MC1508-8 PHILIPS | Alldatasheet
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Technical content
Philips Semiconductors Linear Products Product specification MC1508-8/1408-88-bit multiplying D/A converter 737August 31, 1994 853-0935 13721
DESCRIPTION
The MC1508/MC1408 series of 8-bit monolithic digital-to-analog converters provide high-speed performance with low cost. They are designed for use where the output current is a linear product of an 8-bit digital word and an analog reference voltage
FEATURES
- Fast settling time — 70ns (typ)
- Relative accuracy ±0.19% (max error)
- Non-inverting digital inputs are TTL and CMOS compatible
- High-speed multiplying rate 4.0mA/µs (input slew)
- Output voltage swing +0.5V to –5.0V
- Standard supply voltages +5.0V and –5.0V to –15V
- Military qualifications pending
APPLICATIONS
- Tracking A-to-D converters
- 2 1/2-digit panel meters and DVMs
- Waveform synthesis
- Sample-and-Hold
- Peak detector
- Programmable gain and attenuation
- CRT character generation
- Audio digitizing and decoding
- Programmable power supplies
- Analog-digital multiplication
- Digital-digital multiplication
- Analog-digital division
- Digital addition and subtraction
- Speech compression and expansion
- Stepping motor drive modems
- Servo motor and pen drivers PIN CONFIGURATIONS F, N Packages D Package1 NC GND VEE COMPEN TOP VIEW 8 9 8 9 VREF(–) IO MSB A 1 A 2 A 3 A 4 VREF(+) VCC A 8 LSB A 7 A 6 A 5 A 1 MSB A 2 A 3 A 4 A 8 LSB A 7 A 6 A 5 VREF(–) VREF(+) COMPEN NC GND IO NOTE: 1. SO and non-standard pinouts.
ORDERING INFORMATION
DESCRIPTION TEMPERATURE RANGE ORDER CODE DWG # 16-Pin Ceramic Dual In-Line Package (CERDIP) -55 to +125°C MC1508-8F 0582B 16-Pin Ceramic Dual In-Line Package (CERDIP) 0 to +70°C MC1408-8F 0582B 16-Pin Plastic Dual In-Line Package (DIP) 0 to +70°C MC1408-8N 0406C 16-Pin Small Outline (SO) Package 0 to +70°C MC1408-8D 0005D
Philips Semiconductors Linear Products Product specification MC1508-8/1408-88-bit multiplying D/A converter August 31, 1994 738 BLOCK DIAGRAM CURRENT SWITCHES 5 6 7 8 9 10 11 12 MSB LSB REFERENCE CURRENT AMPLIFIER GND COMPEN NPN CURRENT SOURCE PAIR A 1 A 2 A 3 A 4 A 5 A 6 A 7 A 8 BIAS CURRENTR-2R LADDER (+) (–) VREF VREF VCC 3VEE IO CIRCUIT DESCRIPTION The MC1508/MC1408 consists of a reference current amplifier, an R-2R ladder, and 8 high-speed current switches. For many applications, only a reference resistor and reference voltage need be added. The switches are non-inverting in operation; therefore, a high state on the input turns on the specified output current component. The switch uses current steering for high speed, and a termination amplifier consisting of an active load gain stage with unity gain feedback. The termination amplifier holds the parasitic capacitance of the ladder at a constant voltage during switching, and provides a low impedance termination of equal voltage for all legs of the ladder. The R-2R ladder divides the reference amplifier current into binarily-related components, which are fed to the remainder current which is equal to the least significant bit. This current is shunted to ground, and the maximum output current is 255/256 of the reference amplifier current, or 1.992mA for a 2.0mA reference amplifier current if the NPN current source pair is perfectly matched. ABSOLUTE MAXIMUM RATINGS SYMBOL PARAMETER RATING UNIT VCC Positive power supply voltage +5.5 V VEE Negative power supply voltage –16.5 V V5 – V12 Digital input voltage 0 to VCC V VO Applied output voltage –5.2 to +18 V I14 Reference current 5.0 mA V14, V15 Reference amplifier inputs VEE to VCC PD Maximum power dissipation, TA = 25°C (still-air)1 F package 1190 mW N package 1450 mW D package 1080 mW TSOLD Lead soldering temperature (10 sec) 300 °C TA Operating temperature range 300 °C MC1508 –55 to +125 °C MC1408 0 to +75 °C TSTG Storage temperature range -65 to +150 °C NOTES: 1. Derate above 25°C, at the following rates: F package at 9.5mW/°C; N package at 11.6mW/°C; D package at 8.6mW/°C
