EVAL-AD7877EBZ Analog Devices Inc, EVAL-AD7877EBZ Datasheet
![BOARD EVALUATION FOR AD7877](/photos/9/8/90827/eval-ad7877ebz_sml.jpg)
EVAL-AD7877EBZ
Specifications of EVAL-AD7877EBZ
Related parts for EVAL-AD7877EBZ
EVAL-AD7877EBZ Summary of contents
Page 1
FEATURES 4-wire touch screen interface LCD noise reduction feature (STOPACQ pin) Automatic conversion sequencer and timer User-programmable conversion parameters On-chip temperature sensor: −40°C to +85°C On-chip 2.5 V reference On-chip 8-bit DAC 3 auxiliary analog inputs 1 dedicated and 3 ...
Page 2
AD7877 TABLE OF CONTENTS Features .............................................................................................. 1 Applications....................................................................................... 1 Functional Block Diagram .............................................................. 1 General Description ......................................................................... 1 Revision History ............................................................................... 2 Specifications..................................................................................... 3 Timing Specifications .................................................................. 5 Timing Diagrams.......................................................................... 5 Absolute Maximum Ratings............................................................ 6 ESD Caution.................................................................................. 6 Pin Configurations ...
Page 3
SPECIFICATIONS 2.5 V internal or external REF Table 1. Parameter Min DC ACCURACY Resolution 12 No Missing Codes 11 1 Integral Nonlinearity 1 Differential Nonlinearity (DNL) Negative DNL Positive ...
Page 4
AD7877 Parameter Min 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 INL Input Current Input Capacitance, C ...
Page 5
TIMING SPECIFICATIONS unless otherwise noted MIN MAX signals are specified with (10 Table 2. Parameter Limit ...
Page 6
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 Input Current to ...
Page 7
PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS BAT2 2 BAT1 3 AD7877 AUX3/GPIO3 4 TOP VIEW (Not to Scale) AUX2/GPIO2 5 AUX1/GPIO1 ...
Page 8
AD7877 Pin No. Mnemonic Description 29 ARNG When the DAC is in current output mode, a resistor from ARNG to GND sets the output range. 30 AOUT Analog Output Voltage or Current from DAC Reference Output for the ...
Page 9
TYPICAL PERFORMANCE CHARACTERISTICS T = 25° REF SAMPLE 800 ADC, REF, AND DAC 700 ADC AND REF 600 500 –50 –30 – TEMPERATURE (°C) Figure 6. Supply ...
Page 10
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 ...
Page 11
TEMPERATURE (°C) Figure 18. ADC Code vs. Temperature (2.7 V Supply) 1183 1182 1181 1180 1179 1178 1177 1176 2.7 2.8 2.9 3.0 ...
Page 12
AD7877 TEMPERATURE = 25°C 1 CH1 200mV CH2 100mV M2.00μs Figure 24. DAC O/P Settling Time (Zero Scale to Half Scale) 600 500 400 DAC SINK CURRENT 300 200 100 NOTE: MAXIMUM DAC SINK CURRENT IS ...
Page 13
TERMINOLOGY Integral Nonlinearity The maximum deviation from a straight line passing through the endpoints of the ADC transfer function. The endpoints of the transfer function are zero scale at 1 LSB below the first code transition, and full scale at ...
Page 14
AD7877 CIRCUIT INFORMATION The AD7877 is a complete, 12-bit data acquisition system for digitizing positional inputs from a touch screen in PDAs and other devices. In addition, it can monitor two battery voltages, ambient temperature, and three auxiliary analog voltages, ...
Page 15
X– Y+ Y– AUX1/GPIO2 I/P MUX AUX2/GPIO3 AUX3/GPIO4 IN+ BAT1 BAT2 TEMPERATURE SENSOR Figure 28. Analog Input Structure The AD7877 can be set up to automatically convert either specific input channels or a sequence ...
Page 16
AD7877 For greater accuracy, the ratiometric method has two significant advantages: • The reference to the ADC is provided from the actual voltage across the screen; therefore, when the voltage drops across the switches, it has no effect. • Because ...
Page 17
It is only during the sample or acquisition phase of the ADC operation of the AD7877 that noise from the LCD screen has an effect on the ADC measurements. During the hold or conversion phase, the noise has no effect, ...
Page 18
AD7877 Temperature Calculations If an explicit temperature reading in °C is required, then this is calculated as follows for the single measurement method: 1. Calculate the scale factor of the ADC in degrees per LSB: Degrees per LSB = ADC ...
Page 19
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 ...
Page 20
AD7877 CONTROL REGISTERS Control Register 1 contains the ADC channel address, the SER/ DFR bit (to choose single or differential methods of touch screen measurement), the register read address, and the ADC mode bits. Control Register 1 should always be ...
Page 21
Table 6. Codes for Selecting Input Channel and Normal or Ratiometric Conversion SER/DFR Channel CHADD(3: ...
