ADL5317

The ADL5317 is a high-voltage, wide dynamic range biasing and current monitoring device optimized for use with avalanche photodiodes. With the provision of a stable high-voltage supply up to 80 V, the bias voltage at the VAPD pin can be varied from 6 V to 75 V using the 3 V compatible VSET pin. The current sourced from the VAPD pin, over a range of 5 nA to 5 mA, is accurately mirrored with an attenuation of 5 and sourced from the IPDM monitor output. In a typical application, the monitor output drives a current-input logarithmic amplifier to produce an output representing the optical power incident upon the photodiode. The photodiode anode may be connected to a high-speed transimpedance amplifier for the extraction of the data stream.

A signal of 0.2 V to 2.5 V with respect to ground applied at the VSET pin is amplified by a fixed gain of 30 to produce the 6 V to 75 V bias at Pin VAPD. The accuracy of the bias control interface of the ADL5317 allows for straightforward calibration, thereby maintaining a constant avalanche multiplication factor of the photodiode over temperature. The current monitor output, IPDM, maintains its high linearity vs. photodiode current over the full range of APD bias voltage. The current ratio of 5:1 remains constant as V_SET and V_PHV are varied.

The ADL5317 also offers a supply tracking mode compatible with adjustable high voltage supplies. The VAPD pin accurately follows 2.0 V below the VPHV supply pin when VSET is tied to a voltage from 3.0 V to 5.5 V (or higher with a current limiting resistor), and the VCLH pin is open.

Protection from excessive input current at VAPD as well as excessive die temperature is provided. The voltage at VAPD falls rapidly from its setpoint when the input current exceeds 18 mA nominally. A die temperature in excess of 140°C will cause the bias controller and monitor to shut down until the temperature falls below 120°C. Either overstress condition will trigger a logic low at the FALT pin, an open collector output loaded by an external pull-up to an appropriate logic supply (1 mA max).

The ADL5317 is available in a 16-lead LFCSP package and is specified for operation from −40°C to +85°C.

APPLICATIONS

• Optical power monitoring and biasing in APD systems
• Wide dynamic range voltage sourcing and current monitoring in high voltage systems