TLC5940

Hello,

Basically, your circuit may work, but you should carefully choose ballast resistor in series with each LED, thus to make sure 350mA for each LED. Also should pay attention to the power rating of those ballast resistors.

One problem is: You short VPRG to ground, which means the data shifted in will always be latched to GS register, and the DC register have no chance be initialized. Since DC register value is random when power on, this may be an issue. You may change DCPRG connection from VCC to GND, thus the EEPROM data will be used as DC data. EEPROM data default is all '1', needn't be initialized.

Nowthat you use the output of TLC5940 as logic input for ULN2803, with VCC=5V and 10k pull up resistor used, then only 0.5mA sink current is needed for each output of TLC5940, this is out of the range of 5940 (5940 support output current 5mA~120mA).  You may change R4 to 7.8k, this set output current of each channel to 5mA. then choose pull up resistor (RN1 & RN2) at 5V/5mA=1k

Regards

Mike

Sorry, just notice I missed one point.

TLC5940 is designed to drive LED directly, it output a 'low' when need turn on LED. If you want use this output as logic signal to control UNL2803, then one additional inverter is need, such as 74HC04.

Regards

Mike

Thank you for your very full answer.

I'll make changes to VPRG and DCPRG.

Would a simpler scheme that using a ULN?
Looking for some days how to use a P MOSFET with TLC but nothing conclusive.

The thermal pad can  be connected to GND?

I want a circuit that takes time.

Again thank you

Yes, please connect thermal pad of 5940 to GND.

Thank you

Mike

Would a simpler way that using a ULN?
Looking for some days how to use a P MOSFET with TLC but nothing conclusive.

Sorry for my bad english ( I'm french ^^ )

Thank you

Hi Vadim,

It looks like you want to do something similar to what Levente is showing in this post:

http://e2e.ti.com/support/power_management/led_driver/f/192/p/334159/1166540.aspx#1166540

She was using the TLC59108 which is the 8-bit version of the TLC59116, but she has already proven the concept works.  Also, I would highly encourage you to consider TI NexFETs for this application. 

Best Regards,

Adam Hoover

Drivers and Load Switch Applications

Thnaks for your reply.

I will look at the position on the TLC59108.

I looked at the P MOSFET NexFET but they are all in a package small enough :/
Impossible to solder with a soldering iron.
Is what I can use that same post with the TLC59108 namely IRLML9301? 

Thank you very much.

Hello,

I saw you changed VPRG connection from GND to MCU output. It's good, now you can write both DC and GS data by toggle voltage level at VPRG.
As you keep DCPRG at high(choose DC register to control output current), pls remember initialize DC register before turn on channels, as I mentioned before.

Your connection about PMOS is NOT correct. See below my suggested connection.

consider VINSTRIP is 12V, with R26=R27=1k, we need sink current of each output is 6mA. R4 should be changed to 6.5k

Best regards

Mike

Thank you for the schematic, I changed mine.
I would still have some question.

First on the PINOUT of the MOSFET.

Gate = OUTn of TLC,
Source = VINSTRIP,
Drain = LED

That correct?

Else resistor R4. 6.5k is not very common as a reference. A 3.9K resistor may be work? What would a current of 10mA out.

Thank you for your reply

Hello,

Yes, your connction is correct.

For R4, how about 6.8k or 6.2k resistor if you think 6.49k is difficult to find.

3.9k is not acceptable.

Best regards

Mike

Why pin OUTx must have only 6mA?

I try to understand how does it work ^^

Thank you for your answers!

Hello,

6mA x 2kohm =12V. When channel turn on, OUTx pin will be 0V. The voltage accross Source and Gate of PMOS will be 6V, enough to turn on that PMOS.

Regards

Mike

Hello Mike,

I had a query on the schematic on this thread is that the LED is unable use the grey scale of TLC.

Please correct me if I'm wrong.

Regards,

Mrinal