DAC121C081/ DAC121C085 12-Bit Micro Power Digital-to-Analog Converter with an I2C-Compatible Interface General Description Features The DAC121C081 is a 12-bit, single channel, voltage-output digital-to-analog converter (DAC) that operates from a +2.7V to 5.5V supply. The output amplifier allows rail-to-rail output swing and has an 8.5µsec settling time. The DAC121C081 uses the supply voltage as the reference to provide the widest dynamic output range and typically consumes 132µA while operating at 5.0V. It is available in 6-lead TSOT and LLP packages and provides three address options (pin selectable). As an alternative, the DAC121C085 provides nine I2C addressing options and uses an external reference. It has the same performance and settling time as the DAC121C081. It is available in an 8-lead MSOP. The DAC121C081 and DAC121C085 use a 2-wire, I2C-compatible serial interface that operates in all three speed modes, including high speed mode (3.4MHz). An external address selection pin allows up to three DAC121C081 or nine DAC121C085 devices per 2-wire bus. Pin compatible alternatives to the DAC121C081 are available that provide additional address options. The DAC121C081 and DAC121C085 each have a 16-bit register that controls the mode of operation, the power-down condition, and the output voltage. A power-on reset circuit ensures that the DAC output powers up to zero volts. A powerdown feature reduces power consumption to less than a microWatt. Their low power consumption and small packages make these DACs an excellent choice for use in battery operated equipment. Each DAC operates over the extended industrial temperature range of −40°C to +125°C. The DAC121C081 and DAC121C085 are each part of a family of pin compatible DACs that also provide 8 and 10 bit resolution. For 8-bit DACs see the DAC081C081 and DAC081C085. For 10-bit DACs see the DAC101C081 and DAC101C085. ■ ■ ■ ■ Guaranteed Monotonicity to 12-bits Low Power Operation: 156 µA max @ 3.3V Extended power supply range (+2.7V to +5.5V) I2C-Compatible 2-wire Interface which supports standard (100kHz), fast (400kHz), and high speed (3.4MHz) modes ■ Rail-to-Rail Voltage Output ■ Very Small Package Key Specifications ■ ■ ■ ■ ■ ■ ■ Resolution INL DNL Settling Time Zero Code Error Full-Scale Error Supply Power — Normal — Power Down 12 bits ±8 LSB (max) +0.6 / -0.5 LSB (max) 8.5 µs (max) +10 mV (max) −0.7 %FS (max) 380 µW (3V) / 730 µW (5V) typ 0.5 µW (3V) / 0.9 µW (5V) typ Applications ■ ■ ■ ■ ■ Industrial Process Control Portable Instruments Digital Gain and Offset Adjustment Programmable Voltage & Current Sources Test Equipment Pin-Compatible Alternatives All devices are fully pin and function compatible. Resolution TSOT-6 and LLP-6 MSOP-8 Package w/ Packages External Reference 12-bit DAC121C081 DAC121C085 10-bit DAC101C081 DAC101C085 8-bit DAC081C081 DAC081C085 Connection Diagrams 30004901 30004902 30004910 I2C® is a registered trademark of Phillips Corporation. © 2008 National Semiconductor Corporation 300049 www.national.com DAC121C081/ DAC121C085 12-Bit Micro Power Digital-to-Analog Converter March 13, 2008 DAC121C081/ DAC121C085 Ordering Information Order Code Temperature Range Package Top Mark DAC121C081CIMK −40°C ≤ TA ≤ +125°C TSOT X84C DAC121C081CIMKX −40°C ≤ TA ≤ +125°C TSOT Tape-and-Reel X84C DAC121C081CISD −40°C ≤ TA ≤ +125°C LLP X87 DAC121C081CISDX −40°C ≤ TA ≤ +125°C LLP Tape-and-Reel X87 DAC121C085CIMM −40°C ≤ TA ≤ +125°C MSOP X90C DAC121C085CIMMX −40°C ≤ TA ≤ +125°C MSOP Tape-and-Reel X90C DAC121C08XEB Evaluation Board Block Diagram 30004903 www.national.com 2 Symbol Type VOUT Analog Output VA Supply Power supply input. For the TSOT and LLP versions, this supply is used as the reference. Must be decoupled to GND. GND Ground Ground for all on-chip circuitry. SDA Digital Input/Output Serial Data bi-directional connection. Data is clocked into or out of the internal 16-bit register relative to the clock edges of SCL. This is an open drain data line that must be pulled to the supply (VA) by an external pull-up resistor. SCL Digital Input Serial Clock Input. SCL is used together with SDA to control the transfer of data in and out of the device. ADR0 Digital Input, three levels Tri-state Address Selection Input. Sets the two Least Significant Bits (A1 & A0) of the 7-bit slave address. (see Table 1) ADR1 Digital Input, three levels Tri-state Address Selection Input. Sets Bits A6 & A3 of the 7-bit slave address. (see Table 1) VREF Supply Unbufferred reference voltage. For the MSOP-8, this supply is used as the reference. VREF must be free of noise and decoupled to GND. Ground Exposed die attach pad can be connected to ground or left floating. Soldering the pad to the PCB offers optimal thermal performance and enhances package selfalignment during reflow. PAD (LLP only) Equivalent Circuit Description Analog Output Voltage. Package Pinouts VOUT VA GND SDA SCL ADR0 ADR1 VREF PAD (LLP only) TSOT 1 2 3 4 5 6 N/A N/A N/A LLP 6 5 4 3 2 1 N/A N/A 7 MSOP-8 8 6 5 4 3 1 2 7 N/A 3 www.national.com DAC121C081/ DAC121C085 Pin Descriptions DAC121C081/ DAC121C085 Operating Ratings (Notes 1, 2) Absolute Maximum Ratings (Notes 1, 2) Operating Temperature Range If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage, VA Reference Voltage, VREFIN Digital Input Voltage (Note 7) Output Load Supply Voltage, VA Voltage on any Input Pin Input Current at Any Pin (Note 3) Package Input Current (Note 3) Power Consumption at TA = 25°C ESD Susceptibility (Note 5) VA, GND, VREF, VOUT, ADR0, ADR1 pins: Human Body Model Machine Model Charged Device Model (CDM) SDA, SCL pins: Human Body Model Machine Model Charged Device Model (CDM) Junction Temperature Storage Temperature −0.3V to +6.5V −0.3V to +6.5V ±10 mA ±20 mA See (Note 4) −40°C ≤ TA ≤ +125°C +2.7V to 5.5V +1.0V to VA 0.0V to 5.5V 0 to 1500 pF Package Thermal Resistances 2500V 250V 1000V 5000V 350V 1000V +150°C −65°C to +150°C Package θJA 6-Lead TSOT 6-Lead LLP 8-Lead MSOP 250°C/W 190°C/W 240°C/W Soldering process must comply with National Semiconductor's Reflow Temperature Profile specifications. Refer to www.national.com/packaging. (Note 6) Electrical Characteristics Values shown in this table are design targets and are subject to change before product release. The following specifications apply for VA = +2.7V to +5.5V, VREF = VA, CL = 200 pF to GND, input code range 48 to 4047. Boldface limits apply for TMIN ≤ TA ≤ TMAX and all other limits are at TA = 25°C, unless otherwise specified. Symbol Parameter Conditions Typical (Note 9) Limits (Note 9) Units (Limits) 12 Bits (min) STATIC PERFORMANCE Resolution Monotonicity INL Integral Non-Linearity DNL Differential Non-Linearity 12 Bits (min) +2.2 +8 LSB (max) −1.5 −8 LSB (min) +0.18 +0.6 LSB (max) −0.12 −0.5 LSB (min) ZE Zero Code Error IOUT = 0 +1.1 +10 mV (max) FSE Full-Scale Error IOUT = 0 −0.1 −0.7 %FSR (max) GE Gain Error All ones Loaded to DAC register −0.2 −0.7 %FSR (max) −20 µV/°C VA = 3V −0.7 ppm FSR/°C VA = 5V −1.0 ppm FSR/°C ZCED TC GE Zero Code Error Drift Gain Error Tempco ANALOG OUTPUT CHARACTERISTICS (VOUT) DAC121C085 0 VREF V (min) V (max) DAC121C081 0 VA V (min) V (max) Output Voltage Range(Note 10) ZCO FSO IOS Zero Code Output Full Scale Output Output Short Circuit Current (ISOURCE) www.national.com VA = 3V, IOUT = 200 µA 1.3 mV VA = 5V, IOUT = 200 µA 7.0 mV VA = 3V, IOUT = 200 µA 2.984 V VA = 5V, IOUT = 200 µA 4.989 V VA = 3V, VOUT = 0V, Input Code = FFFh. 56 mA VA = 5V, VOUT = 0V, Input Code = FFFh. 69 mA 4 IOS Output Short Circuit Current (ISINK) IO Continuous Output Current (Note 10) CL Maximum Load Capacitance ZOUT Conditions Typical (Note 9) VA = 3V, VOUT = 3V, Input Code = 000h. −52 mA VA = 5V, VOUT = 5V, Input Code = 000h. −75 mA Parameter Available on the DAC output Limits (Note 9) 11 Units (Limits) mA (max) RL = ∞ 1500 pF RL = 2kΩ 1500 pF 7.5 Ω DC Output Impedance REFERENCE INPUT CHARACTERISTICS- (DAC121C085 only) Input Range Minimum VREF 0.2 Input Range Maximum Input Impedance 1.0 V (min) VA V (max) 120 kΩ LOGIC INPUT CHARACTERISTICS (SCL, SDA) VIH Input High Voltage 0.7 x VA V (min) VIL Input Low Voltage 0.3 x VA V (max) IIN Input Current ±1 µA (max) CIN Input Pin Capacitance (Note 10) 3 pF (max) 0.1 x VA V (min) VHYST Input Hysteresis LOGIC INPUT CHARACTERISTICS (ADR0, ADR1) VIH Input High Voltage VA- 0.5V V (min) VIL Input Low Voltage 0.5 V (max) IIN Input Current ±1 µA (max) ISINK = 3 mA 0.4 V (max) ISINK = 6 mA 0.6 V (max) ±1 µA (max) LOGIC OUTPUT CHARACTERISTICS (SDA) VOL Output Low Voltage IOZ High-Impedence Output Leakage Current 5 www.national.com DAC121C081/ DAC121C085 Symbol DAC121C081/ DAC121C085 Symbol Parameter Conditions Typical (Note 9) Limits (Note 9) Units (Limits) POWER REQUIREMENTS VA Supply Voltage Minimum 2.7 V (min) Supply Voltage Maximum 5.5 V (max) Normal -- VOUT set to midscale. 2-wire interface quiet (SCL = SDA = VA). (output unloaded) IST_VA-1 VA DAC121C081 Supply Current VA = 2.7V to 3.6V 105 156 µA (max) VA = 4.5V to 5.5V 132 214 µA (max) VA = 2.7V to 3.6V 86 118 µA (max) VA = 4.5V to 5.5V 98 152 µA (max) 37 43 µA (max) 61 µA (max) IST_VA-5 VA DAC121C085 Supply Current IST_VREF VREF Supply Current (DAC121C085 only) VA = 2.7V to 3.6V VA = 4.5V to 5.5V 53 Power Consumption (VA & VREF for DAC121C085) VA = 3.0V 380 µW VA = 5.0V 730 µW PST Continuous Operation -- 2-wire interface actively addressing the DAC and writing to the DAC register. (output unloaded) fSCL=400kHz ICO_VA-1 VA DAC121C081 Supply Current fSCL=3.4MHz fSCL=400kHz ICO_VA-5 VA DAC121C085 Supply Current fSCL=3.4MHz ICO_VREF PCO VREF Supply Current (DAC121C085 only) Power Consumption (VA & VREF for DAC121C085) fSCL=400kHz fSCL=3.4MHz VA = 2.7V to 3.6V 134 220 µA (max) VA = 4.5V to 5.5V 192 300 µA (max) VA = 2.7V to 3.6V 225 320 µA (max) VA = 4.5V to 5.5V 374 500 µA (max) VA = 2.7V to 3.6V 101 155 µA (max) VA = 4.5V to 5.5V 142 220 µA (max) VA = 2.7V to 3.6V 193 235 µA (max) VA = 4.5V to 5.5V 325 410 µA (max) VA = 2.7V to 3.6V 33.5 55 µA (max) VA = 4.5V to 5.5V 49.5 71.4 µA (max) VA = 3.0V 480 µW VA = 5.0V 1.06 mW VA = 3.0V 810 µW VA = 5.0V 2.06 mW Power Down -- 2-wire interface quiet (SCL = SDA = VA) after PD mode written to DAC register. (output unloaded) IPD Supply Current (VA & VREF for DAC121C085) All Power Down Modes VA = 2.7V to 3.6V 0.13 1.52 µA (max) VA = 4.5V to 5.5V 0.15 3.25 µA (max) PPD Power Consumption (VA & VREF for DAC121C085) All Power Down Modes VA = 3.0V 0.5 µW VA = 5.0V 0.9 µW www.national.com 6 Values shown in this table are design targets and are subject to change before product release. The following specifications apply for VA = +2.7V to +5.5V, VREF = VA, RL = Infinity, CL = 200 pF to GND. Boldface limits apply for TMIN ≤ TA ≤ TMAX and all other limits are at TA = 25°C, unless otherwise specified. Symbol Typical (Note 9) Limits (Notes 9, 13) Units (Limits) 400h to C00h code change RL = 2kΩ, CL = 200 pF 6 8.5 µs (max) 1 V/µs Code change from 800h to 7FFh 12 nV-sec 0.5 nV-sec Multiplying Bandwidth(Note 12) VREF = 2.5V ± 0.1Vpp 160 kHz Total Harmonic Distortion(Note 12) VREF = 2.5V ± 0.1Vpp input frequency = 10kHz 70 dB VA = 3V 0.8 µsec VA = 5V 0.5 µsec Conditions (Note 13) Parameter ts Output Voltage Settling Time (Note 10) SR Output Slew Rate Glitch Impulse Digital Feedthrough tWU Wake-Up Time DIGITAL TIMING SPECS (SCL, SDA) Serial Clock Frequency Standard Mode Fast Mode High Speed Mode, Cb = 100pF High Speed Mode, Cb = 400pF 100 400 3.4 1.7 kHz (max) kHz (max) MHz (max) MHz (max) SCL Low Time Standard Mode Fast Mode High Speed Mode, Cb = 100pF High Speed Mode, Cb = 400pF 4.7 1.3 160 320 µs (min) µs (min) ns (min) ns (min) tHIGH SCL High Time Standard Mode Fast Mode High Speed Mode, Cb = 100pF High Speed Mode, Cb = 400pF 4.0 0.6 60 120 µs (min) µs (min) ns (min) ns (min) tSU;DAT Data Setup Time Standard Mode Fast Mode High Speed Mode 250 100 10 ns (min) ns (min) ns (min) Standard Mode 0 3.45 µs (min) µs (max) Fast Mode 0 0.9 µs (min) µs (max) High Speed Mode, Cb = 100pF 0 70 ns (min) ns (max) High Speed Mode, Cb = 400pF 0 150 ns (min) ns (max) fSCL tLOW tHD;DAT Data Hold Time tSU;STA Setup time for a start or a repeated start condition Standard Mode Fast Mode High Speed Mode 4.7 0.6 160 µs (min) µs (min) ns (min) tHD;STA Standard Mode Hold time for a start or a repeated start Fast Mode condition High Speed Mode 4.0 0.6 160 µs (min) µs (min) ns (min) tBUF Bus free time between a stop and start Standard Mode condition Fast Mode 4.7 1.3 µs (min) µs (min) tSU;STO Setup time for a stop condition 4.0 0.6 160 µs (min) µs (min) ns (min) Standard Mode Fast Mode High Speed Mode 7 www.national.com DAC121C081/ DAC121C085 A.C. and Timing Characteristics DAC121C081/ DAC121C085 Symbol Parameter Limits (Notes 9, 13) Units (Limits) 1000 ns (max) 20+0.1Cb 300 ns (min) ns (max) High Speed Mode, Cb = 100pF 10 80 ns (min) ns (max) High Speed Mode, Cb = 400pF 20 160 ns (min) ns (max) Standard Mode 250 ns (max) 20+0.1Cb 250 ns (min) ns (max) High Speed Mode, Cb = 100pF 10 80 ns (min) ns (max) High Speed Mode, Cb = 400pF 20 160 ns (min) ns (max) Standard Mode 1000 ns (max) 20+0.1Cb 300 ns (min) ns (max) High Speed Mode, Cb = 100pF 10 40 ns (min) ns (max) High Speed Mode, Cb = 400pF 20 80 ns (min) ns (max) 1000 ns (max) 20+0.1Cb 300 ns (min) ns (max) High Speed Mode, Cb = 100pF 10 80 ns (min) ns (max) High Speed Mode, Cb = 400pF 20 160 ns (min) ns (max) Standard Mode 300 ns (max) 20+0.1Cb 300 ns (min) ns (max) High Speed Mode, Cb = 100pF 10 40 ns (min) ns (max) High Speed Mode, Cb = 400pF 20 80 ns (min) ns (max) 400 pF (max) 50 10 ns (max) ns (max) 270 60 ns (max) ns (max) Conditions (Note 13) Typical (Note 9) Standard Mode Fast Mode trDA Rise time of SDA signal Fast Mode tfDA Fall time of SDA signal Fast Mode trCL Rise time of SCL signal Standard Mode trCL1 Rise time of SCL signal after a repeated start condition and after an acknowledge bit. Fast Mode Fast Mode tfCL Fall time of a SCL signal Cb Capacitive load for each bus line (SCL and SDA) tSP Pulse Width of spike suppressed (Notes 11, 10) Fast Mode High Speed Mode toutz SDA output delay (see Section 1.9) Fast Mode High Speed Mode 87 38 Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test conditions. Operation of the device beyond the maximum Operating Ratings is not recommended. Note 2: All voltages are measured with respect to GND = 0V, unless otherwise specified. Note 3: When the input voltage at any pin exceeds 5.5V or is less than GND, the current at that pin should be limited to 10 mA. The 20 mA maximum package input current rating limits the number of pins that can safely exceed the power supplies with an input current of 10 mA to two. Note 4: The absolute maximum junction temperature (TJmax) for this device is 150°C. The maximum allowable power dissipation is dictated by TJmax, the junction-to-ambient thermal resistance (θJA), and the ambient temperature (TA), and can be calculated using the formula PDMAX = (TJmax − TA) / θJA. The values for maximum power dissipation will be reached only when the device is operated in a severe fault condition (e.g., when input or output pins are driven beyond the operating ratings, or the power supply polarity is reversed). Note 5: Human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor. Machine model is a 220 pF capacitor discharged through 0 Ω. Charge device model simulates a pin slowly acquiring charge (such as from a device sliding down the feeder in an automated assembler) then rapidly being discharged. www.national.com 8 Note 7: The inputs are protected as shown below. Input voltage magnitudes up to 5.5V, regardless of VA, will not cause errors in the conversion result. For example, if VA is 3V, the digital input pins can be driven with a 5V logic device. 30004904 Note 8: To guarantee accuracy, it is required that VA and VREF be well bypassed. Note 9: Typical figures are at TJ = 25°C, and represent most likely parametric norms. Test limits are guaranteed to National's AOQL (Average Outgoing Quality Level). Note 10: This parameter is guaranteed by design and/or characterization and is not tested in production. Note 11: Spike suppression filtering on SCL and SDA will supress spikes that are less than 50ns for standard-fast mode and less than 10ns for hs-mode. Note 12: Applies to the Multiplying DAC configuration. In this configuration, the reference is used as the analog input. The value loaded in the DAC Register will digitally attenuate the signal at Vout. Note 13: Cb refers to the capacitance of one bus line. Cb is expressed in pF units. MAXIMUM LOAD CAPACITANCE is the maximum capacitance that can be driven by the DAC with output stability maintained. MONOTONICITY is the condition of being monotonic, where the DAC has an output that never decreases when the input code increases. MOST SIGNIFICANT BIT (MSB) is the bit that has the largest value or weight of all bits in a word. Its value is 1/2 of VA. MULTIPLYING BANDWIDTH is the frequency at which the output amplitude falls 3dB below the input sine wave on VREFIN with a full-scale code loaded into the DAC. POWER EFFICIENCY is the ratio of the output current to the total supply current. The output current comes from the power supply. The difference between