LTC2644IMS-L12#PBF

LTC2644 Dual 12-/10-/8-Bit PWM to VOUT DACs with 10ppm/°C Reference FEATURES DESCRIPTION No Latency PWM-to-Voltage Conversion n Voltage Output Updates and Settles within 8µs n 100kHz to 30Hz PWM Input Frequency n ±2.5LSB Max INL; ±1LSB Max DNL (LTC2644-12) n Guaranteed Monotonic n Pin-Selectable Internal or External Reference n 2.7V to 5.5V Supply Range n 1.71V to 5.5V Input Voltage Range n Low Power: 2.7mA at 3V, 1GΩ). Normal operating current resumes when PD returns high for transparent operation (IDLSEL = GND). For sample/ hold operation (IDLSEL = VCC), the LTC2644 remains in full power-down until the first rising edge is received on any PWM input. Any pair of PWM input rising edges separated by less than the idle mode timeout delay t3 (50ms minimum) will cause the DAC code to be updated. The DAC output(s) will remain in Hi-Z until the channel is updated following the second rising PWM input edge. Voltage Output The LTC2644’s integrated rail-to-rail amplifier has guaranteed load regulation when sourcing or sinking up to 10mA at 5V, and 5mA at 3V. Load regulation is a measure of the amplifier’s ability to maintain the rated voltage accuracy over a wide range of load current. The measured change in output voltage per change in forced load current is expressed in LSB/mA. DC output impedance is equivalent to load regulation, and may be derived from it by simply calculating a change in units from LSB/mA to Ω. The amplifier’s DC output impedance is 0.1Ω when driving a load well away from the rails. When drawing a load current from either rail, the output voltage headroom with respect to that rail is limited by the 50Ω typical channel resistance of the output devices (e.g., when sinking 1mA, the minimum output voltage is 50Ω • 1mA, or 50mV). See the graph Headroom at Rails vs Output Current in the Typical Performance Characteristics section. The amplifier is stable driving capacitive loads of up to 500pF. Rail-to-Rail Output Considerations In any rail-to-rail voltage output device, the output is limited to voltages within the supply range. Since the analog output of the DAC cannot go below ground, it may limit the lowest codes reachable as shown in Figure 2b. Similarly, limiting can occur near full-scale when the REF pin is tied to VCC. If VREF = VCC and the DAC full-scale error (FSE) is positive, the output for the highest codes limits at VCC, as shown in Figure 2c. No full-scale limiting will occur if VREF is less than VCC–FSE. Offset and linearity are defined and tested over the region of the DAC transfer function where no output limiting can occur. Board Layout The PC board should have separate areas for the analog and digital sections of the circuit. A single, solid ground plane should be used, with analog and digital signals carefully routed over separate areas of the plane. This keeps digital signals away from sensitive analog signals and minimizes the interaction between digital ground currents and the analog section of the ground plane. The resistance from the LTC2644 GND pin to the ground plane should be as low as possible. Resistance here will add directly to the effective DC output impedance of the device (typically 0.1Ω). Note that the LTC2644 is no more susceptible to this effect than any other parts of this type; on the contrary, it allows layout-based performance improvements to shine rather than limiting attainable performance with excessive internal resistance. Rev. B For more information www.analog.com 15 LTC2644 OPERATION Another technique for minimizing errors is to use a separate power ground return trace on another board layer. The trace should run between the point where the power supply is connected to the board and the DAC ground pin. Thus the DAC ground pin becomes the common point for analog ground, digital ground, and power ground. When the LTC2644 is sinking large currents, this current flows out of the ground pin and directly into the power ground trace without affecting the analog ground plane voltage. It is sometimes necessary to interrupt the ground