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LD7832GS Datasheet(PDF) 11 Page - Leadtrend Technology |
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LD7832GS Datasheet(HTML) 11 Page - Leadtrend Technology |
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11 / 16 page  LD7832 11 Leadtrend Technology Corporation www.leadtrend.com.tw LD7832-DS-00 April 2013 ZCD Lower Clamp UVP Level t ZCD UVP Tripped t OUT Switching Switching Non-Switching Inductor Voltage t Upper Clamp Vcc t LED Shorted Vout ZCD UVP Delay Time -Vin UVLO(on) UVLO(off) VD+VRS GND ZCD UVP Delay Time CSSP Blacking Time 4 times Hiccup Fig. 5 Over Current Protection (OCP) The LD7832 detects the MOSFET current from the CS pin, which is for the pulse-by-pulse current limit and output current feedback. The maximum voltage threshold of the CS pin is set at 1.0V. From above, the MOSFET peak current can be obtained from below. S ) MAX ( PEAK R V 0 . 1 I CS Short Protection (CSSP) – Auto Recovery In order to prevent the LED driver from damage due to the shorted sense resistor (Rs), CS pin is built in with CSSP protection. See Fig. 6. Once the fault condition occurs, the CS voltage will drop to GND level instantaneously and it will enable the protection with CSSP delay time to avoid the false-trigger. When VCC achieves the UVLO(on), the LD7832 will start the CSSP blanking time to ignore CSSP function to pass the start-up transient. t OUT Switching Switching Non-Switching VRS t Vcc t RS Shorted VRS_PEAK CSSP Delay Time UVLO(on) UVLO(off) CSSP Delay Time CSSP Blacking Time CSSP Level CSSP Tripped 4 times Hiccup Fig. 6 Over Voltage Protection (VCC OVP) The maximum rating of the VCC pin is limited below 30V. To prevent VCC from damage due to fault condition, the LD7832 is implemented with OVP function on VCC pin. As soon as the VCC voltage is over OVP threshold voltage, the output gate drive circuit will be shutdown simultaneously thus to stop the switching of the power MOSFET until the next UVLO(on) arrives. The VCC OVP function of the LD7832 is an auto-recovery protection. The Fig. 7 shows its operation. Upon removal of the OVP condition will resume the VCC level and the output operation VCC UVLO(on) UVLO(off) t OVP Tripped t OUT Switching Switching Non-Switching OVP Level Fig. 7 |
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