Digital isolators protect from spikes in LEO smallsats
Two plastic packaged, radiation-tolerant digital isolators from Renesas Electronics provide the highest isolation protection (2,500V RMS) from high voltage spikes in power supply stages and serial communications interfaces used in low earth orbit (LEO) small satellites (smallsats). Many private companies plan to launch thousands of smallsats to form large constellations that operate in multiple LEO planes. Smallsat mega-constellations provide broadband IoT communications across the globe and earth observation high-resolution imaging for sea, air, and land asset tracking.
The passive input ISL71610M and active input ISL71710M operate across key electrical specifications, including isolation voltage, data rate, common mode transient immunity, propagation delay, quiescent current, and dynamic current. Renesas’ giant magneto resistive (GMR) digital isolators can be used as replacements for optocouplers that are susceptible to cloudy optics from total ionising dose (TID) radiation. Both GMR isolators are also claimed to out-perform transformer-based digital isolators that experience electromagnetic interference (EMI) due to radiated emissions from edge and dipole radiation. The Renesas GMR digital isolators are characterisation tested at a total ionising doze (TID) of up to 30krads(Si), and for single event effects (SEE) at a linear energy transfer (LET) of 43MeV•cm2/mg.
In isolation-partitioned power supply designs, the ISL71610M and ISL71710M provide an instantaneous 2.5kVRMS of isolation and 600VRMS continuous working voltage at 85 degrees C. In serial communications subsystems that need the transmitter and receiver to be electrically isolated from each other, the ISL71610M operates up to 100Mbits per second and the ISL71710M up to 150Mbits per second. Both offer data rates that are claimed to be six times higher than competitive solutions–which make them ideal for serial communications links, such as RS-422, RS-485, and controller area network (CAN). The ISL71610M and ISL71710M both have “significantly” lower quiescent current than currently available alternative. The ISL71710M has nearly four times lower dynamic current than Class V isolators.
The ISL71610M passive input digital isolator is used in Renesas’ radiation-hardened half-bridge power stage reference design. The reference design’s ISL73040SEH4Z evaluation board demonstrates a half-bridge power stage design capable of taking 100V input from a satellite’s solar panels and generating step-down power rail voltages of 28, 12, 5.0, and 3.3V, with a power efficiency of up to 94 per cent. The ISL73040SEHEV4Z user manual describes how to build a half bridge power stage with isolation using the ISL71610M, ISL73040SEH low side GaN driver and the ISL73024SEH 200V GaN FET. It provides the bill of materials (BoM) and explains how to power the isolator and achieve dead-time control, and it includes layout guidelines to minimise overshoot and ringing on the GaN FET gate.
The ISL71710M can be used with a single-ended CAN bus input signal to provide fault tolerant serial communications isolation between the CAN bus controller and ISL71026M rad-tolerant CAN bus transceiver, or the ISL72026SEH rad-hard CAN bus transceiver. This application can be extended to RS-422 by using the ISL71710 with the HS-26C31 rad-hard RS-422 transmitter and HS-26C32 rad-hard RS-422 receiver.
The ISL71610M and ISL71710M radiation-tolerant digital isolators are available now in eight-lead 5.0 x 4.0mm SOIC packages.
