Switching Waveform DATA BITS VALID DAC DATA lOUT louT? SETTLED TO ±LS ww.national. com
Switching Waveform 00560802 DAC0830/DAC0832 www.national.com 6
Definition of Package Pinouts Control Signals (All control signals level actuated) resistor for the amp which is used to CS: Chip Select(active low). The CS in combination provide an output the DAC. This on-chip with ILE will enable WR1 resistor should used(not an external ILE: Input Latch Enable(active high). The ILE in com- resistor)since it le resistors which are bination with cs enables wr used in the on-chip R-2R ladder and tracks these WR,: Write 1. The active low WR, is used to load the resistors over temperature digital input data bits(DI) into the input latch. The VREF: Reference Voltage Input. This input connects an data in the input latch is latched when WR, is high extemal precision voltage source to the internal To update the input latch-CS and WR, must be low R-2R ladder VREF can be selected over the range while ILE is high. of +10 to-10V. This is also the analog voltage input WR2 Write 2(active low). This signal, in combination with for a 4-quadrant multiplying DAC application. XFER. causes the 8-bit data which is available in the Vcc: Digital Supply Voltage. This is the power supply input latch to transfer to the DAC register pin for the part. Vcc can be from +5 to +15voc Operation is optimum for +15Voc XFER: Transfer control signal (active low). The XFER will GND 10 voltage must be at the same ground Other Pin Functions of potential 10)will result in a linearity change of DIo DI7: Digital Inputs. DIo is the least significant bit(LSB) and DI, is the most significant bit(MSB) lOuT1: DAC Current Output 1. lOuT1 is a maximum for a Vos pin 10 digital code of all 1,s in the DAC register, and is zero for all Os in DAC register. lOUT?: DAC Current Output 2. louT? For example, if VReF 10V and pin 10 n OuT1, or louTH constant (I full scale for a lOUT1 and lOuTz the linearity change will be 0.03%. fixed reference voltage) Pin 3 can be offset t 100mv with no linearity change, but the Rt: Feedback Resistor. The feedback resistor is ogic input threshold will shift vided on the Ic chip for use as the shunt feed Linearity Error 坠 LSB ERRDR 1 LSB ERROR EAL RESPONSE a) End point test afterzero and fs b) Best straight line c)shifting fs adj. to pas best straight line test Definition of terms Resolution: Resolution is directly related to the number of after a single full scale adjust. (One adjustment vs. multiple switches or bits within the DAC. For example, the DAC0830 iterations of the adjustment. ) The"end point test"uses a has 2 or 256 steps and therefore has 8-bit resolution standard zero and F.s. adjustment procedure and is a much Linearity Error: Linearity Error is the maximum deviation more stringent test for DAC linearity. from a straight line passing through the endpoints of the Power Supply Sensitivity: Power supply sensitivity is a DAC transfer characteristic. It is measured after adjusting for measure of the effect of power supply changes on the DAC zero and full-scale. Linearity error is a parameter intrinsic to full-scale output the device and cannot be externally adjusted Settling Time: Settling time is the time required from a code National's linearity " end point test(a) and the "best straight transition until the daC output reaches within tyLSB of the line test(b, c)used by other suppliers are illustrated above final output value. Full-scale settling time requires a zero to The end point test" greatly simplifies the adjustment proce- full-scale or full-scale to zero output change dure by eliminating the need for multiple iterations of check Full Scale Error: Full scale error is a measure of the output g the linearity and then adjusting full scale until the linearity error between an ideal DAC and the actual device output. is met. The"end point test" guarantees that linearity is met ww.national. com
Definition of Package Pinouts Control Signals (All control signals level actuated) CS: Chip Select (active low). The CS in combination with ILE will enable WR1. ILE: Input Latch Enable (active high). The ILE in combination with CS enables WR1. WR1: Write 1. The active low WR1 is used to load the digital input data bits (DI) into the input latch. The data in the input latch is latched when WR1 is high. To update the input latch–CS and WR1 must be low while ILE is high. WR2: Write 2 (active low). This signal, in combination with XFER, causes the 8-bit data which is available in the input latch to transfer to the DAC register. XFER: Transfer control signal (active low). The XFER will enable WR2. Other Pin Functions DI0-DI7: Digital Inputs. DI0 is the least significant bit (LSB) and DI7 is the most significant bit (MSB). IOUT1: DAC Current Output 1. IOUT1 is a maximum for a digital code of all 1’s in the DAC register, and is zero for all 0’s in DAC register. IOUT2: DAC