MOTOROLA | SEMICONDUCTOR Po TECHNICAL DATA EIGHT-BIT MULTIPLYING DIGITAL-TO-ANALOG CONVERTER . designed for use where the output current is a linear product of an eight-bit digital word and an analog input voltage. @ Ejight-Bit Accuracy Available in Both Temperature Ranges Relative Accuracy: +0.19% Error maximum (MC1408L8, MC1408P8, MC1508L8} Seven and Six-Bit Accuracy Available with MC1408 Designated by 7 or 6 Suffix after Package Suffix Fast Settling Time 300 ns typical Noninverting Digital Inputs are MTTL and CMOS Compatible Output Voltage Swing +0.4 V to -5.0V High-Speed Multiplying Input Slew Rate 4.0 mA/ps @ Standard Supply Voltages: +5.0 V and -5.0V to-15V MC1408 MC1508 EIGHT-BIT MULTIPLYING DIGITAL-TO-ANALOG CONVERTER SILICON MONOLITHIC INTEGRATED CIRCUIT L SUFFIX CERAMIC PACKAGE CASE 620 P SUFFIX PLASTIC PACKAGE CASE 648 ORDERING INFORMATION Device Temperature Range Package MC1408PB Plastic MC1408LB Oto +78C Ceramic MC1508LB 55 to +1255C Ceramic FIGURE 1 D-to-A TRANSFER CHARACTERISTICS io, OUTPUT CURRENT (mA) 2.0 (a0000000) (11411191) INPUT DIGITAL WORD FIGURE 2 BLOCK DIAGRAM MSB LSB A19 A290 ASO Aad ABQ ABO A7Q ABO RANGE CONTROL =o 10-4 O4 R 2 Ladder O2 GND Vreti+) 149 b013 Reference Vee 16 OF Current Vret(-) Amplifier 16 COMPEN Verbs NPN Current Source Pair MOTOROLA LINEAR/INTERFACE ICs DEVICE DATA 6-15MC1408, MC1508 MAXIMUM RATINGS (Tp = +25C unless otherwise noted.) Rating Symbol Value Unit Power Supply Voltage Vec +6,5 Vde VEE ~16.5 Digital Input Voltage V5 thru V412 Oto +5.5 Vde Applied Output Voltage Vo +0,5,-5.2 Vde Reference Current 144 5.0 mA Reference Amplifier inputs Via.V15 Voc. VEE Vde Operating Temperature Range Ta C MC1508 -56 to +125 MC 1408 Series Oto +75 Storage Temperature Range Tstg ~65 to +150 % Vref ELECTRICAL CHARACTERISTICS (Vcc = +5.0 Vdc, VEE =-15 Vde, R14 MC1408L Series: Ta = 0 to + 75C unless otherwise noted. Ail digital inputs at high logic level.) = 2.0 mA, MC1508L8: Ta = -55C to +125C. Characteristics Figure | Symbol Min Typ Max Unit Relative Accuracy (Error relative to full scale Io) 4 Er Yo MC1508L8, MC1408L8, MC1408P8 _ 0.19 _ _ +0.39 = +0.78 Settling Time to with + 1/2 LSB [includes tpLWI(Ta = + 25C) (Note 2) 5 ts _ 300 = ns Propagation Delay Time 5 tPHL _ 30 100 ns Ta = + 25C tPHL Output Full Scale Current Drift TClo _ - 20 _ PPM/C Digital Input Logic Levels (MSB) 3 Vde High Level, Logic 1 VIH 2.0 _ Low Level, Logic 0 VIL 0.8 Digital Input Current (MSB) 3 mA High Level, VjH = 5.0 V WH 0 0.04 Low Level, Vi, = 0.8 V fe _ ~ 0.4 -0.8 Reference Input Bias Current (Pin 15) 3 hs _ - 1.0 -5.0 pA Output Current Range 3 lor mA Veg =-5.0V 0 2.0 2.1 VEE =- 15 V, Ta = 26C 0 2.0 4.2 Output Current 3 lo mA VREF = 2.000 V, R14 = 1000 2 1.9 1.99 2.1 Output Current 3 to(min) 0 4.0 HA {All Bits Low) Output Voltage Compliance (E, < 0.19% at Ta = + 25C) 3 Vo Vde Pin 1 Grounded _ _ -0.55, +0.4 Pin 1 Open, Veg below - 10 V _ -5.0, +0.4 Reference Current Slew Rate 6 SR lref _ 4.0 _ mA/us Output Current Power Supply Sensitivity PSRR(-} 0.5 2.7 pA Power Supply Current 3 lec _ + 13.5 +22 mA (All Bits Low) IEE -75 ~13 Power Supply Voltage Range 3 VCCR +45 +5.0 +55 Vdc (Ta = + 25C) VEER -45 -15 - 16.5 Power Dissipation 3 Pp mw All Bits Low VEE = 5.0 Vde VEE =-15 Vde _ 105 170 _ 190 305 All Bits High Vee = 5.0 Vde 90 _ Veg =-15 Vde _ 160 _ Notes: 1. All current switches are tested to guarantee at least 50% of rated output current. 