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DAC7545 датащи(PDF) 5 Page - Burr-Brown (TI) |
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DAC7545 датащи(HTML) 5 Page - Burr-Brown (TI) |
5 / 7 page DAC7545 5 SBAS150A www.ti.com APPLICATIONS UNIPOLAR OPERATION Figure 2 shows the DAC7545 connected for unipolar opera- tion. The high-grade DAC7545 is specified for a 1LSB gain error, so gain adjust is typically not needed; however, the resistors shown are for adjusting full-scale errors. The value of R1 should be minimized to reduce the effects of mismatch- ing temperature coefficients between the internal and exter- nal resistors. A range of adjustment of 1.5 times the desired range will be adequate. For example, for a DAC7545JP, the gain error is specified to be ±25LSB, therefore, a range of adjustment of ±37LSB will be adequate. Equation 1 results in a value of 458W for the potentiometer (use 500 Ω). R R Gain Error LADDER 1 4096 3 = ( ) • (1) FIGURE 2. Unipolar Binary Operation. BINARY CODE ANALOG OUTPUT MSB LSB 1111 1111 1111 –VIN (4095/4096) 1000 0000 0000 –VIN (2048/4096) = –1/2VIN 0000 0000 0001 –VIN (1/4096) 0000 0000 0000 0V TABLE I. Unipolar Codes. OPA604 V IN R 1 R 2 V DD R FB DAC7545 AGND DGND OUT 1 DB 0-DB11 C 1 33pF +5V V OUT V REF R3, R4, and R5 must match within 0.01% and must be the same type of resistors (preferably wire-wound or metal foil), so that the temperature coefficients match; mismatch of R3 value to R4 causes both offset and full-scale error. Mismatch of R5 to R4 and R3 causes full-scale error. FIGURE 3. Bipolar Operation (binary two’s complement code). OPA604 or 1/2 OPA2604 V IN R 1 R 2 V DD R FB DAC7545 AGND DB 10-DB0 OUT 1 Data Input C 1 33pF +5V DB 11 V REF V OUT R 3 10k Ω R 4 20k Ω R 5 20k Ω R 6 5k Ω 10% U 1 (see text) 12 11 Analog Common 2 1 18 20 19 4 OPA604 or 1/2 OPA2604 DATA INPUT ANALOG OUTPUT MSB LSB 0111 1111 1111 +VIN (2047/2048) 0000 0000 0001 +VIN (1/2048) 0000 0000 0000 0V 1111 1111 1111 –VIN (1/2048) 1000 0000 0000 –VIN (2048/2048) TABLE II. Binary Two’s Complement Code Table for Circuit of Figure 3. tance. Eliminating this capacitor will result in excessive ringing and an increase in glitch energy, therefore, this capacitor must be as small as possible to minimize settling time. The circuit of Figure 2 can be used with input voltages up to ±20V as long as the output amplifier is biased to handle the excursions. Table I represents the analog output for four codes into the DAC for Figure 2. BIPOLAR OPERATION Figure 3 and Table II illustrate the recommended circuit and code relationship for bipolar operation. The DAC function uses offset binary code. The inverter, U1, on the MSB line converts binary two’s complement input code to offset binary code. If the inversion is done in software, U1 can be omitted. The addition of R1 will cause a negative gain error. To compensate for this error, R2 must be added. The value of R2 should be one-third the value of R1. The capacitor across the feedback resistor is used to compen- sate for the phase shift due to stray capacitances of the circuit board, the DAC output capacitance, and op amp input capaci- |
Аналогичный номер детали - DAC7545 |
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Аналогичное описание - DAC7545 |
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