User-programmable HO current transducers launched at PCIM
LEM  has announced the HO series of current transducers at PCIM in Nuremberg earlier this week. The HO series of open-loop ASIC based current transducers deliver improved performance in areas such as thermal drift, response time, power supply and noise driven by technology advances in power electronics applications.
LEM’s HO series are open-loop devices, based on Hall-effect current sensing technology, that measure AC, DC or pulsed currents with a nominal value of 8, 15 or 25 ARMS, with a response time of 2 to 6 μsec. Both of these parameters, and several others, are user-programmable by a simple serial digital bit-sequence, generated by the system’s host microcontroller. Other parameters that are user-programmable include reference voltage, over-current detection limits, fault reporting and low power mode.
The HO series delivers its output as a scaled analogue voltage; in most systems this will be converted to a digital value by an analogue/digital converter (ADC) which requires a reference voltage. The designer can program the LEM HO-series transducer to output a reference of 0.5, 1.5, 1.65 or 2.5V on a dedicated pin. Alternatively, the HO-series can be configured to make measurements relative to an external reference.
For the HO models, LEM designed a completely new ASIC. The HO provides offset and gain drift figures twice as good (over the temperature range -25 to +85ºC) as previous-generation open-loop Hall-effect-ASIC based transducers. It achieves a typical accuracy of 1% and 2.8%, at +25°C and +85°, respectively, without offset, and with a high level of insulation between primary and measurement circuits.
An innovative feature of the HO series is programmable over-current detection, separate from the main current measurement. Using a single measurement range (for both detection and measuring functions), if the transducer must detect an over-current condition at (say) five times the nominal full-scale value, the measurement range must extend up to the over-current limit, reducing available accuracy within the nominal range. Separate over-current detection, with programmable threshold, ensures maximum resolution is maintained up to the nominal full-scale value.
LEM’s HO-series transducer operates from a single supply voltage at 3.3 or 5V. It occupies a PCB-mountable, small (12 mm wide x 23 mm long x 12 mm high), lightweight (5g) package which incorporates three separate primary conductors to allow for multi-range measurement configurations (enabling nominal measurement as low as 2.67 ARMS when programmed at 8 ARMS for the nominal range). Versions of the HO-series transducers will be available for both through-hole and surface-mount assembly. The construction provides long creepage and clearance distances (8 mm) and a CTI (comparative tracking index) of 600 for excellent insulation.