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LMR50410-Q1 Datasheet(PDF) 13 Page - Texas Instruments |
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LMR50410-Q1 Datasheet(HTML) 13 Page - Texas Instruments |
13 / 37 page VIN(V) 20 22 24 26 28 30 32 34 36 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 IOUT=0.2A IOUT=0.5A IOUT=1A VOUT = 3.3 V fSW = 2.1 MHz Figure 8-4. Frequency Foldback at TON_MIN VIN(V) 4.5 5.5 6.5 7.5 8.5 9.5 10.5 11.5 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 IOUT=0.2A IOUT=0.5A IOUT=1A VOUT = 5 V fSW = 2.1 MHz Figure 8-5. Frequency Foldback at TOFF_MIN 8.3.5 Bootstrap Voltage The LMR50410-Q1 provides an integrated bootstrap voltage converter. A small capacitor between the CB and SW pins provides the gate drive voltage for the high-side MOSFET. The bootstrap capacitor is refreshed when the high-side MOSFET is off and the low-side switch is on. The recommended value of the bootstrap capacitor is 0.1 µF. A ceramic capacitor with an X7R or X5R grade dielectric with a voltage rating of 16 V or higher is recommended for stable performance over temperature and voltage. 8.3.6 Overcurrent and Short Circuit Protection The LMR50410-Q1 incorporates both peak and valley inductor current limit to provide protection to the device from overloads and short circuits and limit the maximum output current. Valley current limit prevents inductor current runaway during short circuits on the output, while both peak and valley limits work together to limit the maximum output current of the converter. Cycle-by-cycle current limit is used for overloads, while hiccup mode is used for sustained short circuits. High-side MOSFET overcurrent protection is implemented by the nature of the Peak Current Mode control. The high-side switch current is sensed when the high-side is turned on after a set blanking time. The high-side switch current is compared to the output of the Error Amplifier (EA) minus slope compensation every switching cycle. See Section 8.2 for more details. The peak current of high-side switch is limited by a clamped maximum peak current threshold Isc (see Section 7.5), which is constant. The current going through low-side MOSFET is also sensed and monitored. When the low-side switch turns on, the inductor current begins to ramp down. The low-side switch is not turned OFF at the end of a switching cycle if its current is above the low-side current limit ILS_LIMIT (see the Section 7.5). The low-side switch is kept ON so that inductor current keeps ramping down, until the inductor current ramps below the ILS_LIMIT. Then the low-side switch is turned OFF and the high-side switch is turned on after a dead time. After ILS_LIMIT is achieved, peak and valley current limit controls the max current deliver and it can be calculated using Equation 6. LS_LIMIT SC OUT max I +I I = 2 (6) If the feedback voltage is lower than 40% of the VREF, the current of the low-side switch triggers ILS_LIMIT for 256 consecutive cycles and hiccup current protection mode is activated. In hiccup mode, the converter shuts down and keeps off for a period of hiccup, THICCUP (135 ms typical) before the LMR50410-Q1 tries to start again. If overcurrent or short-circuit fault condition still exist, hiccup repeats until the fault condition is removed. Hiccup mode reduces power dissipation under severe overcurrent conditions, prevents over-heating and potential damage to the device. www.ti.com LMR50410-Q1 SLUSDW4 – JULY 2020 Copyright © 2020 Texas Instruments Incorporated Submit Document Feedback 13 Product Folder Links: LMR50410-Q1 |
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