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L5107L-P16-T Datasheet(PDF) 6 Page - Unisonic Technologies |
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L5107L-P16-T Datasheet(HTML) 6 Page - Unisonic Technologies |
6 / 9 page L5107 Preliminary LINEAR INTEGRATED CIRCUIT UNISONICTECHNOLOGIESCO.,LTD 6 of 9 www.unisonic.com.tw QW-R125-026.A FUNCTIONAL DESCRIPTIOM The UTC L5107 DC-DC converter is based on a peak current mode PWM architecture which regulates the feedback voltage at 0.25V under normal operating conditions. The constant output current converter is the preferred method for driving LEDs. Figure 2 shows the typical application schematic. The UTC L5107 configured as a boost controller can allow for the design of multiple LEDs in series to help maintain color and brightness. The input voltage range of the UTC L5107 is very wide, from 6V to 45V. In addition, the LED current and the switching frequency can be programmed to a wide range of values through the external resistors for diffident LED systems. The UTC L5107 can also control the brightness of the LEDs through its PWMD pin. POWER TOPOLOGY Constant Output Current Controller The UTC L5107 as a peak current mode boost controller has been designed to provide a constant output current. In the boost configuration, the output can be set from VIN up to 100V. This LED driver features a built-in soft-start circuitry in order to prevent start-up surges. Other protection features include: * Current Limit (ILIMIT)-Current sensing for over current and overload protection * Over Voltage Protection (OVP)-Output over voltage protection to prevent operation above a safe upper limit * Under Voltage Lockout (UVLO)-UVLO designed to prevent operation at very low input voltages Setting the LED Current The current through the LED string is set by the resistor, RADJ. This value can be calculated using Equation 1: Eq. (1) ADJ LED R 0.25V I VDD VDD is an internal linear regulator power supply for the internal circuitry of the UTC L5107. A 10μF ceramic bypass capacitor is required at the VDD pin. This pin is for filtering only and should not connect an external load to this pin. Soft Start A soft start build in the boost switching converter is used to limit the inrush current from the line supply. The soft start delay can be set using the compensation capacitor (CCOMP in Figure 2). A 10nF ceramic capacitor will be OK at all operating conditions. Oscillator and Switching Frequency Selection In the UTC L5107, the switching frequency can be set by choosing the appropriate value for the resistor, RFS according to Equation 2: Eq. (2) 1.035 SW FS kHz F 7530 KΩ R Dithering The UTC L5107 has a feature which dithers the switching frequency by ±10%. The purpose of this dithering is to help achieve a spread spectrum of the conducted EMI noise. This can allow for an overall reduction in noise emission by approximately 10dB. LED Dimming The UTC L5107 of LED drivers can dim the brightness of the LED string. A PWM input signal of up to 500Hz can be applied to the PWMD pin (see Figure 2) to pulse the LED string ON and OFF. It is recommended to use PWM dimming signals above 120Hz to avoid any recognizable flicker by the human eye. PWM dimming is the preferred way to dim a LED in order to prevent color/wavelength shifting, as occurs with analog dimming. The output current level remains constant during each PWMD pulse. |
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