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LM2831XSD Datasheet(PDF) 10 Page - Texas Instruments |
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LM2831XSD Datasheet(HTML) 10 Page - Texas Instruments |
10 / 38 page 0 0 VIN VD TON t t Inductor Current D = TON/TSW VSW TOFF TSW IL IPK SW Voltage LM2831 SNVS422D – AUGUST 2006 – REVISED SEPTEMBER 2015 www.ti.com Feature Description (continued) is proportional to the difference between the feedback voltage and VREF. When the PWM comparator output goes high, the output switch turns off until the next switching cycle begins. During the switch off-time, inductor current discharges through the Schottky catch diode, which forces the SW pin to swing below ground by the forward voltage (VD) of the Schottky catch diode. The regulator loop adjusts the duty cycle (D) to maintain a constant output voltage. Figure 18. Typical Waveforms 7.3.2 Soft Start This function forces VOUT to increase at a controlled rate during start up. During soft start, the error amplifier’s reference voltage ramps from 0 V to its nominal value of 0.6 V in approximately 600 µs. This forces the regulator output to ramp up in a controlled fashion, which helps reduce inrush current. 7.3.3 Output Overvoltage Protection The overvoltage comparator compares the FB pin voltage to a voltage that is 15% higher than the internal reference VREF. Once the FB pin voltage goes 15% above the internal reference, the internal PMOS control switch is turned off, which allows the output voltage to decrease toward regulation. 7.3.4 Undervoltage Lockout Undervoltage lockout (UVLO) prevents the LM2831 from operating until the input voltage exceeds 2.73 V (typical). The UVLO threshold has approximately 430 mV of hysteresis, so the part will operate until VIN drops below 2.3 V (typical). Hysteresis prevents the part from turning off during power up if VIN is non-monotonic. 7.3.5 Current Limit The LM2831 uses cycle-by-cycle current limiting to protect the output switch. During each switching cycle, a current limit comparator detects if the output switch current exceeds 2.5 A (typical), and turns off the switch until the next switching cycle begins. 7.3.6 Thermal Shutdown Thermal shutdown limits total power dissipation by turning off the output switch when the IC junction temperature exceeds 165°C. After thermal shutdown occurs, the output switch doesn’t turn on until the junction temperature drops to approximately 150°C. 10 Submit Documentation Feedback Copyright © 2006–2015, Texas Instruments Incorporated Product Folder Links: LM2831 |
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