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
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