AD7877 Analog Devices, AD7877 Datasheet
AD7877
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AD7877 Summary of contents
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... The AD7877 features direct battery measurement on two inputs, temperature and touch-pressure measurement. The AD7877 also has an on-board reference of 2.5 V. When not in use, it can be shut down to conserve power. An external reference can also be applied and varied from analog input range ...
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... A to Rev. B Added Wafer Level Chip Scale Package ........................... Universal Changes to Table 3 ............................................................................ 6 Control Registers ............................................................................ 20 Control Register 1 ...................................................................... 20 Control Register 2 ...................................................................... 21 Sequencer Registers ................................................................... 22 Interrupts ..................................................................................... 24 Syncronizing the AD7877 to the Host CPU ........................... 25 8-Bit DAC ........................................................................................ 26 Serial Interface ................................................................................ 28 Writing Data ............................................................................... 28 Write Timing ............................................................................... 29 Reading Data ............................................................................... 29 V Pin ..................................................................................... 29 DRIVE General-Purpose I/O Pins ...
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... Calibrated at 25° REF 14 kΩ Sampling, 1 GΩ when the battery monitor is off 1 3.2 % External/internal reference, see Figure 26 Rev Page AD7877 REF ; typically 25 Ω when the on-board CC = 2.5 V ...
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... AD7877 Parameter Min DAC Resolution Integral Nonlinearity Differential Nonlinearity Voltage Mode Output Voltage Range Slew Rate Output Settling Time Capacitive Load Stability Output Impedance Short-Circuit Current Current Mode Output Current Range 0 Output Impedance LOGIC INPUTS Input High Voltage, V 0.7 V INH Input Low Voltage, V ...
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... MSB Figure 2. Detailed Timing Diagram 200µ OUTPUT PIN C L 50pF 200µ Figure 3. Load Circuit for Digital Output Timing Specifications Rev Page quoted in the timing characteristics is the true bus LSB t 8 LSB 1.6V AD7877 ...
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... AD7877 ABSOLUTE MAXIMUM RATINGS T = 25°C, unless otherwise noted. A Table 3. Parameter V to GND CC Analog Input Voltage to GND Digital Input Voltage to GND Digital Output Voltage to GND V to GND REF V to GND BAT Input Current to Any Pin Except Supplies ESD Rating (IEC 1000-4-2, Air Discharge) Tablet Pins (X+, X− ...
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... Chip Select Input. Active low logic input. This input provides the dual function of initiating conversions on the AD7877 and enabling the serial input/output register. 19 DIN SPI® Serial Data Input. Data to be written to the AD7877 registers are provided on this input and clocked into the register on the rising edge of DCLK. 20 STOPACQ Stop Acquisition Pin ...
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... Analog Output Voltage or Current from DAC Reference Output for the AD7877. The internal 2.5 V reference is available on this pin for use external to the REF device. The reference output must be buffered before it is applied elsewhere in a system. To reduce system noise effects strongly recommended to place a capacitor of 100 nF between the V Alternatively, an external reference can be applied to this input ...
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... Figure 9. Full Power-Down I vs. Temperature DD 0.6 0.5 0.4 0.3 0.2 0.1 0 –0.1 –0.2 –0.3 –0.4 –0.5 –0.6 –50 –30 – TEMPERATURE (°C) Figure 10. Change in ADC Offset vs. Temperature 1.0 0.8 0.6 0.4 0.2 0 –0.2 –0.4 –0.6 –0.8 –1.0 0 500 1000 1500 2000 2500 3000 CODE Figure 11. ACD INL Plot AD7877 3500 4000 ...
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... AD7877 1.0 0.8 0.6 0.4 0.2 0 –0.2 –0.4 –0.6 –0.8 –1.0 0 500 1000 1500 2000 2500 CODE Figure 12. ADC DNL Plot 2.7 3.1 3.5 3.9 4.3 V (V) CC Figure 13. Switch On Resistance vs. V (X+, Y Pin; X−, Y−: Pin to GND X– TO GND 18 16 ...
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... V (V) CC Figure 20. Temp0 vs 3.3 3.4 3.5 3.6 Figure 22. Typical FFT Plot for the Auxiliary Channels of the AD7877 CC 3.3 3.4 3.5 3.6 CC Rev Page CAP 0.711µs SETTLING TIME 2.5 100nF CAP 54.64µs SETTLING TIME 0 – TURN-ON TIME (µs) Figure 21 ...
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... AD7877 TEMPERATURE = 25°C 1 CH1 200mV CH2 100mV M2.00µs Figure 24. DAC Output Settling Time (Zero Scale to Half Scale) 600 500 400 DAC SINK CURRENT 300 200 100 NOTE: MAXIMUM DAC SINK CURRENT IS SET ACCORDING TO THE EQUATION /(R × 6) MAX CC RNG ...
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... The deviation of the last code transition (111…110) to (111…111) from the ideal (V error has been adjusted out. On Resistance A measure of the ohmic resistance between the drain and the source of the switch drivers. Rev Page AD7877 − 1 LSB) after the offset REF ...
