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APL5332K Datasheet(PDF) 8 Page - Anpec Electronics Coropration |
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APL5332K Datasheet(HTML) 8 Page - Anpec Electronics Coropration |
8 / 17 page Copyright ANPEC Electronics Corp. Rev. A.3 - Oct., 2003 APL5332 www.anpec.com.tw 8 Functional Description General APL5332 is a source-sink linear regulator designed for motherboard front side bus. The device can supply loads from -1A to 2A in either fixed or adjustable volt- age mode. APL5332 has a 0.8V reference, an error amplifier, two pass transistors, fixed voltage selection, an internal feedback resistor-divider, soft-start control and fault protections(current-limit and thermal shutdown). The output voltage is either 1.225V or 1. 45V selected by the BS pin when fixed voltage mode is active by setting FB=VIN. When the FB is con- nected with a feedback resistor-divider, the IC oper- ates in adjustable voltage mode and the voltage of FB is regulated to 0.8V. In the mode, the input of BS pin is ignored. APL5332 is available in the SOP, SOP-8- P, and TO-252-5 packages to meet different power dissipation applications. Output Voltage Regulation The error amplifier working with the temperature-com- pensated 0.8V reference and the two pass transistors (high-side and low-side) regulates the output to the preset voltage. The error amplifier compares the refer- ence with the feedback voltage and amplifies the dif- ference to drive one of the pass transistors. The high- side pass transistor provides current from VIN to VOUT and increases the output voltage when the feedback voltage is lower than the reference. The low-side pass transistor provides current from VOUT to GND and de- creases the output voltage when the feedback voltage is higher than the reference. The two pass transistors are well controlled by the error amplifier and prevented short- through conditions. An internal output voltage sense pad is bonded to the VOUT pin for perfect load regulation in fixed voltage mode. Current Limit The APL5332 monitors the sourcing or sinking cur- rents and limits the maximum output current to pre- vent damages during overload or short-circuit conditions. Power-On-Reset and Soft-Start A Power-On-Reset circuit monitors input voltage of the VIN pin and prevents wrong logic controls. When the input voltage rises up more than the Power-On- Reset threshold voltage, the device starts to output current. Therefore, a soft-start circuit which controls the reference voltage to rise up is required, limiting surge input currents. The typical soft-start interval is about 1mS. Thermal Shutdown A thermal shutdown circuit limits the junction tem- perature of the APL5332. When the junction tempera- ture exceeds +150oC, a thermal sensor turns off the both pass transistors, allowing the device to cool down. The regulator starts to regulate again after the junction temperature cools by 25oC, resulting in a pulsed output during continuous thermal overload conditions. The thermal shutdown designed with a 25oC hysteresis lowers the average junction temperature during continuous thermal overload conditions, extend- ing life time of APL5332. For normal operation, device power dissipation should be externally limited so that junction temperatures will not exceed +125oC. |
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