• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Subscribers 64 subscribers
  • Views 1115 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

tlc 5971 typical app circuit

mahmut turk
Intellectual 300 points
Other Parts Discussed in Thread: TLC5971

Hello;

i am going to use tlc5971 in the design of a led screen. However i have some problems with the typical application circuits given in the datasheet. I intend to use the first application circuit in which internal linear regulator is used. My vcc is 12v and i will connect three leds in series per channel group and adjust the current as 40ma. The voltage across leds is 10,5v  maximum for 40ma current. For this application, is the third app circuit in datasheet more suitable or not? in the third app circuit, should vled be exactly 15v? And i wonder why there are many leds in series in third app circuit whereas in the first app circuit there is only one led in datasheet figures?

My last question is if i use the first application circuit in datasheet, is it enough to use the given passive circuit components (capacitors,resistors) in application circuit or should i put some extra components to make the circuit more stable/rigid/goodWorking?

Thanks for your replies.

  • 0
    TI__Intellectual 955 points

     Hello Mahmut,

     I think one of the third application advantage is saving power. For example, when LDO is used at 15V VCC, the power calculated by (VIN-VCC :15V-3.3V) * ICC (14mA but depend on conditions) is dissipated at LDO circuit.

     The other is the device input voltage range is 3.3V not 5V range when LDO is used. So if you want to input 5V range ligic signal into the first TLC5971 with higher LED anode side voltage (VLED) than 5.5V, you should use their application if LED anode side voltage (VLED) is higher than 5.5V. 

     I think the application is a example so you can change the number of LED connected in series depend on LED anode side voltage (VLED) as long as the device absolute maximum are not violated.

     I think the given passive components in the first application circuit is enough to work the device. But the capacitor placed between VCC and GND should be big to stabilize VCC voltage and to reduce noise. It may be better to use ceramic capacitor and electrolytic capacitors.

     Also I reccoment you to pay attention the wire thickness because the difference voltage between Nth of TLC5971 and N+1th TLC5971must be less than 0.3V.

     Best regards,

     Kazuya Nakai.

     

     

     

  • 0 in reply to Kazuya Nakai
    Intellectual 300 points

    Hello Kazuya,

    Thanks for your (really) immediate reply. I understand the LDO power dissipation and device input vaoltage range concepts.

    But i couldnt understand what you mean by saying "voltage difference should be less than 0.3 volt between tlc's that are in series". Is there any limitation about this in datasheet? And the voltage at which pin of tlc? By mentioning wire thickness, do you impress the importance of resistance of wire?

    Thank you.  

  • 0 in reply to mahmut turk
    TI__Intellectual 955 points

     Hello Mahmut,

     I'm sorry that my explanation was not enough.

     Yes, I wanted to say that the different voltage between N'th TLC5971 GND pin and N+1'th TLC5971 GND pin should be less than 0.3V because large difference voltage between the GND pins is generated when the wire registance and inductance of the GND wire are large. If N+1'th TLC5971 GND voltage is 0.3V higher than N'th one, N+1'th TLC5971 SDTI and SCKI, signal input pin voltage is lower than -0.3V when N'th TLC5971 SDTO and SCKO is 0V.  The voltage violates the device absolute max rating. 

    Best regards,

    Kazuya Nakai.

  • 0 in reply to Kazuya Nakai
    Intellectual 300 points

    Hello Kazuya;

    I will take your recommendations into consider. Thank you very much.

  • 0 in reply to Kazuya Nakai
    Prodigy 20 points

    Hi Kazuya,

    I am using TLC5971 for Driving RGB LED strips as Light Ring with perimeter of 200mm for Dimming and Alarm/Status Application. For my design requirement ,i have to drive atleast 12 LEDS in series per channel. This 12 LED series current (either R/G/B) will be around 58mA ( Current Limiting resistor set not exceed 60mA/Channel)

    The application circuit 3 in datasheet shows only three LEDs in series and One LED as optional. Is that maximum 4 LEDs in series i can drive?

    Can I use internal regulator as application for driving my design requirement. 

    There is note in datasheet  mentioning Number of series LEDS depends on VCC?

    Can you please explain in detail these constraints and share design calculations /recommendations for using Number of LEDs in series per channel.

    Thanks

    Sharath