ADL5304ACPZ-R7

The ADL5304 is a high-speed logarithmic converter with fast response and low noise across its full 200 dB (1 pA to 10 mA) measurement range. The ADL5304 has a nominal log slope of 10 mV/dB (200 mV/decade); other values are easily configured. The log intercept can be programmed over a wide range via an internal 100 nA current source, or programmed externally for log-ratio applications. The default intercept of 3.162 fA places the midpoint of the 100 nA measurement range at ΔV_LOG = 1.5 V.

A single 5 V positive supply is sufficient for operation over the rated 1 pA to 3 mA input range. Dual-supply operation extends the rated input current range to 10 mA.

The ADL5304 supports dual current inputs for the logarithmic argument. The numerator input I_NUM flows through the collector of an NPN transistor, connecting into the feedback path near a low-offset JFET amplifier. The denominator current I_DEN is handled in the same manner, enabling log-ratio operation. The input summing nodes (INUM and IDEN) operate at a constant default voltage of 1.5 V. Pins VSM1 through VSM4 are located adjacent to the INUM and IDEN inputs to provide guard voltages, minimizing leakage currents.

Adaptive photodiode biasing is provided for optical measurements. The monitor current is 1.1× INUM, output at the IMON pin; the external resistor R_MNTR is 10× the photodiode series resistance (R_s), applying a voltage across the photodiode that keeps the internal PD junction at 0.0 V to first order, thereby minimizing dark current.

The VLOG output is buffered and can be rescaled using internal gain-setting resistors. As ΔI_NUM varies 10× from 1 pA to 10 mA, the internal I_LOG varies over the range of −400 μA to +400 μA. This corresponds to a voltage swing of 0.5 V to 2.5 V at the VLOG pin in the default configuration.

Accurate 1.5 V (1P5V pin) and 2.0 V (2VLT pin) reference outputs allow precise intercept repositioning using external resistors.

The ADL5304 is available in a 32-lead 5 mm × 5 mm LFCSP package and is rated for operation over the −40°C to +85°C temperature range.