DEMO MANUAL DC570A LTC2440 24-Bit High Speed Delta Sigma ADC Description The LTC®2440 is a high speed 24-bit Δ∑ ADC with 5ppm INL and 5μV offset. It uses a proprietary delta-sigma architecture enabling variable speed and resolution with no latency. Ten speed/resolution combinations (6.9Hz/200nVRMS to 3.5kHz/25μVRMS) are programmed through a simple serial interface. Alternatively, by pulling the serial input pin HIGH or LOW, a fast (880Hz/2μVRMS) or ultra low noise (6.9Hz, 200nVRMS, 50Hz/60Hz rejection) speed/resolution combination can be easily selected. The accuracy (offset, full-scale, linearity, drift) and power dissipation are independent of the speed selected. Since there is no latency, a speed/resolution change may be made between conversions with no degradation in performance. DC570A is a member of Linear Technology’s QuikEval™ family of demonstration boards. It is designed to allow easy evaluation of the LTC2440 and may be connected directly to the target application’s analog signals while using the DC590 USB Serial Controller board and supplied software to measure performance. The exposed ground planes allow proper grounding to prototype circuitry. After evaluating with LTC’s software, the digital signals can be connected to the application’s processor/controller for development of the serial interface. Design files for this circuit board are available at http://www.linear.com/demo/DC570A L, LT, LTC, LTM, µModule, Linear Technology and the Linear logo are registered trademarks and QuikEval is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. dc570fa 1 DEMO MANUAL DC570A Quick Start Procedure Connect DC570A to a DC590 USB Serial Controller using the supplied 14-conductor ribbon cable. Connect DC590 to host PC with a standard USB A/B cable. Run the evaluation software supplied with DC590 or downloaded from www.linear.com/software. The correct program will be loaded automatically. Click the COLLECT button to start reading the input voltage. Click the slider at the bottom 2 of the strip chart display to change the oversample ratio (OSR) which will in turn change the data output rate. Tools are available for logging data, changing reference voltage, changing the number of points in the strip chart and histogram, and changing the number of points averaged for the DVM display. dc570fa DEMO MANUAL DC570A Hardware Setup Jumpers JP1: Select the source for REF+, either external or 5.00V from the onboard LT1236 reference (default.) JP2: Select the source for REF–, either external or Ground (0 volts, default.) JP3: Trigger mode, either normal (default) or externally triggered. JP4: Trigger input signal. Pin 1 is a 5V logic signal, pin 2 is ground. When triggered mode is selected on JP3, a rising edge starts a new conversion. Connection to DC590 Serial Controller J2 is the power and digital interface connector. Connect to DC590 serial controller with supplied 14-conductor ribbon cable. Analog Connections Analog signal connections are made via the row of turret posts along the edge of the board. Also, if you are connecting the board to an existing circuit, the exposed ground planes along the edges of the board may be used to form a solid connection between grounds. VCC: This is the supply for the ADC. Do not draw any power from this point. External power may be applied to this point after disabling the switching supply on DC590. If the DC590 serial controller is being used, the voltage must be regulated 5V only, as the isolation circuitry will also be powered from this supply. REF+, REF–: These turrets are connected to the LTC2440 REF+ and REF– pins. If the onboard reference is being used, the reference voltage may be monitored from this point. An external reference may be