2. All bits switched. MOTOROLA LINEAR/INTERFACE ICs DEVICE DATA 6-16MC1408, MC1508 TEST CIRCUITS FIGURE 3 NOTATION DEFINITIONS TEST CIRCUIT Vec t t CC typical Values 13 . laa V| and |, apply to inputs At 14 R14 Al 5 -_ thru AS a2 0% \ The resistor tied to pin 15 is to temperature compensate the Ag on 15 15 bias current and may not be necessary for ail applications. 8 1 R15 Lt Digital? 4451 metacs [> ~ Al A2 AS A& AB AB AP AB (Inputs ) A5 O- Series lo=K __ _ ew yp yg Ge tot ag ol] mcis08 ja = Vo 2 4 8 16 32 64 128 256 14 Output Viet ATOR 16 where K = - A8 oO lo R14 - RL ty c and Aq = 1 if Ay is at high level vig ' AN = "0" if An is at low level = (See text for I ee ie vaiues of C) FIGURE 4 RELATIVE ACCURACY TEST CIRCUIT MSB OAT ___ oo A2 --o a3 12-Bit D-t0-A o a4 Oto +10 V Output ag Converter o- | {40.02% [On AB error max) -o- a7 5k pO AS AD AID Al A12 LsB 50 k Veet E2v | OT UF + 100 = Error (1 V = 1%! 950 v R14 cc MC1556 use it 13 5 6 7 8 . -o- MC 1408 Series 4 8-Bit Counter to > 9 Mc1508 10 11 }$o 12 LsB 1s] i} 3} 2, 1 1K c + + = VEE FIGURE 5 TRANSIENT RESPONSE and SETTLING TIME Vec FE Key tPHL = 'PLH G10 ns Internal Clamp Level orv-4 SETTLING TIM 0.1 uF LING TIME me T wk @o for Figures Use Ry to GND for turn off measurement (see text}. Mc 1408 Series bee For settling time Tao ; ele Mc1508 measurement. 30 " vRica (All bits switched to+1/2 LSB low to high) 15 pF ARCO S25 pF a | ; TRANSIENT R502 L RESPONSE pin 4 to GND + ~100 Vee mv ol tL ee ter MOTOROLA LINEAR/INTERFACE ICs DEVICE DATA 6-17MC1408, MC1508 TEST CIRCUITS (continued) FIGURE 6 REFERENCE CURRENT SLEW RATE MEASUREMENT RL =50 Scope dl 1 dv 10% -F7- 90% at RL at 2.0 mA Slewing Time FIGURE 7 POSITIVE Vyoe Vee l., R14 =A15 ae 6 14 R14 A204 [oO Vice 7 15 ASO 8 Ri5 A4Q- 4 1 + 9 | Mc1408 2 A50 Series R 4 = L Ab QW MC 1508 oe 1 16 ou = ATO 12 See text for values of C A8 O-+ c 3 VEE FIGURE 8 NEGATIVE Vye Vee I, A146=RI15 atom 6 14 R14 aro [MT 1 A304 po a) Veet 1 RIS sor 8 | f= | 9 | mc1408 2 as Series 1 R 10 4 = L AGO MC 1508 v1 tw 10 1 A704 12 See text for values of C AB c 3 VEE MOTOROLA LINEARANTERFACE ICs DEVICE DATA 6-18MC1408, MC1508 FIGURE 9 MC1408, MC 1508 SERIES EQUIVALENT CIRCUIT SCHEMATIC DIGITAL INPUTS 9OA5 if CURRENT SWITCHES : 800 : 800 : R-2R 800 800 800 Fe00. 800 : 800... : = LADDER ne ie v 400 400 00 400 400 400 ia Voc : : REFERENCE - CURRENT 35 14 AMPLIFIER 255 Vrefi+)0 : : 12.5% 103 & - K q : 3 y BIAS CIRCUIT aks F 3k 160 150 js 61 62 COMPENSATION Vref (-) Vee OUTPUT GND RANGE CONTROL CIRCUIT DESCRIPTION The MC1408 consists of a reference current amplifier, an R-2R ladder, and eight high-speed current switches. For many applications, only a reference resistor and reference voltage need be added. The switches are noninverting 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 alt legs of the ladder. The R-2R ladder divides the reference amplifier current into binarily-related components, which are fed to the switches. Note that there is always a 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 amptifier current, or 1.992 mA for a 2.0 mA reference amplifier current if the NPN current source pair is perfectly matched. MOTOROLA LINEAR/INTERFACE ICs DEVICE DATA 6-19MC1408, MC1508 GENERAL INFORMATION Reference