LTC2642AIMS-16#PBF

LTC2641/LTC2642 16-/14-/12-Bit VOUT DACs in 3mm × 3mm DFN FEATURES DESCRIPTION Tiny 3mm × 3mm 8-Pin DFN Package Maximum 16-Bit INL Error: ±1LSB over Temperature Low 120µA Supply Current Guaranteed Monotonic over Temperature Low 0.5nV•sec Glitch Impulse 2.7V to 5.5V Single Supply Operation Fast 1µs Settling Time to 16 Bits Unbuffered Voltage Output Directly Drives 60k Loads 50MHz SPI/QSPI/MICROWIRE Compatible Serial Interface n Power-On Reset Clears DAC Output to Zero Scale (LTC2641) or Midscale (LTC2642) n Schmitt-Trigger Inputs for Direct Optocoupler Interface n Asynchronous CLR Pin n 8-Lead MSOP and 3mm × 3mm DFN Packages (LTC2641) n 10-Lead MSOP and 3mm × 3mm DFN Packages (LTC2642) The LTC®2641/LTC2642 are families of 16-, 14- and 12‑bit unbuffered voltage output DACs. These DACs operate from a single 2.7V to 5.5V supply and are guaranteed monotonic over temperature. The LTC2641A-16/LTC2642A‑16 provide 16‑bit performance (±1LSB INL and ±1LSB DNL) over temperature. Unbuffered DAC outputs result in low supply current of 120µA and a low offset error of ±1LSB. n n n n n n n n n APPLICATIONS n n n n High Resolution Offset and Gain Adjustment Process Control and Industrial Automation Automatic Test Equipment Data Acquisition Systems Both the LTC2641 and LTC2642 feature a reference input range of 2V to VDD. VOUT swings from 0V to VREF . For bipolar operation, the LTC2642 includes matched scaling resistors for use with an external precision op amp (such as the LT1678), generating a ±VREF output swing at RFB. The LTC2641/LTC2642 use a simple SPI/MICROWIRE compatible 3-wire serial interface which can be operated at clock rates up to 50MHz and can interface directly with optocouplers for applications requiring isolation. A power-on reset circuit clears the LTC2641’s DAC output to zero scale and the LTC2642’s DAC output to midscale when power is initially applied. A logic low on the CLR pin asynchronously clears the DAC to zero scale (LTC2641) or midscale (LTC2642). These DACs are all specified over the commercial and industrial ranges. L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and SoftSpan is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION Bipolar 16-Bit DAC LTC2642 0.1µF VDD 1µF REF 0.1µF POWER-ON RESET CS SCLK DIN CLR 1.0 VDD = 5V VREF = 2.5V ±2.5V RANGE 0.8 RFB INV 16-BIT DAC LTC2642-16 Integral Nonlinearity VREF 2V TO VDD 0.6 5pF – 1/2 LT1678 + VOUT 0.4 BIPOLAR VOUT –VREF TO VREF INL (LSB) 2.7V TO 5.5V 0.2 0 –0.2 –0.4 –0.6 CONTROL LOGIC 16-BIT DATA LATCH 16-BIT SHIFT REGISTER INL 25°C INL 90°C INL –45°C –0.8 –1.0 GND 26412 TA01a 0 16384 32768 CODE 49152 65535 26412 TA01b 26412fd For more information www.linear.com/LTC2641 1 LTC2641/LTC2642 ABSOLUTE MAXIMUM RATINGS (Note 1) VDD to GND................................................... –0.3V to 6V CS, SCLK, DIN, CLR to GND..........................–0.3V to (VDD + 0.3V) or 6V REF, VOUT, INV to GND.........–0.3V to (VDD + 0.3V) or 6V RFB to INV........................................................ –6V to 6V RFB to GND...................................................... –6V to 6V GND to GND (S8 Package) OBSOLETE ..... –0.3V to 0.3V Operating Temperature Range LTC2641C/LTC2642C................................ 0°C to 70°C LTC2641I/LTC2642I..............................–40°C to 85°C Maximum Junction Temperature (Note 2)............. 125°C Storage Temperature Range................... –65°C to 150°C Lead Temperature (Soldering, 10 sec).................... 300°C PIN CONFIGURATION LTC2641 LTC2641 LTC2641 TOP VIEW REF 1 CS 2 SCLK 3 9 DIN 4 TOP VIEW 8 GND 7 VDD 6 VOUT 5 TOP VIEW REF CS SCLK DIN CLR 1 2 3 4 8 7 6 5 GND VDD VOUT CLR VOUT 1 8 VDD GND 2 7 GND REF 3 6 DIN CS 4 5 SCLK MS8 PACKAGE 8-LEAD PLASTIC MSOP DD PACKAGE 8-LEAD (3mm × 3mm) PLASTIC DFN S8 PACKAGE 8-LEAD PLASTIC SO TJMAX = 125°C (NOTE 2), θJA = 120°C/W TJMAX = 125°C, θJA = 110°C/W TJMAX = 125°C (NOTE 2), θJA = 43°C/W EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB OBSOLETE PACKAGE LTC2642 LTC2642 TOP VIEW REF 1 10 GND CS 2 9 VDD SCLK 3 DIN 4 8 RFB 7 INV CLR 5 6 VOUT 11 TOP VIEW REF CS SCLK DIN CLR 1 2 3 4 5 10 9 8 7 6 GND VDD RFB INV VOUT MS PACKAGE 10-LEAD PLASTIC MSOP DD PACKAGE 10-LEAD (3mm × 3mm) PLASTIC DFN TJMAX = 125°C (NOTE 2), θJA = 43°C/W EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB TJMAX = 125°C (NOTE 2), θJA = 120°C/W 26412fd 2 For more information www.linear.com/LTC2641 LTC2641/LTC2642 ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC2641ACDD-16#PBF LTC2641ACDD-16#TRPBF LCZP 8-Lead (3mm × 3mm) Plastic DFN 0°C to 70°C LTC2641CDD-16#PBF LTC2641CDD-16#TRPBF LCZP 8-Lead (3mm × 3mm) Plastic DFN 0°C to 70°C LTC2641CDD-14#PBF LTC2641CDD-14#TRPBF LCZN 8-Lead (3mm × 3mm) Plastic DFN 0°C to 70°C LTC2641CDD-12#PBF LTC2641CDD-12#TRPBF LCZM 8-Lead (3mm × 3mm) Plastic DFN 0°C to 70°C LTC2641AIDD-16#PBF LTC2641AIDD-16#TRPBF LCZP 8-Lead (3mm × 3mm) Plastic DFN –40°C to 85°C LTC2641IDD-16#PBF LTC2641IDD-16#TRPBF LCZP 8-Lead (3mm × 3mm) Plastic DFN –40°C to 85°C LTC2641IDD-14#PBF LTC2641IDD-14#TRPBF LCZN 8-Lead (3mm × 3mm) Plastic DFN –40°C to 85°C LTC2641IDD-12#PBF LTC2641IDD-12#TRPBF LCZM 8-Lead (3mm × 3mm) Plastic DFN –40°C to 85°C LTC2641ACMS8-16#PBF LTC2641ACMS8-16#TRPBF LTCZS 8-Lead Plastic MSOP 0°C to 70°C LTC2641CMS8-16#PBF LTC2641CMS8-16#TRPBF LTCZS 8-Lead Plastic MSOP 0°C to 70°C LTC2641CMS8-14#PBF LTC2641CMS8-14#TRPBF LTCZR 8-Lead Plastic MSOP 0°C to 70°C LTC2641CMS8-12#PBF LTC2641CMS8-12#TRPBF LTCZQ 8-Lead Plastic MSOP 0°C to 70°C LTC2641AIMS8-16#PBF LTC2641AIMS8-16#TRPBF LTCZS 8-Lead Plastic MSOP –40°C to 85°C LTC2641IMS8-16#PBF LTC2641IMS8-16#TRPBF LTCZS 8-Lead Plastic MSOP –40°C to 85°C LTC2641IMS8-14#PBF LTC2641IMS8-14#TRPBF LTCZR 8-Lead Plastic MSOP –40°C to 85°C LTC2641IMS8-12#PBF LTC2641IMS8-12#TRPBF LTCZQ 8-Lead Plastic MSOP –40°C to 85°C LTC2642ACDD-16#PBF LTC2642ACDD-16#TRPBF LCZW 10-Lead (3mm × 3mm) Plastic DFN 0°C to 70°C LTC2642CDD-16#PBF LTC2642CDD-16#TRPBF LCZW 10-Lead (3mm × 3mm) Plastic DFN 0°C to 70°C LTC2642CDD-14#PBF LTC2642CDD-14#TRPBF LCZV 10-Lead (3mm × 3mm) Plastic DFN 0°C to 70°C LTC2642CDD-12#PBF LTC2642CDD-12#TRPBF LCZT 10-Lead (3mm × 3mm) Plastic DFN 0°C to 70°C LTC2642AIDD-16#PBF LTC2642AIDD-16#TRPBF LCZW 10-Lead (3mm × 3mm) Plastic DFN –40°C to 85°C LTC2642IDD-16#PBF LTC2642IDD-16#TRPBF LCZW 10-Lead (3mm × 3mm) Plastic DFN –40°C to 85°C LTC2642IDD-14#PBF LTC2642IDD-14#TRPBF LCZV 10-Lead (3mm × 3mm) Plastic DFN –40°C to 85°C LTC2642IDD-12#PBF LTC2642IDD-12#TRPBF LCZT 10-Lead (3mm × 3mm) Plastic DFN –40°C to 85°C LTC2642ACMS-16#PBF LTC2642ACMS-16#TRPBF LTCZZ 10-Lead Plastic MSOP 0°C to 70°C LTC2642CMS-16#PBF LTC2642CMS-16#TRPBF LTCZZ 10-Lead Plastic MSOP 0°C to 70°C LTC2642CMS-14#PBF LTC2642CMS-14#TRPBF LTCZY 10-Lead Plastic MSOP 0°C to 70°C LTC2642CMS-12#PBF LTC2642CMS-12#TRPBF LTCZX 10-Lead Plastic MSOP 0°C to 70°C LTC2642AIMS-16#PBF LTC2642AIMS-16#TRPBF LTCZZ 10-Lead Plastic MSOP –40°C to 85°C LTC2642IMS-16#PBF LTC2642IMS-16#TRPBF LTCZZ 10-Lead Plastic MSOP –40°C to 85°C LTC2642IMS-14#PBF LTC2642IMS-14#TRPBF LTCZY 10-Lead Plastic MSOP –40°C to 85°C LTC2642IMS-12#PBF LTC2642IMS-12#TRPBF LTCZX 10-Lead Plastic MSOP –40°C to 85°C LTC2641CS8-16#PBF LTC2641CS8-16#TRPBF 264116 8-Lead Plastic SO 0°C to 70°C LTC2641IS8-16#PBF LTC2641IS8-16#TRPBF 264116 8-Lead Plastic SO –40°C to 85°C OBSOLETE Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ 26412fd For more information www.linear.com/LTC2641 3 LTC2641/LTC2642 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VDD = 3V or 5V, VREF = 2.5V, CL = 10pF, GND = 0, RL = ∞ unless otherwise specified. LTC2641-12 LTC2642-12 SYMBOL PARAMETER CONDITIONS LTC2641-14 LTC2642-14 LTC2641-16 LTC2642-16 MIN TYP MAX MIN TYP MAX MIN TYP MAX LTC2641A-16 LTC2642A-16 MIN TYP MAX UNITS Static Performance N Resolution l 12 14 16 16 Bits Monotonicity l 12 14 16 16 Bits DNL Differential Nonlinearity (Note 3) l ±0.5 ±0.5 ±1 ±0.5 ±1 ±0.5 ±1 LSB INL Integral Nonlinearity (Note 3) l ±0.5 ±0.5 ±1 ±0.5 ±2 ±0.5 ±1 LSB ZSE Zero Code Offset Error Code = 0 l 1 2 LSB ZSTC Zero Code Tempco GE Gain Error ±0.05 GETC Gain Error Tempco ROUT DAC Output Resistance (Note 4) Bipolar Resistor Matching (LTC2642) RFB/RINV l ±0.5 Bipolar Zero Offset Error (LTC2642) BZSTC Bipolar Zero Tempco (LTC2642) PSR Power Supply Rejection ΔVDD = ±10% l ±0.05 ±2 ±1 2 ±0.05 ±4 ±2 ±0.05 ±5 ±2 ppm/°C ±5 LSB ±0.1 ±0.1 ±0.1 ±0.1 ppm/°C 6.2 6.2 6.2 6.2 kΩ 1 1 1 1 ±0.1 Ratio Error (Note 7) l BZE 2 ±0.5 ±2 ±0.1 ±0.03 ±0.5 ±0.1 ±0.5 l ±0.015 ±4 ±2 ±0.015 ±5 ±2 ±0.1 ±0.5 ±0.1 ±1 % ±5 LSB ppm/°C ±1 LSB The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VDD = 3V or 5V, VREF = 2.5V, CL = 10pF, GND = 0, RL = ∞ unless otherwise specified. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS VDD V Reference Input VREF Reference Input Range RREF Reference Input Resistance (Note 5) Unipolar Mode (LTC2641) Bipolar Mode (LTC2642) l 2.0 l l 11 8.5 14.8 11.4 kΩ kΩ 15 V/µs Dynamic Performance—VOUT SR Voltage Output Slew Rate Measured from 10% to 90% Output Settling Time To ±0.5LSB of FS DAC Glitch Impulse Major Carry Transition 0.5 nV•s Digital Feedthrough Code = 0000hex; NCS = VDD; SCLK, DIN 0V to VDD Levels 0.2 nV•s 10 nV/√Hz 1.3 MHz 1 Output Voltage Noise Density µs Dynamic Performance—Reference Input BW Reference –3dB Bandwidth Code = FFFFhex Reference Feedthrough Code = 0000hex, VREF = 1VP-P at 100kHz SNR Signal-to-Noise Ratio CIN(REF) Reference Input Capacitance Code = 0000hex Code = FFFFhex Digital Input High Voltage VCC = 3.6V to 5.5V VCC = 2.7V to 3.6V 1 mVP-P 92 dB 75 120 pF pF Digital Inputs VIH l l 2.4 2.0 V V 26412fd 4 For more information www.linear.com/LTC2641 LTC2641/LTC2642 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VDD = 3V or 5V, VREF = 2.5V, CL = 10pF, GND = 0, RL = ∞ unless otherwise specified. SYMBOL PARAMETER CONDITIONS MIN TYP VIL Digital Input Low Voltage VCC = 4.5V to 5.5V VCC = 2.7V to 4.5V l l 0.8 0.6 V V IIN Digital Input Current VIN = GND to VDD l ±1 µA CIN Digital Input Capacitance (Note 6) l 10 pF VH Hysteresis Voltage 3 MAX UNITS 0.15 V Power Supply VDD Supply Voltage IDD Supply Current, VDD Digital Inputs = 0V or VDD PD Power Dissipation Digital Inputs = 0V or VDD, VDD = 5V Digital Inputs = 0V or VDD, VDD = 3V l 2.7 120 l 5.5 V 200 µA 0.60 0.36 mW mW TIMING CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VDD = 3V or 5V, VREF = 2.5V, CL = 10pF, GND = 0, RL = ∞ unless otherwise specified. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS t1 DIN Valid to SCLK Setup Time l 10 ns t2 DIN Valid to SCLK Hold Time l 0 ns t3 SCLK Pulse Width High l 9 ns t4 SCLK Pulse Width Low l 9 ns t5 CS Pulse High Width l 10 ns t6 LSB SCLK High to CS High l 8 ns t7 CS Low to SCLK High l 8 ns t8 CS High to SCLK Positive Edge l 8 ns t9 CLR Pulse Width Low l 15 fSCLK SCLK Frequency 50% Duty Cycle VDD High to CS Low (Power-Up Delay) Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: Continuous operation above the specified maximum operating junction temperature may impair device reliability. Note 3: LTC2641-16/LTC2642-16 ±1LSB = ±0.0015% = ±15.3ppm of full scale. LTC2641-14/LTC2642-14 ±1LSB = ±0.006% = ±61ppm of full scale. LTC2641-12/LTC2642-12 ±1LSB = ±0.024% = ±244ppm of full scale. ns 50 l MHz 30 µs Note 4: ROUT tolerance is typically ±20%. Note 5: Reference input resistance is code dependent. Minimum is at 871Chex (34,588) in unipolar mode and at 671Chex (26, 396) in bipolar mode. Note 6: Guaranteed by design and not production tested. Note 7: Guaranteed by gain error and offset error testing, not production tested. 26412fd For more information www.linear.com/LTC2641 5 LTC2641/LTC2642 TYPICAL PERFORMANCE CHARACTERISTICS Integral Nonlinearity (INL) vs Supply (VDD) Integral Nonlinearity (INL) LTC2642-16 VREF = 2.5V VDD = 5V 0.8 0.6 INL vs VREF 1.0 VREF = 2.5V 0.8 0.4 0.2 0.2 0 –0.2 0.6 +INL 0 –INL –0.2 –0.6 –0.6 –0.6 –0.8 –0.8 –0.8 –1.0 –1.0 –1.0 32768 CODE 65535 49152 3 2 4 VDD (V) 6 5 1.0 1.0 VREF = 2.5V 0.8 0.6 0.4 0.4 0.2 0.2 DNL (LSB) DNL (LSB) –0.2 +DNL 0 –DNL –0.2 0.2 –0.4 –0.4 –0.6 –0.6 –0.8 –0.8 –0.8 –1.0 –1.0 –1.0 32768 CODE 49152 65535 3 2 4 VDD (V) 6 5 INL vs Temperature DNL vs Temperature 1.0 VREF = 2.5V VDD = 5V 0.8 +INL VREF = 2.5V VDD = 5V 4 DNL (LSB) 0 –INL –0.2 2 0.2 +DNL 0 –DNL –0.2 1 0 –1 –0.4 –0.4 –2 –0.6 –0.6 –3 –0.8 –0.8 –4 –1.0 –40 –1.0 –40 –15 35 10 TEMPERATURE (°C) 60 85 26412 G07 VREF = 2.5V VDD = 5V 3 0.4 0.2 6 5 Bipolar Zero Error vs Temperature 5 0.6 0.6 0.4 4 VREF (V) 26412 G06 BZE (LSB) 0.8 3 2 26412 G05 26412 G04 1.0 –DNL –0.2 –0.6 16384 +DNL 0 –0.4 0 VDD = 5.5V 0.8 0.6 0 6 5 DNL vs VREF 1.0 0.4 0.6 4 VREF (V) 3 2 26412 G03 Differential Nonlinearity (DNL) vs Supply (VDD) LTC2642-16 VREF = 2.5V VDD = 5V 0.8 –INL 26412 G02 Differential Nonlinearity (DNL) DNL (LSB) 0 –0.2 –0.4 26412 G01 INL (LSB) 0.2 –0.4 16384 +INL 0.4 –0.4 0 VDD = 5.5V 0.8 0.6 0.4 INL (LSB) INL (LSB) 1.0 INL (LSB) 1.0 –15 35 10 TEMPERATURE (°C) 60 85 26412 G08 –5 –40 –15 35 10 TEMPERATURE (°C) 60 85 26412 G09 26412fd 6 For more information www.linear.com/LTC2641 LTC2641/LTC2642 TYPICAL PERFORMANCE CHARACTERISTICS Unbuffered Zero Scale Error vs Temperature (LTC2641-16) Bipolar Gain Error vs Temperature 5 VREF = 2.5V VDD = 5V 1.0 0.8 0.6 0.6 2 0.4 0.4 1 0.2 0.2 0 –1 FSE (LSB) 0.8 ZSE (LSB) BGE (LSB) 1.0 3 4 0 –0.2 –0.4 –0.4 –3 –0.6 –0.6 –4 –0.8 –0.8 –5 –40 –1.0 –40 –15 35 10 TEMPERATURE (°C) 60 85 –15 35 10 TEMPERATURE (°C) 60 