Circuit Note CN-0235 Devices Connected/Referenced Circuits from the Lab™ reference circuits are engineered and tested for quick and easy system integration to help solve today’s analog, mixed-signal, and RF design challenges. For more information and/or support, visit www.analog.com/CN0235. AD7280A Lithium Ion Battery Monitoring System AD8280 Lithium Ion Battery Safety Monitor ADuM5404 Quad-Channel Isolators with Integrated DC-to-DC Converter ADuM1400 Quad-Channel Digital Isolators Fully Isolated Lithium Ion Battery Monitoring and Protection System EVALUATION AND DESIGN SUPPORT CIRCUIT FUNCTION AND BENEFITS Circuit Evaluation Boards CN-0235 Circuit Evaluation Board (EVAL-CN0235-SDPZ) System Demonstration Platform (EVAL-SDP-CB1Z) Design and Integration Files Schematics, Layout Files, Bill of Materials Lithium ion (Li-Ion) battery stacks contain a large number of individual cells that must be monitored correctly in order to enhance the battery efficiency, prolong the battery life, and ensure safety. FERRITE 10kΩ VDD1 TOP ENBI AD7280A AIOUTOV AIOUTUV AIOUTOT VIN11 AD8280 TESTI VIN5 BOT CB6 10kΩ VIN6 VIN5 VIN4 VIN3 VIN2 VIN1 VIN0 VTOPx VIN12 VIN11 VIN10 VIN9 VIN8 VIN7 VIN6 VBOTx SDIhi ALERThi SDOhi VIN6 0.1µF CNVSThi 10kΩ CShi 10kΩ SCLKhi VDD0 34Ω 1kΩ 0.1µF VDD +5V VIN7 ALERTlo SDOlo CNVST 22pF 22pF 22pF VDD0 10µF VIN6 VIN5 VIN4 VIN3 VIN2 VIN1 VIN0 22pF 10kΩ 0.1µF SDIhi ALERThi SDOhi SCLKhi VIN5 AD7280A ADuM5404 CB1 VIN0 VSS0 0.1µF 1µF ALERTlo 0.1µF +3.3V AVOUTUV GND2 VOA GND1 VIA ENBI TESTI VOB VIB VOC VIC VOD VID +3.3V ADuM1400 PD VIN1 VIN0 FERRITE CShi ALERT CNVST VSS 10kΩ VOD AVOUTOV CS 10kΩ 10kΩ PDhi CB6 VIN5 34Ω VID DRIVE 10kΩ VIN1 VOB VOC VDD1 10kΩ 0.1µF SDOlo 10kΩ AD8280 VIB VDD2 VSS0 VIN6 VREF 34Ω CNVSThi 10kΩ CREF VIN6 MASTER VDD 0.1µF VIN6 VIN5 VIN4 VIN3 VIN2 VIN1 VIN0 VDD1 GND1 VOA VIC ENBO 22pF TESTO 22pF BOT 22pF VTOPx 10kΩ VBOTx 22pF TOP 22pF VDD0 GNDISO VIA 22pF 22pF FERRITE VISO 22pF AIINOV AIINUV AIINOT VIN0 SDI 10kΩ SCLK CB1 CS 0.1µF PD 10kΩ VSS 34Ω 10kΩ VIN1 SCLK SDI SDO 1kΩ VDD2 VDD1 GND2 VOA GND1 VIA VOB VIB VOC VIC VID VOD ADuM1401 1kΩ 10135-001 VIN12 VDD1 10µF PDhi 0.1µF Figure 1. Lithium Ion Battery Monitoring and Protection System Simplified Schematic Rev.0 Circuits from the Lab™ circuits from Analog Devices have been designed and built by Analog Devices engineers. Standard engineering practices have been employed in the design and construction of each circuit, and their function and performance have been tested and verified in a lab environment at room temperature. However, you are solely responsible for testing the circuit and determining its suitability and applicability for your use and application. Accordingly, in no event shall Analog Devices be liable for direct, indirect, special, incidental, consequential or punitive damages due to any cause whatsoever connected to the use of any Circuits from the Lab circuits. (Continued on last page) One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 ©2012 Analog Devices, Inc. All rights reserved. CN-0235 Circuit Note The 6-channel AD7280A devices in the circuit shown in Figure 1 act as the primary monitor providing accurate voltage measurement data to the System Demonstration Platform (SDP-B) evaluation board, and the 6-channel AD8280 devices act as the secondary monitor and protection system. Both devices can operate from a single wide supply range of 8 V to 30 V and operate over the industrial temperature range of −40°C to +105°C. The AD7280A contains an internal ±3 ppm reference that allows a cell voltage measurement accuracy of ±1.6 mV. The ADC resolution is 12 bits and allows conversion of up to 48 cells within 7 μs. The AD7280A has cell balancing interface outputs designed to control external FET transistors to allow discharging of individual cells and forcing all the cells in the stack to have identical voltages. The AD8280 functions independently of the primary monitor and provides alarm functions