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SI4735-C40-GU AM/FM Radio IC

Replacement: None. We don't carry a direct replacement for this IC, which has been obsolesced. There is a similar IC available (SI4735-D60-GU) but it's not a drop-in replacement. This page is for reference only.

The Si4735-C40-GU is the first digital CMOS AM/FM radio receiver IC that integrates the complete tuner function from antenna input to audio output. With this IC you can make your own radio.

The Si4735 is a feature-rich solution including advanced seek algorithms, soft mute, auto-calibrated digital tuning, and FM stereo processing. In addition, the Si4735 provides analog or digital audio output and a programmable reference clock. The device supports I2C compatible 2-wire control interface, SPI, and a Si4700/01 backwards-compatible 3-wire control interface.

The Si4735 also incorporates a digital processor for the European Radio Data System (RDS) and the North American Radio Broadcast Data System (RBDS), including all required symbol decoding, block synchronization, error detection, and error correction functions. Using RDS, the Si4735 enables broadcast data such as station identification and song name to be displayed by the user.

  • Worldwide FM band support (64-108 MHz)
  • Worldwide AM band support (520-1710 kHz)
  • SW band support (2.3-26.1 MHz)
  • LW band support (153-279 kHz)
  • Digital FM stereo decoder
  • RDS/RBDS processor


Looking for answers to technical questions?

We welcome your comments and suggestions below. However, if you are looking for solutions to technical questions please see our Technical Assistance page.

  • Any changes gettin breakout board of this? With all the needed parts, coils etc..

  • The datasheet is a little vague on some things, but it mentions two additional application notes:<br />
    <br />
    AN332: Si47xx Programming Guide<br />
    <br />
    AN383: Si47xx Antenna, Schematic, Layout, and Design Guidelines<br />
    <br />
    You should consider hosting copies of these along with the datasheet.<br />

  • breakout board of this would be better

    • I made a SSOP to DIP Adapter specifically to fit this chip and put it for sale on batchpcb:
      Si4735 SSOP to DIP Adapter

    • Looking back - I should have held out until a breakout board was available. I bought the 28-pin (BOB-00500) to attempt a fit, but it really is too narrow. It barely touches the landing pads on each side. Chalk it up to a failed $15 soldering lesson :(

      • It works, its a VERRRRRY tight fit, but it works! =]

        • By "tight fit", you mean gently tug every leg of the IC out to its extreme reach and hand solder with a tiny soldering iron. Personally I bet less than 1 in 10 is successful attempting this.

    • Or you can adapt the Sparkfun SSOP to DIP Adapter 28-Pin
      sku: BOB-00500
      You would just have 4 unused pins

    • Go to Facebook and lookup a Group called Learn Electronics Lessons and projects...... There in the Suppliers area there is a link to a site that has breakout board.

  • any chance of a breakout board for this?

  • +1 to see this in a breakout board

  • Any chance you guys could get the FM receiver chip from Silicon Labs that includes the weather band and SAME decoding? I have not had any luck finding a supplier of chip with the weather band and SAME decoding in small qty.<br />

    • Me Three!
      weather band!
      Sparkfun people: EDXL is coming out, which will be transmitted over SAME on the weather channels. Much more fun than shortwave.

    • I agree... I searched everywhere for the SI4737 but you have to buy hundreds of these!! I would really like to get the weather band chips...

  • Yeah, a breakout board with supporting circuitry for a typical application would be awesome!

  • Pretty please can we get a breakout board for these soon? This is an awesome (Evil, yet awesome) product! :)

  • any one have "Basic Stamp" example code to send and receive data?

  • Can it be overclocked into the 145Mhz band by feeding it a higher reference clock?

  • What is the advantage of using an external crystal oscillator ?

