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DAC7741 数据表(PDF) 14 Page - Texas Instruments |
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DAC7741 数据表(HTML) 14 Page - Texas Instruments |
14 / 23 page DAC7741 14 SBAS248B www.ti.com ANALOG OUTPUTS The output amplifier can swing to within 1.4V of the supply rails, specified over the –40 °C to +85°C temperature range. This allows for a ±10V DAC voltage output operation from ±12V supplies with a typical 5% tolerance. When the DAC7741 is configured for a unipolar, 0V to 10V output, a negative voltage supply is required. This is due to internal biasing of the output stage. Please refer to the “Electrical Characteristics” table for more information. The minimum and maximum voltage output values are de- pendent upon the output configuration implemented and reference voltage applied to the DAC7741. Please note that VSS (the negative power supply) must be in the range of –4.75V to –15.75V for unipolar operation. The voltage on VSS sets several bias points within the converter and is required in all modes of operation. If VSS is not in one of these two configurations, the bias values may be in error and proper operation of the device is not ensured. Supply sequence is important in establishing the correct startup of the DAC. The digital supply (VDD) needs to estab- lish correct bias conditions before the analog supplies (VCC, VSS) are brought up. If the digital supply cannot be brought up first, it must come up before either analog supply (VCC or VSS), with the preferred sequence of: VSS (device substrate), VDD then VCC. REFERENCE INPUTS The DAC7741 provides a built-in +10V voltage reference and on-chip buffer to allow external component reference drive. To use the internal reference, REFEN must be LOW, enabling the reference circuitry of the DAC7741 (see Table I) and the REFOUT pin must be connected to REFIN. This is the input to the on-chip reference buffer. The buffers output is provided at REFEN ACTION 1 Internal Reference disabled; REFOUT = HIGH Impedance 0 Internal Reference enabled; REFOUT = +10V TABLE I. REFEN Action. TABLE II. DAC7741 Logic Truth Table. the VREF pin. In this configuration, VREF is used to setup the DAC7741 output amplifier into one of three voltage output modes as discussed earlier. VREF can also be used to drive other system components requiring an external reference. The internal reference of the DAC7741 can be disabled when use of an external reference is desired. When using an external reference, the reference input, REFIN , can be any voltage between 4.75V (or VSS + 14V, whichever is greater) and VCC – 1.4V. DIGITAL INTERFACE Table III shows the data format for the DAC7741 and Table II illustrates the basic control logic of the device. The interface consists of a chip select input (CS), read/write control input (R/W), data inputs (DB0-DB15) and a load DAC input (LDAC). An asynchronous reset input (RST) which is active low, is provided to simplify start-up conditions, periodic resets, or emergency resets to a known state, depending on the status of the reset select (RSTSEL) signal. The DAC code is provided via a 16-bit parallel interface, as shown in Table II. The input word makes up the DAC code to be loaded into the data input register of the device. The data is latched into the input register on rising CS and is loaded into the DAC register upon reception of a rising edge on the LDAC input. This action updates the analog output, VOUT, to the desired value. LDAC inputs of multiple DAC7741 devices can be connected when a synchronized update of numerous DAC outputs is desired. Please refer to the timing section for more detailed data I/O information. CONTROL STATUS COMMAND R/W CS RST RSTSEL LDAC Input Register DAC Register Mode L L H X H, L, ↓ Write Hold Write Data to Input Register XH H X ↑ Hold Write Update DAC register with data from input register. LL H X ↑ Transparent Write Write DAC register directly from data bus H L H X H, L, ↓ Read Hold Read data in input register. X H H X H, L, ↓ Hold Hold No Change XX L L X Reset to Min-Scale Reset to Min-Scale Reset to Input and DAC Register (0000 H) Min-Scale XX L H X Reset to Mid-Scale Reset to Mid-Scale Reset to Input and DAC Register (8000 H) Mid-Scale ANALOG OUTPUT TABLE III. DAC7741 Data Format. DIGITAL INPUT Unipolar Configuration Bipolar Configuration Unipolar Straight Binary Bipolar Offset Binary 0x0000 Zero (0V) –Full-Scale (–VREF or –VREF/2) 0x0001 Zero + 1LSB –Full-Scale + 1LSB :: : 0x8000 1/2 Full-Scale Bipolar Zero 0x8001 1/2 Full-Scale + 1LSB Bipolar Zero + 1LSB :: : 0xFFFF Full-Scale (VREF – 1LSB) +Full-Scale (+VREF – 1LSB or +VREF/2 – 1LSB) |
类似零件编号 - DAC7741 |
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类似说明 - DAC7741 |
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