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AD7873 Datasheet(PDF) 14 Page - Analog Devices |
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AD7873 Datasheet(HTML) 14 Page - Analog Devices |
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14 / 29 page  Data Sheet AD7873 Rev. F | Page 13 of 28 CIRCUIT INFORMATION The AD7873 is a fast, low power, 12-bit, single-supply analog- to-digital converter (ADC). 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 on-chip track-and-hold, multiplexer, ADC, reference, temperature sensor, and serial interface, housed in a tiny 16-lead QSOP, TSSOP, or LFCSP package, offering the user considerable space-saving advantages over alternative solutions. The serial clock input (DCLK) accesses data from the part and also provides the clock source for the successive approximation ADC. 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 multiplexer. This analog input can be any one of the X, Y, and Z panel coordinates, the battery voltage, or the 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 could 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 (that is, 1 LSB, 2 LSBs, and so on). The LSB size is VREF/4096. The ideal transfer characteristic for the AD7873 is shown in Figure 24. Figure 24. Transfer Characteristic TYPICAL CONNECTION DIAGRAM Figure 25 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 sets the input range of the converter. The conversion result is output MSB first, followed by the remaining 11 bits and three trailing zeros, depending on the number of clocks used per conversion (see the Serial Interface section). For applications where power consumption is a concern, the power management option should be used to improve power perform- ance. See Table 8 for available power management options. Figure 25. Typical Application Circuit ANALOG INPUT 1LSB 0V +VREF – 1LSB 1LSB = VREF/4096 111...111 111...110 111...000 011...111 000...010 000...001 000...000 16 15 14 13 12 11 9 8 1 2 3 4 7 6 5 10 TOUCH SCREEN 1µF TO 10µF (OPTIONAL) 2.2V TO 5V 0.1µF 0.1µF AUXILIARY INPUT AD7873 +VCC X+ Y+ X– Y– GND VBAT AUX DCLK CS DIN BUSY DOUT PENIRQ +VCC VREF SERIAL/CONVERSION CLOCK CHIP SELECT SERIAL DATA IN CONVERTER STATUS SERIAL DATA OUT PEN INTERRUPT 50k Ω TO BATTERY VOLTAGE REGULATOR + + + |
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Similar Description - AD7873_17 |
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