    • The advantage is that there is less noise on the chip, if the clock is external. Would have go through the docs again to figure out where I read this. In the application information, it also says that during s seek operation, suppress the I2C bus activity, as well. Some pins are dual function, so if you want to use the digital outputs, then you have to use an external oscillator. In my design, I used an NXP PCA8565 RTC, as the clock source to this part. Same price, or cheaper, than using a regular oscillator chip. Note that Si4735-C40-GU is obsolete, replaced by Si4735-D60-GU. There are feature additions and some of the registers have changed as well. Suggest to get a login account at SI so that you can download all the documents.

  • This is the same chip used in the Tecsun PL390. (Nearly the same, PL390 uses SI4734, same as SI4735 without RDS/RBDS.)
    I've been quite impressed with its performance on shortwave. Just connect a whip antenna or a length of wire and tune the shortwave bands.
    Limitations include 1 kHz tuning resolution, the I/Q outputs aren't accessible, no SSB or CW, just AM.

  • It's almost half the price of digikey ! cheaper than newark and almost the same as mouser!!!, sparkfun prices are getting really competitive or is it black market parts ? :P

    • The ones I received are genuine. I find it near impossible that anyone would be able to clone this part and compete with SI. You can not buy these in small quantities from either Digi-Key nor Mouser, that is why I got mine from Sparkfun.

  • Did anyone notice that the available stock dropped from around 151 units yesterday to 48 today? Can you say, "Production run of a breakout board"? Maybe?

    • ... I am impressed. We must make a script that can find out when sparkfun is going to come out with a breakout (or shield).

  • See below

  • I would buy this in an instance, if there was a breakout board to stick it on :(

  • I made a SSOP to DIP Adapter specifically to fit this chip and put it for sale on batchpcb:
    Si4735 SSOP to DIP Adapter

    • Cool, but I already made myself one. I was looking for a Sparkfun-esk (Is that a thing?) approach to one, with a total integrated solution that breaks out only the pins you need and has some example code.
      Sigh ... looks like I'll have to break out my logic analyzer and do it myself! :P

  • Just so everyone else knows, there's an error on the datasheet. The chip is actually a QSOP, not an SSOP as described. This is why the chip isn't wide enough to fit on the SSOP adapter that SparkFun offers.

    • Yes, the C40 datasheet has the wrong footprint diagram, this is a QSOP, 0.635mm (25mil) pitch. I reported this to SI, when I was building my library. They have since corrected this on the Si4735-D50 datasheet.

  • Can we see an official breakout board soon (With a little bit of example code) this chip is a little evil to get working, but works well and I'd rather pay a few dollars extra for a pre-assembled board and some example code. Thanks! :)

  • Does anybody know if this uses a standard 455khz IF for AM or if not what it does use? I wonder b/c I would like to try to use a BFO with one to receive SSB. I'm thinking I would feed the bfo into a small coil placed near or maby glued to the top of the chip would do it. I didn't see the IF frequency mentioned in the Datasheet anywhere.
    Either way I hope SF comes out with a breakout board soon!

  • There is a Link to a website that has breakout borads for this chip,It is on Facebook (Group) page called Learn Electronics Lessons and projects

    • JUST GIVE THE LINK! Anyone that wants to join the group will find it on their own. LINK TO BREAKOUT BOARD OR IT DOESN'T EXIST.

      • The link he gives is just a link to the Proto Advantage store. There doesn't appear to be any breakout board that is specific to this chip. They carry generic SMT to DIP adapters as does SparkFun.

  • You should really link to the application notes as rbean points out. They are on the forums here: http://forum.sparkfun.com/viewtopic.php?f=14&t=26428

  • Hi this is my project SI4735 RDS.


  • breakout board please :]

    • is a DIP adapter good enough? http://www.sparkfun.com/products/500

      • Never mind. I just tried and it doesn't fit. It's just a hair too narrow.

        • It is a narrow fit but if you get it aligned correctly it will work. It took some time but I got mine on there.

  • Is this part in the SparkFun Eagle library?

  • This would be cool to see in 7 meter ham radio project!

  • Would the 2.4GHz antenna work with this chip?

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