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AL8807 Datasheet(PDF) 9 Page - Diodes Incorporated |
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AL8807 Datasheet(HTML) 9 Page - Diodes Incorporated |
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9 / 21 page  AL8807 Document number Applicatio The AL8807 i packages tha currents/smalle temperature ra AL8807 Ope In normal ope sense resistor voltage +Vin a This rising cur applies a prop When this volt flow through R determined by This decaying voltage across the internal sw sense resistor LED Current The LED curre Connected bet I LED For example fo = V 1 R DC Dimming Further contro the average LE LED I = With 0.5V ≤ VC 2.5V, the LED When the CTR r: DS35281 Rev. 4 on Informat is a hysteretic t provide a P er PCBs that ange. eration ration, when v r R1, inductor L and the inducto rrent produces ortional voltage tage reaches a R1, L1, the LED y the forward vo current produ s R1 is applied witch is turned R1. t Control ent is controlled tween VIN and 1 R V THD = or a desired LE ≈ = 66 . 0 1 . 0 I V LED THD g l of the LED cu ED current bec SET THD REF CTRL R V V V = CTRL ≤ 2.5V the current will be RL voltage falls - 2 tion c (also known PCB area-pow the MSOP-8E voltage is appli L1, and the LE r L1. a voltage ram e to the input o an internally set Ds and the sc oltage drop of t ces a falling v at the input of on again. This d by the resisto SET the nomin ED current of 66 Ω ≈ m 150 urrent can be a comes: e LED current clamped to ap s below the thre HIGH E ww as equal ripp wer dissipation EP version is u ed at +VIN, the EDs. The curre mp across R1. T of the internal c t upper thresho hottky diode D the LEDs and t voltage at R1, w the internal co s switch-on-an or R1 in Figure Fig. 30 Typic nal average ou 60mA and a de chieved by driv varies linearly pproximately 10 eshold, 0.4V, th FFICIENCY 9 of 21 ww.diodes.com ple) LED drive n capability co used to maxim e AL8807 inter ent ramps up l The internal ci comparator. old, the interna D1, and back to the schottky dio which is sense mparator. Whe d-off cycle con 30. cal Applicati utput current in efault voltage V ving the CTRL y with VCTRL, a 00% and follow he output switc Y LOW EM r with integrat ompromise. It mize the allowa rnal switch is t linearly, and th rcuit of the AL al switch is turn o the supply ra ode. ed by the AL88 en this voltage ntinues to prov on Circuit the LED(s) is d VCTRL=2.5V the pin with an ext as in figure 2. ws SET THD LED R V I = ch is turned off MI 36V 1A B ted power swit is recommen able LED curre turned on. Cur he ramp rate is L8807 senses t ned off. The ind ail, but it deca 807. A voltage falls to the inte vide the averag defined as: e resulting resis ternal voltage ( If the CTRL p . which allows P AL BUCK LED © Diodes tch. It is avail nded that at h ent over a wid rrent starts to f s determined b the voltage acr ductor current c ays, with the ra proportional to ernally set lowe ge LED curren stor is: (between 0.4V in is brought h PWM dimming. L8807 DRIVER June 2012 s Incorporated lable in two higher LED der ambient flow through by the input ross R1 and continues to ate of decay o the sense er threshold, nt set by the and 2.5V); higher than |
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