plane to confine digital ground currents to the digital portion of the plane. When doing this, make the gap in the plane only as long as it needs to be to serve its purpose and ensure that no traces cross over the gap. VREF = VCC POSITIVE FSE VREF = VCC OUTPUT VOLTAGE OUTPUT VOLTAGE INPUT CODE (c) OUTPUT VOLTAGE 0V NEGATIVE OFFSET 0V 2048 INPUT CODE (a) 4095 INPUT CODE (b) 16 0 2645 F02 Figure 2. Effects of Rail-to-Rail Operation on a DAC Transfer Curve (Shown for 12 Bits). (a) Overall Transfer Function (b) Effect of Negative Offset for Codes Near Zero (c) Effect of Positive Full-Scale Error for Codes Near Full-Scale Rev. B For more information www.analog.com LTC2644 TYPICAL APPLICATIONS 2.7V TO 5.5V C3 0.1µF EXT INPUT: 1V TO VCC C4 0.1µF 5V C2 0.1µF IOVCC ISOLATION BARRIER ANALOG PWM DUTY CYCLE CONTROL (0V TO 1V) PS9851-1 LTC6992 MOD OUT GND V+ SET DIV REF LTC2644 -12 INA PWM TO BINARY DAC A INB PWM TO BINARY DAC B 2.25V TO 5.5V C1 0.1µF VCC IDLSEL REFSEL PD RSET 50k VOUTA VOUTB DAC CONTROL VOLTAGE OUTPUT (0V TO VREF) VOUTB = Hi-Z GND 2644 F03 Figure 3. Analog Control Voltage with PWM Transmission to DAC Control Voltage Output Rev. B For more information www.analog.com 17 LTC2644 PACKAGE DESCRIPTION MS Package 12-Lead Plastic MSOP (Reference LTC DWG # 05-08-1668 Rev A) 0.889 ±0.127 (.035 ±.005) 5.10 (.201) MIN 3.20 – 3.45 (.126 – .136) 4.039 ±0.102 (.159 ±.004) (NOTE 3) 0.65 (.0256) BSC 0.42 ±0.038 (.0165 ±.0015) TYP 12 11 10 9 8 7 RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) DETAIL “A” 3.00 ±0.102 (.118 ±.004) (NOTE 4) 4.90 ±0.152 (.193 ±.006) 0° – 6° TYP 0.406 ±0.076 (.016 ±.003) REF GAUGE PLANE 0.53 ±0.152 (.021 ±.006) DETAIL “A” 0.18 (.007) SEATING PLANE 1.10 (.043) MAX 0.22 – 0.38 (.009 – .015) TYP 1 2 3 4 5 6 0.650 (.0256) BSC NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX 18 0.86 (.034) REF 0.1016 ±0.0508 (.004 ±.002) MSOP (MS12) 0213 REV A Rev. B For more information www.analog.com LTC2644 REVISION HISTORY REV DATE DESCRIPTION A 02/17 Corrected VOUT(IDEAL) equation PAGE NUMBER 13 B 11/18 Corrected units of Output Voltage Noise 5 Rev. B Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representamore information tion that the interconnectionFor of its circuits as describedwww.analog.com herein will not infringe on existing patent rights. 19 LTC2644 TYPICAL APPLICATION 5V C3 0.1µF C4 0.1µF 0.1µF 4.7µF 2.2k IOVCC PD INA INB VCC IDLSEL REFSEL REF 0.1µF LTC2644 -12 PWM TO BINARY DAC A VOUTA 10k PWM TO BINARY DAC B VIN ILM 143k PGOOD INTVCC LTC3850EUF RJK0305DPB TG1 BOOST1 FREQ 0.1µF 2.2µH SW1 VOUTB = Hi-Z 1nF CMDSH-3 100k 10k 0.1µF VOUTB VIN 6.5V TO 14V VOUT 3.3V ±10% RJK0301DPB BG1 3.32k 0.008k PGND GND FOR NO MARGINING, KEEP INA LOW. (VOUTA = Hi-Z) TO MARGIN 10% HIGH, SET INA DUTY CYCLE TO 1/4096 (VOUTA = 0V) TO MARGIN 10% LOW, SET INA DUTY CYCLE TO 2621/4096 (VOUTA = 1.6V) 1nF 500kHz 100pF 10k 10k SENSE1+ ITH1 MODE/PLLIN RUN1 1nF SENSE1– TKSS1 10nF 10k VFB1 SGND 63.4k 15pF 2645 F04 20k Figure 4. Voltage Margining Application with LTC3850 (3.3V ±10%) RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC2645 Quad 12-/10-/8-Bit PWM to VOUT DACs with 10ppm/°C Reference Zero Latency Bus Update, 100kHz to 30Hz Input Frequency, ±2.5LSB INL, 2.7V to 5.5V Supply Range, 16-Lead MSOP Package LT®1991 Precision, 100µA Gain Selectable Amplifier Gain Accuracy of 0.04%, Gains from –13 to 14, 100µA Precision Op Amp LT1469-2 Dual 200MHz, 30V/µs 16-Bit Accurate Op Amp 200MHz Gain Bandwidth, 125µV Offset, 30V/µs Slew Rate Precision Op Amp LTC2055 Dual Micropower Zero-Drift Op Amp 2.7V Minimum Supply Voltage, 150µA Supply Current per Amplifier, Zero-Drift Op Amp LTC6992 Timer Blox: Voltage-Controlled Pulse Width Modulator (PWM) 3.8Hz to 1MHz Output Frequency Range, 0V to 1V Analog Input, < 1.7% Maximum Frequency Error LTC2632/LTC2633 Dual 12-/10-/8-Bit SPI/I2C VOUT DACs with 10ppm/°C Reference 20 ±2.5LSB INL, 2.7V to 5.5V Supply Range, 10ppm/°C Reference, External REF Mode, 8-Lead ThinSOT™ Package Rev. B 11/18 www.analog.com For more information www.analog.com  ANALOG DEVICES, INC. 2018