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NCP3020B Datasheet(PDF) 9 Page - ON Semiconductor |
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NCP3020B Datasheet(HTML) 9 Page - ON Semiconductor |
9 / 23 page NCP3020A, NCP3020B http://onsemi.com 9 DETAILED DESCRIPTION OVERVIEW The NCP3020A/B operates as a 300/600 kHz, voltage mode, pulse width modulated, (PWM) synchronous buck converter. It drives high−side and low−side N−channel power MOSFETs. The NCP3020 incorporates an internal boost circuit consisting of a boost clamp and boost diode to provide supply voltage for the high side MOSFET gate driver. The NCP3020 also integrates several protection features including input undervoltage lockout (UVLO), output undervoltage (OUV), output overvoltage (OOV), adjustable high−side current limit (ISET and ILIM), and thermal shutdown (TSD). The operational transconductance amplifier (OTA) provides a high gain error signal from Vout which is compared to the internal 1.5 V pk-pk ramp signal to set the duty cycle converter using the PWM comparator. The high side switch is turned on by the positive edge of the clock cycle going into the PWM comparator and flip flop following a non-overlap time. The high side switch is turned off when the PWM comparator output is tripped by the modulator ramp signal reaching a threshold level established by the error amplifier. The gate driver stage incorporates fixed non− overlap time between the high−side and low−side MOSFET gate drives to prevent cross conduction of the power MOSFET’s. POR and UVLO The device contains an internal Power On Reset (POR) and input Undervoltage Lockout (UVLO) that inhibits the internal logic and the output stage from operating until VCC reaches its respective predefined voltage levels (4.3 V typical). Startup and Shutdown Once VCC crosses the UVLO rising threshold the device begins its startup process. Closed−loop soft−start begins after a 400 ms delay wherein the boost capacitor is charged, and the current limit threshold is set. During the 400 ms delay the OTA output is set to just below the valley voltage of the internal ramp. This is done to reduce delays and to ensure a consistent pre−soft−start condition. The device increases the internal reference from 0 V to 0.6 V in 24 discrete steps while maintaining closed loop regulation at each step. Each step contains 64 switching cycles. Some overshoot may be evident at the start of each step depending on the voltage loop phase margin and bandwidth. The total soft−start time is 6.8 ms for the NCP3020A and 4.4 ms for the NCP3020B. Figure 21. Soft−Start Details Internal Reference Voltage 0 V 0.7 V OTA Output Internal Ramp 24 Voltage Steps 25 mV Steps 0.6 V |
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Similar Description - NCP3020B |
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