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MP2159A датащи(PDF) 11 Page - Monolithic Power Systems |
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MP2159A датащи(HTML) 11 Page - Monolithic Power Systems |
11 / 15 page MP2159A – 1 A, 6 V, 1.5 MHz SYNCHRONOUS STEP-DOWN CONVERTER MP2159A Rev. 1.02 www.MonolithicPower.com 11 6/30/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2016 MPS. All Rights Reserved. OPERATION The MP2159A uses constant-on-time (COT) control with input voltage feed forward to stabilize the switching frequency over a full input range. At light load, the MP2159A employs a proprietary control of the low-side switch and the inductor current to eliminate ringing on the switching node and improve efficiency. Constant-On-Time (COT) Control Compare to fixed frequency PWM control, constant-on-time control offers the advantage of a simpler control loop and faster transient response. By using input voltage feed forward, MP2159A maintains a nearly 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 load transient, the MP2159A fixes the minimum off time at 60 ns. However, this minimum-off time limit will not affect operation of the MP2159A in steady-state operation. Light-Load Operation In a light-load condition, the MP2159A uses a proprietary control scheme to save power and improve efficiency. It turns off the low-side switch when the inductor current begins to reverse. Then it works in discontinuous conduction mode (DCM) operation. There is a zero current cross circuit to detect if the inductor current starts to reverse. Considering the internal circuit propagation time, the typical delay is 50 ns. This means the inductor current will still fall after the ZCD is triggered in this delay. If the inductor current falling slew rate is fast (Vo voltage is high or close to Vin), the low-side MOSFET (LS-FET) is turned off, and the inductor current may be negative. This phenomena prevents the MP2159A from entering DCM operation even if there is no load. If DCM is required, the off time of the LS-FET in CCM should be longer than 100 ns (2 times the propagation delay). For example, if Vin is 3.6 V and Vo is 3.3 V, the off time in CCM is 55 ns. It is difficult to enter DCM at light load. Using a smaller inductor improves this problem, making it easier to enter DCM. Enable (EN) When the input voltage is greater than the under-voltage lockout threshold (2.3 V, typically), the MP2159A is enabled by pulling EN higher than 1.2 V. Floating EN or pulling EN down to ground disables the MP2159A. There is an internal 1 MΩ resistor from EN to ground. Soft Start (SS) MP2159A has built-in soft start that ramps up the output voltage in a controlled slew rate, avoiding overshoot at start-up. The soft-start time period is about 1.15 ms, typically. Power GOOD Indicator (PG) MP2159A has an open drain with a 550 kΩ pull- up resistor pin that functions as a power good indicator (PG). When FB is within +/-10% of the regulation voltage (i.e., 0.6 V), PG is pulled up to VIN by the 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 Rdson of less than 400 Ω. Current Limit MP2159A has a minimum 2 A current limit for the high-side switch. When the high-side switch hits the current limit, the MP2159A remains at the hiccup threshold until the current decreases. This prevents the inductor current from continuing to build up, which will result in damage to the components. Short Circuit and Recovery The MP2159A enters short-circuit protection mode when the current limit is reached, and it tries to recover from the short circuit with hiccup mode. During a short-circuit protection, the MP2159A disables the output power stage, discharges the soft-start capacitor, and then automatically tries to soft-start again. If the short-circuit condition still holds after the soft- start ends, the MP2159A repeats this operation cycle until the short circuit disappears, and the output rises back to regulation level. |
Аналогичный номер детали - MP2159A |
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Аналогичное описание - MP2159A |
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