An optically isolated sigma-delta modulator, the Avago ACPL-C799 from Broadcom, claims to convert an analogue input signal into a high-speed data stream with galvanic isolation. It features a low differential input range of ±50mV, allowing designers to reduce power dissipation across a current-sensing shunt resistor in servo drive and motor applications.

Compared to previous generation products with an input range of ±200mV, the ACPL-C799 enables the use of a smaller shunt resistor with one-quarter the value, thereby eliminating 75% of shunt resistor’s power losses. Despite the reduced input voltage range, the device is said to deliver high SNR, ENOB and offset drift performance and enables a high precision motor control in space constrained, high temperature environments.

Combined with optical coupling technology, the modulator delivers high noise margins and immunity against isolation-mode transients. With 0.5mm minimum distance through insulation, the device provides reinforced insulation and insulation voltage, which is suitable for fail-safe designs.

Key features:

  • ±50mV linear input range
  • Low power dissipation across shunt resistor
  • 1bit, 2nd order sigma-delta modulator
  • 77dB SNR typical
  • 16bit resolution with no missing codes (12bit ENOB)
  • 1.3µV/°C maximum offset drift over temperature
  • 10MHz internal clock
  • Robust optical isolation and insulation
  • 25kV/µs minimum common mode transient immunity (CMTI)
  • Wide creepage and clearance of 8.3mm
  • High reinforced insulation voltage of VIORM = 1414 VPEAK
  • Safety approvals from CSA, UL and IEC
  • Compact stretched SO-8 package
  • Temperatures ranging from -40 to 105°C