the supply and output currents is the power consumed by the device without a load. SETTLING TIME is the time for the output to settle to within 1/2 LSB of the final value after the input code is updated. TOTAL HARMONIC DISTORTION (THD) is the measure of the harmonics present at the output of the DACs with an ideal sine wave applied to VREFIN. THD is measured in dB. WAKE-UP TIME is the time for the output to exit power-down mode. This time is measured from the rising edge of SCL during the ACK bit of the lower data byte to the time the output voltage deviates from the power-down voltage of 0V. ZERO CODE ERROR is the output error, or voltage, present at the DAC output after a code of 000h has been entered. Specification Definitions DIFFERENTIAL NON-LINEARITY (DNL) is the measure of the maximum deviation from the ideal step size of 1 LSB, which is VREF / 4096 = VA / 4096. DIGITAL FEEDTHROUGH is a measure of the energy injected into the analog output of the DAC from the digital inputs when the DAC output is not updated. It is measured with a full-scale code change on the data bus. FULL-SCALE ERROR is the difference between the actual output voltage with a full scale code (FFFh) loaded into the DAC and the value of VA x 4095 / 4096. GAIN ERROR is the deviation from the ideal slope of the transfer function. It can be calculated from Zero and FullScale Errors as GE = FSE - ZE, where GE is Gain error, FSE is Full-Scale Error and ZE is Zero Error. GLITCH IMPULSE is the energy injected into the analog output when the input code to the DAC register changes. It is specified as the area of the glitch in nanovolt-seconds. INTEGRAL NON-LINEARITY (INL) is a measure of the deviation of each individual code from a straight line through the input to output transfer function. The deviation of any given code from this straight line is measured from the center of that code value. The end point method is used. INL for this product is specified over a limited range, per the Electrical Tables. LEAST SIGNIFICANT BIT (LSB) is the bit that has the smallest value or weight of all bits in a word. This value is LSB = VREF / 2n where VREF is the supply voltage for this product, and "n" is the DAC resolution in bits, which is 12 for the DAC121C081. 9 www.national.com DAC121C081/ DAC121C085 Note 6: Reflow temperature profiles are different for lead-free packages. DAC121C081/ DAC121C085 Transfer Characteristic 30004905 FIGURE 1. Input / Output Transfer Characteristic Timing Diagrams 30004960 FIGURE 2. Serial Timing Diagram www.national.com 10 VREF = VA, fSCL = 3.4MHz, TA = 25°C, Input Code Range 48 to INL DNL 30004920 30004921 INL/DNL vs Temperature at VA = 3.0V INL/DNL vs Temperature at VA = 5.0V 30004922 30004923 INL/DNL vs VREFIN at VA = 3.0V INL/DNL vs VREFIN at VA = 5.0V 30004924 30004925 11 www.national.com DAC121C081/ DAC121C085 Typical Performance Characteristics 4047, unless otherwise stated. DAC121C081/ DAC121C085 INL/DNL vs VA Zero Code Error vs. VA 30004926 30004927 Zero Code Error vs. Temperature Full Scale Error vs. VA 30004928 30004936 Full Scale Error vs. Temperature Total Supply Current vs. VA 30004929 www.national.com 30004930 12 Total Supply Current vs. Temperature @ VA = 3V 30004932 30004931 Total Supply Current vs. Temperature @ VA = 5V 5V Glitch Response 30004934 30004933 Power-On Reset 30004935 13 www.national.com DAC121C081/ DAC121C085 VREF Supply Current vs. VA DAC121C081/ DAC121C085 1.0 Functional Description 1.1 DAC SECTION The DAC121C081 is fabricated on a CMOS process with an architecture that consists of switches and resistor strings that are followed by an output buffer. For simplicity, a single resistor string is shown in Figure 3. This string consists of 4096 equal valued resistors with a switch at each junction of two resistors, plus a switch to ground. The code loaded into the DAC register determines which switch is closed, connecting the proper node to the amplifier. The input coding is straight binary with an ideal output voltage of: 1.2 OUTPUT AMPLIFIER The output amplifier is rail-to-rail, providing an output voltage range of 0V to VA when the reference is VA. All amplifiers, even rail-to-rail types, exhibit a loss of linearity as the output approaches the supply rails (0V and VA, in this case). For this reason, linearity is specified over less than the full output range of the DAC. However, if the reference is less than VA, there is only a loss in linearity in the lowest codes. The output capabilities of the amplifier are described in the Electrical Tables. The output amplifiers are capable of driving a load of 2 kΩ in parallel with 1500 pF to ground or to VA. The zero-code and full-scale outputs for given load currents are available in the Electrical Characteristics Table. VOUT = VREF x (D / 4096) where D is the decimal equivalent of the binary code that is loaded into the DAC register. D can take on any integer value between 0 and 4095. This configuration guarantees that the DAC is monotonic. 1.3 REFERENCE VOLTAGE The DAC121C081 uses the supply (VA) as the reference. With that said, VA must be treated as a reference. The Analog output will only be as clean as the reference (VA). It is recommended that the reference be driven by a voltage source with low output impedance. The DAC121C085 comes with an external reference supply pin (VREF). For the DAC121C085, it is important that VREF be kept as clean as possible. The Applications section describes a handful of ways to drive the reference appropriately. Refer to Section 2.1 for details. 