Page 22
AD7877 STOPACQ Polarity (Control Register 2, Bit<3>) This bit should be set according to the polarity of the signal applied to the STOPACQ pin. If that signal is active high, that is, no acquisitions should occur during the high period ...
Page 23
HOST PROGRAMS AD7877 IN MODE 01 IS FCD NO REQUIRED? YES START FCD TIMER IS FCD FINISHED? NO YES YES IS STOPACQ SIGNAL ACTIVE? NO START ACQUISITION TIMER IS STOPACQ YES SIGNAL ACTIVE ACQUISITION TIME FINISHED? YES ...
Page 24
AD7877 HOST PROGRAMS AD7877 IN MODE 11 VALID NO SEQUENCE MODE 00 YES IS NO SCREEN TOUCHED? YES SELECT NEXT CHANNEL IS FCD NO REQUIRED? YES START FCD TIMER IS FCD NO FINISHED? YES YES IS STOPACQ ...
Page 25
MHz (maximum), then t DCLK DCLK t = 512 μs with timer set to 1024 (TMR bits = 01b clk period × t WRITE READ DCLK t = maximum time ...
Page 26
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. ...
Page 27
V falls. If the DAC output exceeds starts to source current, REF and V has to further decrease to compensate. When the OUT DAC output is at full ...
Page 28
AD7877 SERIAL INTERFACE The AD7877 is controlled via a 3-wire serial peripheral interface (SPI). The SPI has a data input pin (DIN) for inputting data to the device, a data output pin (DOUT) for reading data back from the device, ...
Page 29
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 ...
Page 30
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 ...
Page 31
If the ALERT source is a GPIO, then masking out the interrupt by clearing the corresponding ALEN bit removing the source of the interrupt on the GPIO pin causes ALERT to go high again. If the ALERT ...
Page 32
AD7877 GROUNDING AND LAYOUT It is recommended that the ground pins, AGND and DGND, be shorted together as close as possible to the device itself on the user’s PCB. For more information on grounding and layout considerations for the AD7877, ...
Page 33
REGISTER MAPS Table 13. Write Register Map Register Address Binary WADD3 WADD2 WADD1 WADD0 ...
Page 34
AD7877 Table 15. Read Register Map Register Address Binary RADD4 RADD3 RADD2 RADD1 ...
Page 35
DETAILED REGISTER DESCRIPTIONS Register Name: Control Register 1 Write Address: 0001; Read Address: 00001; Default Value: 0x000; Type: Read/Write. Table 16. Bit Name Read/Write Description 0 MODE0 R/W LSB of ADC mode code. 1 MODE1 R/W MSB of ADC mode ...
Page 36
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 ...
Page 37
Register Name: Alert Status/Enable Register Write Address: 0011; Read Address: 00011; Default Value: 0x000; Type: Read/Write. Table 18. Bit Name Read/Write Description 0 AUX1LO R/W When this bit is 1, the AUX1 channel is below its low limit 1 BAT1LO ...
Page 38
AD7877 Register Name: Sequencer Register 0 Write Address: 1100; Read Address: 01100; Default Value: 0x000; Type: Read/Write. Table 19. Bit Name Read/Write Description 0 Not Used R/W This bit is not used 1 Z1_SS R/W Setting this bit includes the ...
Page 39
Register Name: DAC Register Write Address: 1110; Read Address: 01110; Default Value: 0x000; 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 ...
Page 40
AD7877 Register Name: TEMP1 Write Address: N/A; Read Address: 11000; Default Value: 0x000; Type: Read Only. This register contains the 12-bit result of a temperature measurement using single-ended conversion. Register Name: TEMP2 Write Address: N/A; Read Address: 11001; Default Value: ...
Page 41
Register Name: GPIO Control Register 2 Write Address: [1111] 0001; Read Address: 11100; Default Value: 0x000; Type: Read/Write. Table 23. Bit Name Read/Write 0 GPIO4_ALEN R/W 1 GPIO4_DIR R/W 2 GPIO4_POL R/W 3 Not Used 4 GPIO3_ALEN R/W 5 GPIO3_DIR ...
Page 42
... Figure 50. 25-Ball Wafer Level Chip Scale Package [WLCSP] 2.5 mm × 2.8 mm Body (CB-25) Dimensions shown in millimeters Package Description 32-Lead LFCSP_VQ 32-Lead LFCSP_VQ 32-Lead LFCSP_VQ 32-Lead LFCSP_VQ 32-Lead LFCSP_VQ 32-Lead LFCSP_VQ 25-Ball WLCSP 25-Ball WLCSP Evaluation Board Rev Page 0.60 MAX PIN 1 INDICATOR 3.25 EXPOSED PAD 3.10 SQ (BOTTOM VIEW) 2 ...
Page 43
NOTES Rev Page AD7877 ...
Page 44
AD7877 NOTES ©2006 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D03796-0-7/06(B) Rev Page ...