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ACE711E 데이터시트(PDF) 6 Page - ACE Technology Co., LTD. |
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ACE711E 데이터시트(HTML) 6 Page - ACE Technology Co., LTD. |
6 / 9 page ACE711E 2A, Step-Up DC/DC Regulator 20V VER 1.2 6 Output Open Circuit Protection Output open circuit protection circuitry prevents IC damage as the result of output open circuit (e.g. LED string absence). The ACE711E monitors the voltage at the SW pin and FB pin during each switching cycle. The circuitry turns off the switch FET and shuts down the IC when both of the following conditions persist for 8 switching clock cycles: (1) the SW voltage exceeds the VOVP threshold, which is 25V and (2) the FB voltage is less than half of regulation voltage. As a result, the output voltage falls to the level of the input supply. The device remains in shutdown mode until it is enabled by toggling the EN pin logic. The output voltage plus the 200mV reference voltage cannot exceed the minimum OVP threshold or OUTPUT VOLTAGE + 200 mV ≤ VOVP(MIN). Shutdown The ACE711E enters shutdown mode when the EN voltage is logic low for more than 2.5ms. During shutdown, the input supply current for the device is less than 1μA (max). Although the internal FET does not switch in shutdown, there is still a DC current path between the input and the output through the inductor and Schottky diode. For LED driving application, the minimum forward voltage of the LED array must exceed the maximum input voltage to ensure that the LEDs remain off in shutdown. However, in the typical application with two or more LEDs, the forward voltage is large enough to reverse bias the Schottky and keep leakage current low. Output Voltage Setting The FB voltage is regulated by a low 0.2V reference voltage. The output voltage is set externally by using a resistor divider. The value of the R1/R2 divider is calculated using Equation 1.1: VOUT =VFB/R2*(R1+R2) (1.1) Where VOUT = output voltage, R2 = resistance between FB and GND, R1 = resistance between OUT and FB. The output current tolerance depends on the FB accuracy and the current sensor resistor accuracy. LED Driving Current Setting The FB voltage is regulated by a low 0.2V reference voltage. The LED current is set externally using a current-sense resistor in series with the LED string. The value of the RSET is calculated using Equation 1.2: ILED =VFB/RSET (1.2) Where ILED = output current of LEDs, RSET = current sense resistor The output current tolerance depends on the FB accuracy and the current sensor resistor accuracy. |
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