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ACT4910QW Arkusz danych(PDF) 20 Page - Active-Semi, Inc |
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ACT4910QW Arkusz danych(HTML) 20 Page - Active-Semi, Inc |
20 / 34 page ACT4910QW Rev 1.0, 15-Sept-2017 Innovative PowerTM www.active-semi.com ActiveSwitcherTM is a trademark of Active-Semi Copyright © 2017 Active-Semi, Inc. 20 EFUSE General Description The ACT4910 eFuse is an “electronic” fuse that disconnects the input from the output. It has considerable advantages over mechanical fuses because it has adjustable current thresholds and it resets after the fault condition is gone. The eFuse consists of two back-to-back MOSFETS to provide bi- directional protection. This provides protection against both input and output short circuit conditions by preventing current flow in both directions. Hot swap functionality is provided by the eFuse softstart function and current limiting circuitry. This prevents large inrush currents from pulling down the input voltage. The eFuse also provides protection against high input voltage transients up to 24V by opening when the input voltage goes above the programmed threshold. The eFuse turns off in the following conditions. 1. EN voltage below UV threshold 2. EN voltage above the OV threshold 3. Input voltage above the OV threshold 4. eFuse current above the OC threshold 5. VIN – VOUT > 560mV Current Limit Setting A resistor connected between the ISET pin and VSS program the ACT4910 eFuse inrush and maximum DC current limits. The input current limit is linearly proportional to the resistor value on the ISET pin. The following equation calculates the correct resistor value to get the desired current limit threshold. Equation (1) Where RILIM is the current limit resistor in ohms and IILIM is the desired current limit threshold in Amperes. Figure 5 shows the current limit setting vs RILIM value. Figure 5: Current Limit Threshold vs RILIM Note that the eFuse current can be measured using the ILIM pin. If eFuse current is measured via the ILIM pin, the measurement circuit must have a high impedance input to minimize errors. The current flowing out of ILIM is 1/50000 of the current through the eFuse. The following equation calculates the eFuse current when measured via the ILIM pin. ∗ Equation (2) Where RILIM is the current limit resistor in ohms and VILIM is the voltage on the ILIM pin in volts. When the eFuse reaches the current limit threshold, it clamps the output current. If the load tries to draw additional current, the eFuse opens. Soft-Start The SS pin controls the eFuse start-up. The SS pin drives a constant 5μA internal current source into the external soft-start capacitor to provide a linear ramping voltage at the SS pin. The output voltage linearly ramps with the SS pin voltage, resulting in a well-controlled linear softstart ramp on VOUT, regardless of the load conditions. The following equation calculates the required soft-start capacitance. Equation 2 Where the TSS is the soft-start time in ms and VOUT is the output voltage. The softstart current must be less than 90% of the programmed eFuse current limit. If the softstart current is greater than 90% of the eFuse current limit, the IC enters the SHUTDOWN2 state, turns off the eFuse, and 0.000 2.000 4.000 6.000 8.000 10.000 12.000 14.000 0 102030405060 RISET (kΩ) |
Podobny numer części - ACT4910QW |
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Podobny opis - ACT4910QW |
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