ISL5757IA

S W DESIGN E D F OR N E D N E T M N M E O M EPLACE NOT REC t MENDED R rt Center a NO RECOM ical Suppo .com/tsc n h c e T r u o il contact w.inters RSIL or ww 1-888-INTE ISL5757 DATASHEET 10-bit, +3.3V, 260+MSPS, High Speed D/A Converter The ISL5757 is a 10-bit, 260+MSPS (Mega Samples Per Second), CMOS, high speed, low power, D/A (digital to analog) converter, designed specifically for use in high performance communication systems such as base transceiver stations utilizing 2.5G or 3G cellular protocols. This device complements the ISL5x57 family of high speed converters, which include 10, 12, and 14-bit devices. Ordering Information PART NUMBER TEMP. RANGE (°C) • Low Power . . . . . 103mW with 20mA Output at 130MSPS • Adjustable Full Scale Output Current . . . . . 2mA to 20mA • +3.3V Power Supply • 3V LVCMOS Compatible Inputs • Excellent Spurious Free Dynamic Range (71dBc to Nyquist, f S = 130MSPS, fOUT = 10MHz) PACKAGE CLOCK SPEED • EDGE/GSM SFDR = 83dBc at 11MHz in 20MHz Window • Pin compatible, 3.3V, Lower Power Replacement For The AD9750 and HI5760 -40 to 85 28 Ld SOIC M28.3 260MHz ISL5757IBZ (See Note) -40 to 85 28 Ld SOIC (Pb-free) M28.3 260MHz ISL5757IA -40 to 85 28 Ld TSSOP M28.173 260MHz ISL5757IAZ (See Note) -40 to 85 28 Ld TSSOP (Pb-free) M28.173 260MHz SOIC Evaluation Platform 260MHz 25 Features • UMTS Adjacent Channel Power = 65dB at 19.2MHz PKG. DWG. # ISL5757IB ISL5757EVAL1 FN6078 Rev 1.00 November 12, 2004 NOTE: Intersil Pb-free products employ special Pb-free material sets; molding compounds/die attach materials and 100% matte tin plate termination finish, which are RoHS compliant and compatible with both SnPb and Pb-free soldering operations. Intersil Pb-free products are MSL classified at Pb-free peak reflow temperatures that meet or exceed the Pb-free requirements of IPC/JEDEC J STD-020C. • Pb-Free Available (RoHS Compliant) Applications • Cellular Infrastructure - Single or Multi-Carrier: IS-136, IS-95, GSM, EDGE, CDMA2000, WCDMA, TDS-CDMA • BWA Infrastructure • Medical/Test Instrumentation • Wireless Communication Systems • High Resolution Imaging Systems • Arbitrary Waveform Generators Pinout ISL5757 TOP VIEW D9 (MSB) 1 27 DVDD D7 3 26 DCOM D6 4 25 NC D5 5 24 AVDD D4 6 23 COMP D3 7 22 IOUTA D2 8 21 IOUTB D1 9 20 ACOM D0 (LSB) 10 FN6078 Rev 1.00 November 12, 2004 28 CLK D8 2 19 NC DCOM 11 18 FSADJ DCOM 12 17 REFIO DCOM 13 16 REFLO DCOM 14 15 SLEEP Page 1 of 13 ISL5757 Typical Applications Circuit ISL5757 ONE CONNECTION (25, 19) NC (15) SLEEP (16) REFLO DCOM ACOM (17) REFIO D9 D9 (1) D8 D8 (2) D7 D7 (3) D6 D6 (4) D5 D5 (5) D4 D4 (6) D3 D3 (7) D2 D2 (8) D1 D1 (9) D0 D0 (LSB) (10) 0.1µF (18) FSADJ RSET 1:1, Z1:Z2 (22) IOUTA (21) IOUTB (50) 50 REPRESENTS ANY 50 LOAD (23) COMP CLK (28) DCOM (26, 11-14) 50 0.1µF (20) ACOM BEAD + 10µF 10µH 1.91k FERRITE BEAD (24) AVDD DVDD (27) + 10µH 0.1µF 0.1µF 10µF +3.3V (VDD) Functional Block Diagram IOUTA IOUTB CASCODE (LSB) D0 CURRENT SOURCE INPUT LATCH D1 36 D2 SWITCH MATRIX D3 36 5 LSBs + 31 MSB SEGMENTS D4 D5 D6 D7 D8 UPPER 5-BIT DECODER (MSB) D9 COMP CLK INT/EXT VOLTAGE BIAS GENERATION REFERENCE REFLO REFIO FN6078 Rev 1.00 November 12, 2004 FSADJ SLEEP Page 2 of 13 ISL5757 Pin Descriptions PIN NO. PIN NAME 1-10 D9 (MSB) Through D0 (LSB) 15 SLEEP Control Pin for Power-Down mode. Sleep Mode is active high; Connect to ground for Normal Mode. Sleep pin has internal 20A active pulldown current. 