US manufacturer Freescale Semiconductor has introduced the MC34845 LED driver for 10 to 17-inch LCD panels. The MC34845 is available in a 4 x 4 x 0.65mm 24-terminal QFN package that can drive six white LED strings. The maximum number of LEDs that can be connected to each white LED string is 16. Therefore, the total drive can be as many as 96 white LEDs.
The basic structure of the white LED driver circuit is a step-up DC-DC converter with a power MOSFET with a maximum output current of 2.0A. The input voltage range is +5.0 to 21V, and the output voltage is up to +60V. The current supplied to the LED string is in the range of 3.0m to 30mA, which can be adjusted with an external resistor. The supply current deviation between the LED strings is ±2%.
According to the switching frequency of the DC-DC converter, there are two products, the MC34845 of 600kHz and the MC34845A of 1.2MHz. A dimming function based on a 100 kHz PWM signal is also available. The dimming range is 50000:1. In addition, it has an LED open/short protection function, an overvoltage protection function that allows the user to set the threshold voltage, and a low voltage shutdown function. The current consumption when shutting down is up to 1μA.
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The basic structure of the white LED driver circuit is a step-up DC-DC converter with a power MOSFET with a maximum output current of 2.0A. The input voltage range is +5.0 to 21V, and the output voltage is up to +60V. The current supplied to the LED string is in the range of 3.0m to 30mA, which can be adjusted with an external resistor. The supply current deviation between the LED strings is ±2%.
According to the switching frequency of the DC-DC converter, there are two products, the MC34845 of 600kHz and the MC34845A of 1.2MHz. A dimming function based on a 100 kHz PWM signal is also available. The dimming range is 50000:1. In addition, it has an LED open/short protection function, an overvoltage protection function that allows the user to set the threshold voltage, and a low voltage shutdown function. The current consumption when shutting down is up to 1μA.
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