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AD5551BRZ-REEL7 Fiches technique(PDF) 12 Page - Analog Devices |
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AD5551BRZ-REEL7 Fiches technique(HTML) 12 Page - Analog Devices |
12 / 16 page AD5551/AD5552 Rev. A | Page 12 of 16 Assuming a perfect reference, the worst-case output voltage may be calculated from the following equation: () INL V V V D V ZSE GE REF UNI OUT + + + × = − 14 2 where: VOUT–UNI is the unipolar mode worst-case output. D is the decimal code loaded to the DAC. VREF is the reference voltage applied to part. VGE is the gain error in volts. VZSE is the zero-scale error in volts. INL is the integral nonlinearity in volts. BIPOLAR OUTPUT OPERATION With the aid of an external op amp, the AD5552 may be confi- gured to provide a bipolar voltage output. A typical circuit of such operation is shown in Figure 24. The matched bipolar offset resistors RFB and RINV are connected to an external op amp to achieve this bipolar output swing where RFB = RINV = 28 kΩ. Table 7 shows the transfer function for this output operating mode. Also provided on the AD5552 are a set of Kelvin connections to the analog ground inputs. +5V –5V VOUT INV RFB VREFF AGNDF AGNDS VDD DIN SCLK CS AD5552 VREFS DGND 0.1µF 0.1µF 10µF UNIPOLAR OUTPUT EXTERNAL OP AMP 2.5V 5V LDAC SERIAL INTERFACE RINV RFB Figure 24. Bipolar Output (AD5552 Only) Table 7. Bipolar Code Table DAC Latch Contents MSB LSB Analog Output 11 1111 1111 1111 +VREF × (8191/8192) 10 0000 0000 0000 +VREF × (1/8192) 00 0000 0000 0001 0 V 00 0000 0000 0000 −VREF × (1/8192) 00 0000 0000 0000 −VREF × (8191/8192) = –VREF Assuming a perfect reference, the worst-case bipolar output voltage may be calculated from the following equation. A RD RD V RD V V V REF OS UNI OUT BIP OUT / ) 2 ( 1 ) 1 ( ) 2 )( [( + + + − + + = − − where: VOS is the external op amp input offset voltage. RD is the RFB and RIN resistor matching error, unitless. A is the op amp open-loop gain. OUTPUT AMPLIFIER SELECTION For bipolar mode, use a precision amplifier, supplied from a dual power supply. This provides the ±VREF output. In a single- supply application, selection of a suitable op amp may be more difficult as the output swing of the amplifier does not usually include the negative rail, in this case AGND. This can result in some degradation of the specified performance unless the application does not use codes near zero. The selected op amp needs to have a very low-offset voltage, (the DAC LSB is 152 μV with a 2.5 V reference), to eliminate the need for output offset trims. Input bias current should also be very low as the bias current multiplied by the DAC output impedance (approximately 6K) adds to the zero-code error. Rail-to-rail input and output performance is required. For fast settling, the slew rate of the op amp should not impede the settling time of the DAC. Output impedance of the DAC is constant and code-independent, but to minimize gain errors, the input impedance of the output amplifier should be as high as possible. The amplifier should also have a 3 dB bandwidth of 1 MHz or greater. The amplifier adds another time constant to the system, therefore increasing the settling time of the output. A higher 3 dB amplifier bandwidth results in a faster effective settling time of the combined DAC and amplifier. FORCE SENSE BUFFER AMPLIFIER SELECTION These amplifiers can be single-supply or dual supplies, low noise amplifiers. A low-output impedance at high frequencies is preferred as they need to be able to handle dynamic currents of up to ±20 mA. |
Numéro de pièce similaire - AD5551BRZ-REEL7 |
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Description similaire - AD5551BRZ-REEL7 |
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