connected to these terminals if JP1 and JP2 are configured for external reference. Note: The REF+ and REF– terminals are decoupled to ground with 0.1μF and 10μF capacitors in parallel. Thus any source connected to these terminals must be able to drive a capacitive load and have very low impedance at DC. Examples are series references that require an output capacitor and C-load stable op amps such as the LT®1219 and LT1368. IN+, IN–: These are the differential inputs to the LTC2440. These terminals have a filter consisting of a 1μF capacitor and 100Ω resistor to attenuate sampling glitches from the LTC2440 input network. These terminals should be driven by a low impedance source or op amp that is compensated to drive capacitive loads. GND: Ground turrets are connected directly to the internal ground planes. dc570fa 3 DEMO MANUAL DC570A Experiments Input Noise Bipolar Symmetry Solder a short wire from the IN– turret post to the IN+ turret post. Set the demo software to OSR32768 (6.8 samples per second.) Noise should be approximately 0.04ppm of VREF (200nV.) Next, select different oversample ratios. Measured noise for each oversample ratio should be close to values given in the LTC2440 data sheet. To demonstrate the symmetry of the ADCs transfer function, connect a stable, low noise, floating voltage source (with a voltage less than VREF/2) from IN+ to IN– and note the indicated voltage. Reverse the polarity; the indicated voltage should be within 75μV of the first reading multiplied by –1, and will typically be much closer. Common Mode Rejection Tie the two inputs (still connected together from previous experiment) to ground through a short wire and note the indicated voltage. Tie the inputs to REF+; the difference should be less than 5μV due to the 120dB CMRR of the LTC2440. Resolving Milliamps with Milliohm Shunts One application that can benefit greatly from the LTC2440’s input resolution is current measurement. It is advantageous to use a very low resistance shunt to minimize the voltage drop. To demonstrate this, make a simple current shunt by soldering a 1 inch length of 24 gage copper wire from the IN+ turret to the IN– turret. This is a resistance of approximately 2.4 milliohms. Connect the IN– turret to the GND turret through a short wire. Start the demonstration software and note the initial voltage, which should be close to zero. Next, connect IN+ to REF+ through a 5k resistor, which will allow approximately 1mA to flow through the shunt. The indicated voltage should increase by approximately 2.4μV (The actual increase will depend on the tolerance of the wire material, diameter, and length.) Since the common mode range of the inputs extends from ground to VCC, the current shunt can also be used at the high side. To demonstrate this, tie the IN+ turret to VCC and connect the resistor from IN– to ground. Thus the supply current of a circuit can be monitored with minimal impact on supply voltage and without breaking any ground connections. 4 One convenient voltage source is a single alkaline battery. While a battery is fairly low noise, it is sensitive to temperature drift and will slowly discharge due to the LTC2440 input current. It is best to use a large (D-size) battery that is insulated from air currents. A better source is a battery powered series reference that can drive the 1μF input capacitor such as the LT1790. This part is available with output voltages of 1.25V, 2.048V, 2.5V, 3V, 3.3V, 4.096V and 5V. Input Normal Mode Rejection The LTC2440’s SINC4 digital filter is trimmed to strongly reject both 50Hz and 60Hz line noise when operated with the internal conversion clock and oversample ratio 32768 (6.8 samples per second.) To measure input normal mode rejection, connect