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MP2228 Datasheet(PDF) 9 Page - Monolithic Power Systems |
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MP2228 Datasheet(HTML) 9 Page - Monolithic Power Systems |
9 / 16 page MP2228 – SYNCHRONOUS STEP-DOWN CONVERTER MP2228 Rev. 1.1 www.MonolithicPower.com 9 8/20/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. OPERATION The MP2228 is a high-frequency, synchronous, rectified, step-down, switch-mode converter with built-in power MOSFETs. It offers a very compact solution that achieves a 2A continuous output current with excellent load and line regulation over a wide input supply range. The MP2228 operates in a fixed-frequency, peak-current–control mode to regulate the output voltage. An internal clock initiates a PWM cycle. The integrated high-side power MOSFET turns on and remains on until the current reaches the value set by the COMP voltage. When the power switch is off, it remains off until the next clock cycle starts. If, within 95% of one PWM period, the current in the power MOSFET does not reach the value set by the COMP value, the power MOSFET is forced off. Internal Regulator A 5V internal regulator powers most of the internal circuitries. This regulator takes VIN and operates in the full VIN range. When VIN exceeds 5.0V, the output of the regulator is in full regulation. When VIN is less than 5.0V, the output decreases, and the part requires a 0.1µF ceramic decoupling capacitor. Error Amplifier The error amplifier compares the FB pin voltage to the internal 0.807V reference (VREF) and outputs a current proportional to the difference between the two. This output current then charges or discharges the internal compensation network to form the COMP voltage, which controls the power MOSFET current. The optimized internal compensation network minimizes the external component counts and simplifies the control loop design. Under-Voltage Lockout (UVLO) The MP2228 has under-voltage lock-out protection (UVLO). When the VCC voltage exceeds the UVLO rising threshold voltage, the MP2228 powers up. It shuts off when the VCC voltage drops below the UVLO falling threshold voltage. This is non-latch protection. Soft-Start Adjust the soft-start time by connecting a capacitor from SS pin to ground. When the soft- start begins, an internal 11µA current source charges the external capacitor. During soft-start, the soft-start capacitor connects to the non- inverting input of the error amplifier. The soft- start period continues until the voltage on the soft-start capacitor exceeds the 0.8V reference. Then the non-inverting amplifier uses the reference voltage takes as the input. Use the following equation to calculate the soft-start time: SS 0.8V Css(nF) t(ms) 11 A × = μ Over-Current-Protection and Hiccup The MP2228 has a cycle-by-cycle over-current limit when the inductor current peak value exceeds the set current limit threshold. Meanwhile, the output voltage drops until VFB is below the Under-Voltage (UV) threshold— typically 50% below the reference. Once UV is triggered, the MP2228 enters hiccup mode to periodically restart the part. This protection mode is especially useful when the output is dead-shorted to ground, and greatly reduces the average short circuit current to alleviate thermal issues and protect the regulator. The MP2228 exits the hiccup mode once the over- current condition is removed. Thermal Shutdown Thermal shutdown prevents the chip from operating at exceedingly high temperatures. When the silicon die reaches temperatures that exceed 150°C, it shuts down the whole chip. When the temperature drops below its lower threshold, typically 130°C, the chip is enabled again. Floating Driver and Bootstrap Charging An external bootstrap capacitor powers the floating power MOSFET driver. This floating driver has its own UVLO protection. This UVLO’s rising threshold is 2.2V with a hysteresis of 150mV. The bootstrap capacitor voltage is regulated internally by VIN through D1, M1, R3, C4, L1 and C2 (Figure 2). If (VIN-VSW) |
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