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AD5546 Datasheet(PDF) 11 Page  Analog Devices 

AD5546 Datasheet(HTML) 11 Page  Analog Devices 
11 / 16 page AD5546/AD5556 Rev. 0  Page 11 of 16 CIRCUIT OPERATION D/A CONVERTER SECTION The AD5546/AD5556 are 16/14bit multiplying, current out put, and parallel input DACs. The devices operate from a single 2.7 V to 5.5 V supply, and provide both unipolar 0 V to –VREF, or 0 V to +VREF, and bipolar ±VREF output ranges from a –18 V to +18 V reference. In addition to the precision conversion RFB commonly found in current output DACs, there are three addi tional precision resistors for 4quadrant bipolar applications. The AD5546/AD5556 consist of two groups of precision R2R ladders, which make up the 12/10 LSBs, respectively. Further more, the four MSBs are decoded into 15 segments of resistor value 2R. Figure 19 shows the architecture of the 16bit AD5546. Each of the 16 segments in the R2R ladder carries an equally weighted current of onesixteenth of full scale. The feedback resistor, RFB, and 4quadrant resistor, ROFS, have values of 10 kΩ. Each 4quadrant resistor, R1 and R2, equals 5 kΩ. In 4quadrant operation, R1, R2, and an external op amp work together to invert the reference voltage and apply it to the REF input. With ROFS and RFB connected as shown in Figure 2, the output can swing from –VREF to +VREF. The reference voltage inputs exhibit a constant input resistance of 5 kΩ ±20%. The DAC output, IOUT, impedance is code depen dent. External amplifier choice should take into account the variation of the AD5546/AD5556 output impedance. The feedback resistance in parallel with the DAC ladder resistance dominates output voltage noise. To maintain good analog performance, it is recommended to bypass the power supply with a 0.01 µF to 0.1 µF ceramic or chip capacitor in parallel with a 1 µF tantulum capacitor. Also, to minimize gain error, PCB metal traces between VREF and RFB should match. Every code change of the DAC corresponds to a step function; gain peaking at each output step may occur if the op amp has limited GBP and excessive parasitic capacitance present at the op amp inverting node. A compensation capacitor, therefore, may be needed between the IV op amp inverting and output nodes to smooth the step transition. Such a compensation capacitor should be found empirically, but a 20 pF capacitor is generally adequate for the compensation. The VDD power is used primarily by the internal logic and to drive the DAC switches. Note that the output precision degrades if the operating voltage falls below the specified voltage. Users should also avoid using switching regulators because device power supply rejection degrades at higher frequencies. 2R 80k Ω R 40k Ω 2R 80k Ω 2R 80k Ω 2R 80k Ω 2R 80k Ω 2R 80k Ω R 40k Ω 2R 80k Ω R 2R 80k Ω R 2R 80k Ω R 2R 80k Ω R 2R 80k Ω 2R 80k Ω R 40k Ω R2 5k Ω R1 5k Ω REF 2R 80k Ω R 40k Ω 2R 80k Ω R 40k Ω 2R 80k Ω R 40k Ω 2R 80k Ω R 40k Ω 2R 80k Ω R 40k Ω 2R 80k Ω RCOM R1 ADDRESS DECODER DAC REGISTER INPUT REGISTER LDAC WR RS RS 4 MSB 15 SEGMENTS 8BIT R2R 4BIT R2R 16 8 4 LDAC WR D15 D14 D0 RS 10k Ω 10k Ω ROFS RFB IOUT GND RA RB Figure 19. 16Bit AD5546 Equivalent R2R DAC Circuit with Digital Section 
Similar Part No.  AD5546 

Similar Description  AD5546 


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