16 REFLO Connect to analog ground to enable internal 1.2V reference or connect to AVDD to disable internal reference. 17 REFIO Reference voltage input if internal reference is disabled. Reference voltage output if internal reference is enabled. Use 0.F cap to ground when internal reference is enabled. 18 FSADJ Full Scale Current Adjust. Use a resistor to ground to adjust full scale output current. Full Scale Output Current = 32 x VFSADJ/RSET. 19, 25 NC 21 IOUTB The complementary current output of the device. Full scale output current is achieved when all input bits are set to binary 0. 22 IOUTA Current output of the device. Full scale output current is achieved when all input bits are set to binary 1. 23 COMP Connect 0.1F capacitor to ACOM. 24 AVDD Analog Supply (+3.0V to +3.6V). 20 ACOM Connect to Analog Ground. 26, 11-14 DCOM Connect to Digital Ground. 27 DVDD Digital Supply (+3.0V to +3.6V). 28 CLK FN6078 Rev 1.00 November 12, 2004 DESCRIPTION Digital Data Bit 9, (Most Significant Bit) through Digital Data Bit 0, (Least Significant Bit). No Connect. These should be grounded, but can be left disconnected. Clock Input. Page 3 of 13 ISL5757 Absolute Maximum Ratings Thermal Information Digital Supply Voltage DVDD to DCOM . . . . . . . . . . . . . . . . . +3.6V Analog Supply Voltage AVDD to ACOM. . . . . . . . . . . . . . . . . . +3.6V Grounds, ACOM TO DCOM . . . . . . . . . . . . . . . . . . . -0.3V to +0.3V Digital Input Voltages (D9-D0, CLK, SLEEP). . . . . . . . DVDD + 0.3V Reference Input Voltage Range. . . . . . . . . . . . . . . . . . AVDD + 0.3V Analog Output Current (IOUT) . . . . . . . . . . . . . . . . . . . . . . . . . 24mA Thermal Resistance (Typical, Note 1) Operating Conditions JA(°C/W) SOIC Package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 TSSOP Package . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 Maximum Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . 150°C Maximum Storage Temperature Range . . . . . . . . . . . -65°C to 150°C Maximum Lead Temperature (Soldering 10s) . . . . . . . . . . . . . 300°C (SOIC - Lead Tips Only) Temperature Range . . . . . . . . . . . . . . . . . . . . . . . . . . .-40°C to 85°C CAUTION: Stresses above those listed in “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress only rating and operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. NOTE: 1. JA is measured with the component mounted on an evaluation PC board in free air. Electrical Specifications AVDD = DVDD = +3.3V, VREF = Internal 1.2V, IOUTFS = 20mA, TA = 25°C for All Typical Values TA = -40°C TO 85°C PARAMETER TEST CONDITIONS MIN TYP MAX UNITS 10 - - Bits SYSTEM PERFORMANCE Resolution Integral Linearity Error, INL “Best Fit” Straight Line (Note 8) -0.5 0.1 +0.5 LSB Differential Linearity Error, DNL (Note 8) -0.5 0.1 +0.5 LSB Offset Error, IOS IOUTA (Note 8) +0.006 % FSR Offset Drift Coefficient (Note 8) - 0.1 - ppm FSR/°C Full Scale Gain Error, FSE With External Reference (Notes 2, 8) -3 0.5 +3 % FSR With Internal Reference (Notes 2, 8) -3 0.5 +3 % FSR With External Reference (Note 8) - 50 - ppm FSR/°C With Internal Reference (Note 8) - 100 - ppm FSR/°C 2 - 20 mA -1.0 - 1.25 V 260 300 - MHz Full Scale Gain Drift -0.006 Full Scale Output Current, IFS Output Voltage Compliance Range (Note 3) DYNAMIC CHARACTERISTICS Maximum Clock Rate, fCLK Output Rise Time Full Scale Step - 1.5 - ns Output Fall Time Full Scale Step - 1.5 - ns - 10 - pF IOUTFS = 20mA - 50 - pA/Hz IOUTFS = 2mA - 30 - pA/Hz fCLK = 210MSPS, fOUT = 80.8MHz, 30MHz Span (Notes 4, 8) - 72 - dBc fCLK = 210MSPS, fOUT = 40.4MHz, 30MHz Span (Notes 4, 8) - 75 - dBc fCLK = 130MSPS, fOUT = 20.2MHz, 20MHz Span (Notes 4, 8) - 77 - dBc Output Capacitance Output Noise AC CHARACTERISTICS (Using Figure 13 with RDIFF = 50 and RLOAD= 50, Full Scale Output = -2.5dBm Spurious Free Dynamic Range, SFDR Within a Window FN6078 Rev 1.00 November 12, 2004 Page 4 of 13 ISL5757 Electrical Specifications AVDD = DVDD = +3.3V, VREF = Internal 1.2V, IOUTFS = 20mA, TA = 25°C for All Typical Values (Continued) TA = -40°C TO 85°C PARAMETER TEST CONDITIONS MIN TYP MAX UNITS fCLK = 260MSPS, fOUT = 80.8MHz (Notes 4, 8) - 47 - dBc fCLK = 260MSPS, fOUT = 40.4MHz (Notes 4, 8) - 58 - dBc fCLK = 260MSPS, fOUT = 20.2MHz (Notes 4, 8) - 60 - dBc fCLK = 210MSPS, fOUT = 80.8MHz (Notes 4, 8) - 50 - dBc fCLK = 210MSPS, fOUT = 40.4MHz (Notes 4, 8, 10) - 58 - dBc fCLK = 200MSPS, fOUT = 20.2MHz, T = 25°C (Notes 4, 8) 58 60 - dBc fCLK = 200MSPS, fOUT = 20.2MHz, T = -40°C to 85°C (Notes 4, 8) 56 - - dBc fCLK = 130MSPS, fOUT = 50.5MHz (Notes 4, 8) - 55 - dBc fCLK = 130MSPS, fOUT = 40.4MHz (Notes 4, 8) - 60 - dBc fCLK = 130MSPS, fOUT = 20.2MHz (Notes 4, 8) - 68 - dBc fCLK = 130MSPS, fOUT = 10.1MHz (Notes 4, 8) - 70 - dBc fCLK = 130MSPS, fOUT = 5.05MHz, T = 25°C (Notes 4, 8) 68 75 - dBc fCLK = 130MSPS, fOUT = 5.05MHz, T = -40°C to 85°C (Notes 4, 8) 66 - - dBc fCLK = 100MSPS, fOUT = 40.4MHz (Notes 4, 8) - 58 - dBc fCLK = 80MSPS, fOUT = 30.3MHz (Notes 4, 8) - 61 - dBc fCLK = 80MSPS, fOUT = 20.2MHz (Notes 4, 8) - 67 - dBc fCLK = 80MSPS, fOUT = 10.1MHz (Notes 4, 8, 10) - 69 - dBc fCLK = 80MSPS, fOUT = 5.05MHz (Notes 4, 8) - 74 - dBc fCLK = 50MSPS, fOUT = 20.2MHz (Notes 4, 8) - 66 - dBc fCLK = 50MSPS, fOUT = 10.1MHz (Notes 4, 8) - 72 - dBc fCLK = 50MSPS, fOUT = 5.05MHz (Notes 4, 8) - 75 - dBc fCLK = 210MSPS, fOUT = 28.3MHz to 45.2MHz, 2.1MHz Spacing, 50MHz Span (Notes 4, 8, 10) - 63 - dBc fCLK = 130MSPS, fOUT =17.5MHz to 27.9MHz, 1.3MHz Spacing, 35MHz Span (Notes 4, 8) - 66 - dBc fCLK = 80MSPS, fOUT = 10.8MHz to 17.2MHz, 811kHz Spacing, 15MHz Span (Notes 4, 8) - 73 - dBc fCLK = 50MSPS, fOUT = 6.7MHz to 10.8MHz, 490kHz Spacing, 10MHz Span (Notes 4, 8) - 75 - dBc Spurious Free Dynamic Range, fCLK = 78MSPS, fOUT = 11MHz, in a 20MHz Window, RBW = 30kHz SFDR in a Window with EDGE or GSM (Notes 4, 8,10) - 83 - dBc Adjacent Channel Power Ratio, ACPR with UMTS - 65 - dB 1.2 1.23 1.3 V - 40 - ppm/°C - 0 - A Reference Input Impedance - 1 - M Reference Input Multiplying Bandwidth (Note 8) - 1.0 - MHz Spurious Free Dynamic Range, SFDR to Nyquist (fCLK/2) Spurious Free Dynamic Range, SFDR in a Window with Eight Tones fCLK = 76.8MSPS, fOUT = 19.2MHz, RBW=30kHz (Notes 4, 8, 10) VOLTAGE REFERENCE Internal Reference Voltage, VFSADJ Pin 18 Voltage with Internal Reference Internal Reference Voltage Drift Internal Reference Output Current Sink/Source Capability FN6078 Rev 1.00 November 12, 2004 Reference is not intended to be externally loaded (REFIO pin) Page 5 of 13 ISL5757 Electrical Specifications AVDD = DVDD = +3.3V, VREF = Internal 1.2V, IOUTFS = 20mA, TA = 25°C for All Typical Values (Continued) TA = -40°C TO 85°C PARAMETER DIGITAL INPUTS TEST CONDITIONS MIN TYP MAX UNITS D9-D0, CLK Input Logic High Voltage with 3.3V Supply, VIH (Note 3) 2.3 3.3 - V Input Logic Low Voltage with 3.3V Supply, VIL (Note 3) - 0 1.0 V Sleep Input Current, IIH -25 - +25 A Input Logic Current, IIH, IL -20 - +20 A Clock Input Current, IIH, IL -10 - +10 A - 5 - pF Digital Input Capacitance, CIN TIMING CHARACTERISTICS Data Setup Time, tSU See Figure 15 - 1.5 - ns Data Hold Time, tHLD See Figure 15 - 1.5 - ns Propagation Delay Time, tPD See Figure 15 - 1 - Clock Cycles CLK Pulse Width, tPW1 , tPW2 See Figure 15 (Note 3) 0.9 - - ns POWER SUPPLY CHARACTERISTICS AVDD Power Supply (Note 9) 2.7 3.3 3.6 V DVDD Power Supply (Note 9) 2.7 3.3 3.6 V Analog Supply Current (IAVDD) 3.3V, IOUTFS = 20mA - 27.5 28.5 mA 3.3V, IOUTFS = 2mA - 10 - mA 3.3V (Note 5) - 3.7 5 mA 3.3V (Note 6) - 6.5 8 mA Supply Current (IAVDD) Sleep Mode 3.3V, IOUTFS = Don’t Care - 1.5 - mA Power Dissipation 3.3V, IOUTFS = 20mA (Note 5) - 103 111 mW 3.3V, IOUTFS = 20mA (Note 6) - 110 120 mW 3.3V, IOUTFS = 20mA (Note 7) - 157 - mW 3.3V, IOUTFS = 2mA (Note 5) - 45 - mW -0.125 - +0.125 %FSR/V Digital Supply Current (IDVDD) Power Supply Rejection Single Supply (Note 8) NOTES: 2. Gain Error measured as the error in the ratio between the full scale output current and the current through RSET (typically 625A). Ideally the ratio should be 32. 3. Parameter guaranteed by design or characterization and not production tested. 4. Spectral measurements made with differential transformer coupled output and no external filtering. For multitone testing, the same pattern was used at different clock rates, producing different output frequencies but at the same ratio to the clock rate. 5. Measured with the clock at 130MSPS and the output frequency at 5MHz. 6. Measured with the clock at 200MSPS and the output frequency at 20MHz. 7. Measured with the clock at 260MSPS and the output frequency at 40MHz. 8. See “Definition of Specifications”. 9. Recommended operation is from 3.0V to 3.6V. Operation below 3.0V is possible with some degradation in spectral performance. Reduction in analog output current may be necessary to maintain spectral performance. 10. See Typical Performance Plots. FN6078 Rev 1.00 November 12, 2004 Page 6 of 13 ISL5757 Typical Performance (+3.3V Supply, Using Figure 13 with RDIFF = 100 and RLOAD = 50) SPECTRAL MASK FOR GSM900/DCS1800/PCS1900 P>43dBm NORMAL BTS WITH 30kHz RBW FIGURE 1. EDGE AT 11MHz, 78MSPS CLOCK (83+dBc @ f = +6MHz) FIGURE 2. EDGE AT 11MHz, 78MSPS CLOCK (75dBc -NYQUIST, 6dB PAD) SPECTRAL MASK FOR GSM900/DCS1800/PCS1900 P>43dBm NORMAL BTS WITH 30kHz RBW FIGURE 3. GSM AT 11MHz, 78MSPS CLOCK (86+dBc @ f = +6MHz, 3dB PAD) FIGURE 4. GSM AT 11MHz, 78MSPS CLOCK (78dBc - NYQUIST, 9dB PAD) FIGURE 5. FOUR EDGE CARRIERS AT 12.4-15.6MHz, 800kHz SPACING, 78MSPS (67dBc - 20MHz WINDOW) FIGURE 6. FOUR GSM CARRIERS AT 12.4-15.6MHz, 78MSPS (71dBc - 20MHz WINDOW, 6dB PAD) FN6078 Rev 1.00 November 12, 2004 Page 7 of 13 ISL5757 Typical Performance (+3.3V Supply, Using Figure 13 with RDIFF = 100 and RLOAD = 50) (Continued) SPECTRAL MASK UMTS TDD P>43dBm BTS FIGURE 7. UMTS AT 19.2MHz, 76.8MSPS (65dB 1st ACPR, 64dB 2nd ACPR) FIGURE 9. ONE TONE AT 40.4MHz, 210MSPS CLOCK (61dBc - NYQUIST, 6dB PAD) FIGURE 11. TWO TONES (CF = 6) AT 8.5MHz, 50MSPS CLOCK, 500kHz SPACING (80dBc - 10MHz WINDOW, 6dB PAD) FN6078 Rev 1.00 November 12, 2004 FIGURE 8. ONE TONE AT 10.1MHz, 80MSPS CLOCK (71dBc - NYQUIST, 6dB PAD) FIGURE 10. EIGHT TONES (CREST FACTOR = 8.9) AT 37MHz, 210MSPS CLOCK, 2.1MHz SPACING (64dBc - NYQUIST) FIGURE 12. FOUR TONES (CF = 8.1) AT 14MHz, 80MSPS CLOCK, 800kHz SPACING (70dBc - NYQUIST, 