IN– to a 2.5V source such as an LT1790-2.5 reference or a power supply. Apply a 10Hz, 2V peak-to-peak sine wave to IN+ through a 1µF capacitor. Note that this will form a 2:1 divider with the 1µF load capacitor on the board. A larger capacitor may be used to reduce this attenuation. Select OSR32768 (6.8 samples per second) in the demo software and start taking data. The input noise will be quite large, and the graph of output vs time should show large variations. dc570fa DEMO MANUAL DC570A Experiments Next, slowly increase the frequency to 55Hz. The noise should be almost undetectable in the graph. Note that the indicated noise in ppm may still be above that of the data sheet specification because the inputs are not connected to a DC source. Change the OSR to 16384 (13.75 samples per second;) the noise will increase substantially, as the first notch at this OSR is at 110Hz. Increase the signal generator frequency to 110Hz, the noise will drop again. Buffering the Inputs The input current of the LTC2440 may be as much as 63μA (depending on input and reference voltages; see applications information in the LTC2440 data sheet for details). If this produces unacceptable errors due to source impedance, a buffer may be necessary. Most op amps will not drive a 1µF capacitor directly. The following schematic shows how to compensate almost any amplifier to drive the capacitors on the DC570A board while maintaining DC accuracy. The LTC2050HV (or the dual LTC2051HV) is a good general purpose autozero amplifier for use as a buffer in DC applications. 5k – INPUT + 0.01µF TO LTC2440 10k 1µF (ON DC570) dc570 F03 dc570fa 5 DEMO MANUAL DC570A Parts List ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER Required Circuit Components 1 5 C1, C3, C7, C10, C11 CAP., X7R 0.1µF 16V 20% 0603 AVX, 0603YC104MAT1A 2 2 C2, C6 CAP., X5R 4.7µF 6.3V 20% 0805 TAIYO YUDEN, JMK212BJ475MGT 3 1 C4 CAP., X5R 10µF 6.3V 20% 0805 TDK, C2012X5R0J106M 4 1 C5 CAP., X7R 0.01µF 16V 10% 0603 AVX, 0603YC103KAT1A 2rls 5 2 C8, C9 CAP., X5R 1µF 6.3V 20% 0603 TAIYO YUDEN, JMK107ABJ105MA-T 6 7 E1, E2, E3, E4, E5, E6, E7 TESTPOINT, TURRET, 0.061" PbF MILL-MAX, 2308-2-00-80-00-00-07-0 7 3 JP1, JP2, JP3 HEADER, 3 PIN 0.079" SINGLE ROW SAMTEC, TMM-103-02-L-S 8 3 SHUNTS FOR JP1-JP3 SHUNT, 0.079" CENTER SAMTEC, 2SN-BK-G 9 0 JP4 JMP, HD1X2-079 OPT 10 0 J1 CONN., 5 PIN GOLD, STRAIGHT OPT 11 1 J2 HEADER, 2X7 PIN, 0.079CC MOLEX, 87831-1420 12 1 R1 RES., CHIP 49.9Ω 1/16W 1% 0603 AAC, CR16-49R9FM 13 3 R2, R8, R10 RES., CHIP 100Ω 1/16W 5% 0603 AAC, CR16-101JM 3rls 14 3 R3, R7, R9 RES., CHIP 0Ω 1/16W 5% 0603 AAC, CJ06-000M 15 1 R4 RES., CHIP 10k 1/16W 5% 0603 AAC, CR16-103JM 16 2 R5, R11 RES., CHIP 4.99k 1/16W 1% 0603 AAC, CR16-4991FM 17 0 R6 RES., 0603 OPT 18 1 U1 I.C., LTC2440CGN#PBF, SSOP16GN LINEAR TECH., LTC2440CGN#PBF 19 1 U2 I.C., LT1236ACS8-5, SO8 LINEAR TECH., LT1236ACS8-5#PBF 20 1 U3 I.C., NC7SZ157P6X, SC70-6P FAIRCHILD SEMI., NC7SZ157P6X 21 1 U4 I.C., FLIP FLOP D-TYPE LOG US8 ON SEMI., NL17SZ74USG 22 1 U5 I.C., EEPROM 2k BIT 400kHz 8TSSOP MICROCHIP, 24LC025-I /ST 3rls 6 dc570fa 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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. A B C GND IN- IN+ REF- REF+ VCC GND E6 E7 R9 0 E5 5 C6 4.7UF,6.3V 0805 C9 1UF R10 100 C8 1UF R8 100 1 5V 2 EXT IN- IN+ REF- REF+ C4 10UF,6.3V 0805 VOUT C5 0.01UF U1 EXT 10 GND 9 SD0 12 CS 11 FO 14 SCK 13 LTC2440CGN 7 SDI 8 GND 5 IN+ 6 IN- 3 REF+ 4 REF- GND 16 BUSY 15 2. INSTALL SHUNT ON JP1-JP3 PIN 1 AND 2. 1. ALL RESISTORS ARE IN OHMS, 0603. ALL CAPACITORS ARE IN MICROFARADS, 0603. 