14-Bit Differential Nonlinearity (DNL) (LTC2642-14) 1.0 LTC2642-14 VREF = 2.5V VDD = 5V 0.8 0.6 0.6 0.4 0.2 DNL (LSB) 0.4 0.2 –0.2 –0.2 –0.4 –0.6 –0.6 –0.8 –0.8 0 4096 8192 CODE 12288 –1.0 16383 0 4096 8192 CODE 1.0 0.6 0.4 0.2 DNL (LSB) 0.4 0.2 –0.2 –0.6 –0.6 –0.8 –0.8 1024 2048 CODE 3072 4095 26412 G16 32768 49152 –1.0 65535 IREF vs Code (Bipolar LTC2642) VREF = 2.5V 200 –0.2 –0.4 0 16384 26412 G15 250 0 –0.4 –1.0 0 CODE LTC2642-12 VREF = 2.5V VDD = 5V 0.8 0 100 0 16383 12288 IREF (µA) 0.6 150 12-Bit Differential Nonlinearity (DNL) (LTC2642-12) LTC2642-12 VREF = 2.5V VDD = 5V 0.8 VREF = 2.5V 26412 G14 12-Bit Integral Nonlinearity (INL) (LTC2642-12) 85 50 26412 G13 1.0 60 200 0 –0.4 –1.0 35 10 TEMPERATURE (°C) IREF vs Code (Unipolar LTC2641) 250 LTC2642-14 VREF = 2.5V VDD = 5V 0.8 0 –15 26412 G12 IREF (µA) 1.0 –1.0 –40 85 26412 G11 14-Bit Integral Nonlinearity (INL) (LTC2642-14) INL (LSB) 0 –0.2 –2 26412 G10 INL (LSB) Unbuffered Full-Scale Error vs Temperature (LTC2641-16) 150 100 50 0 1024 2048 CODE 3072 4095 0 0 16384 32768 49152 65535 CODE 26412 G17 26412 G18 26412fd For more information www.linear.com/LTC2641 7 LTC2641/LTC2642 TYPICAL PERFORMANCE CHARACTERISTICS Supply Current (IDD) vs Temperature 150 VREF = 2.5V 125 800 700 75 50 75 –15 10 35 TEMPERATURE (°C) 0 85 60 2.5 3.5 3 4 4.5 5 150 100 IDD (µA) 100 IDD (µA) 125 75 50 25 25 2.5 3 3.5 4 4.5 5 0 VREF (V) 1.5 2 VREF (V) 2.5 3 26412 G25 CODE 32768 500ns/DIV CODE 32767 26412 G24 VOUT vs VDD = 0V to 5.5V (POR Function) LTC2641 VDD = VREF 0V TO 5.5V 2V/DIV SETTLE RESIDUE 250µV/DIV 500ns/DIV LTC2641-16 UNBUFFERED CL = 10pF Full-Scale Settling (Zoomed In) CS 5V/DIV LTC2641-16 UNBUFFERED CL = 10pF VREF = 2.5V VDD = 5V CODE 32767 VOUT 20mV/DIV 1 5 26412 G23 Full-Scale Transition VOUT 1V/DIV 1 1.5 2 2.5 3 3.5 4 4.5 DIGITAL INPUT VOLTAGE (V) CS 5V/DIV VDD = 3V 26412 G22 CS 5V/DIV 0.5 Midscale Glitch Impulse 75 50 2 0 26412 G21 Supply Current (IDD) vs VREF , VDD = 3V 125 1.5 0 26412 G20 VDD = 5V 1 5.5 VDD (V) Supply Current (IDD) vs VREF , VDD = 5V 0 VDD = 3V 100 26412 G19 150 400 200 25 0 –40 500 300 50 25 VDD = 5V 600 100 VDD = 3V IDD (µA) IDD (µA) 900 VREF = 2.5V 125 VDD = 5V 100 Supply Current (IDD) vs Digital Input Voltage IDD (µA) 150 Supply Current (IDD) vs Supply Voltage (VDD) VOUT 10mV/DIV LTC2641-16 500ns/DIV VREF = 2.5V CONSULT FACTORY FOR MEASUREMENT CIRCUIT 26412 G26 LTC2641-16 UNBUFFERED CL = 10pF 50ms/DIV 26412 G27 26412fd 8 For more information www.linear.com/LTC2641 LTC2641/LTC2642 PIN FUNCTIONS LTC2641 – MSOP, DFN Packages REF (Pin 1): Reference Voltage Input. Apply an external reference at REF between 2V and VDD. CS (Pin 2): Serial Interface Chip Select/Load Input. When CS is low, SCLK is enabled for shifting in data on DIN. When CS is taken high, SCLK is disabled, the 16-bit input word is latched and the DAC is updated. SCLK (Pin 3): Serial Interface Clock Input. CMOS and TTL compatible. DIN (Pin 4): Serial Interface Data Input. Data is applied to DIN for transfer to the device at the rising edge of SCLK. CLR (Pin 5): Asynchronous Clear Input. A logic low clears the DAC to code 0. VOUT (Pin 6): DAC Output Voltage. The output range is 0V to VREF . VDD (Pin 7): Supply Voltage. Set between 2.7V and 5.5V. GND (Pin 8): Circuit Ground. Exposed Pad (DFN Pin 9): Circuit Ground. Must be soldered to PCB ground. LTC2641 – SO Package OBSOLETE VOUT (Pin 1): DAC Output Voltage. The output range is 0V to VREF. GND (Pin 2): Circuit Ground. REF (Pin 3): Reference Voltage Input. Apply an external reference at REF between 2V and VDD. CS (Pin 4): Serial Interface Chip Select/Load Input. When CS is low, SCLK is enabled for shifting in data on DIN. When CS is taken high, SCLK is disabled, the 16-bit input word is latched and the DAC is updated. GND (Pin 7): Circuit Ground Pin. Must be connected to Pin 2 (GND). VDD (Pin 8): Supply Voltage. Set between 2.7V and 5.5V. LTC2642 – MSOP, DFN Packages REF (Pin 1): Reference Voltage Input. Apply an external reference at REF between 2V and VDD. CS (Pin 2): Serial Interface Chip Select/Load Input. When CS is low, SCLK is enabled for shifting in data on DIN. When CS is taken high, SCLK is disabled, the 16-bit input word is latched and the DAC is updated. SCLK (Pin 3): Serial Interface Clock Input. CMOS and TTL compatible. DIN (Pin 4): Serial Interface Data Input. Data is applied to DIN for transfer to the device at the rising edge of SCLK. CLR (Pin 5): Asynchronous Clear Input. A logic low