Current Output 2. IOUT2 is a constant minus IOUT1 , or IOUT1 + IOUT2 = constant (I full scale for a fixed reference voltage). Rfb: Feedback Resistor. The feedback resistor is provided on the IC chip for use as the shunt feedback resistor for the external op amp which is used to provide an output voltage for the DAC. This on-chip resistor should always be used (not an external resistor) since it matches the resistors which are used in the on-chip R-2R ladder and tracks these resistors over temperature. VREF: Reference Voltage Input. This input connects an external precision voltage source to the internal R-2R ladder. VREF can be selected over the range of +10 to −10V. This is also the analog voltage input for a 4-quadrant multiplying DAC application. VCC: Digital Supply Voltage. This is the power supply pin for the part. VCC can be from +5 to +15VDC. Operation is optimum for +15VDC GND: The pin 10 voltage must be at the same ground potential as IOUT1 and IOUT2 for current switching applications. Any difference of potential (VOS pin 10) will result in a linearity change of For example, if VREF = 10V and pin 10 is 9mV offset from IOUT1 and IOUT2 the linearity change will be 0.03%. Pin 3 can be offset ±100mV with no linearity change, but the logic input threshold will shift. Linearity Error 00560823 a) End point test afterzero and fs adj. 00560824 b) Best straight line 00560825 c) Shifting fs adj. to pass best straight line test Definition of Terms Resolution: Resolution is directly related to the number of switches or bits within the DAC. For example, the DAC0830 has 28 or 256 steps and therefore has 8-bit resolution. Linearity Error: Linearity Error is the maximum deviation from a straight line passing through the endpoints of the DAC transfer characteristic. It is measured after adjusting for zero and full-scale. Linearity error is a parameter intrinsic to the device and cannot be externally adjusted. National’s linearity “end point test” (a) and the “best straight line” test (b,c) used by other suppliers are illustrated above. The “end point test’’ greatly simplifies the adjustment procedure by eliminating the need for multiple iterations of checking the linearity and then adjusting full scale until the linearity is met. The “end point test’’ guarantees that linearity is met after a single full scale adjust. (One adjustment vs. multiple iterations of the adjustment.) The “end point test’’ uses a standard zero and F.S. adjustment procedure and is a much more stringent test for DAC linearity. Power Supply Sensitivity: Power supply sensitivity is a measure of the effect of power supply changes on the DAC full-scale output. Settling Time: Settling time is the time required from a code transition until the DAC output reaches within ±1⁄2LSB of the final output value. Full-scale settling time requires a zero to full-scale or full-scale to zero output change. Full Scale Error: Full scale error is a measure of the output error between an ideal DAC and the actual device output. DAC0830/DAC0832 7 www.national.com
Definition of Terms (Continued) Monotonic: If the output of a DAC increases for ind digital input code, then the DAC is monotonic. An 8- Ideally, for the DAC0830 series, full scale is VREF -1LSB. which is monotonic to 8 bits simply means that in 10V and unipolar operation, VFULL-SCALE digital input codes will produce an increasing analog output s2 10,0000V-39mV 9.961V. Full-scale error is adjustable to Differential Nonlinearity: The difference between any two consecutive codes in the transfer curve from the theoretical 1 LSB to differential nonlinearity. 叫吹叫叫咖 DREGISTER OREGISTER O (LS 鼎8D NN:=::R5 FIGURE 1. DAC0830 Functional diagram Typical Performance Characteristics Digital Input Threshold Digital Input Threshold Gain and Linearity Error vS Temp vS Vcc Variation vS. Temperature 20.05 55-35-15525456585105125 55-35-15525456585105125 TA. AMBIENT TEMPERATURE ICI Vcc SUPPLY VOLTAGE IV ww.national. com
Definition of Terms (Continued) Ideally, for the DAC0830 series, full scale is VREF −1LSB. For VREF = 10V and unipolar operation, VFULL-SCALE = 10,0000V–39mV 9.961V. Full-scale error is adjustable to zero. Differential Nonlinearity: The difference between any two consecutive codes in the transfer curve from the theoretical 1 LSB to differential nonlinearity. Monotonic: If the output of a DAC increases for increasing digital input code, then the DAC is monotonic. An 8-bit DAC which is monotonic to 8 bits simply means that increasing digital input codes will produce an increasing analog output. Typical Performance Characteristics Digital Input Threshold vs. Temperature Digital Input Threshold vs. VCC Gain and Linearity Error Variation vs. Temperature 00560826 00560827 00560828 00560804 FIGURE 1. DAC0830 Functional Diagram DAC0830/DAC0832 www.national.com 8
Typical Performance Characteristics (Continued) Gain and Linearity Error /rite Pulse width Variation Vs Supply Voltage Data hold time +0.D25 INEARITY ERROR 4△ GAIN ERROR 3王减 100 12V,15V -0.125 =25°c 下: 6585105125 55-35-15525456585105125 VEc- SUPPLY VDLTAGE (VD TA AMBIENT TEMPERATURE TA AMBIENT TEMPERATURE (CI DACo830 Series Application Hints These DAC's are the industry's first microprocessor compat- The timing requirements and logic level convention of the ible, double-buffered 8-bit multiplying D to A converters register control signals have been designed to minimize or Double-buffering allows the utmost application flexibility from eliminate external interfacing logic when applied to most a digital control point of view. This 20-pin device is also pin popular microprocessors and development systems. It is for pin compatible(with one exception)with the DAC 1230, a think of thes 12-bit MICRO-DAC. In the event that a systems analog memory locations that provide an analog output quantity. All puts to these DAC's meet TTL voltage level specs and can ng the DAC 1230 can be easily accomplished. By also be driven directly with high voltage CMOs logic in ddress bit Ao to the ILE pin, a two-byte uP write inst non-microprocessor based systems. To prevent damage (double precision) which automatically increments the chip from static discharge, all unused digital inputs dress for the second byte write(starting with Ao=1) can be should be tied to Vcc or ground. If any of the digital inputs used. This allows either an 8-bit or the 12-bit part to be used are inadvertantly left floating the DAC interprets the pin as a with no hardware or software changes. For the sin ogc“1 pplication, this pin should be tied to Vcc(also see other uses in section 1.1) 1.1 Double-Buffered o Analog signal control versatility is provided by a precision Updating the analog output of these DAC's in a R-2R ladder network which allows full 4-quadrant multiplica double-buffered manner is basically a two step or double tion of a wide range bipolar reference voltage by an applied write operation. In a microprocessor system two unique digital word. system addresses must be decoded, one for the input latch controlled by the Cs pin and a second for the DAC latch 1.0 DIGITAL CONSIDERATIONS which is controlled by the XFER line. If more than one DAC A most unique characteristic of these DAC's is that the 8-bi is being driven, Figure 2, the CS line of each DAC would digital input byte is double-buffered. This means that the typically be decoded individually, but all of the converters data must transfer through two independently controlled 8-bit ould share a common xFer address to allow simultaneous latching registers before being applied to the R-2R ladder network to change the analog output. The addition of a tion is shown, Figure Of DAC's. The timing for this opera- second register allows two useful control features. First, any It is important to note that the analog outputs that will change DAC in a system can simultaneously hold the current DAC after a simultaneous transfer are those from the dAcs data in one register(DAC register) and the next data word in whose input register had been modified prior to the the second register (input register) to allow fast updating of command the DAC output on demand. Second, and probably more system to be updated to their new analog output levels simultaneously via a common strobe signal ww.national. com
Typical Performance Characteristics (Continued) Gain and Linearity Error Variation vs. Supply Voltage Write Pulse Width Data Hold Time 00560829 00560830 00560831 DAC0830 Series Application Hints These DAC’s are the industry’s first microprocessor compatible, double-buffered 8-bit multiplying D to A converters. Double-buffering allows the utmost application flexibility from a digital control point of view. This 20-pin device is also pin for pin compatible (with one exception) with the DAC1230, a 12-bit MICRO-DAC. In the event that a system’s analog output resolution and accuracy must be upgraded, substituting the DAC1230 can be easily accomplished. By tying address bit A0 to the ILE pin, a two-byte µP write instruction (double precision) which automatically increments the address for the second byte write (starting with A0=“1”) can be used. This allows either an 8-bit or the 12-bit part to be used with no hardware or software changes. For the simplest 8-bit application, this pin should be tied to VCC (also see other uses in section 1.1). Analog signal control versatility is provided by a precision R-2R ladder network which allows full 4-quadrant multiplication of a wide range bipolar reference voltage by an applied digital word. 1.0 DIGITAL CONSIDERATIONS A most unique characteristic of these DAC’s is that the 8-bit digital input byte is double-buffered. This means that the data must transfer through two independently controlled 8-bit latching registers before being applied to the R-2R ladder network to change