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CS5155H Datenblatt(PDF) 9 Page - Cherry Semiconductor Corporation |
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CS5155H Datenblatt(HTML) 9 Page - Cherry Semiconductor Corporation |
9 / 14 page Applications Information: continued 9 Figure 9: CS5155H demonstration board response to 13A load turn off (output set for 2.8V). V2™ control topology immediately connects inductor to ground, providing 0% duty cycle. Regulation is achieved in less than 10µs. VCC1 Monitor To maintain predictable startup and shutdown character- istics an internal VCC1 monitor circuit is used to prevent the part from operating below 3.75V minimum startup. The VCC1 monitor comparator provides hysteresis and guaran- tees a 3.70V minimum shutdown threshold. Short Circuit Protection A lossless hiccup mode short circuit protection feature is provided, requiring only the soft start capacitor to imple- ment. If a short circuit condition occurs (VFFB < 1V), the VFFB low comparator sets the FAULT latch. This causes the top MOSFET to shut off, disconnecting the regulator from it’s input voltage. The soft start capacitor is then slowly dis- charged by a 2µA current source until it reaches it’s lower 0.7V threshold. The regulator will then attempt to restart nor- mally, operating in it’s extended off time mode with a 50% duty cycle, while the soft start capacitor is charged with a 60µA charge current. If the short circuit condition persists, the regulator output will not achieve the 1V low VFFB comparator threshold before the soft start capacitor is charged to it’s upper 2.5V threshold. If this happens the cycle will repeat itself until the short is removed. The soft start charge/discharge current ratio sets the duty cycle for the pulses (2µA/60µA = 3.3%), while actual duty cycle is half that due to the extended off time mode (1.65%). This protection feature results in less stress to the regulator components, input power supply, and PC board traces than occurs with constant current limit protection (see Figures 10 and 11). If the short circuit condition is removed, output voltage will rise above the 1V level, preventing the FAULT latch from being set, allowing normal operation to resume. Figure 10: CS5155H demonstration board hiccup mode short circuit pro- tection. Gate pulses are delivered while the soft start capacitor charges, and cease during discharge. Figure 11: Startup with regulator output shorted. Overvoltage Protection Overvoltage protection (OVP) is provided as result of the normal operation of the V2™ control topology and requires no additional external components. The control loop responds to an overvoltage condition within 100ns, causing the top MOSFET to shut off, disconnecting the regulator from it’s input voltage. The bottom MOSFET is then acti- vated, resulting in a “crowbar” action to clamp the output voltage and prevent damage to the load (see Figures 12 and 13). The regulator will remain in this state until the over- voltage condition ceases or the input voltage is pulled low. Trace 4 = 5V from PC Power Supply (2V/div.) Trace 2 = Inductor Switching Node (2V/div.) Trace 4 - 5V Supply Voltage (2V/div.) Trace 3 - Soft Start Timing Capacitor (1V/div.) Trace 2 - Inductor Switching Node (2V/div.) Protection and Monitoring Features Trace1 - Regulator Output Voltage (1V/div.) Trace 2 - Inductor Switching Node (5V/div.) Trace 3 - Output Current (13 to 0.5 Amps) (20V/div.) |
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Ähnliche Beschreibung - CS5155H |
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