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ACT4514 Datasheet(PDF) 5 Page - Active-Semi, Inc |
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ACT4514 Datasheet(HTML) 5 Page - Active-Semi, Inc |
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5 / 16 page  ACT4514 Rev 1, 21-Jul-11 Active-Semi Innovative Power TM - 5 - www.active-semi.com Copyright © 2011 Active-Semi, Inc. FUNCTIONAL BLOCK DIAGRAM FUNCTIONAL DESCRIPTION CV/CC Loop Regulation As seen in Functional Block Diagram, the ACT4514 is a peak current mode pulse width modulation (PWM) converter with CC and CV control. 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. 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 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 0.808V reference. If FB is lower than the reference voltage, COMP tends to go higher to increase current to the output. Output current will increase until it reaches the CC limit set by the ISET resistor. At this point, the device will transition from regulating output voltage to regulating output current, and the output voltage will drop with increasing load. The Oscillator normally switches at 200kHz. However, if FB voltage is less than 0.6V, then the switching frequency decreases until it reaches a typical value of 30kHz at VFB = 0.15V. Enable Pin The ACT4514 has an enable input EN for turning the IC on or off. The EN pin contains a precision 0.8V comparator with 75mV hysteresis and a 4µA pull-up current source. The comparator can be used with a resistor divider from VIN to program a startup voltage higher than the normal UVLO value. It can be used with a resistor divider from VOUT to disable charging of a deeply discharged battery, or it can be used with a resistor divider containing a thermistor to provide a temperature-dependent shutoff protection for over temperature battery. The thermistor should be thermally coupled to the battery pack for this usage. If left floating, the EN pin will be pulled up to roughly 5V by the internal 4µA current source. It can be driven from standard logic signals greater than 0.8V, or driven with open-drain logic to provide digital on/off control. Thermal Shutdown The ACT4514 disables switching when its junction temperature exceeds 155°C and resumes when the temperature has dropped by 20°C. EN FB BANDGAP, REGULATOR, & SHUTDOWN CONTROL + - OSCILLATOR VREF = 0.808V EMI CONTROL PWM CONTROLLER CC CONTROL SW HSB IN AVIN PVIN COMP ISET VREF = 0.808V |
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