How to suppress backlight drive interference in HMI (Human Machine Interface)?

Suppressing interference in HMI backlight drivers requires design consideration of their switching mode characteristics. LED backlight drivers typically employ Boost or Buck-Boost topologies, with switching frequencies ranging from tens to hundreds of kHz, making switching noise a major source of interference. Firstly, a large-capacity electrolytic capacitor, such as 100μF/25V, should be placed at the input Vin terminal of the driver chip to provide low-frequency current and suppress input voltage ripple. A parallel RC snubber circuit on the path from the switching node (SW) to ground can absorb switching voltage spikes and reduce high-frequency radiation. At the driver output, where the LED anodes are connected in series, a power bead, such as PBZ2012E102Z0T, can be added to form an LC filter with the output capacitor, smoothing the output current.

If the PWM dimming signal line is long, twisted-pair or shielded cable should be used, with a resistor, such as 100Ω, connected in series near the driver chip to reduce edge noise. The backlight driver circuit should be placed in a separate area on the PCB, away from analog and high-speed digital signals, and isolated using grounded copper foil. The ground wire of the drive circuit should be thick and short, and connected to the power supply ground at a single point to prevent noise from polluting other circuits through the ground wire. For high-voltage backlight drives, attention should be paid to the shielding of the transformer or inductor. Select the PBZ series power beads from Etymotic, whose high saturation current characteristics are suitable for backlight drive output filtering, effectively suppressing switching frequency and its harmonic noise.