Analog Devices: CN0240 Reference Design for Bidirectional Isolated High-Side Current Sense with 270 V Common-Mode Rejection

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Kit Overview

This EVAL-CN0240-SDPZEVAL-CN0240-SDPZ circuit monitors bidirectional current from sources with dc voltages of up to ±270 V with less than 1% linearity error. The load current passes through a shunt resistor, which is external to the circuit. The shunt resistor value is chosen so that the shunt voltage is approximately 100 mV at maximum load current.

The AD629AD629 amplifier accurately measures and buffers (G = 1) a small differential input voltage and rejects large positive common-mode voltages up to 270 V.

The dual AD8622AD8622 is used to amplify the output of the AD629 by a factor of 100. The AD8475AD8475 funnel amplifier attenuates the signal (G = 0.4), converts it from single-ended to differential, and level shifts the signal to satisfy the analog input voltage range of the AD7170AD7170 sigma-delta ADC.

Galvanic isolation is provided by the ADuM5402ADuM5402 quad channel isolator. This is not only for protection but also to isolate the downstream circuitry from the high common-mode voltage. In addition to isolating the output data, the ADuM5402 digital isolator can supply isolated +5.0 V for the circuit.

The measurement result from the AD7170AD7170 is provided as a digital code utilizing a simple 2-wire, SPI-compatible serial interface. This combination of parts provides an accurate high voltage positive and negative rail current sense solution with a small component count, low cost, and low power.

This circuit uses the EVAL-CN0240-SDPZEVAL-CN0240-SDPZ circuit board and the EVAL-SDP-CB1ZEVAL-SDP-CB1Z System Demonstration Platform (SDP-B) evaluation board. The two boards have 120-pin mating connectors, allowing for the quick setup and evaluation of the circuit’s performance. The EVAL-CN0240-SDPZ board contains the circuit to be evaluated and the SDP evaluation board is used with the CN0240 evaluation software to capture the data from the EVAL-CN0240-SDPZ circuit board.

Key Applications: Metering & Energy Monitoring, Power Supplies

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PC with a USB port and Windows XP or Windows Vista (32-bit), or Windows 7 (32-bit)
EVAL-CN0240-SDPZEVAL-CN0240-SDPZ circuit evaluation board
EVAL-SDP-CB1ZEVAL-SDP-CB1Z SDP evaluation board
- Blackfin Processor ADSP-BF527
- USB 2.0 Interface to PC
- JTAG header footprint
- 32MB SDRAM
- 2 x Small Footprint 120 Pin Connectors
- Configurable Peripheral Interfaces - SPI - SPORT - I2C - GPIOs - Parallel - Timers
CN0240 evaluation software
Power supply: +6 V @ 1 A, or +6 V “wall wart”
Dual power supply: ±15 V@ 10 mA
Shunt resistor with maximum voltage of 100 mV at the maximum load current.
Source voltage and electronic load

Technical Documents

Learning Center

Type	Description
User Manual	ADI: User Manual for CN-0240 Bidirectional Isolated High-Side Current Sense with 270 V Common-Mode Rejection
User Guide	ADI: User Guide for EVAL-SDP-CB1Z
Datasheet	ADI: Datasheet for ADuM5401/ADuM5402/ADuM5403/ADuM5404: Quad-Channel Isolators with Integrated DC-to-DC Converter (Rev C)
Datasheet	ADI: Datasheet for AD629: High Common-Mode Voltage, Difference Amplifier Data Sheet (Rev C)
Datasheet	ADI: Datasheet for AD8622/AD8624: Low Power, Precision Rail-to-Rail Output Op Amp (Rev C)
Datasheet	ADI: Datasheet for AD7170: 12-Bit Low Power Sigma-Delta ADC (Rev A)
Datasheet	ADI: Datasheet for AD8475: Precision, Selectable Gain, Fully Differential Funnel Amplifier (Rev B)

Design Elements

Type	Description
Schematics	ADI: Schematics for EVAL-CN0240-SDPZ Evaluation Board
Layout	ADI: Layout for EVAL-CN0240-SDPZ
BOM	ADI: Bill Of Material (BOM) for EVAL-CN0240-SDPZ Evaluation Board

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Kit Features

EVAL-CN0240-SDPZEVAL-CN0240-SDPZ Evaluation Board Features:

+/- 270 V common mode voltage
Creates isolated supply for digital control
Bidirectional current monitor system
Galvanic isolation protects processor
Wireless base stations and telecommunications

Devices Used for the EVAL-CN0240-SDPZEVAL-CN0240-SDPZ Evaluation Board
Key Features for AD629AD629: Improved replacement for: INA117P and INA117KU ±270 V common-mode voltage range Input protection to ±500 V common mode ±500 V differential mode Wide power supply range (±2.5 V to ±18 V) ±10 V output swing on ±12 V supply 1 mA maximum power supply current	Key Features for AD8622AD8622: Very low offset voltage 125 μV maximum Supply current: 215 μA/amp typical Input bias current: 200 pA maximum Low input offset voltage drift: 1.2 μV/°C maximum Very low voltage noise: 11 nV/√Hz Operating temperature: −40°C to +125°C Rail-to-rail output swing Unity gain stable ±2.5 V to ±15 V operation

