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MP2234S Scheda tecnica(PDF) 12 Page - Monolithic Power Systems |
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MP2234S Scheda tecnica(HTML) 12 Page - Monolithic Power Systems |
12 / 19 page MP2234S – SYNCHRONOUS STEP-DOWN CONVERTER MP2234S Rev.1.0 www.MonolithicPower.com 12 4/3/2015 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. network minimizes the external component counts and simplifies the control loop design. Enable/SYNC Control EN/SYNC is a digital control pin that turns the regulator on and off. Drive EN high to turn on the regulator; drive it low to turn it off. An internal 1MΩ resistor from EN/SYNC to GND allows EN/SYNC to be floated to shut down the chip. The EN/SYNC pin is clamped internally using a 6.5V series-Zener-diode (see Figure 4). Connecting the EN/SYNC input pin through a pull-up resistor to the voltage on the IN pin limits the EN input current to less than 100µA. For example, with 12V connected to IN, RPULLUP ≥ (12V – 6.5V) ÷ 100µA = 55kΩ. Connecting the EN pin directly to a voltage source without any pull-up resistor requires limiting the amplitude of the voltage source to ≤6V to prevent damage to the Zener diode. Figure 4. 6.5V Zener Diode Connection For external clock synchronization, connect a clock with a frequency range between 300kHz and 2MHz 2ms after the output voltage is set: The internal clock rising edge will synchronize with the external clock rising edge. Select an external clock signal with a pulse width less than 1μs. Under-Voltage Lockout (UVLO) The MP2234S has under-voltage lock-out protection (UVLO). When the VCC voltage exceeds the UVLO rising threshold voltage, the device begins to power-up. It shuts off when the VCC voltage drops below the UVLO falling threshold voltage. This is non-latch protection. The MP2234S is disabled when the input voltage falls below 3.2V (Typ). If an application requires a higher under-voltage lockout (UVLO) threshold, use the EN pin to adjust the input voltage UVLO by using two external resistors (see Figure 5). For best results, set the UVLO falling threshold (VSTOP) above 4.5V using the enable resistors. Set the rising threshold (VSTART) to provide enough hysteresis to allow for input-supply variations. RENUP RENDOWN Figure 5 . Adjustable UVLO Soft-Start (SS) 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. 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 0.804V reference. Then the non-inverting amplifier takes the reference voltage as the input. Use the following equation to calculate the soft-start time: SS 0.804V Css(nF) t(ms) 11 A × = μ Over-Current-Protection (OCP) and Hiccup The MP2234S 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 MP2234S 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 MP2234S exits the hiccup mode once the over- current condition is removed. |
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