Amplifier Drive and Compensation The reference amplifier provides a voltage at pin 14 for con- verting the reference voltage to a current, and a turn-around circuit or current mirror for feeding the ladder. The reference amplifier input current, 114, must always flow into pin 14 regardless of the setup method or reference voltage polarity. Connections for a positive reference voltage are shown in Figure 7, The reference voltage source supplies the full current 114. For bipolar reference signals, as in the multiplying mode, R15 can be tied to a negative voltage corresponding to the minimum input level. It is possible to eliminate R15 with only a small sacrifice in accuracy and temperature drift. Another method for bipolar inputs is shown in Figure 25. The compensation capacitor value must be increased with in- creases in R14 to maintain proper phase margin; for R14 values of 1.0, 2.5 and 5.0 kilohms, minimum capacitor values are 15, 37, and 75 pF. The capacitor should be tied to VEE as this in- creases negative supply rejection. A negative reference voltage may be used if R14 is grounded and the reference voltage is applied to R15 as shown in Figure 8. A high input impedance is the main advantage of this method. Compensation invoives a capacitor to VEE on pin 16, using the values of the previous paragraph. The negative reference voltage must be at least 3.0-volts above the Veg supply. Bipolar input signals may be handled by connecting R14 to a positive reference valtage equal to the peak positive input level at pin 15. When adc reference voltage is used, capacitive bypass to ground is recommended. The 5.0-V logic supply is not recommended as a reference voltage. If a well regulated 5.0-V supply which drives logic is to be used as the reference, R14 should be decoupled by connecting it to +5.0 V through another resistor and bypassing the junction of the two resistors with 0.1 4F to ground. For reference voltages greater than 5.0 V, a clamp diode is recommen- ded between pin 14 and ground. lI 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 overal! bandwidth. Output Voltage Range The voltage on pin 4 is restricted to a range of ~0.55 to +0.4 volts at +25C, due to the current switching methods employed in the MC1408. When a current switch is turned off, the posi- tive voltage on the output terminal can turn on the output diode and increase the output current level. When a current switch is turned on, the negative output voltage range is restricted. The base of the termination circuit Darlington transistor is one diode voltage below ground when pin 1 is grounded, so a negative voltage below the specified safe level will drive the low current device of the Darlington into saturation, decreasing the output current level. The negative output voltage compliance of the MC1408 may be extended to -5.0 V volts by opening the circuit at pin 1. The negative supply voltage must be more negative than -10 volts. Using a full scale current of 1.992 mA and load resistor of 2.5 kilohms between pin 4 and ground will yield a voltage output of 256 levels between O and -4.980 volts. Floating pin 1 does not affect the converter speed or power dissipation. However, the value of the load resistor determines the switching time due to increased voltage swing. Values of RL up to 500 ohms