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EN5310DI-T Datasheet(PDF) 7 Page - Enpirion, Inc. |
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EN5310DI-T Datasheet(HTML) 7 Page - Enpirion, Inc. |
7 / 10 page Rev 0.95 – March 2005 www.enpirion.com EN5310 7 The EN5310 has been optimized for use with about 20µF of ceramic output capacitance. It is strongly recommended that these be low-cost, low-ESR, ceramic capacitors rated X5R or X7R. (See the Enpirion application note on ripple comparison for optimum selection of number and value of these capacitors based on ripple requirements.) In order to eliminate high-frequency switching spikes on the output ripple, usually a low-value, low-ESR ceramic capacitor is used in parallel with the larger capacitors right at the load. Enable Operation The ENABLE pin provides a means to shut down the power FET switching or enable normal operation. A logic low will disable the converter and cause it to shut down. A logic high will enable the converter into normal operation. Soft-Start Operation The SS pin in conjunction with a small capacitor between this pin and AGND provides the soft start function to limit the in-rush current during start-up. During start-up of the converter the reference voltage to the error amplifier is gradually increased to its final level by an internal current source of typically 10uA. The whole soft-start procedure is designed to take 1ms - 3ms with a 15-30nF soft start capacitor, but can be programmed by capacitor selection using the following equation: Rise Time: TR = Css*80k POK Operation The POK signal is an open drain signal from the converter indicating the output voltage is within the specified range. The POK signal will be a logic high when the output voltage is within 90% - 120% of the programmed output voltage. If the output voltage goes outside of this range, the POK signal will be a logic low until the output voltage has returned to within this range. In the event of an over-voltage condition the POK signal will go low and will remain in this condition until the output voltage has dropped to 95% of the programmed output voltage before returning to the high state (see also Over Voltage Protection) Over-Current Protection The cycle-by-cycle current limit function is achieved by sensing the current flowing through the sense P- MOSFET and a signal generated by a differential amplifier with a preset over-current threshold. During a particular cycle, if the over-current threshold is exceeded, the power P-MOSFET is turned off and the power N-MOSFET is turned on to protect the P- MOSFET. If the over-current condition is removed, the over-current protection circuit will enable the PWM operation. If the over-current condition persists, the converter will eventually go through a full soft- start cycle. This circuit is designed to provide high noise immunity. It is possible to adjust the over-current set point by connecting a resistor between ROCP and GND (increase the trip point) or PVIN (decrease the trip point). The voltage at the ROCP pin is designed to be 0.8V. (see application note for details) Over-Voltage Protection When the output voltage exceeds 120% of the programmed output voltage, the PWM operation stops, the lower N-MOSFET is turned on and the POK signal goes low. When the output voltage drops below 95% of the programmed output voltage, normal PWM operation resumes and POK returns to its high state. Thermal Overload Protection Thermal shutdown will disable operation once the Junction temperature exceeds approximately 160ºC. Once the junction temperature drops by approx 25ºC, the converter will re-start with a normal soft-start. Low Input Voltage Operation Circuitry is provided to ensure that when the input voltage is below the specified voltage range, the operation of the converter is controlled and predictable. Circuits for hysteresis, input de-glitch and output leading edge blanking are included to ensure high noise immunity and prevent false tripping. Compensation The EN5310 is internally compensated through the use of a type 3 compensation network and is optimized for use with about 20µF of output capacitance and will provide excellent loop bandwidth and transient performance for most applications. (See |
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