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ACT2102 Datasheet(PDF) 5 Page - Active-Semi, Inc |
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ACT2102 Datasheet(HTML) 5 Page - Active-Semi, Inc |
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5 / 17 page  ACT2102 Rev 2, 23-May-12 ® Innovative PowerTM - 5 - www.active-semi.com Copyright © 2012 Active-Semi, Inc. FUNCTIONAL BLOCK DIAGRAM FUNCTIONAL DESCRIPTION As seen in Function Block Diagram, the ACT2102 is peak current mode controlled synchronous Buck converter. The converter operates as follows: A switching cycle starts when the rising edge of the Oscillator clock output causes the High-Side Power Switch to turn on and the Low-Side Power Switch to turn off. With the SW side of the inductor now connected to IN, the inductor current ramps up to store energy in the magnetic field. The inductor current level is measured by the Current Sense Amplifier and added to the Oscillator ramp signal. If the resulting summation is higher than the COMP voltage, the output of the PWM Comparator goes high. When this happens or when Oscillator clock output goes low, the High-Side Power Switch turns off and the Low-Side Power Switch turns on. The High-Side Power Switch is driven by logic using HSB as the positive rail. This pin is charged to VSW + 5V when the Low-Side Power Switch turns on. The COMP voltage is the integration of the error between FB input and the internal 0.923V reference. If FB is lower than the reference voltage, COMP tends to go higher to increase current to the output to keep the output voltage regulated. The Oscillator normally switches at 310kHz. Pulse Skipping Mode To decrease the power recycling at very light load, the low-side FET current is sensed to emulate a diode. When the low-side FET current decreases to zero, the FET is turned off to avoid negative inductor current. At no load and very light load, ACT2102 skips pulse automatically and thus achieve very high light load efficiency. With load increasing, ACT2102 goes into Discontinuous Current Mode (DCM) and then Continuous Current Mode (CCM). Soft Startup The ACT2102 builds in internal soft startup function. The internal FB reference voltage rises to steady state of 0.923V in 2ms to avoid inrush input current during startup. Under Voltage Protection (UVP) At output short circuit or over current, the FB voltage is usually pulled low. To protect the IC at over current and short circuit, the ACT2102 builds in Under Voltage Protection (UVP) function. When ACT2102 detects the FB voltage below 80% of the 0.923V reference, it pulls low COMP voltage and discharges internal soft-start capacitor and goes into hiccup mode. The IC restarts in 32ms after going into hiccup mode. If the short circuit or over current is clear, the IC restarts back to normal mode. The UVP is disabled for 6ms starting from startup. If the output is short at startup, the output voltage never rises to nominal voltage. During the 6ms period of time, the output current is limited by cycle-by-cycle current limit. With 32ms shutdown period, the average input and output current at short circuit is significantly reduced and the IC is more reliable. |
Similar Part No. - ACT2102_14 |
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Similar Description - ACT2102_14 |
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