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AD8671 Folha de dados(PDF) 9 Page - Analog Devices |
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AD8671 Folha de dados(HTML) 9 Page - Analog Devices |
9 / 24 page Data Sheet AD5545/AD5555 Rev. G | Page 9 of 24 THEORY OF OPERATION The AD5545/AD5555 contain a 16-/14-bit, current-output, digital-to-analog converter, a serial-input register, and a DAC register. Both parts require a minimum of a 3-wire serial data interface with an additional LDAC for dual channel simultaneous update. DIGITAL-TO-ANALOG CONVERTER The DAC architecture uses a current-steering R-2R ladder design. Figure 17 shows the typical equivalent DAC. The DAC contains a matching feedback resistor for use with an external I-to-V converter amplifier. The RFB pin is connected to the output of the external amplifier. The IOUT terminal is connected to the inverting input of the external amplifier. These DACs are designed to operate with either negative or positive reference voltages. The VDD power pin is used only by the logic to drive the DAC switches on and off. Note that a matching switch is used in series with the internal 5 kΩ feedback resistor. If users attempt to measure the RFB value, power must be applied to VDD to achieve continuity. The VREF input voltage and the digital data (D) loaded into the corresponding DAC register, according to Equation 1 and Equation 2, determine the DAC output voltage. 536 , 65 / – D V V REF OUT × = (1) 384 , 16 / – D V V REF OUT × = (2) Note that the output full-scale polarity is the opposite of the VREF polarity for dc reference voltages. VREF DIGITAL INTERFACE CONNECTIONS OMITTED FOR CLARITY: SWITCHES S1 AND S2 ARE CLOSED, VDD MUST BE POWERED R 2R 2R 2R R 5k Ω S2 S1 R R VDD RFB IOUT GND 02918- 0- 005 Figure 17. Equivalent R-2R DAC Circuit These DACs are also designed to accommodate ac reference input signals. The AD5545/AD5555 accommodate input reference voltages in the range of –12 V to +12 V. The reference voltage inputs exhibit a constant nominal input-resistance value of 5 kΩ, ±30%. The DAC output (IOUT) is code dependent, pro- ducing various output resistances and capacitances. When choosing an external amplifier, the user should take into account the variation in impedance generated by the AD5545/ AD5555 on the amplifiers inverting input node. The feedback resistance in parallel with the DAC ladder resistance dominates output voltage noise. VREFA DIGITAL INTERFACE CONNECTIONS OMITTED FOR CLARITY: SWITCHES S1 AND S2 ARE CLOSED, VDD MUST BE POWERED R 2R 2R 2R R 5k Ω S2 S1 +3V –3V R R VOUT VIN VDD 5V 2.500V RFBA IOUTA AGNDA GND 02918- 0- 006 AD5545/AD5555 ADR03 AD8628 LOAD VOUT VEE VCC Figure 18. Recommended System Connections |
Nº de peça semelhante - AD8671 |
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Descrição semelhante - AD8671 |
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