indicating out of tolerance conditions. It contains its own reference and LDO, both of which are powered completely from the battery cell stack. The reference, in conjunction with external resistor dividers, is used to establish trip points for the over/undervoltages. Each cell channel contains programmable deglitching (D/G) circuitry to avoid alarming from transient input levels. The AD7280A and AD8280, which reside on the high voltage side of the battery management system (BMS) have a daisychain interface, which allows up to eight AD7280A’s and eight AD8280’s to be stacked together and allows for 48 Li-Ion cell voltages to be monitored. Adjacent AD7280A's and AD8280’s in the stack can communicate directly, passing data up and down the stack without the need for isolation. The master devices on the bottom of the stack use the SPI interface and GPIOs to communicate with the SDP-B evaluation board, and it is only at this point that high voltage galvanic isolation is required to protect the low voltage side of the SDP-B board. The ADuM1400, ADuM1401 digital isolator, and the ADuM5404 isolator with integrated dc-to-dc converter combine to provide the required eleven channels of isolation in a compact and cost effective solution. The ADuM5404 also provides isolated 5 V to the VDRIVE input of the lower AD7280A and the VDD2 supply voltage for the ADuM1400 and ADuM1401 isolators. CIRCUIT DESCRIPTION The AD7280A is a complete data acquisition system that includes a high voltage input multiplexer, a low voltage input multiplexer, a 12-bit, 1 µs SAR ADC, and on-chip registers for channel sequencing. The HV MUX is used to measure the series connected Li-Ion battery cells as shown in Figure 1. The LV MUX provides single-ended ADC inputs that can be used with external thermistors to measure the temperature of each battery cell; or, if temperature measurements are not required, the auxiliary ADC inputs can be used to convert any other 0 V to 5 V input signal. A precision 2.5 V reference and an on-chip voltage regulator is also included. The AD8280 is a hardwire-only safety monitor for lithium ion battery stacks. In conjunction with the AD7280A, the AD8280 provides a low cost, redundant, battery backup monitor with adjustable threshold detection and shared or separate alarm outputs. It has a self-test feature, making it suitable for high reliability applications, such as automotive hybrid electric vehicles or higher voltage industrial usage, such as uninterruptible power supplies. Both the AD7280A and the AD8280 obtain power from the battery cells they monitor. The ADuM5404 includes an integrated dc-to-dc converter, which is used to power the high voltage side of the ADuM1400 and ADuM1401 isolators and provide the VDRIVE supply to the AD7280A SPI interface. These 4-channel, magnetically isolated circuits are a safe, reliable, and easy-to-use alternative to optocouplers. To optimize the performance of the daisy-chain communication under noisy conditions, for example, when experiencing electromagnetic interference, the daisy-chain signals are shielded on an inner layer of the printed circuit board (PCB). Shielding is provided above and below by a VSS supply plane, which is connected to the VSS pin of the upper device in the chain. Figure 2 shows the top layer of the EVAL-CN0235-SDPZ PCB, which contains the upper shielding for the AD7280A, and Figure 5 shows the bottom layer, which contains the upper shielding for the AD8280. Figure 3 shows the inner layer (layer 2), which contains the shielded daisy-chain signals, and the shielding below is carried out on Layer 3 as shown in Figure 4. Individual 22 pF capacitors are placed on each daisy-chain connection and are terminated to either the VSS pin of the upper device or the VDD pin of the lower device, depending on the direction in which data is flowing on the daisy chain. The PD, CS, SCLK, SDI, and CNVST daisy-chain connections pass data up the chain, and