100MHz SPI isolators facilitate faster data converters

With a fast SPI interface, 6,000VRMS of galvanic isolation, and additional high speed control signals, the LTM2893 and LTM2895 require no external components and provide a simple µModule solution for isolated data converter communications.

The LTM2893 (read only) and LTM2893-1 (read/write) are designed to isolate Linear Technology’s general purpose Successive Approximation Register (SAR) Analogue-to-Digital Converters (ADCs), including the LTC2378 family of 20-, 18- and 16-bit 1Msps SAR ADCs or the LTC2348 family of octal, 18- and 16-bit 200ksps/channel simultaneous sampling SAR ADCs. Additional high speed control signals provide support for parallel or chain-connected configurations, as well as analogue multiplexers or programmable gain amplifiers. Configurable word length allows SPI access to be tailored to a specific ADC to maximise throughput. With only 30psRMS of additive jitter from input to output, the LTM2893 and LTM2893-1 minimise Signal-to-Noise Ratio (SNR) degradation in ADCs due to jitter.

The LTM2895 is designed to isolate Linear Technology’s general purpose Digital-to-Analogue Converters (DACs), including the unipolar LTC2641 family or bipolar LTC2642 family of 16-/14-/12-bit unbuffered voltage output DACs. Additional high speed control signals provide support for dual channel, dual DAC, or host-to-host (i.e., FPGA to isolated FPGA with page mode data transfer) configurations, while a configurable word length allows SPI access to be tailored to a specific DAC to maximise throughput. A low 30psRMS jitter /LOAD signal path is also available for DACs with an asynchronous LOAD input.

The LTM2893, LTC2893-1 and LTM2895 are housed in a low profile 15x6.25x2.06mm surface mount BGA package; all integrated circuits and passive components are housed in this RoHS-compliant μModule package. All devices are available in commercial, industrial and automotive versions, supporting operating temperature ranges from 0 to 70°C, –40 to 85°C and –40 to 125°C, respectively. The LTM2893 and LTM2893-1 are available now in production quantities, and the LTM2895 will be available later this year.

Key features:

• Isolated Interface: 6000VRMS for 60 seconds
• Up to 100MHz SPI compatible I/O
• Configurable SPI word length: 8 to 32-bits
• Supports multi-data converter configurations
• Low jitter conversion start (LTM2893) & /LOAD (LTM2895) signals
• Three isolated control or multiplexer select signals
• 3-5.5V Supply Voltages 
• High common mode transient immunity: >50kV/µs
• No external components required
• 15x6.25x2.06mm BGA package