APPLICATION NOTE Atmel ATA6870 Broken-wire Detection ATA6870 Scope This application note describes the method of detecting broken wires between the Atmel® ATA6870 and the battery-cell clamps. Broken-wire Detection Figure 1 on page 2 shows the basic circuitry of a battery stack in combination with the Atmel monitoring circuit ATA6870. There are 7 connections between the battery management system (BMS) and the battery cells. 9244B-AUTO-07/15 Figure 1. Battery Stack and Monitoring Circuit Atmel ATA6870 Battery BMS monitoring 10Ω 1kΩ 1kΩ PD_N VDDHVP MISO_IN MOSI_OUT SCK_OUT CS_N_OUT 100nF CLK_OUT IRQ_IN VDDHV MBAT7 MBAT6 1kΩ DISCH6 100nF VDDHVM + 33μF DISCH5 PD_N_OUT MBAT5 POW_ENA 220nF + 10μF 100nF DISCH4 ATST MBAT4 1kΩ BIASRES Atmel ATA6870 100nF DISCH3 121kΩ TEMPVREF MBAT3 1kΩ 100nF PWTST TEMP2 100nF DISCH2 TEMP1 MBAT2 1kΩ TEMPVSS NTC NTC DVDD GND DVSS VDDFUSE AVSS CS_FUSE DTST MISO MOSI SCK CLK IRQ CS_N MBAT1 MFIRST DISCH1 1kΩ SCANMODE 100nF AVDD 10nF 10Ω MISO MOSI SCK CSN CLK IRQ VDD OUT Microcontroller GND The following sequence is used to perform open-load tests: 1. Perform cell measurement without activating DISCH(i) 2. Activate DISCH(i) 3. Perform cell measurement of the corresponding battery cell(i) again. If during discharge (3.) the measured cell voltage is identical to the cell voltage without activating DISCH(i) (1.), the wire between MBAT(i) and the cell in question is not broken. This method works both with and without external discharge switches. 2 ATA6870 [APPLICATION NOTE] 9244B–AUTO–07/15 1. Theory 1.1 Balance Resistors Connected Figure 1-1 shows a broken-wire example in an application with balancing structure. Activating the DISCH(i) will switch the external discharge MOSFET and disbalance the voltage (MBAT(i+1) – MBAT(i)). Figure 1-1. Battery-stack Application with Discharge Switches Battery cells BMS monitoring Atmel ATA6870 MBAT(i+2) 1kΩ 100nF DISCH(i+1) Broken wire MBAT(i+1) 1kΩ 100nF DISCH(i) MBAT(i) 1kΩ 1.2 No Connected Balance Resistors In case of no external discharge transistors, there is no external circuitry to disbalance the cell voltage inputs of MBAT(i). Nevertheless it is possible to detect broken wires, see Figure 1-2. The internal structure of the Atmel® ATA6870’s DISCH(i) pins is basically a transistor and a pull-down resistor. Turning on the balance structure will cause a current through this pull-down resistor of about 50µA. In case of activating DISCH(i), the MBAT(i+1) voltage will be disbalanced. If there is no broken wire, the voltages between (MBAT(i+2) – MBAT(I+1)) and (MBAT(i+1) – MBAT(i)) are equal. If a wire is broken, the two voltages will differ. Figure 1-2. Battery-stack Application without Discharge Switches Battery cells BMS monitoring Atmel ATA6870 MBAT(i+2) 1kΩ DISCH(i+1) 100kΩ Broken wire MBAT(i+1) 1kΩ DISCH(i) 100kΩ MBAT(i) 1kΩ ATA6870 [APPLICATION NOTE] 9244B–AUTO–07/15 3 2. Revision History Please note that the following page numbers referred to in this section refer to the specific revision mentioned, not to this document. 4 Revision No. History 9244B-AUTO-07/15 Put document in the latest template ATA6870 [APPLICATION NOTE] 9244B–AUTO–07/15 XXXXXX Atmel Corporation 1600 Technology Drive, San Jose, CA 95110 USA T: (+1)(408) 441.0311 F: (+1)(408) 436.4200 | www.atmel.com © 2015 Atmel Corporation. / Rev.: 9244B–AUTO–07/15 Atmel®, Atmel logo and combinations thereof, Enabling Unlimited Possibilities®, and others are registered trademarks or trademarks of Atmel Corporation in U.S. and other countries. Other terms and product names may be trademarks of others. DISCLAIMER: The information in this document is provided in connection with Atmel products. No license, express or implied, by estoppel or otherwise, to any intellectual property right is granted by this document or in connection with the sale of Atmel products. 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