Time is the driver of all actions in the technology industry. Technology today relies on extremely accurate measurements of time by real-time clocks (RTCs) to perform certain actions, whether this action is something as complicated as sending communication signals or as simple as telling the date and time on a phone or computer.
The three areas that need to be considered when designing in RTCs are application size constraints, timekeeping accuracy, and power budget requirements. Finding the perfect balance between these three can be challenging. However, the one consideration that is most important to RTCs is its power consumption.
Let’s highlight an example involving two systems. One uses an integrated RTC within a microcontroller and a second system uses an external RTC. The issue with integrated RTCs is the higher power consumption to operate the RTCs, typically 400nA compared with 200nA for a typical external RTC. This is due to the microcontroller’s overhead leakage current in low-power mode versus shutdown mode. Another impact is reliability: any issues with the microcontroller will directly impact the RTC. This is why an external RTC has more market appeal for battery-powered applications that require a high degree of reliability and extended battery life.
Power management is crucial in an RTC because high power consumption reduces the battery life, causing the designer to increase the battery capacity. Low power consumption, on the other hand, would allow for a smaller battery (which lowers cost and enables a smaller design) and also help extend the battery life.
Now, let’s take a look at a couple of techniques for minimizing power in applications with clocking.
Method 1: Placed the crystal as close to the RTC as possible and use a ground plane to avoid interference from other lines. By doing this, you can save board area and reduce the risk of a dip in performance. Going with an external crystal gives you access to a variety of low-cost crystal options, as well as the ideal performance without losing board space.
Method 2: You could also choose to operate at a lower voltage range. Operating at a lower voltage range requires the RTC to draw the lower current from the input. As a result, less power is used. Although many RTCs have wide operating ranges for the main power supply, designers should also consider using power rails that optimize power consumption. Given an RTC with a 1.6V to 3.6V operating range, the power consumption at 1.6V is typically 130nA versus 150nA at 3V. This provides 20nA, or a 13% power savings, at the lower voltage.
Many RTCs on the market force customers to choose one characteristic from a list that includes small size, power management, and low voltage range. However, Maxim offers a solution without tradeoffs: the MAX31341B RTC occupies very little board space with its 2.0mm x 1.5mm size; includes power management capabilities with a battery backup, trickle charger, and power fail threshold; and operates at a low voltage range of 1.6V to 3.6V to minimize the amount of power consumed.
In addition to these characteristics, the MAX31341B includes an external 32.768kHz crystal oscillator. The integrated capacitive load is a 6pF crystal which increases the amount of crystals that can be used and removes the need for any outside resistors or capacitors. The resistive load of 100kΩ along with the capacitive load both contribute to the minimal current draw and minimized power consumption.
With the continually growing desire of people to have all their devices connected and synchronized, the need for RTCs is rising. The ability of the MAX31341B to provide efficient power management, a small size, and operation in low voltage ranges allows it to meet the challenges of minimizing power in clocking applications.
Check out the MAX31341B RTC for your next clocking application with the MAX31341EVKIT evaluation kit. The kit is fully assembled and tested and operates from a single supply. Its onboard crystal provides a 32.768kHz clock signal, and the device can be accessed through an I2C serial interface.Kyle Johnson is a student at Santa Clara University, where he is pursuing a bachelor’s degree in electrical engineering. He is spending this summer interning at Maxim.