5V Generation from V_IN on the Freedom Board RevE


The Freescale Freedom boards like the FRDM-KL25Z feature an Arduino header so I can stack shields on it. Unfortunately, the Freedom board does not generate 5V if not connected to the USB cable. This makes it not possible to be used with many shields like the Adafruit Motor Shield: such shields expect that the Arduino board is providing 5V through the Arduino header (Pin 10 on J9 on the FRDM-KL25Z). So I had to do hardware changes to generate that 5V if I used my board disconnected from USB, e.g. running from batteries through V_IN (pin16 (P5-9V_IN) on the FRDM-KL25Z.

J22 with Capacitors on FRDM-KL25Z RevE

J22 with Capacitors on FRDM-KL25Z RevE

The good news is that the Rev.E of the Freedom FRDM-KL25Z board has now a header J22 to make things easier:

FRDM-KL25Z Schematic

This header can be populated to generate the needed 5V from V_IN:

J22 Schematic (Source: Freescale FRDM-KL25Z RevE Schematic)

J22 Schematic (Source: Freescale FRDM-KL25Z RevE Schematic)

❓ The schematic/board provides footprints for several capacitors to counter LC voltage spikes. As I’m using low loads with short cables, I probably do not need them. Have a look at this Pololu article on this subject.

Pololu 5V Converter

Pololu sells a the “Pololu 5V Step-Up/Step-Down Voltage Regulator S7V7F5” 5V Buck Converter (Part number 2119) which generates 5V from an input voltage between 2.7V and 11.8V. This makes it ideal to generate the 5V from batteries.

The tiny 9×12 mm module has three normal 2.54 mm pins for VIN, GND and VOUT (5V):

S7V7F5 Back Side

S7V7F5 Back Side

S7V7F5 Front Side

S7V7F5 Front Side

Soldering the Headers to the Module

Pololu ships the module with two different headers (straight and right-angle male headers). I used the straight one:

Straight Header Soldered on Module

Straight Header Soldered on Module

Top side with straight header soldered

Top side with straight header soldered

Mounting on FRDM-KL25Z

Then the converter gets soldered on the FRDM-KL25Z:

Module Soldered on FRDM-KL25Z

Module Soldered on FRDM-KL25Z

💡 I intentionally used the header in the above way (with the 3 pins going above the module: that way I have more test or connection points on the board. Of course otherwise it would make sense to cut the pins. Cutting the pins is advised if they could get in contact with components on a shield above the converter.

Summary

As the FRDM boards to not generate the needed 5V from V_IN as needed by many shields, I need to add a buck converter or similar power source to have 5V on the Arduino header. The FRDM-KL25Z RevE board makes it easier to add such a thing like a Pololu 5V Step-Up/Step-Down converter. That converter costs less than $5.

Happy Powering 🙂

8 thoughts on “5V Generation from V_IN on the Freedom Board RevE

  1. I assume you’ve read and considered this comment on the Pololu page:
    When connecting voltage to electronic circuits, the initial rush of current can cause voltage spikes that are much higher than the input voltage. If these spikes exceed the regulator’s maximum voltage, the regulator can be destroyed. If you are connecting more than about 9 V, using power leads more than a few inches long, or using a power supply with high inductance, we recommend soldering a 33 μF or larger electrolytic capacitor close to the regulator between VIN and GND. The capacitor should be rated for at least 16 V.

    Like

      • Oops, sorry. I was a little “quick to click” there. Days after I read your blog post I went to check out the Pololu site, read that, and then posted my comment without re-reading the blog.

        I do like to go overboard though on stuff like protection circuitry and filter/bypass caps. 🙂

        Like

      • Hi Bill, no worries. My students tend to say the same thing about me too. Less on circuitry, but more about global variables, using printf() or missing volatile keyword 😉

        Like

  2. Pingback: Review: New FRDM-KL26Z Board | MCU on Eclipse

  3. Hi Erich,
    Just wondering, with the 5V regulator soldered on the Freedom Board, when USB is connected, will there be a clash of 5V supply to header J9 pin 10?
    Thanks in advance

    Like

What do you think?

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s