30004907 FIGURE 3. DAC Resistor String www.national.com 14 1.4.1 Basic I2C Protocol The I2C interface is bi-directional and allows multiple devices to operate on the same bus. To facilitate this bus configuration, each device has a unique hardware address which is referred to as the "slave address." To communicate with a particular device on the bus, the controller (master) sends the slave address and listens for a response from the slave. This response is referred to as an acknowledge bit. If a slave on the bus is addressed correctly, it Acknowledges (ACKs) the master by driving the SDA bus low. If the address doesn't match a device's slave address, it Not-acknowledges (NACKs) the master by letting SDA be pulled high. ACKs also occur on the bus when data is being transmitted. When the 30004911 FIGURE 4. Basic Operation. output updates to reflect the contents of the 16-bit DAC register. Next, the master either sends another pair of data bytes, generates a Stop condition to end communication, or generates a Repeated Start condition to communicate with another device on the bus. For a read operation, the DAC121C081 sends out the upper eight data bits of the DAC register. This is followed by an ACK by the master. Next, the lower eight data bits of the DAC register are sent to the master. The master then produces a NACK by letting SDA be pulled high. The NACK is followed by a master-generated Stop condition to end communication on the bus, or a Repeated Start to communicate with another device on the bus. 1.4.2 Standard-Fast Mode In Standard-Fast mode, the master generates a start condition by driving SDA from high to low while SCL is high. The Start condition is always followed by a 7-bit slave address and a Read/Write bit. After these eight bits have been transmitted by the master, SDA is released by the master and the DAC121C081 either ACKs or NACKs the address. If the slave address matches, the DAC121C081 ACKs the master. If the address doesn't match, the DAC121C081 NACKs the master. For a write operation, the master follows the ACK by sending the upper eight data bits to the DAC121C081. Then the DAC121C081 ACKs the transfer by driving SDA low. Next, the lower eight data bits are sent by the master. The DAC121C081 then ACKs the transfer. At this point, the DAC 15 www.national.com DAC121C081/ DAC121C085 master is writing data, the slave ACKs after every data byte is successfully received. When the master is reading data, the master ACKs after every data byte is received to let the slave know it wants to receive another data byte. When the master wants to stop reading, it NACKs after the last data byte and creates a Stop condition on the bus. All communication on the bus begins with either a Start condition or a Repeated Start condition. The protocol for starting the bus varies between Standard-Fast mode and Hs-mode. In Standard-Fast mode, the master generates a Start condition by driving SDA from high to low while SCL is high. In Hsmode, starting the bus is more complicated. Please refer to section 1.4.3 for the full details of a Hs-mode Start condition. A Repeated Start is generated to either address a different device, or switch between read and write modes. The master generates a Repeated Start condition by driving SDA low while SCL is high. Following the Repeated Start, the master sends out the slave address and a read/write bit as shown in Figure 4. The bus continues to operate in the same speed mode as before the Repeated Start condition. All communication on the bus ends with a Stop condition. In either Standard-Fast mode or Hs-Mode, a Stop condition occurs when SDA is pulled from low to high while SCL is high. After a Stop condition, the bus remains idle until a master generates a Start condition. Please refer to the Phillips I2C® Specification (Version 2.1 Jan, 2000) for a detailed description of the serial interface. 1.4 SERIAL INTERFACE The I2C-compatible interface operates in all three speed modes. Standard mode (100kHz) and Fast mode (400kHz) are functionally the same and will be referred to as StandardFast mode in this document. High-Speed mode (3.4MHz) is an extension of Standard-Fast mode and will be referred to as Hs-mode in this document. The following diagrams describe the timing relationships of the clock (SCL) and data (SDA) signals. Pull-up resistors or current sources are required on the SCL and SDA busses to pull them high when they are not being driven low. A logic zero is transmitted by driving the output low. A logic high is transmitted by releasing the output and allowing it to be pulled-up externally. The appropriate pull-up resistor values will depend upon the total bus capacitance and operating speed. DAC121C081/ DAC121C085 address to the DAC121C081, and communication continues as shown above in the "Basic Operation" Diagram (see Figure 4). When the master generates a Repeated Start condition while in Hs-mode, the bus stays in Hs-mode awaiting the slave address from the master. The bus continues to run in Hs-mode until a Stop condition is generated by the master. When the master generates a Stop condition on the bus, the bus must be started in Standard-Fast mode again before increasing the bus speed and switching to Hs-mode. ns16705 1.4.3 High-Speed (Hs) Mode For Hs-mode, the sequence of events to begin communication differ slightly from Standard-Fast mode. Figure 5 describes this in further detail. Initially, the bus begins running in Standard-Fast mode. The master generates a Start condition and sends the 8-bit Hs master code (00001XXX) to the DAC121C081. Next, the DAC121C081 responds with a NACK. Once the SCL line has been pulled to a high level, the master switches to Hs-mode by increasing the bus speed and generating a Repeated Start condition (driving SDA low while SCL is pulled high). At this point, the master sends the slave 30004912 FIGURE 5. Beginning Hs-Mode Communication DAC121C085's on the 2-wire bus. When the bus is addressed by the broadcast address, all the DAC121C081's and DAC121C085's will respond and update synchronously. Figure 6 and Figure 7 describe how the master device should address the DAC via the I2C-Compatible interface. Keep in mind that the address selection inputs (ADR0 and ADR1) are only sampled until the DAC is correctly addressed with a non-broadcast address. At this point, the ADR0 and ADR1 inputs TRI-STATE and the slave address is "locked". Changes to ADR0 and ADR1 will not update the selected slave address until the device is power-cycled. 