Current Sense Amplifiers

By combining analog electronic building blocks with a 16-bit ADC, the ISL2802x family of integrated power monitors accurately measure current and voltage and deliver real-time digital output in I2C, PMBus and SMBus compatible formats.

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Digital Power Monitor Products (Current Sense)

Our agenda for today will include some background information, a digital power monitor product overview, applications and the products themselves the ISL28022 (the basic digital power monitor), ISL28023 (the full featured digital power monitor), and ISL28025 (the digital power monitor in a tiny package).

Where and Why?

Example circuitry can be a battery, DC motor or the loading of the circuit as shown.

Knowing the amount of current flow is important for performing such features as: battery charging, motor speed control or short circuit detection.

Amplifiers are used in applications to measure the amount of current flow through a circuit.

An amplifier is used to amplify the voltage developed by the current sense so it can properly drive the ADC.

The digital power monitor integrates the amplifier and ADC into a single IC to measure both current and voltage and now provides digital output to the microcontroller or FPGA.

Current Sense Technologies

There are various current sense technologies available such as shunt resistors, Hall effect, transformers, and other exotics like the Rogowski Coil.

The next focus will be on the shunt resistor as it is easier to design with, offers precision, it is less susceptible to noise, and is usually lower cost than other sensors.

Shunt Current Sensing: Basic Concept

Important features of a current sensing circuit include:

1. Current sensing uses the property of Ohm's Law. To determine the amount of current flow, a sense resistor is placed in the path. The amount of voltage drop across the resistor is proportional to the current. The I-V transformation is used to process the information using an Analog to Digital Converter (ADC).
2. A small sense resistor is desired because a) It will dissipate little power b) It will not affect the overall loading of the circuit.
3. Because of the small sense voltage from using a small sense resistor, an amplifier increases the signal drive for the ADC.
4. The total current sense solution should then accurately sense current while not affecting circuit performance.

Digital Power Monitor/Current Sense Solutions Portfolio

Renesas provides a complete portfolio for power monitor/current sensing solutions.

Renesas op amps provides the basic/flexible building blocks for current sensing circuit. Renesas' current sense amplifier integrates external components (i.e. gain setting resistor) to simplify design and provides analog voltage output. Renesas' digital power monitor integrates ADC to provide digital output to directly interface with microcontroller/FPGAs.

Precision Digital Power Monitor Value Proposition

The precision digital power monitor value propositions include offering a flexible digital power monitor (DPM) solution with the ability to measure current, voltage and calculate power; it has user defined alerts/fault monitor for overvoltage (OV)/undervoltage (UV) and overcurrent (OC); and, there are 16 to 55 slave addresses to enhance digital communication and simplify board design. It offers accurate power measurement at low shunt voltages using a 16-bit ADC and offers user defined conversion time and sample settings. Additionally, the precision digital power monitor offers the ability to add telemetry to existing systems, enables remote diagnostics and monitoring for system optimization and support, improved reliability, faster fault isolation and repair, reduced service and maintenance cost, and it offers predictive fault detection and trend analysis. Finally, it provides a low risk method to upgrade proven systems; eliminates the need to replace proven, qualified devices; allows the user to control risk vs. cost and benefit with selective implementation; and, it reduces time to market and lowers implementation cost due to reduced qualification.

Typical Applications

The digital power monitor was primarily designed for telecom, datacom, and servers but will go into a variety of applications including:

• Battery life indicators and chargers
• Overcurrent protection and supervising circuits
• Current and voltage regulators
• DC/DC converters
• Ground fault detectors
• Linear and switch-mode power supplies
• Proportional solenoid control, linear or PWM
• Medical diagnostic equipment
• Handheld communications devices
• Automotive power electronics
• Low Ohmic shunt sense
• Battery management
• Power management
• mV/µV-meters
• High-precision voltage and current measurement
• Power management in communications, networking, industrial
• Test/DAQ (data acquisition) systems
• Computing and display power management
• Automotive data acquisition
• Alternative energy applications (solar, wind, lighting, etc)
• Power meter/battery tester (DAQ)
• Advanced lighting applications
• HVAC and safety

ISL28022 Basic Digital Power Monitor

ISL28022 Functional Block Diagram

This slide shows the functional block diagram for ISL28022. It is an integrated solution; integrating the analog front end solutions such as switch/mux, ADC, voltage reference, digital processing, and serial output (I²C). It will measures: voltage, current through the shunt resistor, and calculates power. For the current measurement it will do high-side, low-side and bidirectional.

It has a wide common mode voltage input range (0V to 60V).

It offers a serial digital output I²C and it is also SMBus compatible.

It has a dedicated pin for alerts/interrupts. It constantly monitors systems or remote sensors for power, voltage, current. It alerts the system when overvoltage/undervoltage and overcurrent is detected for safety.

It offers accuracy using a 16-bit ADC with <0.3% max measurement error.

