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MP1469 Datasheet(PDF) 10 Page - Monolithic Power Systems |
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MP1469 Datasheet(HTML) 10 Page - Monolithic Power Systems |
10 / 17 page MP1469 – SYNCHRONOUS, STEP-DOWN CONVERTER WITH INTERNAL MOSFETS MP1469 Rev. 1.01 www.MonolithicPower.com 10 8/26/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. OPERATION The MP1469 is a high-frequency, synchronous, rectified, step-down, switch-mode converter with internal power MOSFETs. It offers a very compact solution to achieve a 1.5A continuous output current over a wide input supply range, with excellent load and line regulation. The MP1469 operates in a fixed-frequency, peak-current–control mode to regulate the output voltage. An internal clock initiates the PWM cycle to turn on the integrated high-side power MOSFET. This MOSFET remains on until its current reaches the value set by the COMP voltage. When the power switch is off, it remains off until the next clock cycle starts. If the current in the power MOSFET does not reach the COMP set current value within 90% of one PWM period, the power MOSFET is forced to turn off. Internal Regulator The 5V internal regulator powers most of the internal circuits. This regulator takes VIN and operates in the full VIN range. When VIN exceeds 5.0V, the regulator output is in full regulation. When VIN falls below 5.0V, the output decreases. Error Amplifier The error amplifier compares the FB voltage against the internal 0.8V reference (REF) and outputs a current proportional to the difference between the two. This output current charges or discharges the internal compensation network to form the COMP voltage, which is used to control the power MOSFET current. The optimized internal compensation network minimizes the external component counts and simplifies the control-loop design. Enable EN is a digital control pin that turns the regulator on and off: Drive EN HIGH to turn on the regulator, drive it LOW to turn it off. An internal 1MΩ resistor from EN to GND allows EN to float to shut down the chip. The EN pin is clamped internally using a 6.5V series-Zener-diode as shown in Figure 2. Connecting the EN input pin through a pullup resistor to the voltage on the VIN pin limits the EN input current to less than 100μA. For example, with 12V connected to Vin, RPULLUP≥ (12V-6.5V) ÷ 100μA =55kΩ Connecting the EN pin is directly to a voltage source without any pullup resistor requires limiting the amplitude of the voltage source to ≤ 6V to prevent damage to the Zener diode. Figure 2: 6.5V Zener Diode Connection Under-Voltage Lockout (UVLO) Under-voltage lockout (UVLO) protects the chip from operating at an insufficient supply voltage. The MP1469 UVLO comparator monitors the output voltage of the internal regulator, VCC. The UVLO rising threshold is about 4.2V while its falling threshold is consistently 3.86V. Internal Soft-Start Soft-start prevents the converter output voltage from overshooting during startup. When the chip starts, the internal circuit generates a soft- start voltage (SS) that ramps up from 0V to 1.2V: When SS falls below the internal reference (REF), SS overrides REF so that the error amplifier uses SS as the reference; when SS exceeds REF, the error amplifier resumes using REF as its reference. The SS time is internally set to 1ms. Over-Current-Protection and Hiccup The MP1469 has a cycle-by-cycle over-current limit for when the inductor current peak value exceeds the set current-limit threshold. First, when the output voltage drops until FB falls below the Under-Voltage (UV) threshold (typically 200mV) to trigger a UV event, the MP1469 enters hiccup mode to periodicall restart the part. This protection mode is especially useful when the output is dead- shorted to ground. This greatly reduces the average short-circuit current to alleviate thermal issues and to protect the regulator. The MP1469 exits hiccup mode once the over- current condition is removed. |
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