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MC1408-8D Scheda tecnica(PDF) 5 Page - NXP Semiconductors |
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MC1408-8D Scheda tecnica(HTML) 5 Page - NXP Semiconductors |
5 / 10 page Philips Semiconductors Product data MC1408-8 8-bit multiplying D/A converter 2001 Aug 03 5 TYPICAL PERFORMANCE CHARACTERISTICS D-to-A TRANSFER CHARACTERISTICS 0 1.0 2.0 (00000000) INPUT DIGITAL WORD (11111111) SL00050 Figure 3. Typical Performance Characteristics FUNCTIONAL DESCRIPTION Reference Amplifier Drive and Compensation The reference amplifier input current must always flow into Pin 14. regardless of the setup method or reference supply voltage polarity. Connections for a positive reference voltage are shown in Figure 4. The reference voltage source supplies the full reference current. For bipolar reference signals, as in the multiplying mode, R15 can be tied to a negative voltage corresponding to the minimum input level. R15 may be eliminated and Pin 15 grounded, with only a small sacrifice in accuracy and temperature drift. A1 A2 A3 A4 A5 A6 A7 A8 5 6 7 8 9 10 11 12 3 MC1408 13 14 15 1 2 4 16 SEE TEXT FOR VALUES OF C. C R14 = R15 (+)VREF R14 R15 RL IO VEE VCC SL00051 Figure 4. Positive VREF The compensation capacitor value must be increased with increasing values of R14 to maintain proper phase margin. For R14 values of 1.0, 2.5, and 5.0 k Ω, minimum capacitor values are 15, 37, and 75 pF. The capacitor may be tied to either VEE or ground, but using VEE increases negative supply rejection. (Fluctuations in the negative supply have more effect on accuracy than do any changes in the positive supply.) A negative reference voltage may be used if R14 is grounded and the reference voltage is applied to R15, as shown in Figure 5. A high input impedance is the main advantage of this method. The negative reference voltage must be at least 3.0 V above the VEE supply. Bipolar input signals may be handled by connecting R14 to a positive reference voltage equal to the peak positive input level at Pin 15. Capacitive bypass to ground is recommended when a DC reference voltage is used. The 5.0 V logic supply is not recommended as a reference voltage, but if a well regulated 5.0 V supply which drives logic is to be used as the reference, R14 should be formed of two series resistors and the junction of the two resistors bypassed with 0.1 µF to ground. For reference voltages greater than 5.0 V, a clamp diode is recommended between Pin 14 and ground. If Pin 14 is driven by a high impedance such as a transistor current source, none of the above compensation methods apply and the amplifier must be heavily compensated, decreasing the overall bandwidth. A1 A2 A3 A4 A5 A6 A7 A8 5 6 7 8 9 10 11 12 3 MC1408 13 14 15 1 2 4 16 SEE TEXT FOR VALUES OF C. C R14 = R15 (–)VREF R14 R15 RL IO VEE VCC SL00052 Figure 5. Negative VREF Output Voltage Range The voltage at Pin 4 must always be at least 4.5 V more positive than the voltage of the negative supply (Pin 3) when the reference current is 2 mA or less, and at least 8 V more positive than the negative supply when the reference current is between 2 mA and 4 mA. This is necessary to avoid saturation of the output transistors, which would cause serious degradation of accuracy. Philips Semiconductors MC1408-8 does not need a range control because the design extends the compliance range down to 4.5 V (or 8 V — see above) above the negative supply voltage without significant degradation of accuracy. Philips Semiconductors MC1408-8 can be used in sockets designed for other manufacturers’ MC1408 without circuit modification. |
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