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SC5014 Datasheet(PDF) 15 Page - Semtech Corporation |
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SC5014 Datasheet(HTML) 15 Page - Semtech Corporation |
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15 / 34 page  SC5014 5 Applications Information (continued) The SC504 has a unique DAC architecture which allows it to have excellent LED current accuracy and string-to-string matching over the entire DAC range. The analog dimming method can be used in conjunction with PWM dimming to increase the dimming resolution. The fast loop response of the SC504 allows the LED current to transition to a new value within 60µs or so. Please refer to the graphs in the typical characteristics section. LED PWM Dimming Control The SC504 supports three PWM dimming modes for controlling the brightness of the LEDs. The dimming modes are: () PWM direct, (2) PWM indirect and (3) I2C control It provides flexibility in setting the duty cycle and fre- quency of the LED PWM signal. The PWM dimming mode is set through the device control register (register address: 0x0) DCR [:0] bits. Refer to Table for more details. (1) PWM Direct Control The PWM input needs to be held high for normal opera- tion. PWM dimming can be achieved by cycling the PWM input at a given frequency where a “low” on the PWM input turns off all IO current sinks and a “high” turns on all IO current sinks. The PWM pin can be toggled by external circuitry to allow PWM dimming. In a typical application, a microcontroller sets a register or counter that varies the pulse width on a GPIO pin. The SC504 allows dimming over a wide frequency range (00Hz-30kHz) in order to allow compatibility with a wide range of devices. This includes the newest dimming strategies that avoid the audio band by using high frequency PWM dimming. In this manner, a wide range of illumination can be gener- ated while keeping the instantaneous LED current at its peak value for high efficiency and color temperature. The SC504 provides a 000: dimming range at kHz PWM frequency. The LED current sinks turn on/off very rapidly (<25ns, typical). This allows a wide dimming ratio. An addi- tional advantage of PWM dimming is that it avoids in-rush currents when filling the boost output capacitor. Simply apply the PWM signal to the device at 0% duty for a milli- second or two, and in-rush current is reduced. This dimming time will vary based on the number of LEDs and the size of the output capacitor. This can be easily deter- mined during testing and programmed into the microcon- troller firmware. Table 1 — LED Dimming Control Methods PWM Dim- ming Mode Register Settings DCR[1:0] PWM Input Source LED PWM Output Phase Shift Option PWM Frequency PWM Duty Cycle PWM Direct Control 00 PWMI Pin Input Same as the PWMI Input (Range 00 Hz to 30kHz) Same as the PWMI Input NO PWM Indirect Control (Default Option) 0 PWMI Pin Input Set via the FREQ Register (0x05) and FAST_FREQ Bit 0kHz (max): FAST_FREQ=0 20kHz (max): FAST_FREQ= Same as the Duty Cycle of the PWM Input YES I2C Control I2C Control Set via the FREQ Register (0x05) and FAST_FREQ bit 0kHz (max): FAST_FREQ=0 20kHz (max): FAST_FREQ= Set Via the Duty Cycle Control Register (0x03, 0x04) 0-Bits @ 0kHz Output 9-Bits @ 20kHz Output YES |
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