clears the DAC to midscale. VOUT (Pin 6): DAC Output Voltage. The output range is 0V to VREF . INV (Pin 7): Center Tap of Internal Scaling Resistors. Connect to an external amplifier’s inverting input in bipolar mode. RFB (Pin 8): Feedback Resistor. Connect to an external amplifier’s output in bipolar mode. The bipolar output range is –VREF to VREF . VDD (Pin 9): Supply Voltage. Set between 2.7V and 5.5V. GND (Pin 10): Circuit Ground. Exposed Pad (DFN Pin 11): Circuit Ground. Must be soldered to PCB ground. SCLK (Pin 5): Serial Interface Clock Input. CMOS and TTL compatible. DIN (Pin 6): Serial Interface Data Input. Data is applied to DIN for transfer to the device at the rising edge of SCLK. 26412fd For more information www.linear.com/LTC2641 9 LTC2641/LTC2642 BLOCK DIAGRAMS LTC2641 - SO OBSOLETE PACKAGE LTC2641 - MSOP, DFN 7 VDD 1 8 REF LTC2641-16 LTC2641-14 LTC2641-12 POWER-ON RESET 2 3 4 5 DIN 16-/14-/12-BIT DAC VOUT 6 CLR 4 CONTROL LOGIC REF LTC2641-16 CS SCLK 3 VDD 5 16-BIT DATA LATCH 6 16-BIT SHIFT REGISTER GND 7 8 POWER-ON RESET 16-/14-/12-BIT DAC CONTROL LOGIC 16-BIT DATA LATCH VOUT 1 CS SCLK DIN GND 16-BIT SHIFT REGISTER 2641 BD01a GND 2 2641 BD01b LTC2642 9 VDD 1 REF RFB LTC2642-16 LTC2642-14 LTC2642-12 2 3 4 5 INV POWER-ON RESET 16-/14-/12-BIT DAC CONTROL LOGIC 16-BIT DATA LATCH VOUT 8 7 6 CS SCLK DIN CLR 16-BIT SHIFT REGISTER GND 10 2642 BD 26412fd 10 For more information www.linear.com/LTC2641 LTC2641/LTC2642 TIMING DIAGRAM t1 t2 t3 1 SCK 2 t4 t6 3 15 16 t8 SDI t5 t7 26412 TD CS/LD OPERATION General Description The digital-to-analog transfer function at the VOUT pin is: The LTC2641/LTC2642 family of 16-/14-/12-bit voltage output DACs offer full 16-bit performance with less than ±1LSB integral linearity error and less than ±1LSB differential linearity error, guaranteeing monotonic operation. They operate from a single supply ranging from 2.7V to 5.5V, consuming 120µA (typical). An external voltage reference of 2V to VDD determines the DAC’s full-scale output voltage. A 3-wire serial interface allows the LTC2641/ LTC2642 to fit into a small 8-/10-pin MSOP or DFN 3mm × 3mm package. k VOUT(IDEAL) =   VREF 2N  Digital-to-Analog Architecture The DAC architecture is a voltage switching mode resistor ladder using precision thin-film resistors and CMOS switches. The LTC2641/LTC2642 DAC resistor ladders are composed of a proprietary arrangement of matched DAC sections. The four MSBs are decoded to drive 15 equally weighted segments, and the remaining lower bits drive successively lower weighted sections. Major carry glitch impulse is very low at 500pV•sec, CL = 10pF, ten times lower than previous DACs of this type. where k is the decimal equivalent of the binary DAC input code, N is the resolution, and VREF is between 2.0V and VDD (see Tables 1a, 1b and 1c). The LTC2642 includes matched resistors that are tied to an external amplifier to provide bipolar output swing (Figure 2). The bipolar transfer function at the RFB pin is:  k  VOUT _BIPOLAR(IDEAL) = VREF  – 1 2N–1  (see Tables 2a, 2b and 2c). Serial Interface The LTC2641/LTC2642 communicates via a standard 3‑wire SPI/QSPI/MICROWIRE compatible interface. The chip select input (CS) controls and frames the loading of serial data from the data input (DIN). Following a CS highto-low transition, the data on DIN is loaded, MSB first, into the shift register on each rising edge of the serial clock 26412fd For more information www.linear.com/LTC2641 11 LTC2641/LTC2642 OPERATION input (SCLK). After 16 data bits have been loaded into the serial input register, a low-to-high transition on CS transfers the data to the 16-bit DAC latch, updating the DAC output (see Figures 1a, 1b, 1c). While CS remains high, the serial input shift register is disabled. If there are less than 16 low-to-high transitions on SCLK while CS remains low, the data will be corrupted, and must be reloaded. Also, if there are more than 16 low-to-high transitions on SCLK while CS remains low, only the last 16 data bits loaded from DIN will be transferred to the DAC latch. For the 14-bit DACs, (LTC2641-14/LTC2642-14), the MSB remains in the same (left-justified) position in the input 16-bit data word. Therefore, two “don’t-care” bits must be loaded after the LSB, to make up the required 16 data bits (Figure 1b). Similarly, for the 12-bit family members (LTC2641-12/LTC2642-12) four “don’t-care” bits must follow the LSB (Figure 1c). Power-On Reset The LTC2641/LTC2642 