DAC_connected_for_single_supply_operation

Published:2009/7/25 5:31:00 Author:Jessie | From:SeekIC

Figure 9-34 shows a DAC1000 connected for single-supply operation. The R-2R ladder can be operated as a voltage-switching network to prevent the output-voltage inversion that is so common in the current-switching mode. In this circuit, the reference voltage is applied to the IOUT 1 terminal and is attenuated by the R-2R ladder in proportion to the applied code. The voltage is then output to the VREF terminal with no phase inversion. To ensure linear operation in single-supply modes, the applied voltage must be kept less than 3 V for 10-bit DACs, or less than 5 V for 8-bit DACs. The supply voltage to the DAC must be at least 10 V more positive than the reference voltage to ensure that the CMOS ladder switches have enough voltage Qverdrive to fully turn on. An external op amp can be added to provide gain to the DAC output voltage for a wide overall output span. This circuit provides generally good linearity for 8-bit and 8-bit DACs, but can have a problem with 12-bit DACs (because of the very low reference required). If 12-bit operation is desired, use a DAC specifically designed for single-supply operation. NATIONAL SEMICONDUCTOR, APPLICATION NOTE 271, 1994, P. 666.



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