1.4.4 I2C Slave (Hardware) Address The DAC has a seven-bit I2C slave address. For the MSOP-8 version of the DAC, this address is configured by the ADR0 and ADR1 address selection inputs. For the DAC121C081, the address is configured by the ADR0 address selection input. ADR0 and ADR1 can be grounded, left floating, or tied to VA. If desired, the address selection inputs can be set to VA/ 2 rather than left floating. The state of these inputs sets the address the DAC responds to on the I2C bus (see Table 1). In addition to the selectable slave address, there is also a broadcast address (1001000) for all DAC121C081's and TABLE 1. Slave Addresses DAC121C085 (MSOP-8) DAC121C081 (TSOT & LLP) * Slave Address [A6 - A0] ADR1 ADR0 ADR0 0001100 Floating Floating Floating 0001101 Floating GND GND 0001110 Floating VA VA 0001000 GND Floating --------------- 0001001 GND GND --------------- 0001010 GND VA --------------- 1001100 VA Floating --------------- 1001101 VA GND --------------- 1001110 VA VA --------------- 1001000 --------------- Broadcast Address --------------- * Pin-compatible alternatives to the DAC121C081 options are available with additional address options. www.national.com 16 30004964 FIGURE 6. Typical Write to the DAC Register DAC sends the lower data byte to the master. Assuming only one 16-bit data word is read, the master sends a NACK after receiving the lower data byte. At this point, the master either generates a Stop condition to end communication, or a Repeated Start condition to begin communication with another device on the bus. 1.4.6 Reading from the DAC Register To read from the DAC register, the master addresses the part with the correct slave address (A6-A0) and writes a "one" to the read/write bit. If addressed correctly, the DAC returns an ACK to the master. Next, the DAC sends out the upper data byte. The master responds by sending an ACK to the DAC to indicate that it wants to receive another data byte. Then the 30004963 FIGURE 7. Typical Read from the DAC Register 17 www.national.com DAC121C081/ DAC121C085 either sends the upper byte of the next data word to be converted by the DAC, generates a Stop condition to end communication, or generates a Repeated Start condition to begin communication with another device on the bus. Until generating a Stop condition, the master can continuously write the upper and lower data bytes to the DAC register. This allows for a maximum DAC conversion rate of 188.9 kilo-conversions per second in Hs-mode. 1.4.5 Writing to the DAC Register To write to the DAC, the master addresses the part with the correct slave address (A6-A0) and writes a "zero" to the read/ write bit. If addressed correctly, the DAC returns an ACK to the master. The master then sends out the upper data byte. The DAC responds by sending an ACK to the master. Next, the master sends the lower data byte to the DAC. The DAC responds by sending an ACK again. At this point, the master DAC121C081/ DAC121C085 1.5 DAC REGISTER The DAC register, Figure 8, has sixteen bits. The first two bits are always zero. The next two bits determine the mode of operation (normal mode or one of three power-down modes). The final twelve bits of the shift register are the data bits. The data format is straight binary (MSB first, LSB last), with twelve 0's corresponding to an output of 0V and twelve 1's corresponding to a full-scale output of VA - 1 LSB. When writing to the DAC Register, V OUT will update on the rising edge of the ACK following the lower data byte. 1.8 POWER-DOWN MODES The DAC121C081 has three power-down modes. In powerdown mode, the supply current drops to 0.13µA at 3V and 0.15µA at 5V (typ). The DAC121C081 is put into power-down mode by writing a one to PD1 and/or PD0. The outputs can be set to high impedance, terminated by 2.5 kΩ to GND, or terminated by 100 kΩ to GND (see Figure 8). The bias generator, output amplifier, resistor string, and other linear circuitry are all shut down in any of the power-down modes. When the DAC121C081 is powered down, the value written to the DAC register, including the power-down bits, is saved. While the DAC is in power-down, the saved DAC register contents can be read back. When the DAC is brought out of power-down mode, the DAC register contents will be overwritten and VOUT will be updated with the new 12-bit data value. The time to exit power-down (Wake-Up Time) is typically 0.8µsec at 3V and 0.5µsec at 5V. 30004908 1.9 ADDITIONAL TIMING INFORMATION: toutz The toutz specification is provided to aid the design of the I 2C bus. After the SCL bus is driven low by the I2C master, the SDA bus will be held for a short time by the DAC121C081. This time is referred to as toutz. The following figure illustrates the relationship between the fall of SCL, at the 30% threshold, to the time when the DAC begins to transition the SDA bus. The toutz specification only applies when the DAC is in control of the SDA bus. The DAC is only in control of the bus during an ACK by the DAC121C081 or a data byte read from the DAC (see Figure 7). FIGURE 8. DAC Register Contents 1.6 POWER-ON RESET The power-on reset circuit controls the output voltage of the DAC during power-up. Upon application of power, the DAC register is filled with zeros and the output voltage is 0 Volts. The output remains at 0V until a valid write sequence is made to the DAC. When resetting the device, it is crutial that the VA supply be lowered to a maximum of 200mV before the supply is raised again to power-up the device. Dropping the supply to within 200mV of GND during a reset will ensure the ADC performs as specified. 