include a power-on reset circuit to ensure that the DAC output comes up in a known state. When VDD is first applied, the power-on reset circuit sets the output of the LTC2641 to zero-scale (code 0). The LTC2642 powers up to midscale (bipolar zero). Depending on the DAC number of bits, the midscale code is: 32,768 (LTC2642-16); 8,192 (LTC2642-14); or 2,048 (LTC2642-12). Clearing the DAC A low pulse meeting the t9 (minimum) specification on the CLR pin asynchronously clears the DAC latch to code zero (LTC2641) or to midscale (LTC2642). CS SCLK DIN 1 2 3 4 5 6 D15 D14 D13 D12 D11 D10 7 D9 8 D8 9 D7 10 D6 11 D5 12 D4 13 D3 14 D2 15 D1 MSB 16 DAC UPDATED D0 LSB 26412 F01a DATA (16 BITS) Figure 1a. 16-Bit Timing Diagram (LTC2641-16/LTC2642-16) CS SCLK DIN 1 2 3 4 D13 D12 D11 D10 5 D9 6 D8 7 D7 8 D6 9 D5 10 D4 11 D3 12 D2 13 D1 MSB 14 D0 15 X 16 DAC UPDATED X LSB 26412 F01b DATA (14 BITS + 2 DON’T-CARE BITS) Figure 1b. 14-Bit Timing Diagram (LTC2641-14/LTC2642-14) CS SCLK DIN 1 2 D11 D10 3 D9 4 D8 5 D7 6 D6 7 D5 8 D4 9 D3 10 D2 11 D1 MSB 12 D0 13 X 14 X 15 X LSB 16 DAC UPDATED X 26412 F01c DATA (12 BITS + 4 DON’T-CARE BITS) Figure 1c. 12-Bit Timing Diagram (LTC2641-12/LTC2642-12) 26412fd 12 For more information www.linear.com/LTC2641 LTC2641/LTC2642 APPLICATIONS INFORMATION Unipolar Configuration The external amplifier provides a unity-gain buffer. The LTC2642 can also be used in unipolar configuration by tying RFB and INV to REF . This provides power-up and clear to midscale. Figure 2 shows a typical unipolar DAC application for the LTC2641. Tables 1a, 1b and 1c show the unipolar binary code tables for 16-bit, 14-bit and 12-bit operation. VREF 2.5V 0.1µF 5V/3V 4.7µF OUT IN 5V Table 1a. 16-Bit Unipolar Binary Code Table (LTC2641-16) LT®1019CS8-2.5 GND DIGITAL INPUT BINARY NUMBER IN DAC LATCH 0.1µF 7 VDD 5V/3V 0.1µF 1 REF – MSB 1/2 LTC6078 1111 1111 1111 1111 VREF (65,535/65,536) 1000 0000 0000 0000 VREF (32,768/65,536) = VREF/2 LTC2641-16 2 16-BIT DAC CS 3 SCLK 4 DIN 5 CLR VOUT 6 ANALOG OUTPUT (VOUT) + UNIPOLAR VOUT 0V TO 2.5V LSB 0000 0000 0000 0001 VREF (1/65,536) 0000 0000 0000 0000 0V GND 26412 F02 8 Figure 2. 16-Bit Unipolar Output (LTC2641-16) Unipolar VOUT = 0V to VREF Table 1b. 14-Bit Unipolar Binary Code Table (LTC2641-14) DIGITAL INPUT BINARY NUMBER IN DAC LATCH MSB ANALOG OUTPUT (VOUT) LSB Table 1c. 12-Bit Unipolar Binary Code Table (LTC2641-12) DIGITAL INPUT BINARY NUMBER IN DAC LATCH MSB ANALOG OUTPUT (VOUT) LSB 1111 1111 1111 11xx VREF (16,383/16,384) 1111 1111 1111 xxxx VREF (4,095/4,096) 1000 0000 0000 00xx VREF (8,192/16,384) = VREF/2 1000 0000 0000 xxxx VREF (2,048/4,096) = VREF/2 0000 0000 0000 01xx VREF (1/16,384) 0000 0000 0001 xxxx VREF (1/4,096) 0000 0000 0000 00xx 0V 0000 0000 0000 xxxx 0V 26412fd For more information www.linear.com/LTC2641 13 LTC2641/LTC2642 APPLICATIONS INFORMATION Bipolar Configuration The amplifier circuit provides a gain of +2 from the VOUT pin, and gain of –1 from VREF . Tables 2a, 2b and 2c show the bipolar offset binary code tables for 16-bit, 14-bit and 12-bit operation. Figure 3 shows a typical bipolar DAC application for the LTC2642. The on-chip bipolar offset/gain resistors, RFB and RINV , are connected to an external amplifier to produce a bipolar output swing from –VREF to VREF at the RFB pin. VREF 2.5V 5V/3V 0.1µF 0.1µF 9 VDD OUT 4.7µF RFB 8 C1 10pF LTC2642-16 INV 7 2 16-BIT DAC CS 3 SCLK 4 DIN 5 CLR 5V GND 1 REF IN LT1019CS8-2.5 5V 0.1µF – 1/2 LT1678 + VOUT 6 0.1µF BIPOLAR VOUT –2.5V TO 2.5V –5V GND 26412 F02 10 Figure 3. 16-Bit Bipolar Output (LTC2642-16) VOUT = –VREF to VREF Table 2a. 16-Bit Bipolar Offset Binary Code Table (LTC2642-16) DIGITAL INPUT BINARY NUMBER IN DAC LATCH MSB ANALOG OUTPUT (VOUT) LSB Table 2b. 14-Bit Bipolar Offset Binary Code Table (LTC2642-14) DIGITAL INPUT BINARY NUMBER IN DAC LATCH MSB ANALOG OUTPUT (VOUT) LSB Table 2c. 12-Bit Bipolar Offset Binary Code Table (LTC2642-12) DIGITAL INPUT BINARY NUMBER IN DAC LATCH MSB ANALOG OUTPUT (VOUT) LSB 1111 1111 1111 1111 VREF (32,767/32,768) 1111 1111 1111 11xx VREF (8,191/8,192) 1111 1111 1111 xxxx VREF (2,047/2,048) 1000 0000 0000 0001 VREF (1/32,768) 1000 0000 0000 01xx VREF (1/8,192) 1000 0000 0001 xxxx VREF (1/2,048) 1000 0000 0000 0000 0V 1000 0000 0000 00xx 0V 1000 0000 0000 xxxx 0V 0111 1111 1111 1111 –VREF (1/32,768) 0000 0000 0000 0000 –VREF 0111 1111 1111 11xx –VREF (1/8,192) 0000 0000 0000 00xx –VREF 0111 1111 1111 xxxx –VREF (1/2048) 0000 0000 