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RT8532GQW Datasheet(PDF) 11 Page - Richtek Technology Corporation |
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RT8532GQW Datasheet(HTML) 11 Page - Richtek Technology Corporation |
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11 / 14 page  11 RT8532 DS8532-04 January 2014 www.richtek.com © Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. Brightness Control The RT8532 features the digital dimming control scheme. A very high contrast ratio true digital PWM dimming can be achieved by driving PWM pin with a PWM signal and the recommended PWM frequency is 100Hz to 10kHz. Dimming frequency can be sufficiently adjusted from 100Hz to 20kHz. However, LED current cannot be 100% proportional to duty cycle especially for high frequency and low duty ratio because of physical limitation caused by inductor rising time. Please refer to Table 1 and Table2. Dimming Frequency (Hz) Duty (Min) Duty (Max) 100 < fPWM 200 0.18% 100% 200 < fPWM 500 0.18% 100% 500 < fPWM 1k 0.2% 100% 1k < fPWM 2k 0.2% 100% 2k < fPWM 5k 0.3% 100% 5k < fPWM 10k 0.3% 100% 10k < fPWM 20k 0.6% 100% Dimming Frequency (Hz) Duty (Min) Duty (Max) 100 < fPWM 200 0.02% 100% 200 < fPWM 500 0.02% 100% 500 < fPWM 1k 0.04% 100% 1k < fPWM 2k 0.06% 100% 2k < fPWM 5k 0.15% 100% 5k < fPWM 10k 0.3% 100% 10k < fPWM 20k 0.6% 100% Table 1. Mixed Dimming Mode Table 2. PWM Dimming Mode Note : The minimum duty in Table 1 and Table 2 is based on the application circuit and does not consider the deviation of current linearity when fPWM > 10kHz, ILED may not achieve setting current in duty (min.) due to different VOUT / VIN ratio at VIN = 12V. Over Temperature Protection The RT8532 includes an Over Temperature Protection (OTP) feature to prevent overheating due to excessive power dissipation from damaging the device. The OTP function will shut down LED driver when the junction temperature exceeds 150 °C. It will reactivate the device when powered on again. To maintain continuous operation, the junction temperature should be kept below 125 °C. LED Driver Over Voltage Protection The LED driver equips an Over Voltage Protection (OVP) function. When the voltage at the OVP pin reaches a threshold of approximately 1.2V, the driver will turn off. The drivers turn on again once the voltage at OVP drops below the threshold voltage. Thus, the output voltage can be clamped at a certain voltage level. This voltage level can be calculated by the following equation : OVP2 OUT, OVP OVP OVP1 R VV 1 R where ROVP1 and ROVP2 are the resistors in the voltage divider connected to the OVP pin. It is suggested to use 500k Ω for ROVP2 to reduce loading effect. LED Channel Open Circuit Protection If at least one channel is in normal operation, the LED driver will automatically ignore the open channels and continue to regulate current for the channels in normal operation. Under Voltage Lockout (UVLO) The UVLO circuit compares the LED driver input voltage at VIN with the UVLO threshold to ensure the input voltage is high enough for reliable operation. The 200mV (typ.) hysteresis prevents supply transients from causing a shutdown. Once VIN exceeds the UVLO rising threshold, the LED soft-start will begin after a several ms delay. When VIN falls below the UVLO falling threshold, the controller turns off all LED driver functions. |
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