do not sig- nificantly affect performance, but a 2.5-kilohm load increases worst case settling time to 1.2 us (when all bits are switched on). Refer to the subsequent text section on Settling Time for more details on output loading. If a power supply value between -5.0 V and -10 V is desired, a voltage of between 0 and -5.0 V may be applied to pin 1. The value of this voltage will be the maximum allowable negative out- put swing. Output Current Range The output current maximum rating of 4.2 mA may be used only for negative supply voltages typically more negative than -8.0 volts, due to the increased voltage drop across the 350-ohm resistors in the reference current amplifier. Accuracy Absolute accuracy is the measure of each output current level with respect to its intended value, and is dependent upon relative accuracy and full scale current drift. Relative accuracy is the measure of each output current level as a fraction of the full scale current. The relative accuracy of the MC1408 is essentially constant with temperature due to the excellent temperature track- ing of the monolithic resistor ladder. The reference current may drift with temperature, causing a change in the absolute accuracy of output current. However, the MC1408 has a very iow full scale current drift with temperature. The MC1408/MC1508 Series is guaranteed accurate to with- in +1/2 LSB at +25C at a full scale output current of 1.992 mA. This corresponds to a reference amplifier output current drive to the ladder network of 2.0 mA, with the loss of one LSB = 8.0uA which is the ladder remainder shunted to ground. The input current to pin 14 has a guaranteed value of between 1.9 and 2.1 mA, allowing some mismatch in the NPN current source pair. The accuracy test circuit is shown in Figure 4. The 12-bit converter is calibrated for a full scale output current of 1.992 mA. This is an optional step since the MC1408 accuracy is essentially the same between 1.5 and 2.5 mA. Then the MC1408 circuits 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 an 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 error of +1/2 of one part in 65, 536, or +0.00076%, which is much more accurate than the +0.19% specification provided by the MC1408x8. Multiplying Accuracy The MC1408 may be used in the multiplying mode with eight-bit accuracy when the reference current is varied over a range of 256:1. The major source of error is the bias current of the termination amplifier. Under worst case conditions, these eight amplifiers can contribute a total of 1.6 uA extra current at the output terminal. If the reference current in the multiplying mode ranges from 16 wA to 4.0 mA, the 1.6 wA contributes an error of 0.1 LSB. This is well within eight-bit accuracy referenced to 4.0mA. A monotonic converter is one which supplies an increase in current for each increment in the binary word. Typically, the MC1408 is monotonic for all values of reference current above 0.5mA. The recommended range for operation with a dc reference current is 0.5 to4.0 mA. MOTOROLA LINEAR/INTERFACE ICs DEVICE DATA 6-20MC1408, MC1508 GENERAL INFORMATION (Continued) Settling Time The worst case switching condition occurs when all bits are switched on, which corresponds to a tow-to-high transition for all bits. This time is typically 300 ns for settling