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MP1475 датащи(PDF) 10 Page - Monolithic Power Systems |
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MP1475 датащи(HTML) 10 Page - Monolithic Power Systems |
10 / 16 page MP1475 – SYNCHRONOUS STEP-DOWN CONVERTER MP1475 Rev. 1.01 www.MonolithicPower.com 10 4/3/2014 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. Figure 3 : Adjustable UVLO Internal Soft-Start The soft-start prevents the converter output voltage from overshooting during startup. When the chip starts, the internal circuitry generates a soft-start voltage (VSS) that ramps up from 0V to 1.2V. When VSS is less than VREF, the error amplifier uses VSS as the reference. When VSS exceeds VREF, the error amplifier uses VREF as the reference. The SS time is internally set to 1.2ms. Power Good Indicator MP1475 has an open drain pin as the power- good indicator (PG). Pull this up to VCC or another external source through a 100kΩ resistor. When VFB exceeds 90% of VREF, PG switches goes high with 0.4ms delay time. If VFB goes below 85% of VREF, an internal MOSFET pulls the PG pin down to ground. The internal circuit keeps the PG low once the input supply exceeds 1.2V. Over-Current-Protection and Hiccup The MP1475 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 MP1475 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 MP1475 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 4). If (VIN-VSW) exceeds 5V, U1 will regulate M1 to maintain a 5V BST voltage across C4. A 20Ω resistor placed between SW and BST cap. is strongly recommended to reduce SW spike voltage. VIN D1 5V M1 U1 BST C4 SW L1 VOUT C2 R3 Figure 4: Internal Bootstrap Charging Circuit Startup and Shutdown If both VIN and VEN exceed their respective thresholds, the chip starts. The reference block starts first, generating stable reference voltage and currents, and then the internal regulator is enabled. The regulator provides a stable supply for the remaining circuitries. Three events can shut down the chip: VEN low, VIN low, and thermal shutdown. During the shutdown procedure, the signaling path is first blocked to avoid any fault triggering. The COMP voltage and the internal supply rail are then pulled down. The floating driver is not subject to this shutdown command. |
Аналогичный номер детали - MP1475 |
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Аналогичное описание - MP1475 |
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