1.7 SIMULTANEOUS RESET The broadcast address allows the I2C master to write a single word to multiple DACs simultaneously. Provided that all of the DACs exist on a single I2C bus, every DAC will update when the broadcast address is used to address the bus. This feature allows the master to reset all of the DACs on a shared I2C bus to a specific digital code. For instance, if the master writes a power-down code to the bus with the broadcast address, all of the DACs will power-down simultaneously. 30004965 FIGURE 9. Data Output Timing The toutz specification is typically 87nsec in Standard-Fast Mode and 38nsec in Hs-Mode. www.national.com 18 2.1 USING REFERENCES AS POWER SUPPLIES While the simplicity of the DAC121C081 implies ease of use, it is important to recognize that the path from the reference input (VA for the DAC121C081 & VREF for the DAC121C085) to VOUT will have essentially zero Power Supply Rejection Ratio (PSRR). Therefore, it is necessary to provide a noisefree supply voltage to the reference. In order to use the full dynamic range of the DAC121C085, the supply pin (VA) and VREF can be connected together and share the same supply voltage. Since the DAC121C081 consumes very little power, a reference source may be used as the supply voltage. The advantages of using a reference source over a voltage regulator are accuracy and stability. Some low noise regulators can also be used. Listed below are a few reference and power supply options for the DAC121C081. When using the DAC121C081, it is important to treat the analog supply (VA) as the reference. 2.1.1 LM4132 The LM4132, with its 0.05% accuracy over temperature, is a good choice as a reference source for the DAC121C081. The 4.096V version is useful if a 0 to 4.095V output range is desirable or acceptable. Bypassing the LM4132 VIN pin with a 0.1µF capacitor and the VOUT pin with a 2.2µF capacitor will improve stability and reduce output noise. The LM4132 comes in a space-saving 5-pin SOT23. 30004914 FIGURE 11. The LM4050 as a power supply The minimum resistor value in the circuit of Figure 11 must be chosen such that the maximum current through the LM4050 does not exceed its 15 mA rating. The conditions for maximum current include the input voltage at its maximum, the LM4050 voltage at its minimum, and the DAC121C081 drawing zero current. The maximum resistor value must allow the LM4050 to draw more than its minimum current for regulation plus the maximum DAC121C081 current in full operation. The conditions for minimum current include the input voltage at its minimum, the LM4050 voltage at its maximum, the resistor value at its maximum due to tolerance, and the DAC121C081 draws its maximum current. These conditions can be summarized as R(min) = ( VIN(max) − VZ(min) ) /IZ(max) 30004913 and FIGURE 10. The LM4132 as a power supply R(max) = ( VIN(min) − VZ(max) ) / ( (IDAC(max) + IZ(min) ) where V Z(min) and VZ(max) are the nominal LM4050 output voltages ± the LM4050 output tolerance over temperature, IZ (max) is the maximum allowable current through the LM4050, IZ(min) is the minimum current required by the LM4050 for proper regulation, and IDAC(max) is the maximum DAC121C081 supply current. 19 www.national.com DAC121C081/ DAC121C085 2.1.2 LM4050 Available with accuracy of 0.44%, the LM4050 shunt reference is also a good choice as a reference for the DAC121C081. It is available in 4.096V and 5V versions and comes in a space-saving 3-pin SOT23. 2.0 Applications Information DAC121C081/ DAC121C085 2.2 BIPOLAR OPERATION The DAC121C081 is designed for single supply operation and thus has a unipolar output. However, a bipolar output may be obtained with the circuit in Figure 14. This circuit will provide an output voltage range of ±5 Volts. A rail-to-rail amplifier should be used if the amplifier supplies are limited to ±5V. 2.1.3 LP3985 The LP3985 is a low noise, ultra low dropout voltage regulator with a 3% accuracy over temperature. It is a good choice for applications that do not require a precision reference for the DAC121C081. It comes in 3.0V, 3.3V and 5V versions, among others, and sports a low 30 µV noise specification at low frequencies. Since low frequency noise is relatively difficult to filter, this specification could be important for some applications. The LP3985 comes in a space-saving 5-pin SOT23 and 5-bump micro SMD packages. 30004917 FIGURE 14. Bipolar Operation The output voltage of this circuit for any code is found to be 30004915 VO = (VA x (D / 4096) x ((R1 + R2) / R1) - VA x R2 / R1) FIGURE 12. Using the LP3985 regulator where D is the input code in decimal form. With VA = 5V and R1 = R2, An input capacitance of 1.0µF without any ESR requirement is required at the LP3985 input, while a 1.0µF ceramic capacitor with an ESR requirement of 5mΩ to 500mΩ is required at the output. Careful interpretation and understanding of the capacitor specification is required to ensure correct device operation. VO = (10 x D / 4096) - 5V A list of rail-to-rail amplifiers suitable for this application are indicated in Table 2. TABLE 2. Some Rail-to-Rail Amplifiers 2.1.4 LP2980 The LP2980 is an ultra low dropout regulator with a 0.5% or 1.0% accuracy over temperature, depending upon grade. It is available in 3.0V, 3.3V and 5V versions, among others. 