Features and Benefits
- AEC-Q100 Qualified for Automotive Applications
- 1Mbps Isolated SPI Data Communications
- Simple Galvanic Isolation Using Standard Transformers
- Bidirectional Interface Over a Single Twisted Pair
- Supports Cable Lengths Up to 100 Meters
- Very Low EMI Susceptibility and Emissions
- Configurable for High Noise Immunity or Low Power
- Engineered for ISO26262 Compliant Systems
- Requires No Software Changes in Most SPI Systems
- Ultralow, 2µA Idle Current
- Automatic Wake-Up Detection
- Operating Temperature Range: –40°C to 125°C
- 2.7V to 5.5V Power Supply
- Interfaces to All Logic from 1.7V to 5.5V
- Available in 16-Lead QFN and MSOP Packages
The LTC6820 provides bidirectional SPI communications between two isolated devices through a single twisted-pair connection. Each LTC6820 encodes logic states into signals that are transmitted across an isolation barrier to another LTC6820. The receiving LTC6820 decodes the transmission and drives the slave bus to the appropriate logic states. The isolation barrier can be bridged by a simple pulse transformer to achieve hundreds of volts of isolation.
The LTC6820 drives differential signals using matched source and sink currents, eliminating the requirement for a transformer center tap and reducing EMI. Precision window comparators in the receiver detect the differential signals. The drive currents and the comparator thresholds are set by a simple external resistor divider, allowing the system to be optimized for required cable lengths and desired signal-to-noise performance.
- Industrial Networking
- Battery Monitoring Systems
- Remote Sensors
Markets and Technologies
Product Lifecycle Production
At least one model within this product family is in production and available for purchase. The product is appropriate for new designs but newer alternatives may exist.
Evaluation Kits (6)
The demonstration circuit DC2792B is an SPI serial to dual-port isoSPI adapter that uses a pair of multiplexed LTC6820 isoSPI transceivers and miniaturized isoSPI connectors (2 contact DuraClik). The board can functionally replace a DC1941 in cases where isoSPI battery-management (BMS) devices are being evaluated, but provides a second isoSPI master to exercise the reversible isoSPI feature where available. The SPI interface can be provided via the legacy 14-contact ribbon cable from either a DC590 or DC2026 USB adapter, or directly installed on the DC2026 as a Linduino shield. The two isoSPI ports are MAIN and AUXiliary, with activity of each indicated by blue LEDs. For use in place of DC1941 or non-reversible isoSPI networks, the MAIN port must be used. Power for the DC2792B comes indirectly from the USB port of the host computer, via the USB to serial adapter being used.
Demonstration circuit 1941 is an isoSPI™ transceiver board, based on Linear Technology’s LTC6820. The LTC6820 provides a method of interconnecting standard serial peripheral interface (SPI) devices using a single twisted pair connection. This proprietary 2-wire interface is called isoSPI. The LTC6820 encodes SPI signals, up to 1Mbps, into a differential isoSPI signal which is transmitted via a simple pulse transformer through a twisted pair. At the other end of the twisted pair, the isoSPI signal can be translated back to SPI (using another LTC6820).
Demonstration circuit 2617A implements the isoSPI and isolated CAN interface hardware on a single Arduino shield. It allows Arduino-compatible controller boards to communicate with isoSPI and/or CAN bus networks.
Demonstration Circuit DC2100B-D is a stackable, bidirectional cell balancer slave board using the LTC6804-2 and the LTC3300-1 ICs to achieve active balancing of up to 12 Li-Ion cells. It requires the DC2100B-C for proper operation. The DC2100B-D uses a single LTC6804-2 Multi-Cell Addressable Battery Stack Monitor IC to measure cell voltages and two LTC3300-1 Synchronous Flyback ICs to provide active cell balancing. The DC2100B-C controller board contains a PIC18F47J53 microcontroller, the LTM2884 isolated USB transceiver, the LTC6804-2, two LTC3300-1 ICs, and the LTC6820 isoSPI Interface IC to facilitate isolated communication. Up to seven DC2100B-D boards can be connected to a DC2100B-C to build a stacked system of eight total boards.
This evaluation board is obsolete and no longer recommended. The replacement board is the DC2792B.
Demonstration circuit DC2792A is an SPI serial to dual-port isoSPI adapter that uses a pair of multiplexed LTC6820 isoSPI transceivers. The board can replace a DC1941 in cases where isoSPI battery-management (BMS) devices are being evaluated, but provides a second isoSPI master to exercise the reversible isoSPI feature where available. The SPI interface can be provided via the legacy 14-contact ribbon cable from either a DC590 or DC2026 USB adapter, or directly installed on the DC2026 as a Linduino ‘shield’. The two isoSPI ports are MAIN and AUXiliary, with activity of each indicated by blue LEDs. For use in place of DC1941, the MAIN port must be used. Power for the DC2792A comes indirectly from the USB port of the host computer, via the USB to serial adapter being used.
Documentation & Resources
R525 Reliability Data3/26/2018
SPI Isolation Challenge2/17/2021
Low Voltage Battery Monitor Floats into High Voltage Electric Vehicles10/2/2020 Analog Dialogue
Isolated SPI Communication Made Easy7/1/2019
Higher Reliability, Safety, and 30% Longer Lifetime with Advanced Battery Management in Healthcare Energy Storage Systems6/1/2019
Using the LTC6820 with the LTC24XX Delta Sigma Family2/8/2017
Low Cost isoSPI Coupling Circuitry for High Voltage High Capacity Battery Systems4/1/2014 LT Journal
Reference Designs (1)
LTC6820 Companion Parts
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