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... DAC to control LCD contrast. The high speed SPI serial bus provides control of, and communication with, the device. Operating from a single supply from 2 the AD7877 offers throughput rates 125 kHz. The device is available × 5 mm, 32-lead, lead frame chip scale package (LFCSP), and in a 2.5 mm × ...
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... BAT2 TEMPERATURE SENSOR Figure 28. Analog Input Structure The AD7877 can be set up to automatically convert either specific input channels or a sequence of channels. The results of the ADC conversions are stored in the results registers. See the Serial Interface section for details. When measuring the ancillary analog inputs (AUX1 to AUX3, ...
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... ADC. TOUCH-PRESSURE MEASUREMENT The pressure applied to the touch screen via a pen or finger can also be measured with the AD7877 using some simple calcula- tions. The contact resistance between the X and Y plates is measured providing a good indication of the size of the depressed area and, therefore, the applied pressure ...
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... BE where: V represents the diode voltage the bias current multiple (typical value for AD7877 = 120 Boltzmann’s constant the electron charge. This method provides a resolution of approximately 1.6°C, and a guaranteed accuracy of ±4°C without calibration. Determina- tion of the N value on a part-by-part basis improves accuracy. ...
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... 0.136 × 2490 − 273 = 65°C BATTERY MEASUREMENT The AD7877 can monitor battery voltages from 0 two inputs, BAT1 and BAT2. Figure 34 shows a block diagram of a battery voltage monitored through the BAT1 pin. The voltage to the V desired supply voltage via the dc/dc regulator while the input to the regulator is monitored ...
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... Data Sheet AUXILIARY INPUTS The AD7877 has three auxiliary analog inputs, AUX1 to AUX3. These channels have a full-scale input range from The ADC channel addresses for AUX1 to AUX3 are 0011b, 0100b, and 0101b, and the results are stored in Register 10011b, Register 10100b, and Register 10101b ...
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... The ADC then digitizes the selected channels, and the results are written to the results registers. The AD7877 waits for the screen to be touched again, or for a timer event if the screen remains touched, before beginning another sequence of conversions. ...
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... V. Below this value, use an external reference. If the REF bit is 1, the V internal reference is powered down. This overrides any setting of the PM bits with regard to the reference. An external reference can then be applied to the REF pin. Rev Page AD7877 Y Switches +REF −REF On Y+ Y− ...
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... ADC performs 16 averages per channel SEQUENCER REGISTERS There are two sequencer registers on the AD7877. Sequencer Register 0 controls the measurements performed during a slave mode sequence. Sequencer Register 1 controls the measure- ments performed during a master mode sequence. To include a measurement in a slave mode or master mode sequence, the relevant bit must be set in Sequencer Register 0 or Sequencer Register 1 ...
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... Data Sheet HOST PROGRAMS AD7877 IN MODE 01 IS FCD REQUIRED? YES START FCD TIMER IS FCD FINISHED? YES YES IS STOPACQ SIGNAL ACTIVE? NO START ACQUISITION TIMER IS STOPACQ YES SIGNAL ACTIVE ACQUISITION TIME FINISHED? YES CONVERT SELECTED CHANNEL IS AVERAGING FINISHED? YES WRITE RESULT TO REGISTERS ...
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... CS DAV AD7877 STATUS DAV is useful as a host interrupt in master mode. In this mode, the host can program the AD7877 to automatically perform a sequence of conversions, and can be interrupted by DAV at the NO end of each conversion sequence. When the on-board timer is programmed to perform automatic conversions, a limited time is available to the host to read the results registers before another sequence of conversions begins ...
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... In master mode, DAV can also be used as an interrupt to the host. However, the host should first initialize the AD7877 in Mode 11b. The host can then go into sleep mode to conserve power. The wake-up on touch feature of the AD7877 is active in this mode, therefore, when the screen is touched, the programmed sequence of conversions begins automatically. ...
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... AD7877 8-BIT DAC The AD7877 features an on-chip 8-bit DAC for LCD contrast control. The DAC can be configured for voltage output by clearing Bit 2 of the DAC register (Address 1110b), or for current output by setting this bit. The output voltage range can be set ...
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... The actual adjustment range using these values Rev Page /∆ (R1 × R )/(R1 − and and OUT(MIN) is 1.25 V. Allow 100 µA around the feedback loop. REF = 1.25 V/100 µA = 12.5 kΩ. P AD7877 is OUT(MAX) ...
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... A chip-select pin ( CS ) enables or disables the serial interface. WRITING DATA Data is written to the AD7877 in 16-bit words. The first four bits of the word are the register address that directs the AD7877 to the register to write to. The next 12 bits are data. How the AD7877 handles the data bits depends on the register address ...
