UCC28810EVM-003: Output Constant Current

Payal Dwivedi

Prodigy 50 points

Part Number: UCC28810EVM-003
Other Parts Discussed in Thread: UCC28811,

How do we get an output constant current , while opting for external dimming using UCC28811 IC in buck stage?

What is the relation between duty cycle of the applied PWM signal and the output current being supplied to LEDs?

over 2 years ago

0 Ray DiCecco over 2 years ago

TI__Genius 10755 points

Hello, I responded to this identical question in thread ID 1060700

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1060700/ucc28810evm-003-led-driver

I'm going to close this thread.

0 Payal Dwivedi over 2 years ago in reply to Ray DiCecco

Prodigy 50 points

Can you give the value of PWM external Duty Cycle to be given for the Output Current to be 60 mA, 150 mA, 700 mA respectively using UCC28810EVM-003.

0 Ray DiCecco over 2 years ago in reply to Payal Dwivedi

TI__Genius 10755 points

Hi Payal,

The UCC28810EVM-003 has a maximum output per string of 500mA, so you cannot get 700mA without changing components.

The output current current is inversely proportional to the duty cycle. 100% = 0mA, 0% = 500mA. So output current ~ 0.5A x (1-D)

0 Payal Dwivedi over 2 years ago in reply to Ray DiCecco

Prodigy 50 points

Hi Ray,

Can you tell the components that we need to change in UCC28810EVM-003, to get output current of 700 mA or any higher value .

0 Ray DiCecco over 2 years ago in reply to Payal Dwivedi

TI__Genius 10755 points

Use the calculator tool. Change the value in B13 on User Inputs tab: https://www.ti.com/lit/zip/sluc205

Ray

0 Payal Dwivedi over 2 years ago in reply to Ray DiCecco

Prodigy 50 points

Hi Ray,

Thanks for sharing the file.

How the change in frequency that changes the duty cycle varying the dimming level of LED, provide constant output current. Please briefly explain the concept of OUTPUT CONSTANT CURRENT generated in buck stage, using UCC28810EVM-003.

Also, how can we give software programmable instruction to the microcontroller( used as external source for PWM dimming in buck stage) , with dimming frequency and constant output current for generation of PWM waveform.

+1 Ray DiCecco over 2 years ago in reply to Payal Dwivedi

TI__Genius 10755 points

Hi Payal,

I think this reply to an older E2E post by a former colleague contains an excellent explanation of the current regulation in the buck stage:

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/134430/ucc28810evm-003-related-questions

To control dimming from a micro, you must supply a 0.72V to 1.3V, 200kHz - 1000kHz signal to J4-3/2. This table from UCC28810EVM-002 on the control signal is more complete than the one in -003

By providing PWM pulses to the Vsense pin, the UCC28811 is enabled/disabled. The output current (hence dimming) is controlled by the duty cycle of these PWM pulses. The duty cycle of that signal will scale the output current to a value relative to the maximum current. 0% duty cycle (or no PWM signal) is highest LED current (brightest), and 90% duty cycle is lowest current (dimmest).

Best Regards,

Ray

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UCC28810EVM-003: Output Constant Current