4 VIN 2 NC 1 GND 4 NC 3 LT1236ACS8-5 NC NC VOUT TRIM U2 1 GND 2 VCC 8 7 6 5 NOTES: UNLESS OTHERWISE SPECIFIED GND JP2 REF- EXT C7 0.1UF 3 C3 0.1UF VCC C2 4.7UF,6.3V 0805 R7 0 E4 E3 E2 E1 JP1 REF+ 3 1 D 2 4 0 R3 JP4 OPT C10 0.1UF VCC 3 R4 10K CP 2 D 1 CP VCC Q 5 Q 3 R2 100 DESIGNER: ENGINEER: MARK T. APPROVED: CHECKED: KIM T. APPROVALS CONTRACT NO. 1 NORMAL TRIG MODE DRAWN: 3 JP3 2 TRIGGERED S 6 VCC 5 Z 4 OPT NC7SZ157P6X 3 I0 1 I1 2 GND U3 R6 U4 NL17SZ74US C1 0.1UF 3 4 1 2 GND VCC 8 CLR PR 7 6 2 DATE: SIZE A MOSI 14 13 12 11 10 J2 14 13 12 11 10 9 9 7 7 8 8 5 5 6 6 3 3 4 4 1 1 2 2 FO HD2X7-079-MOLEX 1 R1 49.9,1% J1 SMA 1 SHEET DC570A-2 * LTC2440CGN Tuesday, April 29, 2003 DWG NO. A 1 OF 1 REV 1630 McCarthy Blvd. Milpitas, CA 95035 Phone: (408)432-1900 Fax: (408)434-0507 LTC Confidential-For Customer Use Only R11 R5 4.99K 4.99K 1% 1% TECHNOLOGY SCL 6 SDA 5 VCC 8 WP 7 SCHEMATIC 24LC025 3 A2 4 VSS U5 1 A0 2 A1 C11 0.1UF CS MISO SCK VCC VIN FO 1 HIGH SPEED DELTA SIGMA ADC TITLE: 2 2 3 4 5 5 A B C D DEMO MANUAL DC570A Schematic Diagram dc570fa 7 DEMO MANUAL DC570A DEMONSTRATION BOARD IMPORTANT NOTICE Linear Technology Corporation (LTC) provides the enclosed product(s) under the following AS IS conditions: This demonstration board (DEMO BOARD) kit being sold or provided by Linear Technology is intended for use for ENGINEERING DEVELOPMENT OR EVALUATION PURPOSES ONLY and is not provided by LTC for commercial use. As such, the DEMO BOARD herein may not be complete in terms of required design-, marketing-, and/or manufacturing-related protective considerations, including but not limited to product safety measures typically found in finished commercial goods. As a prototype, this product does not fall within the scope of the European Union directive on electromagnetic compatibility and therefore may or may not meet the technical requirements of the directive, or other regulations. If this evaluation kit does not meet the specifications recited in the DEMO BOARD manual the kit may be returned within 30 days from the date of delivery for a full refund. THE FOREGOING WARRANTY IS THE EXCLUSIVE WARRANTY MADE BY THE SELLER TO BUYER AND IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING ANY WARRANTY OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE. EXCEPT TO THE EXTENT OF THIS INDEMNITY, NEITHER PARTY SHALL BE LIABLE TO THE OTHER FOR ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES. The user assumes all responsibility and liability for proper and safe handling of the goods. Further, the user releases LTC from all claims arising from the handling or use of the goods. Due to the open construction of the product, it is the user’s responsibility to take any and all appropriate precautions with regard to electrostatic discharge. Also be aware that the products herein may not be regulatory compliant or agency certified (FCC, UL, CE, etc.). No License is granted under any patent right or other intellectual property whatsoever. LTC assumes no liability for applications assistance, customer product design, software performance, or infringement of patents or any other intellectual property rights of any kind. LTC currently services a variety of customers for products around the world, and therefore this transaction is not exclusive. Please read the DEMO BOARD manual prior to handling the product. Persons handling this product must have electronics training and observe good laboratory practice standards. Common sense is encouraged. This notice contains important safety information about temperatures and voltages. For further safety concerns, please contact a LTC application engineer. Mailing Address: Linear Technology 1630 McCarthy Blvd. Milpitas, CA 95035 Copyright © 2004, Linear Technology Corporation 8 dc570fa Linear Technology Corporation LT 0515 REV A • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LINEAR TECHNOLOGY CORPORATION 2012