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AD7418AR-REEL Scheda tecnica(PDF) 8 Page - Analog Devices |
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AD7418AR-REEL Scheda tecnica(HTML) 8 Page - Analog Devices |
8 / 20 page REV. G –8– AD7416/AD7417/AD7418 (continued from page 1) An I 2C compatible serial interface allows the AD7416/AD7417/ AD7418 registers to be written to and read back. The three LSBs of the AD7416/AD7417’s serial bus address can be selected, which allows up to eight AD7416/AD7417s to be connected to a single bus. The AD7417 is available in a narrow body, 0.15'', 16-lead, small outline IC (SOIC) and in a 16-lead, thin shrink, small outline package (TSSOP). The AD7416 and AD7418 are available in 8-lead SOIC and MSOP packages. PRODUCT HIGHLIGHTS 1. The AD7416/AD7417/AD7418 have an on-chip temperature sensor that allows an accurate measurement of the ambient temperature ( ±1°C @ 25°C, ±2°C overtemperature) to be made. The measurable temperature range is –40 °C to +125°C. An overtemperature indicator is implemented by carrying out a digital comparison of the ADC code for Channel 0 (temperature sensor) with the contents of the on-chip over- temperature register. 2. The AD7417 offers a space-saving 10-bit A/D solution with four external voltage input channels, an on-chip temperature sensor, an on-chip reference, and clock oscillator. 3. The automatic power-down feature enables the AD7416/ AD7417/AD7418 to achieve superior power performance. At slower throughput rates, the part can be programmed to operate in a low power shutdown mode, allowing further savings in power consumption. TERMINOLOGY Relative Accuracy Relative accuracy or endpoint nonlinearity is the maximum deviation from a straight line passing through the endpoints of the ADC transfer function. Differential Nonlinearity This is the difference between the measured and the ideal 1 LSB change between any two adjacent codes in the ADC. Offset Error This is the deviation of the first code transition (0000 . . . 000) to (0000 . . . 001) from the ideal, i.e., GND + 1 LSB. Offset Error Match This is the difference in offset error between any two channels. Gain Error This is the deviation of the last code transition (1111 . . . 110) to (1111 . . . 111) from the ideal, i.e., VREF – 1 LSB, after the offset error has been adjusted out. Gain Error Match This is the difference in gain error between any two channels. Track-and-Hold Acquisition Time Track-and-hold acquisition time is the time required for the output of the track-and-hold amplifier to reach its final value, within ±1/2 LSB, after the end of conversion (the point at which the track-and-hold returns to track mode). It also applies to situations where a change in the selected input channel takes place or where there is a step input change on the input voltage applied to the selected AIN input of the AD7417 or AD7418. It means that the user must wait for the duration of the track-and- hold acquisition time after the end of conversion or after a channel change/step input change to AIN before starting another conver- sion, to ensure that the part operates to specification. CIRCUIT INFORMATION The AD7417 and AD7418 are single-channel and four-channel, 15 µs conversion time, 10-bit ADCs with on-chip temperature sensor, reference, and serial interface logic functions on a single chip. The AD7416 has no analog input channel and is intended for temperature measurement only. The ADC section consists of a conventional successive approximation converter based around a capacitor DAC. The AD7416, AD7417, and AD7418 are capable of running on a 2.7 V to 5.5 V power supply, and the AD7417 and AD7418 accept an analog input range of 0 V to +VREF. The on-chip temperature sensor allows an accurate measurement of the ambient device temperature to be made. The working measurement range of the temperature sensor is –40 °C to +125°C. The parts require a 2.5 V reference that can be provided from the part’s own internal reference or from an external reference source. CONVERTER DETAILS Conversion is initiated on the AD7417/AD7418 by pulsing the CONVST input. The conversion clock for the part is internally generated so no external clock is required except when reading from and writing to the serial port. The on-chip track-and-hold goes from track to hold mode and the conversion sequence is started on the falling edge of the CONVST signal. A conversion is also initiated in the automatic conversion mode every time a read or write operation to the AD7416/AD7417/AD7418 takes place. In this case, the internal clock oscillator (which runs the automatic conversion sequence) is restarted at the end of the read or write operation. The track-and-hold goes into hold approximately 3 µs after the read or write operation is complete and a conversion is then initiated. The result of the conversion is available either 15 µs or 30 µs later, depending on whether an analog input channel or the temperature sensor is selected. The track-and-hold acquisition time of the AD7417/AD7418 is 400 ns. A temperature measurement is made by selecting the Channel 0 of the on-chip mux and carrying out a conversion on this channel. A conversion on Channel 0 takes 30 µs to complete. Tempera- ture measurement is explained in the Temperature Measurement section of this data sheet. The on-chip reference is not available to the user, but REFIN can be overdriven by an external reference source (2.5 V only). All unused analog inputs should be tied to a voltage within the nominal analog input range to avoid noise pickup. For mini- mum power consumption, the unused analog inputs should be tied to GND. |
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