Circuit Note CN-0235 Devices Connected/Referenced AD7280A Lithium Ion Battery Monitoring System Circuits from the Lab reference circuits are engineered and tested for quick and easy system integration to help solve todays AD8280 Lithium Ion Battery Safety Monitor analog, mixed-signal, and RF design challenges. For more Quad-Channel Isolators with ADuM5404 information and/or support, visit www.analog.com/CN0235. 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 Lithium ion (Li-Ion) battery stacks contain a large number of CN-0235 Circuit Evaluation Board (EVAL-CN0235-SDPZ) individual cells that must be monitored correctly in order to System Demonstration Platform (EVAL-SDP-CB1Z) enhance the battery efficiency, prolong the battery life, and Design and Integration Files ensure safety. Schematics, Layout Files, Bill of Materials FERRITE V 1 1k V 1 10k DD DD 0.1F 10F 0.1F V 0 DD VIN12 10k VIN12 VIN6 VIN6 VIN11 VIN5 34 0.1F 10k VIN10 VIN4 CB6 AD8280 VIN9 VIN3 10k VIN8 VIN2 VIN5 VIN7 VIN1 VIN11 AD7280A VIN0 VIN6 +5V VIN7 10k VIN1 V V ISO DD1 34 0.1F 22pF 10k GND GND ISO 1 CB1 22pF V V 10k IA OA 22pF VIN0 22pF V V IB OB 22pF 22pF V V IC OC 22pF V 0 DD 10k 22pF V V ID OD 22pF 22pF ADuM5404 +3.3V 22pF VIN6 VIN6 22pF FERRITE V 0 VIN5 VIN5 V V DD AVOUTOV DD2 DD1 VIN4 VIN4 AD8280 GND GND AVOUTUV 10k 2 1 10F 0.1F VIN3 VIN3 V V OA IA VIN2 VIN2 0.1F ENBI VIN1 VIN1 V V OB IB VIN0 VIN0 TESTI V V OC IC V 0 VIN6 SS 10k V V OD ID 10k VIN6 34 DRIVE 0.1F 10k +3.3V ADuM1400 CB6 ALERT 10k CNVST VIN5 AD7280A V V DD2 DD1 PD VIN5 GND GND 2 1 V V OA IA VIN1 CS 10k V V OB IB VIN1 SCLK 34 0.1F 10k V V OC IC CB1 SDI 10k V V ID OD VIN0 SDO VIN0 1k 0.1F 1F FERRITE ADuM1401 V 0 SS 1k 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 One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. suitability and applicability for your use and application. Accordingly, in no event shall Analog Devices Tel: 781.329.4700 www.analog.com 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) Fax: 781.461.3113 2012 Analog Devices, Inc. All rights reserved. V V V DD SS DD V SS MASTER PDhi PD PDhi C REF CShi CS CShi V SCLKhi SCLK SCLKhi REF SDOhi SDI SDOhi CNVSThi CNVST CNVSThi SDOlo SDIhi SDOlo SDIhi ALERTlo ALERThi ALERTlo ALERThi VBOTx VBOTx VTOPx VTOPx TOP TOP BOT BOT TESTO TESTI AIINOV AIOUTOV AIOUTUV AIINUV AIOUTOT AIINOT ENBI ENBO 10135-001CN-0235 Circuit Note The 6-channel AD7280A devices in the circuit shown in CIRCUIT DESCRIPTION Figure 1 act as the primary monitor providing accurate voltage The AD7280A is a complete data acquisition system that measurement data to the System Demonstration Platform includes a high voltage input multiplexer, a low voltage input (SDP-B) evaluation board, and the 6-channel AD8280 devices multiplexer, a 12-bit, 1 s SAR ADC, and on-chip registers for act as the secondary monitor and protection system. Both channel sequencing. The HV MUX is used to measure the devices can operate from a single wide supply range of 8 V to series connected Li-Ion battery cells as shown in Figure 1. The 30 V and operate over the industrial temperature range of LV MUX provides single-ended ADC inputs that can be used 40C to +105C. with external thermistors to measure the temperature of each The AD7280A contains an internal 3 ppm reference that battery cell or, if temperature measurements are not required, allows a cell voltage measurement accuracy of 1.6 mV. the auxiliary ADC inputs can be used to convert any other 0 V The ADC resolution is 12 bits and allows conversion of up to 5 V input signal. A precision 2.5 V reference and an on-chip to 48 cells within 7 s. voltage regulator is also included. The AD7280A has cell balancing interface outputs designed to The AD8280 is a hardwire-only safety monitor for lithium ion control external FET transistors to allow discharging of battery stacks. In conjunction with the AD7280A, the AD8280 individual cells and forcing all the cells in the stack to have provides a low cost, redundant, battery backup monitor with identical voltages. adjustable threshold detection and shared or separate alarm outputs. It has a self-test feature, making it suitable for high The AD8280 functions independently of the primary monitor reliability applications, such as automotive hybrid electric and provides alarm functions indicating out of tolerance vehicles or higher voltage industrial usage, such as conditions. It contains its own reference and LDO, both of uninterruptible power supplies. Both the AD7280A and the which are powered completely from the battery cell stack. The AD8280 obtain power from the battery cells they monitor. reference, in conjunction with external resistor dividers, is used to establish trip points for the over/undervoltages. Each cell The ADuM5404 includes an integrated dc-to-dc converter, channel contains programmable deglitching (D/G) circuitry to which is used to power the high voltage side of the ADuM1400 avoid alarming from transient input levels. and ADuM1401 isolators and provide the VDRIVE supply to the AD7280A SPI interface. These 4-channel, magnetically The AD7280A and AD8280, which reside on the high voltage isolated circuits are a safe, reliable, and easy-to-use alternative side of the battery management system (BMS) have a daisy- to optocouplers. chain interface, which allows up to eight AD7280As and eight AD8280s to be stacked together and allows for 48 Li-Ion cell To optimize the performance of the daisy-chain communication voltages to be monitored. Adjacent AD7280A s and AD8280s in under noisy conditions, for example, when experiencing the stack can communicate directly, passing data up and down electromagnetic interference, the daisy-chain signals are the stack without the need for isolation. shielded on an inner layer of the printed circuit board (PCB). Shielding is provided above and below by a VSS supply plane, The master devices on the bottom of the stack use the SPI which is connected to the VSS pin of the upper device in the interface and GPIOs to communicate with the SDP-B chain. Figure 2 shows the top layer of the EVAL-CN0235-SDPZ evaluation board, and it is only at this point that high voltage PCB, which contains the upper shielding for the AD7280A, and galvanic isolation is required to protect the low voltage side of Figure 5 shows the bottom layer, which contains the upper the SDP-B board. The ADuM1400, ADuM1401 digital isolator, shielding for the AD8280. Figure 3 shows the inner layer and the ADuM5404 isolator with integrated dc-to-dc converter (layer 2), which contains the shielded daisy-chain signals, and combine to provide the required eleven channels of isolation in the shielding below is carried out on Layer 3 as shown in Figure 4. a compact and cost effective solution. The ADuM5404 also Individual 22 pF capacitors are placed on each daisy-chain provides isolated 5 V to the VDRIVE input of the lower connection and are terminated to either the VSS pin of the AD7280A and the VDD2 supply voltage for the ADuM1400 and upper device or the VDD pin of the lower device, depending on ADuM1401 isolators. 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