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TPS54233 Datasheet(PDF) 11 Page - Texas Instruments |
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TPS54233 Datasheet(HTML) 11 Page - Texas Instruments |
11 / 29 page TPS54233 www.ti.com SLUS859C – OCTOBER 2008 – REVISED JANUARY 2015 8.3.9 Overcurrent Protection and Frequency Shift The TPS54233 implements current mode control that uses the COMP pin voltage to turn off the high-side MOSFET on a cycle by cycle basis. Every cycle the switch current and the COMP pin voltage are compared; when the peak inductor current intersects the COMP pin voltage, the high-side switch is turned off. During overcurrent conditions that pull the output voltage low, the error amplifier responds by driving the COMP pin high, causing the switch current to increase. The COMP pin has a maximum clamp internally, which limit the output current. The TPS54233 provides robust protection during short circuits. There is potential for overcurrent runaway in the output inductor during a short circuit at the output. The TPS54233 solves this issue by increasing the off time during short circuit conditions by lowering the switching frequency. The switching frequency is divided by 8, 4, 2, and 1 as the voltage ramps from 0 V to 0.8 V on VSENSE pin. The relationship between the switching frequency and the VSENSE pin voltage is shown in Table 2. Table 2. Switching Frequency Conditions SWITCHING FREQUENCY VSENSE PIN VOLTAGE 300 kHz VSENSE ≥ 0.6 V 300 kHz / 2 0.6 V > VSENSE ≥ 0.4 V 300 kHz / 4 0.4 V > VSENSE ≥ 0.2 V 300 kHz / 8 0.2 V > VSENSE 8.3.10 Overvoltage Transient Protection The TPS54233 incorporates an overvoltage transient protection (OVTP) circuit to minimize output voltage overshoot when recovering from output fault conditions or strong unload transients. The OVTP circuit includes an overvoltage comparator to compare the VSENSE pin voltage and internal thresholds. When the VSENSE pin voltage goes above 109% × Vref, the high-side MOSFET will be forced off. When the VSENSE pin voltage falls below 107% × Vref, the high-side MOSFET will be enabled again. 8.3.11 Thermal Shutdown The device implements an internal thermal shutdown to protect itself if the junction temperature exceeds 165°C. The thermal shutdown forces the device to stop switching when the junction temperature exceeds the thermal trip threshold. Once the die temperature decreases below 165°C, the device reinitiates the power up sequence. 8.4 Device Functional Modes 8.4.1 Eco-modeTM The TPS54233 is designed to operate in pulse skipping Eco-modeTM at light load currents to boost light load efficiency. When the peak inductor current is lower than 100 mA typically, the COMP pin voltage falls to 0.5V typically and the device enters Eco-mode™. When the device is in Eco-mode™, the COMP pin voltage is clamped at 0.5V internally which prevents the high side integrated MOSFET from switching. The peak inductor current must rise above 100mA for the COMP pin voltage to rise above 0.5V and exit Eco-mode™. Since the integrated current comparator catches the peak inductor current only, the average load current entering Eco- mode™ varies with the applications and external output filters. Copyright © 2008–2015, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Links: TPS54233 |
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