RoadTest: Enroll to Review the ADI Ultra-Low-Power RTC with Integrated Power Switch
Author: amgalbu
Creation date:
Evaluation Type: Evaluation Boards
Did you receive all parts the manufacturer stated would be included in the package?: False
What other parts do you consider comparable to this product?: NXP PCA8506, STMicro M41T62
What were the biggest problems encountered?: Firmware not installed, unable to find the evaluation kit software on the Maxim website
Detailed Review:
In this post, I am roadtesting the MAX31334SHLD, a shield to evaluate the MAX31334 Ultra-low-power RTC chip
The MAX31334 ultra-low-power, real-time clock (RTC) is a time-keeping device that consumes only 70nA timekeeping current. It features an integrated high-side power pass switch that enables ultra-low-power idle modes on duty-cycled applications by disconnecting power to other devices on the system. The power switch on/off durations can be controlled by periodic interrupt sources such as countdown timer (programmable from 100ms to 1hr) and alarms (1s resolution). The power switch can also be controlled by an external interrupt (from a pushbutton, for example) on the DIN pin. This device is accessed through an I2C serial interface. An integrated power-on reset function ensures deterministic default register status upon power-up. The device also features a backup supply pin (VBAT) and automatically switches over to this supply when the main supply (VCC) drops below the programmed threshold voltage. Other features include two time-of-day alarms, interrupt outputs, a programmable square-wave output, event detection input with timestamping (32-byte timestamp registers double as RAM storage), a serial bus timeout mechanism. The digital Schmitt trigger input (DIN) can also be used to record timestamps and/or assert an interrupt on a falling/rising edge of the DIN signal. The clock/calendar provides seconds, minutes, hours, day, date, month, and year information. A 1/128 seconds register is available for a sub-second timestamp resolution. The date at the end of the month is automatically adjusted for months with fewer than 31 days, including corrections for leap year. The clock operates in 24- hour/12-hour format.
1. Unboxing
Here is a video of the unboxing of the evaluation kit.
According to the roadtest documents, the content of the kit should include a micro-USB cable to connect the MAX32625PICO I2C circuit board to a PC, but in my case this item was not present
The board looks well engineered. It has been designed to host the two different packages of the MAX31334. U1 is for the WLP version (and is mounted on my evkit), whereas U2 is for the 12-FDN version
It features a lot of test points, which is good when you are evaluating the functionalities of a new device. The available test points are
2. Getting started
First, I download the userguide from this link and I followed the "Procedure" section in page 1. Let's go through each single step
After the initial issues related to firmware and PC application, the experience was absolutely smooth: the GUI is clean and easy to use. Configuration parameters are grouped logically and are easy to find
3. Test procedure
After becoming familiar with the GUI, I went through some functional tests
3.1 Setting the clock
To set the clock, you need to enter proper values in the "Date/Time configuration" section and click "Set"
You can now enable "Autoupdate" to see the RTC's date&time in realtime
The problem is that date&time is lost when you disconnect the evkit from USB... which is something you do not expect from an RTC. The problem is the supercapacitor is not charged and the charger is disabled! Trickle charger has a maximum charging current of
If VBAT=0 and VD=0, the maximum current is 3V / 3 kOhm = 1 mA. To charge the 0.33F supercapacitor mounted on the evkit, it will 0.33F * 3V / 0.001 A = 990 s, which means about 16 minutes. I enabled the trickle charger in the "Power management" tab and waited about half an hour before proceeding.
3.2 Clock output measurement
I enabled CLKOUT bit to measure the accuracy of the clock at different frequencies
The oscilloscope probe has been connected to TP1.
The accuracy was quite good out-of-the-box (datasheet states that MAX31334 is factory trimmed to a precision of 10 ppm). If you can eventually compensate for crystal inaccuracy by writing two specific registers (OFFSET_HIGH and OFFSET_LOW)
3.3 Alarm interrupt
MAX31334 has plenty of options for generating timed interrupts. I tested the "Match second" option, where an interrupt is risen when the current time's seconds match a programmed value. The INTB/ output goes low when interrupt occurs and goes back to high when the interrupt is reset. Interrupt may be reset by reading the status register or automatically after a certain programmable time. INTB/ status can be monitored by connecting a probe to TP1
3.4 Timer interrupt
An interrupt can also be generated after a certain amount of time elapses. Timer can be auto-reloaded to generate recurring events at a fixed frequency. INTA/ status can be monitored by connecting a probe to TP3
NOTE: you need to move jumper JU6 to position 1-4. By default, this jumper is in the position 1-3
3.5 Timestamps
On the "TimeStamp" tab in the TimeStamp Configuration section, click on the "TimeStamp Enable" toggle button to enable the TimeStamp Mode. Any of the three TimeStamp event log conditions can be configured by toggling the respective event enable toggle buttons in the Record TimeStamp on section. The TimeStamps sub tab displays the exact time of four consecutive event logs with appropriate event flag. The TimeStamp Overwrite toggle button can be used to log the first four events or the last four events. Using the RESET button clears all the four TimeStamp Registers.
I tested timestamps with the "DIN transition". According to the datasheet, this option should "Record Timestamp on DIN transition. Polarity controlled by DIP bitfield in RTC_Config1 register". So I would expect that a new timestamp is recorded every time I press the SW1 button. Actually, a new timestamp is recorder every two presses!
NOTE: you need to move jumper J11 to position 1-3. By default, this jumper is in the position 1-2. This jumper is not documented in the getting started guide, so I had to refer to the schematics!
3.6 Power switch
MAX3133's has a PSW that can switch on an external load. External load can absorb up to 500 mA. This is an interesting feature because you can easily create low-power devices
MAX3133's devices power management is quite complex. Here is the state machine that controls the PSW pin
3.7 Power management
I tested the power management by connecting an external power supply to the VCC_EXT test point and diminished the voltage to check when the MAX31334 switches to battery.
BTW, the datasheet talks about a bit (D_VBAT_SEL) should enable a sort of battery test mode, but I can't find this bit nowhere
4 Conclusions
Except for the initial issues (which may be limited to the sample that was shipped to me), the overall experience is quite good. The GUI is extremely easy to use and let you experiment with all the available options with no effort. I would like to suggest just some possible improvements/caveats.