Philips Semiconductors Linear Products Product specification MC1508-8/1408-88-bit multiplying D/A converter August 31, 1994 740 TYPICAL PERFORMANCE CHARACTERISTICS D-to-A TRANSFER CHARACTERISTICS I OUTPUT CURRENT (mA)O 1.0 2.0 (00000000) INPUT DIGITAL WORD (11111111) 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 1. 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. R 15 may be eliminated and Pin 15 grounded, with only a small sacrifice in accuracy and temperature drift. 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 5.0kΩ , minimum capacitor values are 15, 37, and 75pF. 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 2. A high input impedance is the main advantage of this method. The negative reference voltage must be at least 3.0V 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 5.0V logic supply is not recommended as a reference voltage, but if a well regulated 5.0V 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 0.1µF to ground. For reference voltages greater than 5.0V, 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. Output Voltage Range The voltage at Pin 4 must always be at least 4.5V more positive than the voltage of the negative supply (Pin 3) when the reference current is 2mA or less, and at least 8V more positive than the negative supply when the reference current is between 2mA and 4mA. This is necessary to avoid saturation of the output transistors, which would cause serious degradation of accuracy. Philips Semiconductors MC1508/MC1408 does not need a range control because the design extends the compliance range down to 4.5V (or 8V — see above) above the negative supply voltage without significant degradation of accuracy. Philips Semiconductors MC1508/MC1408 can be used in sockets designed for other manufacturers’ MC1508/MC1408 without circuit modification. Output Current Range Any time the full-scale current exceeds 2mA, the negative supply must be at least 8V more negative than the output voltage. This is due to the increased internal voltage drops between the negative supply and the outputs with higher reference currents. Accuracy Absolute accuracy is the measure of each output current level with respect to its intended value, and is dependent upon relative accuracy, full-scale accuracy and full-scale current drift. Relative accuracy is the measure of each output current level as a fraction of the full-scale current after zero-scale current has been nulled out. The relative accuracy of the MC1508/MC1408 is essentially constant over the operating temperature range because of the excellent temperature tracking of the monolithic resistor ladder. The reference current may drift with temperature, causing a change in the absolute accuracy of output current; however, the MC1508/MC1408 has a very low full-scale current drift over the operating temperature range. The MC1508/MC1408 series is guaranteed accurate to within ±1/2LSB at +25°C at a full-scale output current of 1.99mA. The relative accuracy test circuit is shown in Figure 3. The 12-bit converter is calibrated to a full-scale output current of 1.99219mA; then the MC1508/MC1408’s full-scale current is trimmed to the same value with R14 so that a zero value appears at the error amplifier output. The counter is activated and the error band may be displayed on the oscilloscope, detected by comparators, or stored in a peak detector. Two 8-bit D-to-A converters may not be used to construct a 16-bit accurate D-to-A converter. 16-bit accuracy implies a total of ±1/2 part in 65,536, or ±0.00076%, which is much more accurate than the ±0.19% specification of the MC1508/MC1408. Monotonicity A monotonic converter is one which always provides an analog output greater than or equal to the preceding value for a corresponding increment in the digital input code. The MC1508/MC1408 is monotonic for all values of reference current above 0.5mA. The recommended range for operation is a DC reference current between 0.5mA and 4.0mA. Settling Time The worst case switching condition occurs when all bits are switched on, which corresponds to a low-to-high transition for all input bits. This time is typically 70ns for settling to within 1/2LSB for 8-bit accuracy. This time applies when RL < 500Ω and CO < 25pF. The slowest single switch is the least significant bit, which typically turns on and settles in 65ns. In applications where the D-to-A converter functions in a positive going ramp mode, the worst-case condition does not occur and settling times less than 70ns may be realized. Extra care must be taken in board layout since this usually is the dominant factor in satisfactory test results when measuring settling time. Short leads, 100µF supply bypassing for low frequencies, minimum scope lead length, good ground planes, and avoidance of ground loops are all mandatory.
Figure 1. Positive VREF Figure 2. Negative VREF Figure 3. Relative Accuracy