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... Data Sheet WRITE TIMING No serial interface operations can take place when CS is high. To write to the AD7877, CS must be taken low. To write to the device, a burst of 16 clock pulses is input to DCLK while the write data is input to DIN. Data is clocked in on the rising edge of DCLK. If multiple write operations are to be performed, CS must be taken high after the end of each write operation before another write operation can be performed by taking CS low again ...
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... AD7877 GENERAL-PURPOSE I/O PINS The AD7877 has one dedicated general-purpose logic input/ output pin (GPIO4), and any or all of the three auxiliary analog inputs can also be reconfigured as GPIOs. Associated with the GPIOs are two 8-bit control registers and one 8-bit data register that are accessed using the extended write mode. ...
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... A change in the data register causes a change in the output voltage on the pin change in input voltage on the pin causes a change in the data register bit. Rev Page AD7877 ALERT Data Bit Pin Voltage ...
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... PCB. For more information on grounding and layout considerations for the AD7877, refer to the AN-577 Application Note, Layout and Grounding Recommendations for Touch Screen Digitizers. PCB DESIGN GUIDELINES FOR CHIP SCALE PACKAGES The lands on the chip scale package (CP-32) are rectangular ...
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... Description 0 GPIO Control Contains polarity, direction, enabling, and interrupt enabling Register 1 settings for GPIO1 and GPIO2 1 GPIO Control Contains polarity, direction, enabling, and interrupt enabling Register 2 settings for GPIO3 and GPIO4 2 GPIO data Contains GPIO1 to GPIO4 data Rev Page AD7877 ...
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... AD7877 Table 15. Read Register Map Register Address Binary RADD4 RADD3 RADD2 RADD1 ...
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... Battery Monitor Input 2 (BAT2) 1000 = Temperature Measurement 1 (used for single conversion) 1001 = Temperature Measurement 2 (used for differential measurement method) 1010 = X+ (Z1) input (used for touch-pressure calculation) 11 R/W Selects normal (single-ended) or ratiometric (differential) conversion SER/DFR 0 = ratiometric (differential normal (single-ended) Rev Page AD7877 ...
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... AD7877 Register Name: Control Register 2 Write Address: 0010 Read Address: 00010 Default Value: 0x000 Type: Read/write Table 17. Bit Name Read/Write Description 0 TMR0 R/W LSB of conversion interval timer 1 TMR1 R/W MSB of conversion interval timer 00 = convert only once 01 = every 1024 clock periods (512 µ every 2048 clock periods (1.024 ms every 16,384 clock periods (8 ...
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... This register contains the 12-bit low limit for Battery Monitoring Input 1. Register Name: BAT2 High Limit Write Address: 1000 Read Address: 01000 Default Value: 0x000 Type: Read/write This register contains the 12-bit high limit for Battery Monitoring Input 2. Rev Page AD7877 ...
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... AD7877 Register Name: BAT2 Low Limit Write Address: 1001 Read Address: 01001 Default Value: 0x000 Type: Read/write This register contains the 12-bit low limit for Battery Monitoring Input 2. Register Name: TEMP1 Low Limit Write Address: 1010 Read Address: 01010 Default Value: ...
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... Setting this bit includes the Z2 touch-pressure measurement (Y− input master mode sequence 10 XPOS_MS R/W Setting this bit includes measurement of the X position (Y+ input master mode sequence 11 YPOS_MS R/W Setting this bit includes measurement of the Y position (X+ input master mode sequence Rev Page AD7877 ...
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... AD7877 Register Name: DAC Register Write Address: 1110 Read Address: 01110 Default Value: 0x008 Type: Read/write Table 21. Bit Name Read/Write 0 RANGE R/W 1 Not Used R/W 2 V/I R R/W 4 DAC0 5 DAC1 6 DAC2 7 DAC3 8 DAC4 9 DAC5 10 DAC6 11 DAC7 Register Name: Y Position Write Address: N/A Read Address: 10000 ...
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... Register Name: Z1 Write Address: N/A Read Address: 11010 Default Value: 0x000 Type: Read only This register contains the 12-bit result of a measurement at the X+ input with excitation voltage applied to Y+ and X− (used for touch-pressure calculation). Rev Page AD7877 ...
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... AD7877 GPIO REGISTERS GPIO registers are written to using an extended 8-bit address. The first four bits of the data-word are always 1111b to access the extended writing map. The next four bits are the register address. This leaves 8 bits for the GPIO data. Register Name: GPIO Control Register 1 ...
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... This bit selects the function of AUX3/GPIO3 0 = AUX3 1 = GPIO3 Description This bit is not used This bit is not used This bit is not used This bit is not used GPIO4 data bit GPIO3 data bit GPIO2 data bit GPIO1 data bit Rev Page AD7877 ...
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... W = Qualified for Automotive Applications AUTOMOTIVE PRODUCTS The AD7877WACPZ models are available with controlled manufacturing to support the quality and reliability requirements of automotive applications. Note that these automotive models may have specifications that differ from the commercial models; therefore, designers should review the Specifications section of this data sheet carefully. Only the automotive grade products shown are available for use in automotive applications ...