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MP2147 Fiches technique(PDF) 14 Page - Monolithic Power Systems |
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MP2147 Fiches technique(HTML) 14 Page - Monolithic Power Systems |
14 / 19 page MP2147 – 5.5V, 4A, 1.2MHz, COT, BUCK SWITCHER MP2147 Rev. 1.1 www.MonolithicPower.com 14 6/8/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2016 MPS. All Rights Reserved. Considering the internal circuit propagation time, the typical delay is 50ns. It means the inductor current still fall after the ZCD is trigger in this delay. If the inductor current falling slew rate is fast (Vo voltage is high or close to Vin), the low side MOSFET is turned off and inductor current may be negative. This phenomena will cause MP2147 can not enter DCM operation. If the DCM mode is required, the off time of low side MOSFET in CCM should be longer than 100ns. For example, Vin is 3.6V and Vo is 3.3V, the off time in CCM is 70ns. It is difficult to enter DCM at light load. And using smaller inductor can improve it and make it enter DCM easily. Enable When the input voltage exceeds the under- voltage lockout (UVLO) threshold—typically 2.55V—the MP2147 can be enabled by pulling the EN pin above 1.6V. Leaving EN pin floating or grounded will disable the MP2147. There is an internal 1MΩ resistor from the EN pin to ground. Mode Selection and Analog Voltage Dynamic Regulation MP2147 has programmable PWM and PFM work mode. When MODE/VCON is more than 1.2V, MP2147 enters PWM mode. When MODE/VCON is lower than 0.4V or floating, MP2147 enters PFM mode. PFM mode can achieve high efficiency by light-load operation. PWM mode can keep constant switch frequency and smaller Vo ripple, but it has low efficiency at light load. VCON (V) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 Figure 5: Reference Voltage change with VCON MP2147 can dynamic regulate output voltage by MODE/VCON pin to meet some situation need change output voltage directly. When MOED/VCON pin get an appropriate voltage value (from 0.6V to 1.1V), MP2147 will work with PWM mode and internal reference voltage changes smoothly to achieve a new output voltage without changing external resistor divider. When VCON function is enabled, set Ref voltage from 0.35V to 0.6V, the accuracy is 3% typically. When set Ref voltage from 0.1V to 0.35V, the accuracy is 10% typically. Detail Ref voltage calculation formula such as below: Ref(V)=0.985 VCON(V)-0.486 Soft-Start The MP2147 has a built-in soft-start that ramps up the output voltage at a constant slew rate that avoids overshooting at startup. The soft- start time is typically about 1.5ms. Pre-Bias Startup The MP2147 can start up with a pre-bias output voltage. If the internal SS voltage is lower than the FB voltage, the HS-FET and LS-FET remain off until the SS voltage crosses the FB voltage. Power-Good Indicator The MP2147 has an open drain with a 500kΩ pull-up resistor as a power-good (PG) indication. When the FB voltage exceeds 90% of the regulation voltage (0.6V), the PG pin is pulled up to VIN by the internal resistor. Otherwise the PG pin is pulled to ground by an internal MOSFET. The MOSFET has a maximum Rdson of less than 100Ω. Current Limit The MP2147 has a 6A min current limit for the HS-FET. When the HS-FET hits its current limit, the MP2147 enters hiccup mode until the current drops to prevent the inductor current from rising and possibly damaging the components. Short Circuit and Recovery The MP2147 enters short-circuit protection (SCP) mode when it hits the current limit, and tries to recover from the short circuit by entering hiccup mode. In SCP, the MP2147 disables the output power stage, discharges a soft-start capacitor, and then enacts a soft-start |
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