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DAC7541A Datasheet(PDF) 5 Page  BurrBrown (TI) 


DAC7541A Datasheet(HTML) 5 Page  BurrBrown (TI) 
5 / 8 page 5 ® DAC7541A DISCUSSION OF SPECIFICATIONS RELATIVE ACCURACY This term (also known as linearity) describes the transfer function of analog output to digital input code. The linearity error describes the deviation from a straight line between zero and full scale. DIFFERENTIAL NONLINEARITY Differential nonlinearity is the deviation from an ideal 1LSB change in the output, from one adjacent output state to the next. A differential nonlinearity specification of ±1.0LSB guarantees monotonicity. GAIN ERROR Gain error is the difference in measure of fullscale output versus the ideal DAC output. The ideal output for the DAC7541A is –(4095/4096) X (V REF). Gain error may be adjusted to zero using external trims. OUTPUT LEAKAGE CURRENT The measure of current which appears at Out1 with the DAC loaded with all zeros, or at Out2 with the DAC loaded with all ones. MULTIPLYING FEEDTHROUGH ERROR This is the AC error output due to capacitive feedthrough from VREF to Out1 with the DAC loaded with all zeros. This test is performed at 10kHz. OUTPUT CURRENT SETTLING TIME This is the time required for the output to settle to a tolerance of ±0.5LSB of final value from a change in code of all zeros to all ones, or all ones to all zeros. PROPAGATION DELAY This is the measure of the delay of the internal circuitry and is measured as the time from a digital code change to the point at which the output reaches 90% of final value. DIGITALTOANALOG GLITCH IMPULSE This is the measure of the area of the glitch energy measured in nVseconds. Key contributions to glitch energy are digital wordbit timing differences, internal circuitry timing differ ences, and charge injected from digital logic. MONOTONICITY Monotonicity assures that the analog output will increase or stay the same for increasing digital input codes. The DAC7541A is guaranteed monotonic to 12 bits. POWER SUPPLY REJECTION Power supply rejection is the measure of the sensitivity of the output (full scale) to a change in the power supply voltage. FIGURE 1. Simplified DAC Circuit. EQUIVALENT CIRCUIT ANALYSIS Figures 2 and 3 show the equivalent circuits for all digital inputs low and high, respectively. The reference current is switched to IOUT 2 when all inputs are low and IOUT 1 when inputs are high. The IL current source is the combination of surface and junction leakages to the substrate; the 1/4096 current source represents the constant onebit current drain through the ladder terminal. DYNAMIC PERFORMANCE Output Impedance The output resistance, as in the case of the output capaci tance, is also modulated by the digital input code. The resistance looking back into the I OUT 1 terminal may be anywhere between 10k Ω (the feedback resistor alone when all digital inputs are low) and 7.5k Ω (the feedback resistor in parallel with approximately 30k Ω of the R2R ladder network resistance when any single bit logic is high). The static accuracy and dynamic performance will be affected by this modulation. The gain and phase stability of the output CIRCUIT DESCRIPTION The DAC7541A is a 12bit multiplying D/A converter consisting of a highly stable thinfilm R2R ladder network and 12 pairs of current steering switches on a monolithic chip. Most applications require the addition of a voltage or current reference and an output operational amplifier. A simplified circuit of the DAC7541A is shown in Figure 1. The R2R inverted ladder binarily divides the input currents that are switched between I OUT 1 and IOUT 2 bus lines. This switching allows a constant current to be maintained in each ladder leg independent of the input code. The input resistance at VREF (Figure 1) is always equal to RLDR (RLDR is the R/2R ladder characteristic resistance and is equal to value “R”). Since RIN at the VREF pin is constant, the reference terminal can be driven by a reference voltage or a reference current, AC or DC, of positive or negative polarity. Bit 12 (LSB) 10k Ω 10k Ω 20k Ω 20k Ω 10k Ω 20k Ω 20k Ω I OUT 2 Bit 3 Bit 2 Bit 1 (MSB) V REF 20k Ω I OUT 1 R FB Digital Inputs (DTL/TTL/CMOScompatible) Switches shown for digital inputs “HIGH”. S 2 S 1 S 3 S 12 
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