the 22 pF capacitors on these pins are terminated to the VSS of the upper device in the chain. Rev. 0 | Page 2 of 6 CN-0235 10135-002 Circuit Note 10135-003 Figure 2. Top Layer of the EVAL-CN0235-SDPZ PCB Contains the Upper Shielding for the Daisy-Chain Signals of the AD7280A Figure 3. Layer 2 of the EVAL-CN0235-SDPZ PCB Contains the Shielded AD7280A Daisy-Chain Signals Rev. 0 | Page 3 of 6 Circuit Note 10135-004 CN-0235 10135-005 Figure 4. Layer 3 of the EVAL-CN0235-SDPZ PCB Contains the Shielded AD8280 Daisy-Chain Signals Figure 5. Bottom Layer of the EVAL-CN0235-SDPZ PCB Contains the Upper Shielding for the Daisy-Chain Signals of the AD8280 Rev. 0 | Page 4 of 6 Circuit Note CN-0235 Test Results 7000 6000 5000 4000 3000 1701 2000 0 531 2555 115 2556 2557 2558 CODE Figure 6. Histogram of Codes for 10,000 Samples, VIN4 – VIN3 of Device 0 6000 5019 5000 4016 4000 3000 2000 921 1000 246 An important measure of the performance of the circuit is the amount of noise in the final output voltage measurement. 0 2404 2405 2406 2407 CODE Figure 6 shows a histogram of 10,000 measurement samples taken for the VIN3−VIN2 channel. This data was taken with the CN0235 Evaluation Board connected to the EVAL-SDP-CB1Z System Demonstration Platform (SDP-B) evaluation board. Details of the setup are described in the Circuit Evaluation and Test section of this circuit note. 10135-006 1000 10135-007 Input-to-output dipole radiation can also be generated when driving a current source across a gap between ground planes. To help minimize this, a continuous shield is used at the isolation gap whereby the ground planes are extended on all layers throughout the PCB to create a cross-barrier coupling using overlapping shields; and the isolation gap on each layer is kept to a minimum, with a gap of 0.008 inches used on the tested board. For further recommendations to control radiated emissions with isoPower® devices, such as the ADuM5404 used in this circuit, please refer to Application Note AN-0971. 7893 8000 NUMBER OF OCCURANCES A ground fence at the isolation barrier is used to enclose the low voltage side, which consists of the left hand side of the PCB. This fence consists of a guard ring laced together by vias and connects to the digital ground on all layers throughout the board. Noise on power and ground planes that reach the edge of the circuit board can radiate causing emissions, but with this shielded structure the noise is reflected back. 9000 NUMBER OF OCCURANCES The SDOlo and ALERTlo daisy-chain connections pass data down the chain, and the 22 pF capacitors on these pins are terminated to the VDD of the lower device in the chain. A direct low impedance trace is used to connect the VDD of the lower device with the VSS of the upper device to hold the two potentials as close as possible together in a noisy environment. Figure 7. Histogram for 10,000 Samples, VIN4 - VIN3 of Device 1 COMMON VARIATIONS Twelve Li-Ion batteries were connected to the input screw terminals. Note that there are only a small percentage of codes that fall outside the primary bin due to noise. Figure 6 and Figure 7 show 3 LSBs peak-to-peak noise, corresponding to approximately 0.5 LSBs rms. A complete design support package for this circuit note can be found at www.analog.com/CN0235-DesignSupport. The circuit is proven to work with good stability and accuracy. Other combinations of isolated channels can be used with the iCoupler isolation products. CIRCUIT EVALUATION AND TEST This circuit uses the EVAL-CN0235-SDPZ circuit board and the EVAL-SDP-CB1Z System Demonstration Platform (SDP-B) evaluation board. The two boards have 120-pin mating connectors, allowing for the quick setup and evaluation of the circuit’s performance. The EVAL-CN0235-SDPZ board contains the circuit to be evaluated, as described in this note, and the SDP-B evaluation board is used with the CN0235 evaluation software to capture the data from the EVAL-CN0235-SDPZ circuit board. Rev. 0 | Page 5 of 6 CN-0235 Circuit Note Equipment Needed Test • PC with a USB port and Windows® XP or Windows Vista® (32-bit), or Windows® 7 (32-bit) Apply power to the +6 V supply (or “wall wart”) connected to EVAL-CN0235-SDPZ circuit board. Launch the evaluation software and connect the USB cable from the PC to the USB mini-connector on the SDP-B board. • EVAL-CN0235-SDPZ circuit evaluation board • EVAL-SDP-CB1Z SDP-B evaluation board Once USB communications are established, the SDP-B board can be used to send, receive, and capture serial data from the EVAL-CN0235-SDPZ board. • CN0235 SDP evaluation software • Power supply: +6 V, or +6 V “wall wart” Information regarding the SDP-B board can be found in the SDP-B User Guide. • Li-Ion batteries or precision dc supply Getting Started Load the evaluation software by placing the CN0235 Evaluation Software disc in the CD drive of the PC. Using "My Computer," locate the drive that contains the evaluation software. LEARN MORE CN0235 Design Support Package: www.analog.com/CN0235-DesignSupport Functional Block Diagram SDP-B User Guide: www.analog.com/SDP See Figure 1 of this circuit note for the circuit block diagram, and the file “EVAL-CN0235-SDPZ-SCH-RevA.pdf ” for the circuit schematics. This file is contained in the CN0235 Design Support Package. Ardizzoni, John. A Practical Guide to High-Speed PrintedCircuit-Board Layout, Analog Dialogue 39-09, September 2005. Setup Connect the 120-pin connector on the EVAL-CN0235-SDPZ circuit board to the connector marked “CON A” on the EVAL-SDP-CB1Z evaluation (SDP-B) board. Nylon hardware should be used to firmly secure the two boards, using the holes provided at the ends of the 120-pin connectors. With power to the supply off, connect a +6 V power supply to the pins marked “+6 V” and “GND” on the board. If available, a +6 V "wall wart" can be connected to the barrel connector on the board and used in place of the +6 V power supply. The only other connections required are to the lithium ion battery stack. The battery stack can be simulated with a resistor divider, which is driven by a precision dc supply voltage. Connect the USB cable supplied with the SDP-B board to the USB port on the PC. Note: Do not connect the USB cable to the mini USB connector on the SDP-B board at this time. MT-031 Tutorial, Grounding Data Converters and Solving the Mystery of “AGND” and “DGND”, Analog Devices. MT-101 Tutorial, Decoupling Techniques, Analog Devices. Data Sheets and Evaluation Boards CN-0235 Circuit Evaluation Board (EVAL-CN0235-SDPZ) System Demonstration Platform (EVAL-SDP-CB1Z) AD7280A Data Sheet and Evaluation Board AD8280 Data Sheet and Evaluation Board ADuM5404 Data Sheet ADuM1400 Data Sheet REVISION HISTORY 1/12—Revision 0: Initial Version (Continued from first page) Circuits from the Lab circuits are intended only for use with Analog Devices products and are the intellectual property of Analog Devices or its licensors. While you may use the Circuits from the Lab circuits in the design of your product, no other license is granted by implication or otherwise under any patents or other intellectual property by application or use of the Circuits from the Lab circuits. Information furnished by Analog Devices is believed to be accurate and reliable. However, "Circuits from the Lab" are supplied "as is" and without warranties of any kind, express, implied, or statutory including, but not limited to, any implied warranty of merchantability, noninfringement or fitness for a particular purpose and no responsibility is assumed by Analog Devices for their use, nor for any infringements of patents or other rights of third parties that may result from their use. Analog Devices reserves the right to change any Circuits from the Lab circuits at any time without notice but is under no obligation to do so. ©2012 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. CN10135-0-1/12(0) Rev. 0 | Page 6 of 6