NFC programming for LEDs using a PWM output to control analog LED-drivers: Page 4 of 5

September 04, 2019 //By Dr. Qi Zhu
NFC programming
In the LED market, more and more LED power suppliers to offer two novel functions: near-field communication (NFC) programming and constant lumen output (CLO). The NFC programming function is designed to replace the labor-intensive “plug-in resistor” current setting method to improve the flexibility across the value chain.

The PWM parameters

The pulse width modulation (PWM) signal consists of three main components that define its behavior: an amplitude, a duty cycle, and a frequency. The duty cycle describes the amount of time the signal is in a high (on) state as a percentage of the total time it takes to complete one cycle. The frequency determines how fast the PWM completes a cycle. A simple RC filter can convert the PWM signal to a DC voltage. The level of the DC voltage is

therefore adjustable by modifying the PWM amplitude or the PWM duty cycle and can be calculated as follows:

Vtarget = DC × (Voh-Vol) + Vol

Where DC is the duty cycle of the PWM, Voh is the high voltage of the PWM output, and Vol is the low voltage of PWM output. Since the stability of the PWM signal has a direct influence on the tolerance level of the finished LED power supply, it is important to evaluate the tolerance requirement and the NFC IC capability at an early design stage. The critical NFC IC parameters are the duty cycle and the absolute PWM amplitude (Voh - Vol).

The products in the NFC-PWM series generate a PWM signal with a fixed amplitude at 2.8 V. Thanks to the integrated voltage re/gulator (LDO), the level and the stability of the external supply voltage does not influence the PWM amplitude. The duty cycle can be configured between 0% - 100% with an accuracy level better than 0.1 percent. The PWM resolution depends on the selected PWM frequency: 15 bit at 1 kHz or 10 bit at 30 kHz.

Therefore, with Infineon’s new NFC-PWM series, customers can achieve the required tolerance level without any significant design efforts. An extreme low tolerance level can be achieved by adding an in-production calibration step into the production test.

Design category: 

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