temperature sensor: –40°C to +85°CBattery monitor inputTouch-pressure measurement capabilityLow power consumption of 1.37 mW max with the reference
off, or 2.41 mW typ with the reference on, at 125 kSPS and
VCC at 3.6 V.Package options include 4 mm � 4 mm LFCSP.Analog input range from 0 V to VREFVersatile serial I/O port
AD7873–SPECIFICATIONS
(+VCC = 2.7 V to 3.6 V, VREF = 2.5 V internal or external, fDCLK = 2 MHz; TA = –40�C to
+85�C, unless otherwise noted.)
AD7873
NOTESTemperature range as follows: A, B Versions: –40°C to +85°C.See Terminology.Difference between Temp0 and Temp1 measurement. No calibration necessary.Temperature Drift is –2.1 mV/°C.Sample tested @ 25°C to ensure compliance.See Power vs. Throughput Rate section.
Specifications subject to change without notice.
TIMING SPECIFICATIONS1
NOTESSample tested at 25°C to ensure compliance. All input signals are specified with tr = tf = 5 ns (10% to 90% of VCC) and timed from a voltage level of 1.6 V.Mark/Space ratio for the DCLK input is 40/60 to 60/40.Measured with the load circuit of Figure 1 and defined as the time required for the output to cross 0.4 V or 2.0 V.t12 is derived from the measured time taken by the data outputs to change 0.5 V when loaded with the circuit of Figure 1. The measured number is then extrapolated
back to remove the effects of charging or discharging the 50 pF capacitor. This means that the time, t12, quoted in the timing characteristics is the true bus relinquish
time of the part and is independent of the bus loading.
Specifications subject to change without notice.
(TA = TMIN to TMAX, unless otherwise noted; VCC = 2.7 V to 5.25 V, VREF = 2.5 V.)
AD7873
ORDERING GUIDE
NOTESLinearity error here refers to integral linearity error.RQ = QSOP = 0.15" Quarter Size Outline Package; RU = TSSOP.This can be used as a standalone evaluation board or in conjunction with the Evaluation Board Controller for evaluation/demonstration purposes.This Evaluation Board Controller is a complete unit allowing a PC to control and communicate with all Analog Devices evaluation boards ending in the CB designators.Contact factory for availability.
ABSOLUTE MAXIMUM RATINGS1
(TA = 25°C unless otherwise noted.)
+VCC to GND . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +7 V
Analog Input Voltage to GND . . . . . . . .–0.3 V to VCC + 0.3 V
Digital Input Voltage to GND . . . . . . . . –0.3 V to VCC + 0.3 V
Digital Output Voltage to GND . . . . . . –0.3 V to VCC + 0.3 V
VREF to GND . . . . . . . . . . . . . . . . . . . . . –0.3 V to VCC + 0.3 V
Input Current to Any Pin Except Supplies2 . . . . . . . . . ±10 mA
Operating Temperature Range
Commercial (A, B Version) . . . . . . . . . . . . –40°C to +85°C
Storage Temperature Range . . . . . . . . . . . –65°C to +150°C
Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . 150°C
QSOP, TSSOP, LFCSP Package, Power Dissipation . . 450 mW
θJA Thermal Impedance . . . . . . . . . . . 149.97°C/W (QSOP)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150.4°C/W (TSSOP)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135.7°C/W (LFCSP)
θJC Thermal Impedance . . . . . . . . . . . . . 38.8°C/W (QSOP)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27.6°C/W (TSSOP)
Lead Temperature, Soldering
Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . . . . 215°C
Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220°C
NOTESStresses above those listed under Absolute Maximum Ratings may cause perma-
nent damage to the device. This is a stress rating only; functional operation of the
device at these or any other conditions above those listed in the operational
sections of this specification is not implied. Exposure to absolute maximum rating
conditions for extended periods may affect device reliability.Transient currents of up to 100 mA will not cause SCR latchup.
