What the AD652KPZ is and where it fits
The AD652KPZ is a synchronous voltage-to-frequency converter from Analog Devices. It accepts an analog input voltage and outputs a pulse train whose frequency is linearly proportional to the input — 2 MHz full-scale output at the rated input span. The ±0.02% typical linearity and ±25 ppm/°C full-scale drift put this in the precision instrumentation class, not a casual VFC. Typical applications include isolated data acquisition, long-haul analog signal transmission over a single twisted pair, and replacing a moderate-resolution ADC in noisy industrial environments where a frequency-domain signal is easier to filter than a voltage.
Package and mounting — the 20-PLCC footprint
The AD652KPZ ships in a 20-lead LCC with J-leads, also described as a 20-PLCC (9x9 mm) supplier package. This is a surface-mount ceramic or plastic leaded chip carrier — J-leads are formed under the body, so the footprint is a 9x9 mm square pad array. The part is specified for surface-mount assembly, not through-hole.