One-Time Programmable Memory in Action: A 3-Channel User-Programmable Clock Generator from IDT

February 16, 2018 by Nick Davis

IDT’s new MicroClock programmable clock generator is a 3-channel (3-PLL-architecture), low-power, user-programmable clock, intended for handheld and wearable devices.

IDT’s new MicroClock programmable clock generator is a 3-channel (3-PLL-architecture), low-power, user-programmable clock, intended for handheld and wearable devices.

IDT recently released the 5X2503 MicroClock programmable clock generator. As stated in the datasheet, this IC uses a 3-channel PLL (phase-locked-loop) architecture, where each PLL is assigned to its own single-ended LVCMOS output pin that provides a programmable-frequency (1 to 125 MHz) clock signal. The device has an internal 26 MHz crystal, and it supports a 32.768 kHz clock for low-power and RTC applications.


Figure 1. The 5X2503's block diagram shows the three individual PLL output pins, from the datasheet.


Channel 1 (OUT1) is the only channel that supports both 1.2V and 1.8V LVCMOS signaling; channels 2 and 3 (OUT2 and OUT3) support only 1.8V logic. See the pin assignment information below.


Figure 2. OUT1 supports both 1.2V and 1.8V signaling, whereas OUT2 and OUT3 support only 1.8V. Information taken from the datasheet.

Programming the Clocks

The 5X2503 is user-configurable, though it also includes the capability of operating—again, according to user-programmable specifications—without the utilization of post power-up programming. This form of user programming is accomplished via the device's internal OTP (one-time programmable) memory.

Take note, however, that the device's OTP memory is configured using the I2C protocol when the device is powered on. And, keep in mind that just as the name "one-time programmable memory" implies, this type of memory can only be programmed once; there's no going back and making changes once the program has been "burned in" to the memory.

The table below displays the I2C control function descriptions of the OTP memory.


Figure 3. The OTP memory is programmed using the I2C interface. Table taken from the datasheet.

A Low-Power IC

While this device is characterized as having a low-power 32.768 kHz clock that uses less than 2µA of current, be mindful that while this description is indeed accurate (according to the table below), this low-current condition is valid only when the device is in Power Suspend mode. The current consumption during normal operation ranges from 1.8 to 3.8mA.


Figure 4. The 2µA current consumption spec applies to Power Suspend mode. Table taken from the datasheet.


An interesting aspect of this low-power functionality is what IDT calls “proactive power saving” (“PPS,” at the bottom of page 4 in the datasheet). It’s described as a “patented unique design” that allows the 5X2503 to switch to the 32.768 kHz clock when it proactively detects “end device power down state.”

The explanation of this functionality is not extremely clear, but the general idea seems to be that the 5X2503 detects a power-down state based on the presence or absence of an external oscillator signal that is affected by the power-down state imposed by some sort of external controller IC. The datasheet includes some diagrams indicating that the transition to and from the low-power 32 kHz mode occurs in only two or three clock cycles.


Figure 5. PPS transition behavior, from the datasheet.

Small Form Factor

While the package for this 3-channel user-programmable clock generator is not minuscule, it is rather small when considering that three clock generators are crammed into a 2.5 × 2.5 mm, 12-pin DFN package.

The image below depicts the datasheet's recommended land pattern for this device; notice that this land pattern is based upon, as called out in Note 5, the IPC-7351B recommendation. So hopefully this "generic requirement" land pattern already exists in your CAD library.


Figure 6. A standard DFN footprint, from the datasheet.


While reading through the datasheet, I noticed at least one area that could stand to be clarified a bit—though, in reality, this may be due to my own lack of knowledge. I'm referring to the use of the, um units, er, acronym, er, abbreviation?—I'm not sure what to call it—of 0mps (see the figure below).

When Googling “0mps,” I found that other datasheets have also used this term, however, on a limited basis. But nowhere have I been able to find its definition. Do you know what "0mps" means in regard to an IC's package thermal impedance? If so, let me know in the comments section.

Figure 8. The datasheet uses an unfamiliar term (at least to me): "0mps"


Have you had a chance to use IDT's new programmable clock generator, the 5X2503, in any of your designs? If so, leave a comment and tell us about your experiences.


Featured image used courtesy of Digi-Key.