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MP24183DQ Datasheet(PDF) 8 Page - Monolithic Power Systems |
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MP24183DQ Datasheet(HTML) 8 Page - Monolithic Power Systems |
8 / 12 page MP24183 – 1A, 55V, PROGRAMABLE FREQUENCY WHITE LED DRIVER MP24183 Rev. 1.0 www.MonolithicPower.com 8 8/28/2008 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2011 MPS. All Rights Reserved. OPERATION The MP24183 is a current mode regulator. The EA output voltage is proportional to the peak inductor current. At the beginning of a cycle, M1 is off. The EA output voltage is higher than the current sense amplifier output, and the current comparator’s output is low. The rising edge of the 1.35MHz CLK signal sets the RS Flip-Flop. Its output turns on M1 thus connecting the SW pin and inductor to the input supply. The increasing inductor current is sensed and amplified by the Current Sense Amplifier. Ramp compensation is summed to the Current Sense Amplifier output and compared to the Error Amplifier output by the PWM Comparator. When the sum of the Current Sense Amplifier output and the Slope Compensation signal exceeds the EA output voltage, the RS Flip- Flop is reset and M1 is turned off. The external Schottky rectifier diode (D1) conducts the inductor current. If the sum of the Current Sense Amplifier output and the Slope Compensation signal does not exceed the EA output for a whole cycle, then the falling edge of the CLK resets the Flip-Flop. The output of the Error Amplifier integrates the voltage difference between the feedback and the 0.198V reference. The polarity is a FB pin voltage lower than 0.198V increases the EA output voltage. Since the EA output voltage is proportional to the peak inductor current, an increase in its voltage also increases the current delivered to the output. Open LED Protection If the LED is open, there is no voltage on the FB pin. The duty cycle will increase until V(VDD)-V(VSS) reaches 55V or OVP-VSS reaches the shutdown threshold set by the external resistor divider. The top switch will turn off till the voltage V(VDD)-V(VSS) and OVP- VSS decreases sufficiently. Dimming Control The MP24183 allows both DC and PWM dimming. When the voltage on EN is less than 0.6V, the chip is turned off. For analog dimming, when the voltage on EN is from 0.7V to 1.4V, the LED current will change from 0% to 100% of the maximum LED current. If the voltage on EN pin is higher than 1.4V, maximum LED current will be generated. For PWM dimming, its amplitude (VDIM – VINGND) must exceed 1.4V. The PWM frequency is recommended in range of 100Hz to 2kHz to get a good dimming linearity. Output Short Circuit Protection The MP24183 integrates output short circuit protection. When the output is shorted to VSS, the voltage on OVP pin which detects the output voltage gets smaller than 0.4V, and FB pin senses no voltage (<0.1V) as no current goes through the WLED. At this condition, the operating frequency is folded back to decrease the power consumption. In Buck-boost application, when there is possibility that the LED+ short circuit to VSS, it is recommended to add a diode from VSS to INGND to protect the IC, as shown in below Figure 2 . Figure 2—Buck-boost Application When LED+ Possibly Short to VSS |
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