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MP2162A 데이터시트(PDF) 11 Page - Monolithic Power Systems |
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MP2162A 데이터시트(HTML) 11 Page - Monolithic Power Systems |
11 / 17 page MP2162A – 2A, 6V, 1.5MHz SYNCHRONOUS STEP-DOWN CONVERTER MP2162A Rev. 1.03 www.MonolihicPower.com 11 6/30/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2016 MPS. All Rights Reserved. OPERATION The MP2162A uses constant-on-time control with an input voltage feed-forward to stabilize the switching frequency over a full input voltage range. During light loads, the MP2162A employs proprietary control of the low-side switches and inductor currents to eliminate ringing on the switching node and improve efficiency. Constant-On-Time Control Compared to the fixed frequency PWM control, the constant-on-time control offers the advantage of a simpler control loop and a faster transient response. By using input voltage feed-forward, the MP2162A maintains a near constant switching frequency across the input and output voltage ranges. The on time of the switching pulse can be estimated with Equation (1): OUT ON IN V T0.667 s V (1) To prevent inductor current runaway during the load transient, the MP2162A has a fixed minimum off time of 60ns. However, this minimum off time limit does not affect the operation of the MP2162A in its steady state in any way. Light-Load Operation In light-load conditions, the MP2162A uses a proprietary control scheme to save power and improve efficiency. The MP2162A 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 then begins working in discontinuous conduction mode (DCM). 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 fast (VOUT is high or close to VIN), then the low-side MOSFET turns off, the inductor current may be negative, and the MP2162A will not be able to enter DCM operation. If DCM mode is required, the off time of the low-side MOSFET in CCM should be longer than 100ns (2x 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 MP2162A enter DCM more easily. Enable (EN) When the input voltage is greater than the under- voltage lockout (UVLO) threshold (typically 2.3V), the MP2162A is enabled by pulling EN higher than 1.2V. Leaving EN floating or grounded disables the MP2162A. There is an internal 1MΩ resistor from EN to ground. Soft Start The MP2162A has a built-in soft start that ramps up the output voltage at a controlled slew rate to avoid overshooting at start-up. The soft-start time is typically about 1.15ms. Power Good Indicator The MP2162A uses an open drain with a 550kΩ pull-up resistor as a power good indicator (PG). When the FB voltage is within +/-10% of the regulation voltage (i.e. 0.6V), PG is pulled up to VIN by an internal resistor. If the FB voltage is out of the +/-10% window, PG is pulled down to ground by an internal MOSFET. The MOSFET has a maximum Rds(on) of less than 400Ω. Current Limit The MP2162A has a typical 3.2A current limit for the high-side switch. When the high-side switch hits its current limit, the MP2162A enters hiccup mode until the current drops. This prevents the inductor current from rising and possibly damaging the components. Short Circuit and Recovery The MP2162A enters short-circuit protection mode when the current limit is hit; it tries to recover from the short circuit by entering hiccup mode. In short-circuit protection, the MP2162A disables the output power stage, discharges a soft-start capacitor, and automatically tries to soft start. If the short-circuit condition still holds after the soft start ends, the MP2162A repeats this operation until the short circuit disappears, and the output rises back to regulation levels. |
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