Six-channel isolator exploits two adjustable power rails

Targeting low voltage components, the LTM2887 is a six-channel SPI/digital or I2C microModule isolator from Linear Technology. It has dual rail regulated power that targets low voltage components, including newer DSPs and microprocessors. Two well-regulated adjustable supply rails (up to 5V) deliver more than 100mA of load current over the isolation barrier, with up to 62 per cent efficiency. The voltages may be adjusted as low as 0.6V for the auxiliary supply, while the isolated logic supply may be as low as 1.8V for SPIs. Each supply provides a precise current limit adjustment pin and the ability to adjust the voltage using external resistors, says the company.

In industrial system applications, ground potentials can vary widely, often exceeding the tolerable range, interrupting communications or even destroying components. The LTM2887 breaks ground loops by electrically isolating the logic level interface on each side of an internal isolation barrier. This inductively coupled barrier withstands very large ground differential voltages up to 2,500VRMS.

A low EMI isolated DC/DC converter powers the isolator and provides the isolated power to the communications interface and output rails. A separate logic supply pin provides direct interfacing with low voltage microcontrollers down to 1.62V. An ‘on’ pin enables shutdown and the use of less than 10microA. The LTM2887 provides uninterrupted communications for common mode transients greater than 30kV/micro sec and ±10kV ESD (HBM) protection across the isolation barrier.

Two interface versions are available. The LTM2887-I is I2C-compliant at up to 400kHz with bidirectional serial data (SDA), clock and three additional, isolated CMOS logic signals that operate at up to 10MHz. The LTM2887-S is SPI-compliant and offers six CMOS digital isolator communication channels. All channels operate at up to 10MHz and include three forward and three reverse direction signals. When configured for SPI communications, the maximum clock rate is 8MHz for unidirectional communication and 4MHz for round-trip bi-directional operation.

The isolator is available in 3.3 or 5.0V supply voltage versions and is offered in a 15 x 11.25mm surface mount BGA package, with ICs and passive components housed in the RoHS-compliant microModule package. Commercial, industrial and automotive versions supporting operating temperature ranges from 0 to +70°C, –40 to +85 and –40 to +105°C respectively.


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