AD7879ACPZ-RL Analog Devices Inc, AD7879ACPZ-RL Datasheet
AD7879ACPZ-RL
Specifications of AD7879ACPZ-RL
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AD7879ACPZ-RL Summary of contents
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FEATURES 4-wire touch screen interface 1 3.6 V operation Median and averaging filter to reduce noise Automatic conversion sequencer and timer User-programmable conversion parameters Auxiliary analog input/battery monitor (0 optional GPIO Interrupt outputs ...
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AD7879 TABLE OF CONTENTS Features .............................................................................................. 1 Applications ....................................................................................... 1 Functional Block Diagram .............................................................. 1 General Description ......................................................................... 1 Revision History ............................................................................... 2 Specifications ..................................................................................... 3 SPI Timing Specifications (AD7879) ......................................... Timing Specifications (AD7879-1) ..................................... 5 ...
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SPECIFICATIONS −40°C to +85°C, unless otherwise noted Table 1. Parameter DC ACCURACY Resolution No Missing Codes 1 Integral Nonlinearity (INL) 1 Differential Nonlinearity (DNL) Negative DNL Positive DNL 2 ...
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AD7879 SPI TIMING SPECIFICATIONS (AD7879 −40°C to +85° 1 3.6 V, unless otherwise noted. Sample tested at 25°C to ensure compliance. All input signals are A CC specified with ...
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I C TIMING SPECIFICATIONS (AD7879- −40°C to +85° 1 3.6 V, unless otherwise noted. Sample tested at 25°C to ensure compliance. All input signals are A CC timed from a voltage level of ...
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AD7879 ABSOLUTE MAXIMUM RATINGS T = 25°C, unless otherwise specified. A Table 4. Parameter V to GND CC Analog Input Voltage to GND AUX/VBAT to GND Digital Input Voltage to GND Digital Output Voltage to GND Input Current to Any ...
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PIN CONFIGURATION AND FUNCTION DESCRIPTIONS BALL A1 INDICATOR AUX/ VBAT/ GPIO V /REF PENIRQ INT/DAV B DOUT DIN X– C SCL Y– GND D TOP VIEW (BALL SIDE DOWN) Not to Scale ...
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AD7879 TYPICAL PERFORMANCE CHARACTERISTICS T = 25° 2 125 kHz SAMPLE 475 470 465 460 455 450 445 440 435 430 425 –40 –25 – TEMPERATURE (°C) Figure 9. ...
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CODE Figure 15. ADC DNL Plot X– TO GND Y– ...
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AD7879 1400 1200 1000 800 600 400 200 0 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6 V (V) CC Figure 19. Temperature Code vs SNR = 61.58dB THD = 72.34dB ...
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TERMINOLOGY Integral Nonlinearity (INL) INL 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 at 1 LSB below the first code transition ...
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AD7879 THEORY OF OPERATION The AD7879 is a complete, 12-bit data acquisition system for digitizing positional inputs from a 4-wire resistive touch screen. To support this function, data acquisition on the AD7879 is highly programmable ensure accurate ...
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Figure 23 shows an equivalent circuit of the analog input structure of the AD7879, showing the touch screen switches, the main analog multiplexer, the ADC, and the dual 3-to-1 multiplexer that selects the reference source for the ADC ...
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AD7879 TOUCH-PRESSURE MEASUREMENT The pressure applied to the touch screen by a pen or finger can also be measured with the AD7879, using some simple calculations. The contact resistance between the X and Y plates is measured providing a good ...
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Temperature Calculations If an explicit temperature reading in degrees Celsius is required, calculate for the single measurement method by 1. Calculate the scale factor of the ADC in degrees per LSB Degrees per LSB = ADC LSB size/−2 ...
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AD7879 MEDIAN AND AVERAGING FILTERS As explained in the Touch Screen Principles section, touch screens are composed of two resistive layers, normally placed over an LCD screen. Because these layers are in close proximity to the LCD screen, noise can ...
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AUX/VBAT/GPIO PIN Pin 1A (AUX/VBAT/GPIO) on the AD7879 can be programmed as either an auxiliary input to the ADC battery monitoring input general-purpose digital input/output. To select the auxiliary measurement, set the ADC channel address ...
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AD7879 GPIO Interrupt Enable (Bit 12, Control Register 3, Address 0x03) The GPIO pin can operate as an interrupt source to trigger the INT output. This is controlled by Bit 12 in Control Register 3. If the GPIO ALERT interrupt ...
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REGISTER MAP Table 9. Register Table 1 Address Name Description 0x00 Unused Unused 0x01 Control Register 1 PENIRQ enable, channel selection for manual selection, ADC mode, acquisition time, and conversion timer 0x02 Control Register 2 ADC power management, GPIO control, ...