to within +1/2 LSB, for 8-bit accuracy, and 200 ns to 1/2 LSB for 7 and 6-bit accuracy. The turn off is typically under 100 ns. These times apply when Ri <500 ohms and Cg <25 pF. The slowest single switch is the least significant bit, which turns on and settles in 250 ns and turns off in 80 ns. tn applica- tions where the D-to-A converter functions in a positive-going ramp mode, the worst case switching condition does not occur, and a settling time of tess than 300 ns may be realized. Bit Al turns on in 200 ns and off in 80 ns, while bit A6 turns on in 150 ns and off in 80 ns. The test circuit of Figure 5 requires a smaller voltage swing for the current switches due to internal voltage clamping in the MC- 1408. A 1.0-kilohm toad resistor from pin 4 to ground gives a typical settling time of 400 ns. Thus, it is voltage swing and not the output RC time constant that determines settling time for most applications. Extra care must be taken in board layout since this is usually the dominant factor in satisfactory test results when measuring settling time. Short leads, 100 uF supply bypassing for low fre- quencies, and minimum scope tead length are al! mandatory. TYPICAL CHARACTERISTICS (Vec = +5.0 V, Vee =-15V, TA= +25C unless otherwise noted.) FIGURE 10 LOGIC INPUT CURRENT versus INPUT VOLTAGE 10 o o B 7 oo (), INPUT CURRENT (mA) S Nn 0 0 1.0 2.0 3.0 40 5.0 Vy), LOGIC INPUT VOLTAGE (Vdc) FIGURE 12 OUTPUT CURRENT versus OUTPUT VOLTAGE (See text for pin 1 restrictions) 2.0 18 Al @ High Level A2-A8 @ Low Level 16 Vo Range 12 for 8-bit Accuracy 06 pin 1 open Veg <-10 Vde ig, OUTPUT CURRENT (mA} a pin + grounded 70 -60 -50 40 - -1.0 0 Vg, OUTPUT VOLTAGE, PIN 4 (Vdc) +2.0 +3.0 FIGURE 11 TRANSFER CHARACTERISTIC versus TEMPERATURE {AS thru A8 thresholds lie within range for A1 thru A4) Ig, CUTPUT CURRENT (mA) 0 10 20 3.0 40 5.0 Vi, LOGIC INPUT VOLTAGE (Vitc} FIGURE 13 OUTPUT VOLTAGE versus TEMPERATURE (Negative range with pin 1 open is -5.0 Vde over full temperature range) +1.0 +0.8 +0.6 +04 40.2 Allowable Vg Range for 8-bit Accuracy -0.2 {ain 1 grounded} -0.4 -0.6 Vg, OUTPUT VOLTAGE, PIN 4 (Vdc) -0.8 1.0 55 0 +50 +100 +150 T, TEMPERATURE (C) MOTOROLA LINEAR/INTERFACE ICs DEVICE DATAMC1408, MC1508 TYPICAL CHARACTERISTICS (continued) (Voc = +5.0 V, Veg = -15 V, Ta = +25C unless otherwise noted.) FIGURE 15 TYPICAL POWER SUPPLY CURRENT FIGURE 14 REFERENCE INPUT FREQUENCY RESPONSE versus TEMPERATURE (all bits low) +8.0 +6.0 +4.0 +2.0 a -2.0 RELATIVE OUTPUT (dB) POWER SUPPLY CURRENT (mA} 0 0.1 10 10 -55 0 +50 +100 +150 f, FREQUENCY (MHz) T, TEMPERATURE (C) FIGURE 16 TYPICAL POWER SUPPLY CURRENT versus Veg (all bits low) Untess otherwise specified 20 R14 = R15 = 1.0kS2 C= 15 pF, pin 16 to Veg 18 RL = 50 $2, pin 4 to GND Curve A: Large Signal Bandwidth Method of Figure 7 Vref = 2.0 Vip-p} offset 1.0 V above GNO Curve B: Smalt Signal Bandwidth Method of Figure 7 Ry = 250 82 Vref = 50 mV(p-p) offset 200 mV above GND POWER SUPPLY CURRENT (mA} Ss Curve C: Large and Smatl Signal Bandwidth Method of Figure 25 (no op-ampt, Ry = 50 92) 60 Rg = 50.92 : Veet = 2.0V Vs = 100 mVip-p) centered at 0 V 40 60 8 -10 1200-14 16-18 Vee, NEGATIVE POWER SUPPLY (Vdc) APPLICATIONS INFORMATION FIGURE 17 OUTPUT CURRENT TO VOLTAGE CONVERSION Vref = 2.0 Vde R14 = R16 = 1.0 kO Ro = 5.0k0 Theoretical Vo MSB