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MP2158A Folha de dados(PDF) 10 Page - Monolithic Power Systems |
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MP2158A Folha de dados(HTML) 10 Page - Monolithic Power Systems |
10 / 14 page MP2158A – 1A, 6V, 1.5MHz SYNCHRONOUS STEP-DOWN CONVERTER MP2158A Rev. 1.02 www.MonolithicPower.com 10 6/30/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2016 MPS. All Rights Reserved. OPERATION The MP2158A uses constant-on-time control with input voltage feed-forward control to stabilize the switching frequency over a full input range. During light loads, the MP2158A employs a proprietary control of low-side switches and inductor currents to eliminate ringing on the switching node and improve efficiency. Constant-On-Time Control When compared to the fixed-frequency PWM control, the constant-on-time control offers a simpler control loop and faster transient response. By using input voltage feed-forward, the MP2158A maintains a near constant switching frequency across the input and output voltage range. The on time of the switching pulse can be estimated using Equation (1): OUT ON IN V T0.667 s V (1) To prevent inductor current runaway during the load transient, the MP2158A sets the minimum off time to 60ns. This minimum off time limit does not affect the operation of the MP2158A in its steady state in any way. Light-Load Operation In a light-load condition, the MP2158A uses a proprietary control scheme to save power and improve efficiency. The MP2158A uses a zero current cross circuit to detect if the inductor current is starting to reverse. The low-side switch turns off when the inductor current starts to reverse and triggers discontinuous conduction mode (DCM) operation. The delay for the internal circuit propagation time is typically 50ns. This means that the inductor current continues falling after the ZCD is triggered in this delay. If the inductor current falling slew rate is too fast (VOUT is high or close to VIN), the low-side MOSFET turns off, the inductor current may be negative, and the MP2158A will not be able to enter DCM operation. If DCM is required, the off time of the low-side MOSFET in CCM should be longer than 100ns (2 times the propagation delay). For example, if VIN is 3.6V and Vo is 3.3V, the off time in CCM is 55ns. It is difficult to enter DCM at a light load. Using a smaller inductor can help the MP2158A enter DCM more easily. Enable When the input voltage is greater than the under-voltage lockout (UVLO) threshold (typically 2.3V), the MP2158A is enabled by pulling EN higher than 1.2V. Leaving EN floating or grounded disables the MP2158A. There is an internal 1MΩ resistor from EN to ground. Soft Start The MP2158A has a built-in soft start that ramps up the output voltage in a controlled slew rate, avoiding overshoot at start-up. The soft- start time is typically about 1.15ms. Power Good Indicator The MP2158A uses an open-drain with a 550kΩ pull-up resistor as a power good indicator (PG). When FB is within +/-10% of the regulation voltage (i.e. 0.6V), PG is pulled up to VIN by the internal resistor. If the FB voltage is out of the +/-10% window, PG is pulled to ground by an internal MOSFET. The MOSFET has a maximum Rdson of less than 400Ω. Current Limit The MP2158A has a 2A minimum current limit for the high-side switch. When the high-side switch hits its current limit, the MP2158A enters the hiccup threshold until the current drops. This prevents the inductor current from rising and possibly damaging the components. Short Circuit and Recovery The MP2158A enters short-circuit protection mode when the current limit is hit and tries to recover from the short circuit by entering hiccup mode. In short-circuit protection, the MP2158A disables the output power stage, discharges a soft-start capacitor, and automatically tries to soft start again. If the short-circuit condition still holds after the soft start ends, the MP2158A repeats this operation until the short circuit disappears and the output rises back to regulation level. |
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