MCPMs can simplify system design and contribute to the overall performance and reliability of the electronic system.
Current sensing and power monitoring are essential design aspects of several automotive systems. Moreover, some kinds of automotive modules may need more than one of these sensing/monitoring operations. Multi-channel power management (MCPM) ICs can help in this regard. They can incorporate up to four energy-monitoring channels, including bus voltage monitors and current sense amplifiers. Thanks to their recent Automotive Electronics Council (AEC) AEC-Q100 stress test qualification for packaged integrated circuits (ICs), these MCPM devices can serve in several automotive applications.
The measurement, monitoring, and control of power is increasingly important for all kinds of electronic systems. Power management can promote power efficiency, optimize the remaining battery life, or enhance other power-related system functions. At its most basic level, power monitoring circuitry usually consists of a sense amplifier circuit operating across a sense resistor. This basic configuration can monitor current, voltage, and power data through an analog output. The sense amp is typically energized continuously and lacks more advanced functions, such as the ability to poll the circuitry and interrupt circuit operation to reduce power consumption.
Contrast this basic current sensing with the actions of a digital power monitor or precision power monitor. This scheme is also called a high-side current sensor and can have other monikers as well. An IC capable of making and digitally communicating more than a single current sensor measurement is more accurately described as an MCPM.
An MCPM can connect to a higher voltage rail without the need for additional protection devices. The newest family members (PAC194X/5X) can measure 0 to 32 V. Measured values go digitally over a two-wire I2C/SMBus to a host computer. The power monitor calculates power consumption on-chip independently of the host controller and makes this value available in a register. This approach saves software overhead, development time, and reduces code complexity associated with monitoring one or more current sensors.
With the appropriate data, the host can proactively disconnect loads to save power and reconnect them as needed. This process also saves time in the awake state while the sensor accumulates data. Additionally, power monitoring activities managed by the host processor can be put to sleep, leaving more of the remaining processing power for the other activities.
Figure 1. The simplest form of current sensing has a single analog output.
The PAC194X/5X is a family of MCPM ICs with up to four bidirectional, high-side/low-side current-sensing channels. Also included are precision voltage measurement capabilities, an integrated power calculation, and a power accumulator. PAC194X devices are specifically designed for lower voltage applications. With 16 bits of resolution, the voltage rail spans 0 to 9 V without requiring additional circuitry. Such qualities make the chips good candidates for dual-cell Li-Ion battery applications. A configuration of 0-to-4.5-V single-cell Li-Ion applications can be realized with the same 16 bits of precision. This allows the ICs to be used for accelerator cards, field-programmable gate arrays (FPGAs), graphics, telematics, computing, and more.
Figure 2. In an MCPM application, data communicated by the I2C/SMBus as well as alerts/interrupts, allow a host computer to efficiently provide power control.
Two flexible alert outputs can help define, capture, warn, and report to the host, alerting it to take the appropriate actions. Thanks to two digital outputs, a spurious current event can be captured separately from a spurious voltage event; consequently, the ICs can respond distinctively differently to the two kinds of anomalies. Another option would be to measure or mask over-voltage (OV), over-current (OC), and over-power (OP) as well as under-current (UC) and undervoltage (UV) occurrences. Such options greatly simplify and improve the system’s response to different power situations.
MCPMs can measure the voltage and current simultaneously with a 16-bits resolution for each. The measurement limits of the two flexible alerts can easily be adjusted by configuring a 16-bit limit register for desired current-voltage events and a wider register for power events.
Figure 3. A four-channel dc power monitor with accumulator — two 16-bit ADCs provide accuracy and high resolution to I2C/ SMBus-communicated data.
Power savings
One challenge in power monitoring is the amount of current consumed when measuring power. A single power monitor can draw up to 360 μA or more. In contrast, an MCPM can use at least 31% less current than a single-channel device that makes two measurements. In this case, the two-channel system only pulls 495 μA compared to 720 μA for two single devices.
The difference in current consumption is even greater with more channels; it is 54% lower with a three-channel system and 66% with a four-channel system. The need to draw less current with multiple devices also saves printed circuit board (PCB) space and simplifies layout.
MCPMs are also suitable for use in vehicles. It is interesting to note that in a typical automotive telematics or radio head module, there can easily be three or more current/voltage nodes to monitor. The PAC194X/5X MCPMs have passed AEC-Q100. The Automotive Electronics Council established AEC-Q100 as a failuremechanism- based stress test qualification for packaged ICs employed in automotive applications. AEC-Q100 basically extends IEC and Jedec specifications for automotive uses. An AECQ100- qualified device has passed specified stress tests that guarantee a certain level of quality/reliability. For example, AEC-Q100 for grade-two semiconductor components requires high-temperature operating life (HTOL) testing of 1,000 hours at 125°C. Typical automotive application examples include graphics cards, dc-dc converters, power inverters, fan control, and more.
Figure 4. A multi-channel power monitor reduces current dissipation over a single channel from 31% to 66%.
Electrostatic discharge also plays a significant role in automotive quality. The PAC194X/5X devices tolerate 7,500-V HBM (human-body model) and 4,000V CDM (charged-device model). HBM simulates ESD caused by discharge from human beings. CDM simulates the discharge of a charged device when it touches a conductive material.
There are two versions of the PAC195X. PAC195X-1 devices are for high-side current sensing; PAC195X-2 devices are for lowside current sensing or floating Vbus applications. The high impedance input of the PAC194X/5X design allows for longer traces on the PCB (up to 1 kΩ) associated with the sense resistors. Thus, sense resistors can be physically separated as is often necessary for quantifying multiple (up to four) current flows from disparate sources.
The PAC194X provides a unique 16-bit resolution on lower Vbus measurements supporting 4.5 and 9 V, while the PAC195X supports 16 and 32 V (with 40 V being the absolute maximum for both families). For applications up to 60 V, a floating voltage node with a resistor divider can be used to keep the voltage under 40 V.
The PAC194X/5X family features a wide dynamic measurement range that enables low-power events — such as trickle charging — and high power-consumption events — such as battery charging — to use the same voltage rail. This feature eliminates the need for separate coding specific to each of these events. It is the 16- bit resolution in the PAC194X/5X family that makes this simplification possible.
In addition, extensive driver support, including MPLAB Code Configurator, MPLAB Harmony, Python code, and Windows 10/11 drivers, is available with Linux drivers coming soon to simplify software development.
For prototyping, a burst mode measurement allows increasing the measurement speed or sampling rate for one rail and using it for better singlechannel characterization and prototyping. Power accumulation registers additionally help the designer to better understand the system over time.
References
Microchip Technology, www.microchip.com
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