Figure 1.Load Circuit for Digital Output Timing
Specifications
PIN CONFIGURATIONS
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000V readily
LFCSP
DOUTBUSY
DIN
VBATGNDY
PIN 1
INDICATOR
TOP VIEW
(Not to Scale)
AD7873
AUX 1
VREF 2
+VCC 3
PENIRQ 4
QSOP, TSSOP
PIN FUNCTION DESCRIPTIONS
TERMINOLOGY
Integral Nonlinearity
This is the maximum deviation from a straight line passing
through the endpoints of the ADC transfer function. The end-
points of the transfer function are zero scale, a point 1 LSB
below the first code transition, and full scale, a point 1 LSB
above the last code transition.
Differential Nonlinearity
This is the difference between the measured and the ideal 1LSB
change between any two adjacent codes in the ADC.
Offset Error
This is the deviation of the first code transition (00 . . . 000) to
(00 . . . 001) from the ideal, i.e., AGND + 1LSB.
Gain Error
This is the deviation of the last code transition (111 . . . 110) to
(111 . . . 111) from the ideal (i.e., VREF – 1 LSB) after the offset
error has been adjusted out.
Track/Hold Acquisition Time
The track/hold amplifier enters the acquisition phase on the fifth
falling edge of DCLK after the START bit has been detected.
Three DCLK cycles are allowed for the Track/Hold acquisition
time and the input signal will be fully acquired to the 12-bit
level within this time even with the maximum specified DCLK
frequency. See Analog Input section for more details.
On Resistance
This is a measure of the ohmic resistance between the drain and
source of the switch drivers.
TEMPERATURE – �C
SUPPLY CURRENT
198806040200–20–40
TPC 1.Supply Current vs. Temperature
+VCC – V
SUPPLY CURRENT
200
TPC 2.Supply Current vs. +VCC
TEMPERATURE – �C
DELTA FROM +25
�C
LSB
0.05
TPC 3.Change in Gain vs. Temperature
AD7873–Typical Performance Characteristics
TEMPERATURE – �C
SUPPLY CURRENT
nA
139
TPC 4.Power-Down Supply Current vs. Temperature
TPC 5.Maximum Sample Rate vs. +VCC
TEMPERATURE – �C
DELTA FROM +25
�C
LSB
0.2
TPC 6.Change in Offset vs. Temperature
SAMPLE RATE – kHz
REFERENCE CURRENT
100
TPC 7.Reference Current vs. Sample Rate
+VCC – V
5.0
TPC 8.Switch On Resistance vs. +VCC
(X+, Y+: +VCC to Pin; X–, Y–: Pin to GND)
SAMPLING RATE – kSPS
ERROR
LSB
1.8
TPC 9.Maximum Sampling Rate vs. RIN
TPC 10.Reference Current vs. Temperature
TPC 11.Switch On Resistance vs. Temperature
(X+, Y+: +VCC to Pin; X–, Y–: Pin to GND)

TPC 12.Internal VREF vs. Temperature
AD7873
TPC 16.Internal VREF vs. Turn-on Time
VSUPPLY – V
TEMP0 DIODE VOLTAGE
mV
2.72.83.62.93.03.13.23.33.43.5
TPC 17.Temp0 Diode Voltage vs. VSUPPLY (25°C)
FREQUENCY – kHz
SNR
dB
37.5
TPC 18.Auxiliary Channel Dynamic Performance
+VCC – V
REF
2.504
TPC 13.Internal VREF vs. +VCC
TPC 14.Temp Diode Voltage vs. Temperature
(2.7 V Supply)
VSUPPLY – V
TEMP1 DIODE VOLTAGE
mV
730
TPC 15.Temp1 Diode Voltage vs. VSUPPLY (25°C)
VDD RIPPLE FREQUENCY – kHz10
PSRR
dB
–12030405060708090100
TPC 19.AC PSRR vs. Supply Ripple Frequency
TPC 18 shows a typical FFT plot for the auxiliary channels of the
AD7873 at 125 kHz sample rate and 15 kHz input frequency.