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AD7879 DETAILED REGISTER DESCRIPTIONS All addresses and default values are expressed in hexadecimal. Table 10. Control Register 1 Data Address Name Bit Description 0x01 Disable PENIRQ 15 Pen interrupt enable PENIRQ pin is enabled PENIRQ is ...
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Table 11. Control Register 2 Data Address Name Bit Description 0x02 PM[1:0] 15:14 ADC power management full shutdown, the ADC, oscillator, BIAS, and temperature sensor are all powered down analog blocks to be powered down depend ...
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AD7879 Table 12. Control Register 3 Data Address Name Bit Description 0x03 TEMP MASK 15 TEMP mask bit 0 = temperature measurement is allowed to cause interrupt 1 = temperature measurement is not allowed to cause interrupt AUX/VBAT 14 AUX/VBAT ...
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Table 14. Measurement Result Registers Address Data Bit Description 0x08 15:0 Measured X+ input with Y excitation (Y position) 0x09 15:0 Measured Y+ input with X excitation (X position) 0x0A 15:0 Measured X+ input with X− and Y+ excitation (touch-pressure ...
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AD7879 CONTROL REGISTERS 15 DIS CHNL CHNL PENIRQ ADD2 ADD1 CONTROL REGISTER 1 Control Register 1 (Address 0x01) contains the ADC channel address and the ADC mode bits. It sets the acquisition time and the timer. It also contains a ...
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ADC Channel (Control Register 1 Bits[14:12]) The ADC channel is selected by Bits[14:12] of Control Register 1 (CHNL ADD2 to CHNL ADD0). A complete list of channel addresses is given in Table 19. For Mode 0 (single-channel) conversion, the channel ...
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AD7879 15 GPIO PM1 PM0 EN CONTROL REGISTER 2 Control Register 2 (Address 0x02) contains the power management bits, the GPIO settings, the SER/ DFR bit (to choose single or differential methods of touch screen measurement), the averaging and median ...
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AUX/ TEMP INT VBAT MASK MODE MASK CONTROL REGISTER 3 Control Register 3 (Address 0x03) includes the interrupt register (Bits[15:8]) and Control Register 3 (Bits[7:0]). Sequencer The sequencer bits control which channels are converted during a conversion sequence in ...
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AD7879 START OF CONVERSION SET CHANNEL SEQUENCE YES REQ’D? START FCD TIMER WAIT FOR FCD CONV_START = 1 START ACQUIST TIMER AND WAIT FOR ACQUISITION CONV_START = 0 COMPARE NEW CONVERT: WAIT FOR READING DATA_READY SHIFT YES READINGS MAV FILTER ...
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When the screen is touched, PENIRQ goes low. This generates an interrupt request to the host. When the screen touch ends, and if the ADC is idle, PENIRQ immediately goes high. If the ADC is converting, PENIRQ goes high when ...
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AD7879 SERIAL INTERFACE The AD7879 is available with an serial peripheral interface (SPI). The AD7879-1 is available with an I interface. Both parts are the same, with the exception of the serial interface recommended not to write to ...
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COMMAND WORD ENABLE WORD R DIN SCL NOTES 1. MULTIPLE SEQUENTIAL REGISTERS CAN BE LOADED ...
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AD7879 16-BIT COMMAND WORD ENABLE WORD R DIN SCL DOUT XXX XXX XXX XXX XXX XXX XXX XXX ...
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START AD7879 DEVICE ADDRESS SDA DEV DEV DEV DEV DEV SCL REGISTER DATA[D15:D8] D15 D14 ACK NOTES 1. A START CONDITION AT ...
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AD7879 START AD7879-1 DEVICE ADDRESS SDA DEV DEV DEV SCL 1 2 AD7879-1 DEVICE ADDRESS SR DEV DEV A6 A5 USING REPEATED START AD7879-1 DEVICE ADDRESS P S DEV DEV A6 A5 ...
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GROUNDING AND LAYOUT For detailed information on grounding and layout considera- tions for the AD7879, refer to the AN-577 Application Note, Layout and Grounding Recommendations for Touch Screen Digitizers. CHIP SCALE PACKAGES The lands on the chip scale package (CP-16-10) ...
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... SEATING PLANE ORDERING GUIDE Model Temperature Range AD7879ACBZ-RL 1 −40°C to +85°C 1 AD7879ACBZ-500R7 −40°C to +85°C AD7879ACPZ-RL 1 −40°C to +85°C 1 AD7879ACPZ-500R7 −40°C to +85°C 1 AD7879-1ACBZ-RL −40°C to +85°C 1 AD7879-1ACBZ-500R7 −40°C to +85°C 1 AD7879-1ACPZ-RL − ...