The LMH34400 is designed to work with photodiode (PD) configurations that can source or sink current; the LMH34400, however, is optimized for a sinking current configuration. It is assumed that the LMH34400 device is being used with a PD that is configured with its cathode tied to the amplifier input and the anode tied to a negative supply voltage, unless stated otherwise.

The LMH34400 features two internal clamps, a fast recovery clamp and a soft clamp. The fast recovery clamp is the active clamp when the photodiode is sinking a photocurrent. The soft clamp is the active clamp when the photodiode is sourcing a photocurrent.

Stray reflections from nearby objects with high reflectivity can produce large output current pulses from the PD. The linear input range of the LMH34400 is approximately 30 µA. Input currents in excess of the linear current range cause the internal nodes of the amplifier to saturate, which increases the amplifier recovery time. The end result is a broadening of the output pulse leading to blind zones in the system. To protect against this condition, the LMH34400 features an integrated clamp that absorbs and diverts the excess current to the positive supply (V_DD) when the amplifier detects its nodes entering a saturated condition. The integrated clamp minimizes the pulse extension to less than a few nanoseconds for input pulses up to 100 mA. When the amplifier is in low-power mode, the clamp circuitry is still active, thereby protecting the TIA input.