A1o=1 Vret Vo = Hef (Ro) [# + A2 AS, Adjust Vref, R14 or Ro so that Vo with all digital inputs at high level is equal to 9.961 volts. Vo = = (5k) Vo = 10V [=| = 9961V MC1741SG 16 or Equiv. VEE pF -20 Al A2. AS, A4 AS AB OA? A8 stato ++ 2 4 8 16 32 64 128 256 MOTOROLA LINEAR/INTERFACE ICs DEVICE DATA 6-22MC1408, MC1508 APPLICATIONS INFORMATION (continued) Voltage outputs of a larger magnitude are obtainable with this circuit which uses an external operational amplifier as a current to voltage converter. This configuration automatically keeps the output of the MC1408 at ground potential and the operational amplifier can generate a positive voltage limited only by its positive supply voltage. Frequency response and settling time are primarily determined by the characteristics of the operational amplifier. In addition, the operational amplifier must be compensated for unity gain, and in some cases overcompensation may be desirable. Note that this configuration results in a positive output voltage only, the magnitude of which is dependent on the digital input. The following circuit shows how the MLM301AG can be used in a feedforward mode resulting in a full scale settling time on the order of 2.0 us. FIGURE 18 65 pF (To pind of MC1508L8} An alternative method is to use the MC1539G and input com- pensation. Response of this circuit is also on the order of 2.0 us. See Motorola Application Note AN-459 for more details on this concept. FIGURE 19 +15 V@ 35 oF It iw 5k w-$4 7 10k 'o 2 8 (To pind _ 6 4 MC1508L8) o 3 |Mcis396 Vo 240 + 8 o2 ue a! tok 2200 oF = 1sv The positive voltage range may be extended by cascading the output with a high beta common base transistor, Q1, as shown. FIGURE 20 EXTENDING POSITIVE VOLTAGE RANGE (Resistor ana diode optional see text) Ge The output voltage range for this circuit is 0 volts to BYVcBO of the transistor. If pin 1 is left open, the transistor base may be grounded, eliminating both the resistor and the diode. Variations in beta must be considered for wide temperature range applica tions. An inverted output waveform may be obtained by using a load resistor from a positive reference voltage to the collector of the transistor. Also, high-speed operation is possible with a large output voltage swing, because pin 4 is held at a constant voltage. The resistor (R) to VEE maintains the transistor emitter voltage when all bits are off and insures fast turn-on of the least significant bit. Combined Output Amplifier and Voltage Reference For many of its applications the MC1408 requires a reference voltage and an operational amplifier. Normally the operational amplifier is used as a current to voltage converter and its output need only go positive. With the popular MC1723G voltage regula- tor both of these functions are provided in a single package with the added bonus of up to 150 mA of output current. See Figure 21. The MC1723G uses both a positive and negative power supply. The reference voltage of the MC1723G is then developed with respect to the negative voltage and appears as a common-mode signal to the reference amplifier in the O-to-A converter. This allows use of its output amplifier as a classic current-to-voltage converter with the non-inverting input grounded. Since +15 V and +5.0 V are normally available in a combina- tion digital-to-analog