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Linear Technology LTC1531 Instrumentation Comparator
Self-Powered Isolated Comparator In Surface Mount Package

The manufacturer says . . .

Chipcenter's Paul McGoldrick says . . .

Linear Technology introduced the LTC1531, an isolated instrumentation comparator whose revolutionary self-powered design and 28-lead SSOP package reduce cost and save space in a wide range of sensing, control and monitoring applications. The LTC1531𢒋 internal capacitive isolation barrier provides 3000VRMS of isolation between the comparator and its output and transmits isolated power as well as data. No secondary power is needed. Thus, the LTC1531 can perform isolated voltage detection without an isolated power supply. In addition to a comparator, regulated power is available on the secondary side for powering sensors. Possible applications for the LTC1531 include temperature control, flow detection and transducer isolation, power monitoring, and analytical measurements. Comparator data is transferred differentially across the isolation barrier to ensure high common mode noise immunity. The LTC1531𢒋 isolated side can supply a 2.5V reference output to power external sensor circuits such as a thermistor bridge. Its instrumentation comparator inputs allow for comparison of two differential voltages as well as single-ended voltages. The LTC1531𢒋 powered side provides a latched data output as well as a pulsed zero-cross comparator output for controlling a triac.

What a fascinating product! The UL listing on this part guarantees the 3 kV rms isolation. The possible hostile environment uses are numerous in the industrial control and production markets, from everything like temperature control to power monitoring and flow control. The provision of the 2.5 V isolated reference is jam for the basic part's potential allowing a large range of add-on sensor functions. There are an enormous number of directions that Linear can take this technology for future products. "Self-powered" is a little misleading, of course, in that energy is still coming from an external source, but the savings in providing an isolated supply in some applications will be financially very significant.

The provision of the zero-cross comparator output on the powered side will allow direct control of some functions detected on the isolated side, such as the adjustment of a supply voltage. The fault redundancy provisions of the part are good. The LTC1531 is in production in a 28-pin SO priced at $4.40 in 1000-piece lots.

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