6dB PAD) Page 8 of 13 ISL5757 Definition of Specifications Adjacent Channel Power Ratio, ACPR, is the ratio of the average power in the adjacent frequency channel (or offset) to the average power in the transmitted frequency channel. Differential Linearity Error, DNL, is the measure of the step size output deviation from code to code. Ideally the step size should be 1 LSB. A DNL specification of 1 LSB or less guarantees monotonicity. EDGE, Enhanced Data for Global Evolution, a TDMA standard for cellular applications which uses 200kHz BW, 8-PSK modulated carriers. Full Scale Gain Drift, is measured by setting the data inputs to be all logic high (all 1s) and measuring the output voltage through a known resistance as the temperature is varied from TMIN to TMAX . It is defined as the maximum deviation from the value measured at room temperature to the value measured at either TMIN or TMAX . The units are ppm of FSR (full scale range) per °C. Full Scale Gain Error, is the error from an ideal ratio of 32 between the output current and the full scale adjust current (through RSET). GSM, Global System for Mobile Communication, a TDMA standard for cellular applications which uses 200kHz BW, GMSK modulated carriers. Integral Linearity Error, INL, is the measure of the worst case point that deviates from a best fit straight line of data values along the transfer curve. Internal Reference Voltage Drift, is defined as the maximum deviation from the value measured at room temperature to the value measured at either TMIN or TMAX . The units are ppm per °C. Offset Drift, is measured by setting the data inputs to all logic low (all 0s) and measuring the output voltage at IOUTA through a known resistance as the temperature is varied from TMIN to TMAX . It is defined as the maximum deviation from the value measured at room temperature to the value measured at either TMIN or TMAX . The units are ppm of FSR (full scale range) per degree °C. Offset Error, is measured by setting the data inputs to all logic low (all 0s) and measuring the output voltage of IOUTA through a known resistance. Offset error is defined as the maximum deviation of the IOUTA output current from a value of 0mA. Output Voltage Compliance Range, is the voltage limit imposed on the output. The output impedance should be chosen such that the voltage developed does not violate the compliance range. Power Supply Rejection, is measured using a single power supply. The nominal supply voltage is varied 10% and the change in the DAC full scale output is noted. FN6078 Rev 1.00 November 12, 2004 Reference Input Multiplying Bandwidth, is defined as the 3dB bandwidth of the voltage reference input. It is measured by using a sinusoidal waveform as the external reference with the digital inputs set to all 1s. The frequency is increased until the amplitude of the output waveform is 0.707 (-3dB) of its original value. Spurious Free Dynamic Range, SFDR, is the amplitude difference from the fundamental signal to the largest harmonically or non-harmonically related spur within the specified frequency window. Total Harmonic Distortion, THD, is the ratio of the RMS value of the fundamental output signal to the RMS sum of the first five harmonic components. UMTS, Universal Mobile Telecommunications System, a W-CDMA standard for cellular applications which uses 3.84MHz modulated carriers. Detailed Description The ISL5757 is a 10-bit, current