0000 xxxx –VREF 26412fd 14 For more information www.linear.com/LTC2641 LTC2641/LTC2642 APPLICATIONS INFORMATION Unbuffered Operation and VOUT Loading Unbuffered VOUT Settling Time The DAC output is available directly at the VOUT pin, which swings from GND to VREF . Unbuffered operation provides the lowest possible offset, full-scale and linearity errors, the fastest settling time and minimum power consumption. The settling time at the VOUT pin can be closely approximated by a single-pole response where: However, unbuffered operation requires that appropriate loading be maintained on the VOUT pin. The LTC2641/ LTC2642 VOUT can be modeled as an ideal voltage source in series with a source resistance of ROUT , typically 6.2k (Figure 4). The DAC’s linear output impedance allows it to drive medium loads (RL > 60k) without degrading INL or DNL; only the gain error is increased. The gain error (GE) caused by a load resistance, RL, (relative to full scale) is: GE = –1 R  1+  OUT   RL  t = ROUT • (COUT + CL) (Figure 4). Settling to 1/2LSB at 16-bits requires about 12 time constants (ln(2 • 65,536)). The typical settling time of 1µs corresponds to a time constant of 83ns, and a total (COUT + CL) of about 83ns/6.2k = 13pF . The internal capacitance, COUT is typically 10pF, so an external CL of 3pF corresponds to 1µs settling to 1/2LSB. VREF LTC2641 LTC2642 + ( )– CODE VREF 2N REF ROUT VOUT COUT GND RL CL IL VOUT 0V TO VREF 26412 F04 In 16-bit LSBs: GE = Figure 4. VOUT Pin Equivalent Circuit –65536   LSB R    OUT 1+    RL  Op Amp Selection ROUT has a low tempco (typically < ±50ppm/°C), and is independent of DAC code. The variation of ROUT, part-topart, is typically less than ±20%. Note on LSB units: For the following error descriptions, “LSB” means 16-bit LSB and 65,536 is rounded to 66k. To convert to 14-bit LSBs (LTC2641-14/LTC2642-14) divide by 4. To convert to 12-bit LSBs (LTC2641-12/LTC2642-12) divide by 16. A constant current, IL, loading VOUT will produce an offset of: VOFFSET = –IL • ROUT For VREF = 2.5V, a 16-bit LSB equals 2.5V/65,536, or 38µV. Since ROUT is 6.2k, an IL of 6nA produces an offset of 1LSB. Therefore, to avoid degrading DAC performance, it is critical to protect the VOUT pin from any sources of leakage current. The optimal choice for an external buffer op amp depends on whether the DAC is used in the unipolar or bipolar mode of operation, and also depends on the accuracy, speed, power dissipation and board area requirements of the application. The LTC2641/LTC2642’s combination of tiny package size, rail-to-rail single supply operation, low power dissipation, fast settling and nearly ideal accuracy specifications makes it impractical for one op amp type to fit every application. In bipolar mode (LTC2642 only), the amplifier operates with the internal resistors to provide bipolar offset and scaling. In this case, a precision amplifier operating from dual power supplies, such as the the LT1678 provides the ±VREF output range (Figure 3). In unipolar mode, the output amplifier operates as a unity gain voltage follower. For unipolar, single supply applications a precision, rail-to-rail input, single supply op amp 26412fd For more information www.linear.com/LTC2641 15 LTC2641/LTC2642 APPLICATIONS INFORMATION such as the LTC6078 is suitable, if the application does not require linear operation very near to GND, or zero scale (Figure 2). The LTC6078 typically swings to within 1mV of GND if it is not required to sink any load current. For an LSB size of 38µV, 1mV represents 26 missing codes near zero scale. Linearity will be degraded over a somewhat larger range of codes above GND. It is also unavoidable that settling time and transient performance will degrade whenever a single supply amplifier is operated very close to GND, or to the positive supply rail. voltage temperature coefficient (referenced to 25°C) of 0.6μV/°C will add 1LSB of zero-scale error. Also, IBIAS and the VOFFSET error it causes, will typically show significant relative variation over temperature. The small LSB size of a 16-bit DAC, coupled with the tight accuracy specifications on the LTC2641/LTC2642, means that the accuracy and input specifications for the external op amp are critical for overall DAC performance. Op amp input common mode rejection ratio (CMRR) is an input-referred error that corresponds to a combination of gain error (GE) and INL, depending on the op amp architecture and operating conditions. A