30004916 FIGURE 13. Using the LP2980 regulator Like any low dropout regulator, the LP2980 requires an output capacitor for loop stability. This output capacitor must be at least 1.0µF over temperature, but values of 2.2µF or more will provide even better performance. The ESR of this capacitor should be within the range specified in the LP2980 data sheet. Surface-mount solid tantalum capacitors offer a good combination of small size and ESR. Ceramic capacitors are attractive due to their small size but generally have ESR values that are too low for use with the LP2980. Aluminum electrolytic capacitors are typically not a good choice due to their large size and have ESR values that may be too high at low temperatures. www.national.com 20 AMP PKGS Typ VOS Typ ISUPPLY LMP7701 SOT23-5 37 uV 0.79 mA LMV841 SC70-5 50 uV 1 mA LMC7111 SOT23-5 0.9 mV 25 µA LM7301 SO-8 SOT23-5 0.03 mV 620 µA LM8261 SOT23-5 0.7 mV 1 mA 2.3.2 Interfacing to a Hs-mode Bus Interfacing to a Hs-mode bus is very similar to interfacing to a Standard-Fast mode bus. In Hs-mode, the specified rise time of SCL is shortened. To create a faster rise time, the master device (microcontroller) can drive the SCL bus high and low. In other words, the microcontroller can drive the line high rather than leaving it to the pull-up resistor. It is also possible to decrease the value of the pull-up resistors or increase the pull-up current to meet the tighter timing specs. Please refer to the I2C Specification for further details. 2.3.1 Interfacing to the 2-wire Bus Figure 15 shows a microcontroller interfacing to the DAC121C081 via the 2-wire bus. Pull-up resistors (Rp) should be chosen to create an appropriate bus rise time and to limit the current that will be sunk by the open-drain outputs of the devices on the bus. Please refer to the I2C Specification for further details. Typical pull-up values to use in StandardFast mode bus applications are 2kΩ to 10kΩ. SCL and SDA series resisters (RS) near the DAC121C081 are optional. If high-voltage spikes are expected on the 2-wire bus, series resistors should be used to filter the voltage on SDA and SCL. The value of the series resistance must be picked to ensure the VIL threshold can be achieved. If used, RS is typically 51Ω. 2.4 LAYOUT, GROUNDING, AND BYPASSING For best accuracy and minimum noise, the printed circuit board containing the DAC121C081 should have separate analog and digital areas. The areas are defined by the locations of the analog and digital power planes. Both of these planes should be located on the same board layer. There should be a single ground plane. A single ground plane is preferred if digital return current does not flow through the analog ground area. Frequently a single ground plane design will utilize a "fencing" technique to prevent the mixing of analog and digital ground current. Separate ground planes should only be utilized when the fencing technique is inadequate. The separate ground planes must be connected in one place, preferably near the DAC121C081. Special care is required to guarantee that digital signals with fast edge rates do not pass over split ground planes. They must always have a continuous return path below their traces. The DAC121C081 power supply should be bypassed with a 4.7µF and a 0.1µF capacitor as close as possible to the device with the 0.1µF right at the device supply pin. The 4.7µF capacitor should be a tantalum type and the 0.1µF capacitor should be a low ESL, low ESR type. The power supply for the DAC121C081 should only be used for analog circuits. Avoid crossover of analog and digital signals and keep the clock and data lines on the component side of the board. These clock and data lines should have controlled impedances. 30004909 FIGURE 15. Serial Interface Connection Diagram 21 www.national.com DAC121C081/ DAC121C085 2.3 DSP/MICROPROCESSOR INTERFACING Interfacing the DAC121C081 to microprocessors and DSPs is quite simple. The following guidelines are offered to simplify the design process. DAC121C081/ DAC121C085 Physical Dimensions inches (millimeters) unless otherwise noted 6-Lead TSOT Order Numbers DAC121C081CIMK NS Package Number MK06A 6-Lead LLP Order Numbers DAC121C081CISD NS Package Number SDB06A www.national.com 22 DAC121C081/ DAC121C085 8-Lead MSOP Order Numbers DAC121C085CIMM NS Package Number MUA08A 23 www.national.com DAC121C081/ DAC121C085 12-Bit Micro Power Digital-to-Analog Converter Notes For more National Semiconductor product information and proven design tools, visit the following Web sites at: Products Design Support Amplifiers www.national.com/amplifiers WEBENCH www.national.com/webench Audio www.national.com/audio Analog University www.national.com/AU Clock Conditioners www.national.com/timing App Notes www.national.com/appnotes Data Converters www.national.com/adc Distributors www.national.com/contacts Displays www.national.com/displays Green Compliance www.national.com/quality/green Ethernet www.national.com/ethernet Packaging www.national.com/packaging Interface www.national.com/interface Quality and Reliability www.national.com/quality LVDS www.national.com/lvds Reference Designs www.national.com/refdesigns Power Management www.national.com/power Feedback www.national.com/feedback Switching Regulators www.national.com/switchers LDOs www.national.com/ldo LED Lighting www.national.com/led PowerWise www.national.com/powerwise Serial Digital Interface (SDI) www.national.com/sdi Temperature Sensors www.national.com/tempsensors Wireless (PLL/VCO) www.national.com/wireless THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. 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