Design Scalability: Up to 16 DPM on a Single I²C Bus to monitor multiple power supplies is possible. There is also external clock input so all of the DPMs can be synced to a single clock.

The ISL28022 is a bidirectional high-side and low-side digital current sense and voltage monitor with serial interface output. Functionality and performance were discussed in the previous slide. It offers high performance with an offset maximum of 75µV, a very high CMRR of 110dB, a measurement error of 0.3%, and an input common mode voltage range of 0V to 60V; it is powered by 3V to 5.5V consuming only 1mA, has a full industrial temperature range from -40 °C to 125 °C, and a high ESD rating of 8kV. ISL28022 is provided in an MSOP 10-pin package and a QFN 16-pin at a 1ku price of $0.95. In the future, ISL28022 will be provided in the full military temperature range -55 °C to 125 °C in an MSOP 10-pin package.

Features include:

• Integrated analog front end with digital output
• Analog switch/mux, ADC, voltage reference
• Digital processing/serial comm, circuitry
• SMBus interface, I²C, supports high-speed I²C (3.4MHz)
• Voltage, current, power monitoring and current direction
• Current sense: high-side, low-side, bidirectional
• Wide common-mode input voltage range: 0V to 60V
• Handles negative system voltages
• 16-bit S.ADC with measurement error <0.3% (both current & voltage)
• Over/Undervoltage and overcurrent fault monitoring
• Alert pins available
• 16 slave addresses available
• Adjustable acquisition/conversion time: 72μs to 64ms

Power Monitor Design Tools (Collateral)

There are various collateral that are available for ISL28022 such as the cookbooks (i.e., application diagrams), app notes, one pager summary, evaluation and demo boards, and simulation tools.

ISL28023 Full Feature DPM

We will now be talking about the full featured digital power monitor, the ISL28023.

ISL28023 Functional Block Diagram

Here is the functional block diagram for the ISL28023, the next generation, full featured digital power monitor in development. It is using the core ISL28022 as the primary channel, with additional features.

It includes an auxiliary channel.

It has an internal temperature sensor.

There is an internal voltage regular (3.3V).

There is an 8-bit margin DAC with voltage output.

VCC can be powered from 3V to 5V, but the I²C module can be powered down to 1.2V to communicate with various I²C protocols.

It is PMBus compatible so it will be communicating with our digital power devices.

There are 55 slave addresses available so you can chain up to 55 ISL28022/23 on a single I²C bus with external clock input so you can sync all of these on a single clock.

There are analog comparators available so that the user-defined alerts can be alerted almost real time with pull-up and push/pulloutputs.

ISL28023 is a full featured digital power monitor offering high performance, function and features previously discussed. It offers specifications such as Vos max of 50µV, CMRR min of 116dB and using a 16-bit ADC for <0.05% max measurement error.

Offers full industrial operating temperature range (-40 °C to 125 °C) and a human body model (HBM) ESD rating of 6kV.

It is suitable for various applications similar to ISL28022, but this is also ideal for telecom/datacom and routers/servers applications.

Power Monitor Design Tools

Similar to ISL28022, there are various collaterals available for ISL28023 such as the application cookbook, application note, a one pager summary, the evaluation platform for ISL28023, and simulation models such as iSim and PowerNavigator are also available.

ISL28025 DPM in Tiny Package

ISL28025 is a digital power monitor in a tiny package, WLCSP.

ISL28025 Functional Block Diagram

Here is a functional block diagram of the ISL28025. ISL28025 offers a subset of features of ISL28023 in a tiny WLCSP package. Similar to ISL28023, it uses a core ISL28022 as the primary channel with an additional feature set.

It offers auxiliary channel (voltage monitor only).

Internal temperature sensor

Internal voltage regulator (3.3V)

Vcc can be powered from the 3.3V up to 5.5V. Additionally, I²C Vcc can be powered down to 1.2V. And, it is PMBus compatible.

Up to 55 slave addresses are available.

Analog comparators for real time with pull-up and push/pull outputs are available.

ISL28025 is a digital power monitor offering high performance with Vos max of 50µV, CMRR min of 114dB and using a 16-bit ADC for <0.05% measurement error.

Offers full industrial operating temperature range (-40 °C to 125 °C) and a human body model (HBM) ESD rating of 4kV.

It is offered in a tiny WLCSP 16-ball package that is ideal for portable or space limited applications.

Power Monitor Design Tools

Similar to ISL28023 and ISL28022, ISL28025 will have various collateral available including, application cookbooks, application notes, a one pager summary, evaluation platform, and simulation tools such as Pspice^® and PowerNavigator^TM.

DPM Portfolio Comparison - ISL28022 vs. ISL28023 vs. ISL28025

Here is a comparison table to show the differences among the products in Renesas' digital power monitor (DPM) family.

• ISL28022 is a basic power monitor
• ISL28023 is a full featured power monitor
• ISL28025 is a digital power monitor in a tiny package