Key features for ADuM5402ADuM5402: isoPower integrated, isolated dc-to-dc converter Regulated 3.3 V or 5.0 V output Up to 500 mW output power Quad dc-to-25 Mbps (NRZ) signal isolation channels 16-lead SOIC package with 7.6 mm creepage High temperature operation: 105°C maximum High common-mode transient immunity: >25 kV/μs	Key Features for AD7170AD7170: Output data rate: 125 Hz Pin-programmable power-down and reset Status function Internal clock oscillator Current: 135 μA Power supply: 2.7 V to 5.25 V –40°C to +105°C temperature range

Key Features for ADR435ADR435: Low noise (0.1 Hz to 10.0 Hz): 3.5 μV p-p @ 2.5 V output No external capacitor required Low temperature coefficient A Grade: 10 ppm/°C maximum B Grade: 3 ppm/°C maximum Load regulation: 15 ppm/mA Line regulation: 20 ppm/V Wide operating range ADR435: 7.0 V to 18 V High output source and sink current: +30 mA and −20 mA Wide temperature range: −40°C to +125°C	Key Features for AD8475AD8475: Precision attenuation: G = 0.4, G = 0.8 Fully differential or single-ended input/output Differential output designed to drive precision ADCs Drives switched capacitor and Σ-Δ ADCs Rail-to-rail output VOCM pin adjusts output common mode Robust overvoltage protection up to ±15 V (VS = +5 V) Single supply: 3 V to 10 V Dual supplies: ±1.5 V to ±5 V High performance Suited for driving 18-bit converter up to 4 MSPS 10 nV/√Hz output noise 3 ppm/°C gain drift 500 μV maximum output offset 50 V/μs slew rate Low power: 3.2 mA supply current

Devices Used for the EVAL-CN0240-SDPZEVAL-CN0240-SDPZ Evaluation Board

Key Features for AD629AD629:

Improved replacement for: INA117P and INA117KU
±270 V common-mode voltage range
Input protection to
±500 V common mode
±500 V differential mode
Wide power supply range (±2.5 V to ±18 V)
±10 V output swing on ±12 V supply
1 mA maximum power supply current

Key Features for AD8622AD8622:

Very low offset voltage
125 μV maximum
Supply current: 215 μA/amp typical
Input bias current: 200 pA maximum
Low input offset voltage drift: 1.2 μV/°C maximum
Very low voltage noise: 11 nV/√Hz
Operating temperature: −40°C to +125°C
Rail-to-rail output swing
Unity gain stable
±2.5 V to ±15 V operation

Key features for ADuM5402ADuM5402:

isoPower integrated, isolated dc-to-dc converter Regulated 3.3 V or 5.0 V output
Up to 500 mW output power
Quad dc-to-25 Mbps (NRZ) signal isolation channels 16-lead SOIC package with 7.6 mm creepage
High temperature operation: 105°C maximum
High common-mode transient immunity: >25 kV/μs

Key Features for AD7170AD7170:

Output data rate: 125 Hz
Pin-programmable power-down and reset
Status function
Internal clock oscillator
Current: 135 μA
Power supply: 2.7 V to 5.25 V
–40°C to +105°C temperature range

Key Features for ADR435ADR435:

Low noise (0.1 Hz to 10.0 Hz): 3.5 μV p-p @ 2.5 V output
No external capacitor required
Low temperature coefficient
A Grade: 10 ppm/°C maximum
B Grade: 3 ppm/°C maximum
Load regulation: 15 ppm/mA
Line regulation: 20 ppm/V
Wide operating range
- ADR435: 7.0 V to 18 V
High output source and sink current: +30 mA and −20 mA
Wide temperature range: −40°C to +125°C

Key Features for AD8475AD8475:

Precision attenuation: G = 0.4, G = 0.8
Fully differential or single-ended input/output
Differential output designed to drive precision ADCs
Drives switched capacitor and Σ-Δ ADCs
Rail-to-rail output
VOCM pin adjusts output common mode
Robust overvoltage protection up to ±15 V (VS = +5 V)
Single supply: 3 V to 10 V
Dual supplies: ±1.5 V to ±5 V
High performance
Suited for driving 18-bit converter up to 4 MSPS
10 nV/√Hz output noise
3 ppm/°C gain drift
500 μV maximum output offset
50 V/μs slew rate
Low power: 3.2 mA supply current

Kit Contents

The Analog Devices EVAL-CN0240-SDPZEVAL-CN0240-SDPZ kit is supplied with below contents:

Evaluation Board