Why System Monitoring ICs Are Good Analog Insurance

March 15, 2017

Steve Logan
  Ani Fayezi By: Steve Logan, Executive Business Manager & Ani Fayezi, Business Director
Core Products Group, Maxim Integrated


System monitoring circuits—think comparators, op amps, current sense amplifiers, supervisory ICs, and the like—can help ensure that voltage levels are where they should be in your design. Think of them as analog insurance.

Analog insurance can be a valuable—and cost-effective—investment even if you’re designing cost-sensitive wearable or portable devices. With these applications, you’re probably most concerned with extending battery life and shrinking the form factor of your designs. This is where small nanoPower system management circuits with less than 1µA of quiescent current can help. Since these components are always running, their ultra-low quiescent current contributes very little to the overall power for the design.

For example, we work with leading consumer electronics companies who integrate comparators in their designs to watch over the microcontroller for voltage spikes. They could, of course, integrate the comparator function directly in their microcontroller versus using an external component. But why burden the already loaded microcontroller when it really won’t break the bank to add a highly reliable, cost-effective component? Plus, using external system monitoring parts provides the redundancy that is so important for many applications.

Maxim offers one of the broadest portfolios of system monitoring ICs—and many of these circuits have nanoPower current levels and are available in both small WLP and also larger packages. While the larger packages (such as SOT23, TDFN, or µMAX) are useful for initial prototyping, the smaller packages are geared toward actual products.

Comparators

Our nanoPower comparators can limit supply-current surges during switching and virtually eliminate the supply glitches that typically occur with many other comparators. The MAX9644, MAX9645, and MAX9646, for example, are ultra-small, low-power comparators ideal for cell phones, electronic toys, notebook computers, portable media players, and portable medical devices. They’re available in a miniature 4-bump UCSP package with a 1mm x 1mm footprint and a 5-pin SOT23 package. Their input voltage range is -0.3V to +5.5V, independent of supply voltage, and they have an ultra-low operating current of 700nA max.

Our MAX40000/ MAX40001 series of comparators deliver ultra-low power in a 0.76mm x 1.11mm footprint with an internal reference featuring under 1µA of quiescent current. They’re great for power monitoring when power dissipation requirements are stringent. Because their lower quiescent current is comparable to the current typical self-discharge rate of the battery cells, these comparators are useful for applications with long sleep times or low duty cycles coupled with the long battery life requirement.

Op Amps

Our MAX44264 is an example of an ultra-low power op amp available in a 6-bump WLP package. For mobile devices, this circuit saves a lot power and space, consuming only 750nA of supply current. Having this low supply current along with low operating voltage and rail-to-rail output mean that this op amp can work well in single lithium ion, two-cell NiCd, and alkaline battery systems.

Current-Sense Amplifiers

Current-sense amplifiers assess load currents running into the microcontroller or elsewhere in the system. If the load goes beyond a set threshold, the current sense amplifier’s linear output, along with a comparator or ADC, can offer an alert to the microcontroller. For example, the MAX9634, with a typical value of 500nA, offers precision accuracy specifications of VOS less than 250uV (max) and gain error under 0.5% (max). It’s available in a 1mm x 1mm UCSP package or a 5-pin SOT23 package, so it can support any small, battery-operated portable device.

Supervisory ICs

Our supervisory ICs ensure that voltage is at the correct level for any controlling component in your design, such as the microcontroller, FPGA, or ASIC. As the brains of the board, these parts clearly need to have valid voltage levels to operate properly. When your system powers up, a supervisory IC would make sure that the voltage is at an acceptable level before the processor can progress to the next step. Supervisors also watch over voltage during normal operation. If something is off, the microprocessor gets an alert to reset. A unique capability of our nanoPower supervisory circuits is their ability to allow either the system or the user to perform a reset using the Manual Reset (MR) feature.

MAX16056 125nA supervisory circuit - typical operating circuit

The MAX16056 125nA supervisory circuit features capacitor-adjustable reset and watchdog timeouts.

For example, the MAX16056 microprocessor supervisory circuit monitors a single system supply voltage. The 125nA capacitor-adjustable, nanoPower circuit triggers an active-low reset signal when the VCC supply voltage drops under a factory-trimmed reset threshold, when manual reset is pulled low, or when the watchdog timer runs out. These components can be used in devices like battery-powered equipment, portable consumer electronics, and patient monitors. Also ideal for small devices like digital cameras, MP3 players, and cell phones are the MAX16072, MAX16073, and MAX16074 ultra-small, ultra-low power microprocessor supervisory circuits. These circuits, with a 0.7µA supply current and available in a 1mm x 1mm, 4-bump UCSP package, feature a precision band-gap reference, comparator, and internally trimmed resistors that set the threshold voltage. They eliminate the need to use external components when monitoring nominal system voltage from 1.8V to 3.6V.

Want to learn more? Read our white paper, Why Low Quiescent Current Matters for Longer Battery Life.

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