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LC5710S Fiches technique(PDF) 11 Page - Sanken electric |
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LC5710S Fiches technique(HTML) 11 Page - Sanken electric |
11 / 42 page LC5710S DATA SHEET Rev.1.9 Copy Right: SANKEN ELECTRIC CO., LTD. Page.11 LED string current is detected by the current detection resistor, RCS. The voltage of RCS is detected by both CSP and CSN pins. This IC compares this voltage with the Current Detection Voltage, VCS, and makes a target value for current control. The constant current is controlled so that the detection voltage of peak current of internal power MOSFET is close to the target value, and thus the LED string current is constant. The constant current of LED string, IOUT, is calculated by the following with RCS as the current detection resistor and ROVP as the resistor for overvoltage protection in the case that LED string is open. CS OVP CS CSN CS OUT R ) R R ( I V I ・・・(2) where; ICSN : the CSN Pin Sink Current, 9.5μA. VCS : the Current Detection Voltage, 100mV. Also, IOUT can be expressed by the following, if ICSN×(RCS+ROVP) is negligibly small against VCS. CS CS OUT R V I ・・・(3) ROVP value should be chosen so that IOUT is within the acceptable accuracy range referring to the calculation in “8.5 Overvoltage Protection Function (OVP)”. 8.3 LED Dimming 8.3.1 Analog dimming The dimming of LC5710S copes with both of Analog (the input of a DC voltage) and PWM-digital-Dimming. Though it is Analog-dimming first, there are relations of the fig.8(A),(B) in the input DC voltage of the DIM pin and the dimming-ratio. Moreover,Dimming by the Pull-down resistor RDIM is possible by using a internal current-source of the IC, too. The relations of the DIM pin voltage and RDIM are shown by the figure 8 (B). Dimming ratio is 100% when the DIM pin voltage is more than DC 2V. fig.8(A) DIM Pin voltage vs. LED Current fig.8(B) Pull-down resistor RDIM vs. DIM pin voltage fig.8I The connection of RDIM and remote ON/OFF application From the port of the microcomputer of the use and so on, and if the DIM pin of LC5710S is held continuously to the “Low” level,LC5710S continues suspension of a movement. The “Low level” voltage must be lower voltage than VDIM (OFF). For reverse logic, put one small signal Transistor as the fig8I. Though LC5710S doesn't have an exclusive "Remote ON/OFF pin", But,"Remote ON/OFF function" is as well as possible by using a DIM pin. |
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