out, CMOS, digital to analog converter. The maximum update rate is at least 260+MSPS and can be powered by a single power supply in the recommended range of +3.0V to +3.6V. It consumes less than 120mW of power when using a +3.3V supply, the maximum 20mA of output current, and the data switching at 210MSPS. The architecture is based on a segmented current source arrangement that reduces glitch by reducing the amount of current switching at any one time. In previous architectures that contained all binary weighted current sources or a binary weighted resistor ladder, the converter might have a substantially larger amount of current turning on and off at certain, worst-case transition points such as midscale and quarter scale transitions. By greatly reducing the amount of current switching at these major transitions, the overall glitch of the converter is dramatically reduced, improving settling time, transient problems, and accuracy. Digital Inputs and Termination The ISL5757 digital inputs are guaranteed to 3V LVCMOS levels. The internal register is updated on the rising edge of the clock. To minimize reflections, proper termination should be implemented. If the lines driving the clock and the digital inputs are long 50 lines, then 50 termination resistors should be placed as close to the converter inputs as possible connected to the digital ground plane (if separate grounds are used). These termination resistors are not likely needed as long as the digital waveform source is within a few inches of the DAC. For pattern drivers with very high speed edge rates, it is recommended that the user consider series termination (50-200prior to the DAC’s inputs in order to reduce the amount of noise. Power Supply Separate digital and analog power supplies are recommended. The allowable supply range is +2.7V to +3.6V. The recommended supply range is +3.0 to 3.6V Page 9 of 13 ISL5757 (nominally +3.3V) to maintain optimum SFDR. However, operation down to +2.7V is possible with some degradation in SFDR. Reducing the analog output current can help the SFDR at +2.7V. The SFDR values stated in the table of specifications were obtained with a +3.3V supply. Ground Planes Separate digital and analog ground planes should be used. All of the digital functions of the device and their corresponding components should be located over the digital ground plane and terminated to the digital ground plane. The same is true for the analog components and the analog ground plane. Noise Reduction To minimize power supply noise, 0.1F capacitors should be placed as close as possible to the converter’s power supply pins, AVDD and DVDD . Also, the layout should be designed using separate digital and analog ground planes and these capacitors should be terminated to the digital ground for DVDD and to the analog ground for AVDD . Additional filtering of the power supplies on the board is recommended. Voltage Reference The internal voltage reference of the device has a nominal value of +1.23V with a 40ppm/°C drift coefficient over the full temperature range of the converter. It is recommended that a 0.1F capacitor be placed as close as possible to the REFIO pin, connected to the analog ground. The REFLO pin (16) selects the reference. The internal reference can be selected if pin 16 is tied low (ground). If an external reference is desired, then pin 16 should be tied high (the analog supply voltage) and the external