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ACT4065 Datasheet(PDF) 4 Page - Active-Semi, Inc |
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ACT4065 Datasheet(HTML) 4 Page - Active-Semi, Inc |
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4 / 9 page  ACT4065 Figure 2. Functional Block Diagram FUNCTIONAL DESCRIPTION As seen in Figure 2, Functional Block Diagram, the ACT4065 is a current mode pulse width modulation (PWM) 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 its 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. At this point, the SW side of the inductor swings to a diode voltage below ground, causing the inductor current to decrease and magnetic energy to be transferred to output. This state continues until the cycle starts again. The High-Side Power Switch is driven by logic using BS bootstrap pin as the positive rail. This pin is charged to VSW + 6V when the Low- Side Power Switch turns on. The COMP voltage is the integration of the error between FB input and the internal 1.293V reference. If FB is lower than the reference voltage, COMP tends to go higher to increase current to the output. Current limit happens when COMP reaches its maximum clamp value of 2.55V. The Oscillator normally switches at 200kHz. However, if FB voltage is less than 0.7V, then the switching frequency decreases until it reaches a minimum of 50kHz at VFB = 0.5V. SHUTDOWN CONTROL The ACT4065 has an enable input EN for turning the IC on or off. When EN is less than 0.7V, the IC is in 8μA low current shutdown mode. When EN is higher than 1.3V, the IC is in normal operation mode. EN is internally pulled up with a 2μA current source and can be left unconnected for always-on operation. Note that EN is a low voltage input with a maximum voltage of 6V; it should never be directly connected to IN. THERMAL SHUTDOWN The ACT4065 automatically turns off when its junction temperature exceeds 160°C. Active-Semi, Inc. - 4 - www.active-semi.com IN EN COMP FB BS SW REGULATOR & REFERENCE OSCILLATOR & RAMP + – + – + – + – PWM COMPARATOR LOGIC THERMAL SHUTDOWN G 2μA ENABLE ERROR AMPLIFIER 1.293V FOLDBACK CONTROL 0.2Ω HIGH-SIDE POWER SWITCH 8Ω LOW-SIDE POWER SWITCH CURRENT SENSE AMPLIFIER |
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