the analog output. The addition of a second register allows two useful control features. First, any DAC in a system can simultaneously hold the current DAC data in one register (DAC register) and the next data word in the second register (input register) to allow fast updating of the DAC output on demand. Second, and probably more important, double-buffering allows any number of DAC’s in a system to be updated to their new analog output levels simultaneously via a common strobe signal. The timing requirements and logic level convention of the register control signals have been designed to minimize or eliminate external interfacing logic when applied to most popular microprocessors and development systems. It is easy to think of these converters as 8-bit “write-only” memory locations that provide an analog output quantity. All inputs to these DAC’s meet TTL voltage level specs and can also be driven directly with high voltage CMOS logic in non-microprocessor based systems. To prevent damage to the chip from static discharge, all unused digital inputs should be tied to VCC or ground. If any of the digital inputs are inadvertantly left floating, the DAC interprets the pin as a logic “1”. 1.1 Double-Buffered Operation Updating the analog output of these DAC’s in a double-buffered manner is basically a two step or double write operation. In a microprocessor system two unique system addresses must be decoded, one for the input latch controlled by the CS pin and a second for the DAC latch which is controlled by the XFER line. If more than one DAC is being driven, Figure 2, the CS line of each DAC would typically be decoded individually, but all of the converters could share a common XFER address to allow simultaneous updating of any number of DAC’s. The timing for this operation is shown, Figure 3. It is important to note that the analog outputs that will change after a simultaneous transfer are those from the DAC’s whose input register had been modified prior to the XFER command. DAC0830/DAC0832 9 www.national.com
DACo830 Series Application Hints (Continued) ANALOG CS FER cs ADDRES DAC n TIE TO LOGIC 1 IF NOT NEEDED (SEE SEC. 1.1). FIGURE 2. Controlling Mutiple DACs DATA BUS DAC REGISTER LATCHED The ILE pin is an active high chip select which can be written to the DAC. This can be particularly useful in multi decoded from the address bus as a qualifier for the normal processing systems to allow a processor other than the one CS signal generated during a write operation. This can be controlling the DAC's to take over control of the data bus and used to provide a higher degree of decoding unique control control lines. If this second system were to use the same signals for a particular DAC, and thereby create a more addresses as those decoded for DAC control(but for a efficient addressing scheme different purpose) the ILE function would prevent the DAC's Another useful application of the iLE pin of each DAC in a from being ultiple DAC system is to tie these inputs together and use In a"Stand-Alone system the control signals are generated this as a control line that can effectively "freeze the outputs by discrete logic. In this case double-buffering can be con- of all the DAC's at their present value. Pulling this line low trolled by simply taking CS and XFER to a logic"0, iLE to a latches the input register and prevents new data from being logic "1and pulling WR, low to load data to the input latch ww.national. com
DAC0830 Series Application Hints (Continued) The ILE pin is an active high chip select which can be decoded from the address bus as a qualifier for the normal CS signal generated during a write operation. This can be used to provide a higher degree of decoding unique control signals for a particular DAC, and thereby create a more efficient addressing scheme. Another useful application of the ILE pin of each DAC in a multiple DAC system is to tie these inputs together and use this as a control line that can effectively “freeze” the outputs of all the DAC’s at their present value. Pulling this line low latches the input register and prevents new data from being written to the DAC. This can be particularly useful in multiprocessing systems to allow a processor other than the one controlling the DAC’s to take over control of the data bus and control lines. If this second system were to use the same addresses as those decoded for DAC control (but for a different purpose) the ILE function would prevent the DAC’s from being erroneously altered. In a “Stand-Alone” system the control signals are generated by discrete logic. In this case double-buffering can be controlled by simply taking CS and XFER to a logic “0”, ILE to a logic “1” and pulling WR1 low to load data to the input latch. 00560835 *TIE TO LOGIC 1 IF NOT NEEDED (SEE SEC. 1.1). FIGURE 2. Controlling Mutiple DACs 00560836 FIGURE 3. DAC0830/DAC0832 www.national.com 10