reference driven into REFIO, pin 17. The full scale output current of the converter is a function of the voltage reference used and the value of RSET. IOUT should be within the 2mA to 20mA range, though operation below 2mA is possible, with performance degradation. If the internal reference is used, VFSADJ will equal approximately 1.2V (pin 18). If an external reference is used, VFSADJ will equal the external reference. The calculation for IOUT (Full Scale) is: IOUT(Full Scale) = (VFSADJ/RSET) X 32. If the full scale output current is set to 20mA by using the internal voltage reference (1.2V) and a 1.91k RSET resistor, then the input coding to output current will resemble the following: Analog Output IOUTA and IOUTB are complementary current outputs. The sum of the two currents is always equal to the full scale output current minus one LSB. If single ended use is desired, a load resistor can be used to convert the output current to a voltage. It is recommended that the unused output be either grounded or equally terminated. The voltage developed at the output must not violate the output voltage compliance range of -1.0V to 1.25V. ROUT (the impedance loading each current output) should be chosen so that the desired output voltage is produced in conjunction with the output full scale current. If a known line impedance is to be driven, then the output load resistor should be chosen to match this impedance. The output voltage equation is: VOUT = IOUT X ROUT. The most effective method for reducing the power consumption is to reduce the analog output current, which dominates the supply current. The maximum recommended output current is 20mA. Differential Output IOUTA and IOUTB can be used in a differential-to-singleended arrangement to achieve better harmonic rejection. With RDIFF = 50and RLOAD = 50, the circuit in Figure 13 will provide a 500mV (-2.5dBm) signal at the output of the transformer if the full scale output current of the DAC is set to 20mA (used for the electrical specifications table). Values of RDIFF = 100and RLOAD = 50 were used for the typical performance curves. The center tap in Figure 13 must be grounded. In the circuit in Figure 14, the user is left with the option to ground or float the center tap. The DC voltage that will exist at either IOUTA or IOUTB if the center tap is floating is IOUTDC x (RA//RB) V because RDIFF is DC shorted by the transformer. If the center tap is grounded, the DC voltage is 0V. Recommended values for the circuit in Figure 14 are RA = RB = 50, RDIFF = 100, assuming RLOAD = 50. The performance of Figure 13 and Figure 14 is basically the same, however leaving the center tap of Figure 14 floating allows the circuit to find a more balanced virtual ground, theoretically improving the even order harmonic rejection, but likely reducing the signal swing available due to the output voltage compliance range limitations. TABLE 1. INPUT CODING vs OUTPUT CURRENT WITH INTERNAL REFERENCE AND RSET = 1.91k INPUT CODE (D9-D0) IOUTA (mA) IOUTB (mA) 11111 11111 20 0 10000 00000 10 10 00000 00000 0 20 FN6078 Rev 1.00 November 12, 2004 Page 10 of 13 ISL5757 Propagation Delay REQ = 0.5 x (RLOAD//RDIFF) AT EACH OUTPUT PIN 21 PIN 22 ISL5757 The converter requires two clock rising edges for data to be represented at the output. Each rising edge of the clock captures the present data word and outputs the previous data. The propagation delay is therefore 1/CLK, plus