FAN5345

[lechik86]

Hi everyone! How are you all doing? I'm a newbie here. I just would like to ask your opinion regarding FAN5345 function testing. What I'm actually doing is implementing the application sheet of this chip on breadboard (See attached figure), I have the exact values of the components except Rset which I replaced with 15 ohm resistor instead of 12.4 ohm. I've also decreased the number of LEDs into 6 instead of 8. I think increasing Rset is just appropriate since I used just 6 LEDs instead of 8. Also, I've added a tact switch connected to EN pin for dimming and a 0.1 uF capacitor to eliminate switch bouncing. I thought everything was all set, However when I plugged in the 5V supply for the Vin line, the LEDs didin't light up at all. By the way since I was using a breadboard to test the application of this chip I had to get a SMD to through hole adapter for this chip so I can mount it on breadboard. Here is the application schematic of the chip.

Any ideas as to why my breadboard prototype failed? I hope to hear from you. Thanks.

 

[OLIVE2222]

Hi,
The FAN5345 is running at 1.2Mhz, not sure that a breadboarded solution can work. however posting sharp picture(s) of your setup can be a good start to help you.
Olivier

 

[lechik86]

Hi Olivier! Okay I'll just post pictures of my setup tomorrow cause I don't have it with me right now. Thanks a lot. Hope you're still here tomorrow.

 

[Harald Kapp]

Two simple questions:
1) EN is set to high level? With EN permanentzly low the chip should not start up.
2) Dumb, maybe, but: All LEDs are connected with correct polarity?

 

[lechik86]

Hi Harald! Currently the en pin is connected to a switch. One end of the switch is connected to 5V. There is also a 0.1uF capacitor connected parallel to the switch to eliminate switch bounce.

Here is the current setup on breadboard.

 

[(*steve*)]

I'd be a little suspicious of the inductor you're using. What ate it's specs.

The wiring is a bit "all over the place" for the frequency

 

[lechik86]

I've used a 10uH inductor as what's indicated on the application sheet. I've also measured it's resistance. It's just around 1 ohm. so everytime I check pin 6 and pin 1 there seems to be a continuity.

 

[lechik86]

Correct me if I'm wrong but from what I understand on the datasheet, this device should be able to give an output of 30V maximum if you plug in 2.5~5V on Vin. Right now what I'm getting is just 4.97V reading on Vout pin after plugging in the 5V supply.

 

[(*steve*)]

What are you using for D9? I hope it's not a 1N400x. It needs to be a high speed diode.

datasheet

What's this pin 0 you show on your schematic?

Are you sure you have the pins wired up correctly (they're not in the order shown on the schematic).

 

[lechik86]

I'm using a 1N5819 Schottky Diode which looks something like this.

 

[lechik86]

I've already doublechecked my connections and everything seems to be connected properly.

 

[lechik86]

Can the chip really work with just a switch connected to it? Or should it be driven by a microcontroller?

 

[OLIVE2222]

This kind of cabling afraid me a bit. As your small pcb as an header I suggest to mount the parts on it with components wire length as short as possible.
The PCB picture is blurry, please post a sharp one to look at the solders. And yes the component is a step-up you should have higher output voltage than 5V
Olivier

 

[lechik86]

This kind of cabling afraid me a bit. As your small pcb as an header I suggest to mount the parts on it with components wire length as short as possible.
The PCB picture is blurry, please post a sharp one to look at the solders. And yes the component is a step-up you should have higher output voltage than 5V
Olivier

The datasheet of the FAN5345 states that the VIn should only range from 2.5V ~ 5V. My question is can FAN5345 really work with just a switch driving it? Or it needs a microcontroller?

 

[lechik86]

Actually this concept came from this schematic. I have the actual module of this design. Basically my goal is to prove that I can replace MIC3289 (which is U1 on this schematic) with FAN5345. From what I understand, the only difference of these 2 LED drivers is MIC3289 operates on 16 levels while FAN5345 operates on 32 levels. Also MIC3289 is negative edge triggered, while FAN5345 is positive edge triggered.

I've actually tried to remove the PIC microcontroller on the board and connected the DC pin of MIC3289 to a switch, a capacitor and a pull down resistor.

Is it safe to say then that it needs a microcontroller to drive the FAN5345 chip?

 

[(*steve*)]

Disconnect everything from pin 4. It should remain turned on like that.

Dimming is just done with PWM, this device has 2 brightness levels, on and off.

And explain pin 0 on your schematic.

 

[OLIVE2222]

The datasheet talk about digital pulses, so a microcontroller will be better, with a push-button you can have bouncess

 

[lechik86]

Disconnect everything from pin 4. It should remain turned on like that.

Dimming is just done with PWM, this device has 2 brightness levels, on and off.

And explain pin 0 on your schematic.

The actual chip doesn't have a pin 0. That schematic that has a pin 0 came from the application sheet of FAN5345.

 

[lechik86]

The datasheet talk about digital pulses, so a microcontroller will be better, with a push-button you can have bouncess

I am trying to eliminate switch bounce by connecting a 0.1uF capacitor.

 

[OLIVE2222]

sure you can try that, or any more elaborate debouching circuit.