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MP4432 Datasheet(PDF) 23 Page - Monolithic Power Systems |
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MP4432 Datasheet(HTML) 23 Page - Monolithic Power Systems |
23 / 29 page MP4432 - 36V, 2.2A, LOW IQ, SYNCHRONOUS STEP-DOWN CONVERTER MP4432 Rev. 1.01 www.MonolithicPower.com 23 1/12/2018 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2018 MPS. All Rights Reserved. For simplification, the output voltage ripple can be estimated with Equation (8): OUT OUT OUT 2 SW OUT IN VV V (1 ) 8 f L C V (8) For tantalum or electrolytic capacitors, the ESR dominates the impedance at the switching frequency. For simplification, the output ripple can be approximated with Equation (9): OUT OUT OUT ESR SW IN VV V (1 ) R f L V (9) The characteristics of the output capacitor also affect the stability of the regulation system. The MP4432 can be optimized for a wide range of capacitance and ESR values. Selecting the Inductor A 1µH to 10µH inductor with a DC current rating at least 25% higher than the maximum load current is recommended for most applications. For higher efficiency, choose an inductor with a low DC resistance. A larger value inductor results in less ripple current and a lower output ripple voltage, but also has a larger physical size, higher series resistance, and lower saturation current. A good rule for determining the inductor value is to allow the inductor ripple current to be approximately 30% of the maximum load current. The inductance value can then be calculated with Equation (10): OUT OUT SW L IN VV L (1 ) f I V (10) Where ∆I L is the peak-to-peak inductor ripple current. Choose the inductor ripple current to be approximately 30% of the maximum load current. The maximum inductor peak current can be calculated with Equation (11): OUT OUT LP LOAD SW IN VV I I (1 ) 2f L V (11) VIN UVLO Setting The MP4432 has an internal, fixed, under- voltage lockout (UVLO) threshold. The rising threshold is 2.8V, while the falling threshold is about 2.65V. For applications requiring a higher UVLO point, an external resistor divider between VIN and EN can be used to achieve a higher equivalent UVLO threshold (see Figure 6). Figure 6: Adjustable UVLO Using EN Divider The UVLO threshold can be calculated with Equation (12) and Equation (13): EN_RISING DOWN UP RISING V R R (1 INUV ) (12) EN_FALLING DOWN UP FALLING V R R (1 INUV ) (13) Where VEN_RISING = 1.05V, and VEN_FALLING = 0.93V. External BST Diode An external BST diode can enhance the efficiency of the regulator when the duty cycle is high. A power supply between 2.5V and 5V can be used to power the external bootstrap diode. VCC or VOUT is recommended for this power supply in the circuit (see Figure 7). CBST COUT L BST SW External BST diode IN4148 VCC / VOUT VCC VOUT RBST Figure 7: Optional External Bootstrap Diode to Enhance Efficiency The recommended external BST diode is IN4148, and the recommended BST capacitor value is 0.1µF to 1μF. VIN EN VIN RUP R DOWN |
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