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LMR23625-Q1 Datasheet(PDF) 16 Page - Texas Instruments |
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LMR23625-Q1 Datasheet(HTML) 16 Page - Texas Instruments |
16 / 40 page IN OUT OUT OUT _ MAX LS _ LIMIT SW IN V V V I I 2 f L V u u u Z _ESR OUT 1 f 2 C ESR S u u 16 LMR23625-Q1 SNVSAR5B – DECEMBER 2016 – REVISED MARCH 2018 www.ti.com Product Folder Links: LMR23625-Q1 Submit Documentation Feedback Copyright © 2016–2018, Texas Instruments Incorporated Feature Description (continued) (8) The CFF creates a time constant with RFBT that couples in the attenuate output voltage ripple to the FB node. If the CFF value is too large, it can couple too much ripple to the FB and affect VOUT regulation. Therefore, calculate CFF based on output capacitors used in the system. At cold temperatures, the value of CFF might change based on the tolerance of the chosen component. This may reduce its impedance and ease noise coupling on the FB node. To avoid this, more capacitance can be added to the output or the value of CFF can be reduced. 8.3.8 Bootstrap Voltage (BOOT) The LMR23625-Q1 provides an integrated bootstrap voltage regulator. A small capacitor between the BOOT and SW pins provides the gate-drive voltage for the high-side MOSFET. The BOOT capacitor is refreshed when the high-side MOSFET is off and the low-side switch conducts. The recommended value of the BOOT capacitor is 0.1 μF. TI recommends a ceramic capacitor with an X7R or X5R grade dielectric with a voltage rating of 16V or higher for stable performance over temperature and voltage. 8.3.9 Overcurrent and Short-Circuit Protection The LMR23625-Q1 is protected from overcurrent conditions by cycle-by-cycle current limit on both the peak and valley of the inductor current. Hiccup mode is activated if a fault condition persists to prevent overheating. High-side MOSFET overcurrent protection is implemented by the nature of the peak-current-mode control. The HS switch current is sensed when the HS is turned on after a set blanking time. The HS switch current is compared to the output of the error amplifier (EA) minus slope compensation every switching cycle. See the Functional Block Diagram for more details. The peak current of HS switch is limited by a clamped maximum- peak-current threshold IHS_LIMIT, which is constant. So the peak-current limit of the high-side switch is not affected by the slope compensation and remains constant over the full duty-cycle range. The current going through LS MOSFET is also sensed and monitored. When the LS switch turns on, the inductor current begins to ramp down. The LS switch is not turned OFF at the end of a switching cycle if its current is above the LS current limit ILS_LIMIT. The LS switch is kept ON so that inductor current keeps ramping down, until the inductor current ramps below the LS current limit ILS_LIMIT. The LS switch is then turned OFF, and the HS switch is turned on after a dead time. This is somewhat different than the more typical peak-current limit and results in Equation 9 for the maximum load current. (9) If the current of the LS switch is higher than the LS current limit for 64 consecutive cycles, hiccup current protection mode is activated. In hiccup mode the regulator is shut down and kept off for 5 ms typically before the LMR23625-Q1 tries to start again. If overcurrent or short-circuit fault condition still exists, hiccup repeats until the fault condition is removed. Hiccup mode reduces power dissipation under severe overcurrent conditions, prevents overheating and potential damage to the device. For FPWM option, the inductor current is allowed to go negative. If this current exceeds IL_NEG, the LS switch is turned off until the next clock cycle. This is used to protect the LS switch from excessive negative current. 8.3.10 Thermal Shutdown The LMR23625-Q1 provides an internal thermal shutdown to protect the device when the junction temperature exceeds 170°C (typical). The device is turned off when thermal shutdown activates. Once the die temperature falls below 155°C (typical), the device reinitiates the power-up sequence controlled by the internal soft-start circuitry. |
Similar Part No. - LMR23625-Q1_18 |
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Similar Description - LMR23625-Q1_18 |
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