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CS5166 Folha de dados(PDF) 10 Page - Cherry Semiconductor Corporation |
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CS5166 Folha de dados(HTML) 10 Page - Cherry Semiconductor Corporation |
10 / 22 page Figure 10: Output Voltage Transient Response to a 14A load turn-off, VOUT = +2.825V (DAC = 10111). Power Supply Sequencing The CS5166 offers inherent protection from undefined start-up conditions, regardless of the 12V and 5V supply power-up sequencing. The turn-on slew rates of the 12V and 5V power supplies can be varied over wide ranges without affecting the output voltage or causing detrimental effects to the buck regulator. Over-Current Protection A loss-less hiccup mode current limit protection feature is provided, requiring only the Soft Start capacitor to imple- ment. The CS5166 provides overcurrent protection by sens- ing the current through a “Droop” resistor, using an inter- nal current sense comparator. The comparator compares this voltage drop to an internal reference voltage of 76mV (typical). If the voltage drop across the “Droop” resistor exceeds this threshold, the current sense comparator allows the fault latch to be set. This causes the regulator to stop switching. During this over current condition, the CS5166 stays off for the time it takes the Soft Start capacitor to slowly discharge by a 2µA current source until it reaches its lower 0.7V threshold. At that time the regulator attempts to restart normally by delivering short gate pulses to both FETs. The CS5166 will operate initially in its extended off time mode with a 50% duty cycle, while the Soft Start capacitor is charged with a 60µA charge current. The gates will switch on while the Soft Start capacitor is charged to its upper 2.7V threshold. During an overload condition the Soft Start charge /dis- charge 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%) when VFB is less than 1V. The Soft Start hiccup pulses last for a 3ms period at the end of which the duty cycle repeats if a fault is detected, otherwise normal operation resumes. This protection scheme minimizes thermal stress to the reg- ulator components, input power supply, and PC board traces, as the over current condition persists. Upon removal of the overload, the fault latch is cleared, allowing normal operation to resume. The current limit trip point can be adjusted through an external resistor, providing the user with the current limit set-point flexibility. Figure 11: Demonstration board hiccup mode short circuit protection. Gate pulses are delivered while the Soft Start capacitor charges, and cease during discharge. Figure 12: Demonstration board Start up with regulator output shorted to ground. Overvoltage Protection Overvoltage protection (OVP) is provided as result of the normal operation of the V2 TM 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 its input voltage. The bottom MOSFET is then activat- ed, resulting in a “crowbar” action to clamp the output voltage and prevent damage to the load (see Figures 13 and 14). The regulator will remain in this state until the overvoltage condition ceases or the input voltage is pulled low. The bottom FET and board trace must be properly designed to implement the OVP function. If a dedicated OVP output is required, it can be implemented using the circuit in Figure 15. In this figure the OVP signal will go high (overvoltage condition), if the output voltage (VCORE) exceeds 20% of the voltage set by the particular DAC code 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 Trace 1 - GATE(H) (10V/div) Trace 2 - Inductor Switching Node (5V/div) Trace 3 -Load Current (5A/div) Trace 4 - VOUT(100mV/div) 10 Application Information: continued |
Nº de peça semelhante - CS5166 |
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Descrição semelhante - CS5166 |
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