High-side monitor

Analog Devices has introduced a high-side monitor that provides a compact solution for the problem of interfacing an optical power monitoring device, such as a logarithmic amplifier, to the cathode-side of a PIN photodiode.

The ADL5315 mirrors the current at the cathode at a 1:1 ratio over a six-decade range  from 3 nA to 3mA, producing an output equal to the reference current monitored. The company claims that competing optical current monitors have much higher mirror ratios over narrower ranges, rendering proportional outputs at very low input currents impossible, while discrete solutions are more complex to implement and may require significantly more board space.

The new chip also sports a linearity of only 1% over the operating range. In PIN photodiode modules where only the cathode is available for connection, this high linearity allows the device to be paired with linear or logarithmic amplifiers to form a complete, precise optical power measurement system.

It also features an adjustable input current limit to protect the photodiode from damage caused by excessive input current.

While the device is optimised for use with PIN photodiodes, its operating range makes it suitable for an array of applications that require accurate current mirroring.

Its miniature single-chip 2 mm × 3 mm 8-lead LFCSP package makes it well-suited for space-constrained applications, such as SFP (small form factor pluggable) optical transceiver modules. The ADL5315 is fully specified from –40 degrees C to +85 degrees C, and operates from a single 2.7 V to 8 V supply.

The device is sampling now, with volume production scheduled for October 2005. It is priced at $1.93 per unit in 1,000-piece quantities.