The DS8500 from Dallas Semiconductor (now Analog Devices via Maxim) is a single-chip HART modem with Highway Addressable Remote Transducer (HART) capabilities. It has received a HART Certificate of Registration, and it modulates and demodulates the 1200Hz/2200Hz Bell 202 FSK signal that HART overlays on a 4-20mA current loop, so a field instrument or host can carry digital data on top of the analog process signal. DS8500-JND+T&R is the 20-pin TQFN version.

The device integrates the modulation and demodulation on one chip: the modulator drives an FSK waveform out (FSK_OUT) to the loop, while the demodulator receives from the loop (FSK_IN) and recovers the digital data. The input signal is sampled by an analog-to-digital converter, processed by a digital filter/demodulator with on-chip band-pass filtering, and a carrier-detect output (OCD) flags a valid received signal. This DSP-based architecture gives reliable signal detection in noisy conditions.

On the digital side, D_IN, D_OUT and RTS connect to the host UART, and the device uses a 3.6864 MHz crystal (XTAL1/XTAL2) or an external clock (XCEN). It runs from a single 2.7 V to 3.6 V supply (separate DVDD/AVDD) drawing about 285 µA, with phase-continuous FSK switching for low loop disturbance. The DS8500 suits low-power, loop-powered process-control transmitters.

Note: Values are taken from the Dallas/Maxim DS8500 datasheet. Confirm every parameter against the latest official documentation before committing a design.

DS8500-JND+T&R is supplied in the 20-pin TQFN-EP (5 mm x 5 mm x 0.75 mm); "+" marks the RoHS-compliant lead-free finish and "T&R" the tape-and-reel packing. Solder the central exposed pad (EP) to the ground plane (DGND/AGND) for thermal and electrical return. Keep the analog FSK_IN/FSK_OUT and REF nodes away from digital switching, place the 3.6864 MHz crystal close to XTAL1/XTAL2, and bypass DVDD and AVDD separately. Package outline and pin-1 orientation are shown below.

📄 Full specifications are detailed in the official Dallas/Maxim DS8500 datasheet.

The 20-pin TQFN groups the digital host pins, the analog loop pins and the clock:

• Digital host: D_IN (pin 20, modulator data in), D_OUT (pin 19, demodulator data out), RTS (pin 6, request to send), RST (pin 4, reset), MODE (pin 17), XCEN (pin 10, external clock enable).
• Analog loop: FSK_OUT (pin 12, modulated output), FSK_IN (pin 14, received signal), REF (pin 13, internal reference).
• Carrier detect: OCD (pin 5, asserts on valid received FSK).
• Clock: XTAL1 (pin 7), XTAL2 (pin 8) for the 3.6864 MHz crystal.
• Power: DVDD (pins 1, 2), AVDD (pin 11), DGND (pins 3, 9, 16, 18), AGND (pin 15), and the exposed pad (EP) to ground.

Pin 1 is marked below; EP is the center pad. Full pin descriptions are in the datasheet.

The parts below are related modem / communication interface ICs in our catalog. A true HART-modem cross is rare; verify the protocol, modulation and interface before substituting.

Selection Tips: For a HART modem, the closest part is the AD5700. The MAX2992 is a power-line (PLC) modem on a different protocol, the MAX3100 is an SPI UART (host-side serial, not a modem), and the 73M-2503 is an FSK modem AFE. Match the HART/Bell 202 requirement carefully - most of these are not drop-in for the DS8500.

Dallas Semiconductor, now part of Analog Devices through Maxim Integrated, built communication and interface ICs for industrial systems. The DS8500 is a HART-Registered single-chip modem that puts the full Bell 202 FSK modulator and demodulator on one low-power device.

The device is backed by full datasheet characterization and application notes on loop coupling, carrier detect, crystal selection and host interfacing - the details that determine a compliant, robust HART field connection.