TPC 19 shows the power supply rejection ratio versus VDD
supply frequency for the AD7873. The power supply rejection
ratio is defined as the ratio of the power in the ADC output at
full-scale frequency f, to the power of a 100 mV sine wave applied
to the ADC VCC supply of frequency fS:
PSRR (dB) = 10 log (Pf/Pfs)
Pf = Power at frequency f in ADC output, Pfs = power at fre-
quency fS coupled onto the ADC VCC supply. Here a 100 mV
peak-to-peak sine wave is coupled onto the VCC supply. Decoupling
capacitors of 10 µF and 0.1 µF were used on the supply.
CIRCUIT INFORMATION
The AD7873 is a fast, low-power, 12-bit, single-supply A/D
converter. The AD7873 can be operated from a 2.2 V to 5.25 V
supply. When operated from either a 5 V supply or a 3 V supply,
the AD7873 is capable of throughput rates of 125 kSPS when
provided with a 2 MHz clock.
The AD7873 provides the user with an on-chip track/hold,
multiplexer, A/D converter, reference, temperature sensor, and
serial interface housed in a tiny 16-lead QSOP, TSSOP, or
LFCSP package, which offers the user considerable space-sav-
ing advantages over alternative solutions. The serial clock input
(DCLK) accesses data from the part but also provides the clock
source for the successive-approximation A/D converter. The
analog input range is 0 V to VREF (where the externally applied
VREF can be between 1 V and +VCC). The AD7873 has a 2.5 V
reference on board with this reference voltage available for
use externally if buffered.
The analog input to the ADC is provided via an on-chip multi-
plexer. This analog input may be any one of the X, Y, and Z
panel coordinates, battery voltage, or chip temperature. The
multiplexer is configured with low-resistance switches that
allow an unselected ADC input channel to provide power and
an accompanying pin to provide ground for an external device.
For some measurements the on resistance of the switches may
present a source of error. However, with a differential input to
the converter and a differential reference architecture this error
can be negated.
ADC TRANSFER FUNCTION
The output coding of the AD7873 is straight binary. The designed
code transitions occur at successive integer LSB values (i.e.,LSB, 2LSBs, etc.). The LSB size is = VREF/4096. The ideal
transfer characteristic for the AD7873 is shown in Figure 2.
ADC CODE
ANALOG INPUT
1LSB+VREF – 1LSB
Figure 2.Transfer Characteristic
TYPICAL CONNECTION DIAGRAM
Figure 3 shows a typical connection diagram for the AD7873 in
a touch screen control application. The AD7873 features an
internal reference but this can be overdriven with an external
low impedance source between 1 V and +VCC. The value of the
reference voltage will set the input range of the converter. The
conversion result is output MSB first, followed by the remaining
11 bits and three trailing zeroes, depending on the number of
clocks used per conversion (see the Serial Interface section). For
applications where power consumption is of concern, the power
management option should be used to improve power perfor-
mance. See Table III for available power management options.
AD7873
Table I.Analog Input, Reference, and Touch Screen Control
*Internal node, not directly accessible by the user.
ANALOG INPUT
Figure 4 shows an equivalent circuit of the analog input struc-
ture of the AD7873 that contains a block diagram of the input
multiplexer, the differential input of the A/D converter, and the
differential reference.
Table I shows the multiplexer address corresponding to each
analog input, both for the SER/DFR bit in the control register
set high and low. The control bits are provided serially to the
device via the DIN pin. For more information on the control
register, see the Control Register section.
When the converter enters the hold mode, the voltage difference
between the +IN and –IN inputs (see Figure 4) is captured on
the internal capacitor array. The input current on the analog
inputs depends on the conversion rate of the device. During the
sample period, the source must charge the internal sampling
capacitor (typically 37 pF). Once the capacitor has been fully
charged, there is no further input current. The rate of charge
transfer from the analog source to the converter is a function of
conversion rate.
Figure 4.Equivalent Analog Input Circuit

Partno	Mfg	Dc	Qty	Available	Descript
AD7873	AD	N/a	12774	avai	Touch Screen Digitizer with Direct Battery and Touch-Pressure Measurement