conservative estimate of total CMRR error is: Op Amp Specifications and Unipolar DAC Accuracy Most op amp accuracy specifications convert easily to DAC accuracy. Op amp input bias current on the noninverting (+) input is equivalent to an IL loading the DAC VOUT pin and therefore produces a DAC zero-scale error (ZSE) (see Unbuffered Operation): ZSE = –IB(IN+) • ROUT [Volts] In 16-bit LSBs:  66k  ZSE = –IB IN+ • 6.2k •   LSB VREF   ( ) Op amp input impedance, RIN, is equivalent to an RL loading the LTC2641/LTC2642 VOUT pin, and produces a gain error of: GE = –66k   LSB 6.2k    1+    RIN  Op amp offset voltage, VOS, corresponds directly to DAC zero code offset error, ZSE: ZSE = VOS • 66k [LSB] VREF Temperature effects also must be considered. Over the –40°C to 85°C industrial temperature range, an offset 16 Op amp open-loop gain, AVOL, contributes to DAC gain error (GE): GE = 66k [LSB] A VOL  CMRR   V    Error = 10 20  •  CMRR _RANGE  • 66k LSB VREF       where VCMRR_RANGE is the voltage range that CMRR (in dB) is specified over. Op amp Typical Performance Characteristics graphs are useful to predict the impact of CMRR errors on DAC performance. Typically, a precision op amp will exhibit a fairly linear CMRR behavior (corresponding to DAC gain error only) over most of the common mode input range (CMR), and become nonlinear and produce significant errors near the edge of the CMR. Rail-to-rail input op amps are a special case, because they have 2 distinct input stages, one with CMR to GND and the other with CMR to V+. This results in a “crossover” CM input region where operation switches between the two input stages. The LTC6078 rail-to-rail input op amp typically exhibits remarkably low crossover linearity error, as shown in the VOS vs VCM Typical Performance Characteristics graphs (see the LTC6078 data sheet). Crossover occurs at CM inputs about 1V below V+, and an LTC6078 operating as a unipolar DAC buffer with VREF = 2.5V and V+ = 5V will typically add only about 1LSB of GE and almost no INL error due to CMRR. Even in a full rail-to-rail application, with VREF = V+ = 5V, a typical LTC6078 will add only about 1LSB of INL at 16-bits. For more information www.linear.com/LTC2641 26412fd LTC2641/LTC2642 APPLICATIONS INFORMATION Op Amp Specifications and Bipolar DAC Accuracy The op amp contributions to unipolar DAC error discussed above apply equally to bipolar operation. The bipolar application circuit gains up the DAC span, and all errors, by a factor of 2. Since the LSB size also doubles, the errors in LSBs are identical in unipolar and bipolar modes. One added error in bipolar mode comes from IB (IN–), which flows through RFB to generate an offset. The full bias current offset error becomes: VOFFSET = (IB (IN–) • RFB – IB (IN+) • ROUT • 2) [Volts] So: ( ) VOFFSET = IB (IN– ) • 28k – IB (IN+ ) • 12.4k • 33k [LSB] VREF Settling Time with Op Amp Buffer When using an external op amp, the output settling time will still include the single pole settling on the LTC2641/ LTC2642 VOUT node, with time constant ROUT • (COUT + CL) (see Unbuffered VOUT Settling Time). CL will include the buffer input capacitance and PC board interconnect capacitance. The external buffer amplifier adds another pole to the output response, with a time constant equal to (fbandwidth/2π). For example, assume that CL is maintained at the same value as above, so that the VOUT node time constant is 83ns = 1μs/12. The output amplifier pole will also have a time constant of 83ns if the closed-loop bandwidth equals (1/2π • 83ns) = 1.9MHz. The effective time constant of two cascaded single-pole sections is approximately the root square sum of the individual time constants, or √2 • 83ns = 117ns, and 1/2 LSB settling time will be ~12 • 117ns = 1.4μs. This represents an ideal case, with no slew limiting and ideal op amp phase margin. In practice, it will take a considerably faster amplifier, as well as careful attention to maintaining good phase margin, to approach the unbuffered settling time of 1μs. The output settling time for bipolar applications (Figure 3) will be somewhat increased due to the feedback resistor network RFB and RINV (each 28k nominal). The parasitic capacitance, CP, on the op amp (–) input node will introduce a feedback loop pole with a time constant of (CP • 28k/2). A small feedback capacitor, C1, should be included, to introduce a zero that will partially cancel this pole. C1 should nominally be