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MP2115 Datasheet(PDF) 8 Page - Monolithic Power Systems |
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MP2115 Datasheet(HTML) 8 Page - Monolithic Power Systems |
8 / 11 page MP2115 – 2A, 6V SYNCHRONOUS STEP-DOWN CONVERTER MP2115 Rev. 1.0 www.MonolithicPower.com 8 2/28/2011 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2011 MPS. All Rights Reserved. OPERATION The MP2115 is a constant frequency current mode PWM step-down converter. The MP2115 is optimized for low voltage, USB port and Li- Ion battery powered applications where high efficiency and small size are critical. The MP2115 uses an external resistor divider to set the output voltage from 0.6V to 6V. The device integrates both a main switch and a synchronous rectifier, which provides high efficiency and eliminates an external Schottky diode. The MP2115 can achieve 100% duty cycle. The duty cycle D of a step-down converter is defined as: % 100 V V % 100 f T D IN OUT OSC ON × ≈ × × = Where TON is the main switch on time, and fOSC is the oscillator frequency. Current Mode PWM Control Slope compensated current mode PWM control provides stable switching and cycle-by-cycle current limit for superior load and line response. This protects the internal main switch and synchronous rectifier. The MP2115 switch is programmable from 0.7MHz to 2MHz. During each cycle the PWM comparator modulates the power transferred to the load by changing the inductor peak current based on the feedback error voltage. During normal operation, the main switch is turned on for a certain time to ramp the inductor current at each rising edge of the internal oscillator, then switched off when the peak inductor current rises above the error voltage. When the main switch is off, the synchronous rectifier will turn on immediately and stay on until the next cycle starts. Dropout Operation The MP2115 allows the main switch to remain on for more than one switching cycle and increases the duty cycle when the input voltage drops close to the output voltage. When the duty cycle reaches 100%, the main switch continuously delivers current to the output up to the PFET current limit. The output voltage is the input voltage minus the voltage drop across the main switch and the inductor. Short Circuit Protection The MP2115 has short circuit protection. When the output is shorted to ground, the oscillator frequency is reduced to prevent the inductor current from increasing beyond the PFET current limit. The PFET current limit is also reduced to lower the short circuit current. The frequency and current limit will return to the normal values once the short circuit condition is removed and the feedback voltage reaches 0.6V. Maximum Load Current The MP2115 can operate down to a 2.8V input voltage; however the maximum load current decreases at lower input due to a large IR drop on the main switch and synchronous rectifier. The slope compensation signal reduces the peak inductor current as a function of the duty cycle to prevent sub-harmonic oscillations at duty cycles greater than 50%. Conversely the current limit increases as the duty cycle decreases. Programmable Input Current Limit The MP2115 has an input current limit protection function. It will insure that the input current doesn't exceed the maximum, when the input is supplied by the USB. Once the input current triggers the set current limit level, the output voltage will shut down and latch off until the input is reset. The input current limit resistor R5 value can be found from Table 1. Table 1—Resistor Selection vs. Input Current Setting VIN (V) VOUT (V) IOUT (A) R5 (kΩ) 5 3.8 0.2 47.2 0.3 33.3 0.4 25.75 0.45 23.29 0.5 24.9 |
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