system, only the ~5.0 V need be developed. A resistor divider is sufficiently accurate since the allowable range on pin 5 is from -2.0 to -8.0 volts. The 5.0 kilohm pulldown resistor on the amplifier output is necessary for fast negative transitions. Full scale output may be increased to as much as 32 volts by increasing Ro and raising the +15 V supply voltage to 35 V maxi- mum. The resistor divider should be altered to comply with the maximum limit of 40 volts across the MC1723G. Cg may be decreased to maintain the same RQCg product if maximum speed is desired. MOTOROLA LINEAR/INTERFACE ICs DEVICE DATAMC1408, MC1508 APPLICATIONS INFORMATION (continued) Programmable Power Supply The circuit of Figure 21 can be used as a digitally programmed Power supply by the addition of thumbwheel switches and a BCD- to-binary converter. The output voltage can be scaled in several ways, including 0 to +25.5 volts in 0.1-volt increments, +0.05 volt; or 0 to 5.1 volts in 20 mV increments, +10 mV. FIGURE 21 COMBINED OUTPUT AMPLIFIER and VOLTAGE REFERENCE CIRCUIT Ro 5k Vee +8 V Co 25 pF 1 13 MsB og Mos Alo a2 A304 aad MC 1408 Series as 02 MC1508 as ol a7 oll ap of LsB ila hh 2 50 L ee 16 16k T BF | Vee -15 V R Vor Vret =< {a} Settling time for a 10-velt stap 1.0 us Bipolar or Negative Output Voltage The circuit of Figure 22 is a variation from the standard volt- age output circuit and will produce bipolar output signals. A positive current may be sourced into the summing node to offset the output voltage in the negative direction. For example, if approximately 1.0 mA is used a bipolar output signal results which may be described as a 8-bit 1's complement offset binary. Vref may be used as this auxiliary reference. Note that Ro has been doubled to 10 kilohms because of the anticipated 20 Vipp) output range. FIGURE 22 BIPOLAR OR NEGATIVE OUTPUT VOLTAGE CIRCUIT MC 1408 Series McC1508 vi Rp-2R14 fC -isv Ris = R14 Vee v Al A2 A3 Ad AB AG A? as] Vv Vo= iting ft. S248 Ae AB AS AT AB - RG) R14 2 4 8 16 32 64 128 256] Rag FIGURE 23 BIPOLAR OR INVERTED NEGATIVE OUTPUT VOLTAGE CIRCUIT MC 1408 Series mc1508 MC1741G or Equiv Yo For A = o0000000 bit configuration Vo= -Vret For a+5.0 volt output range Vref = -5.00 voits R14 = R15 = 2.5k2 ~Vret C = 37 pF (min) Ro =kQ Decrease Ro to 2.5 k for a 0 to -5.0-voit output range. This application provides somewhat lower speed, as previously discussed in the Output Voltage Range section of the General Information. MOTOROLA LINEAR/INTERFACE ICs DEVICE DATA 6-24MC1408, MC1508 APPLICATIONS INFORMATION (continued) Polarity Switching Circuit, 8-Bit Magnitude Plus Sign D-to-A Converter Bipolar outputs may also be obtained by using a polarity switch- ing circuit. The circuit of Figure 24 gives 8-bit magnitude plus asign bit. In this configuration the operational amplifier is switched between a gain of +1.0 and -1.0. Although another operational amplifier is required, no more space is taken when a dual operational amplifier such as the MC1558G is used. The transistor should be selected for a very low saturation voltage and resistance. FIGURE 24 POLARITY SWITCHING CIRCUIT (8-Bit Magnitude Plus Sign D-to-A Converter) R 10k Vo = VoP VoP Polarity Contrai Bit Programmable Gain Amplifier or Digital Attenuator When used in the multiplying mode the MC1408 can be applied as a digital attenuator. See Figure 25. One advantage of this technique is that if Rg = 50 ohms, no compensation capacitor is needed. The small and large signal bandwidths are now identical and are shown in Figure 14. The best frequency response is obtained by not allowing 114 to reach zero. However, the high impedance node, pin 16, is clamped to prevent saturation and insure fast recovery when the current through R14 goes to zero. Rg can be set for a+1.0 mA variation in relation to 114. 144 can never be negative. The output current is always unipolar. The quiescent de output current level changes with the digital word which makes ac coupling necessary. FIGURE 25 PROGRAMMABLE GAIN AMPLIFIER OR DIGITAL ATTENUATOR CIRCUIT Vs Veet When Vg = 0, 114 = 2.0 mA Viet VS Vo: ara | (4) Fe Panel Meter Readout The MC1408 can be used to read out the status of BCD or binary registers or counters in a digital control system The current output can be used to drive directly an analog panel meter. Ex- ternal meter shunts may be necessary if a meter of less than 2.0 mA full scale is used. Full scale calibration can be done by adjust- ing R14 or Veet FIGURE 26 PANEL METER READOUT CIRCUIT Digital Word From Counter or Register usB TH MC1408 Series 4 MC1508 = al 2h6 313 c Observe internal meter resistance (for pin 4 Voc voltage swing] = Vee ~ FIGURE 27 DC COUPLED DIGITAL ATTENUATOR and DIGITAL SUBTRACTION Vv ret 2 5 MC1741G MC 1408 Series or Equiv MC1508 f2t 9 ts ref 1 44 me A144 MC1408 Series AIS, 46 Mc1S508 v L = a} altel sl 13 MC1I741G = or Equiv = c Vee Vec v v 'o2* lB tortor bog2 24 {a} - whe {3} = Riay R149 'atlo='o4 Digital Subtraction: Programmable Amplifier B Veet 1 _ Vret2 Connect Digital Inputs so A Ler - Se wt Piay R149 Vret 1 Vret 1 Vref 2 Vo= R ab - 48 Vor 4A SE LTS R14, olf } { }] { } R144 R149 MOTOROLA LINEAR/INTERFACE ICs DEVICE DATA 6-25MC1408, MC1508 APPLICATIONS INFORMATION (continued) FIGURE 36 TWO-DIGIT BCD CONVERSION Vec 5k 13 J R oa 15 RIS . Yo 12 MC 1741 tse | mc1aosu? [14 = For Equiv os Mc 1408P7 10 Most Significant om = BCD Word oH 5 2 1B k MSB 914 3 we ot 05% R14, LS Veet *7! I Vee 2 ri 1403 hs 4 15 RIS 12 + LSB | Mc1408L6 {1 of Mc14cepe {19 200 0.5% 1 9 Least Significant J OF 7 BCD Word 5 2 sB s 13 { = 1 Vee Two 8-bit, D-to-A converters can be used to build a two digit 4.0mA and 0.4 mA with the outputs connected to sum the currents. BCD D-to-A or A-to-D converter. If both outputs feed the virtual The error of the D-to-A converter handling the least significant ground of an operational amplifier, 10:1 current scating can be bits will be scated down by a factor of ten and thus an MC1408L6 achieved with a resistive current divider. If current output is de- may be used for the least significant word. sired, the units may be operated at full scale current levels of FIGURE 37 DIGITAL QUOTIENT OF TWO ANALOG VARIABLES or ANALOG-TO-DIGITAL CONVERSION Vin Clock Reset Ro Vref | 8-Bit Binary Counter = Comparator 4 R14 12 Veet own_o 1 R15 14 10 v. 15 MC1408 Series {| 9 = cc o+ 3 13 Mc1508 ; VEE TO CARS s 5 16 Q The circuit shown is a simple counter- 1 2 LSB MSB ramp converter, An UP/DOWN counter = > ._-_--_ and dual threshold comparator can be c used to provide faster operation and con- tinuous conversion. ce Vin/Ro Veet/R14 MOTOROLA LINEAR/INTERFACE ICs DEVICE DATA 6-26