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Datenblatt-Suchmaschine für elektronische Bauteile |
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Datenblatt-Suchmaschine für elektronische Bauteile |
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XRP6670 Datenblatt(PDF) 7 Page - Exar Corporation |
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XRP6670 Datenblatt(HTML) 7 Page - Exar Corporation |
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7 / 13 page  X XR RP P6 66 67 70 0 3 3A A 3 30 00 0k kH Hz z- -2 2..5 5M MH Hz z S Sy yn nc ch hr ro on no ou us s S Stte ep p D Do ow wn n R Re eg gu ulla atto or r © 2013 Exar Corporation 7/13 Rev. 1.0.1 THEORY OF OPERATION FUNCTIONAL DESCRIPTION The XRP6670 is a synchronous, current-mode, step-down regulator. It regulates input voltages from 2.6V to 5.5V and supplies up to 3A of output current IOUT. The XRP6670 uses current-mode control to regulate the output voltage VOUT. The VOUT is measured at FB through a resistive voltage divider and input to a transconductance error amplifier. The high- side switch current is compared to the output of the error amplifier to control the output voltage. The regulator utilizes internal P- channel and N-channel MOSFETs to step-down the input voltage. Because the high-side FET is P-channel a bootstrapping capacitor is not necessary and the regulator can operate at 100% duty cycle. The XRP6670 has several powerful protection features including OCP, OTP, UVLO and output short-circuit. SHORT -CIRCUIT AND OVER-CURRENT PROTECTION OCP The XRP6670 protects itself and downstream circuits against accidental increase in current or short-circuit. If peak current through the switching FET increases above 4.2A (nominal) the regulator enters an idle state where the internal FETs are turned off and softstart is pulled low. After a period of 2000xT the regulator will attempt a softstart. If the high current persists the protection cycle will repeat. SOFT -START XRP6670 has an integrated soft-start which is preset at 1.5ms (nominal). This feature limits the inrush current during startup and allows the output voltage to smoothly rise to its programmed value. POWER GOOD FLAG This open drain output (PGOOD) can be used to monitor whether the output voltage is within regulation (±15%). PGOOD is pulled to ground when VOUT is not in regulation. PGOOD should be tied to VDD with a 100k resistor. PROGRAMMABLE FREQUENCY The switching frequency is programmable within a range of 300kHz to 2.5MHz via a resistor placed between SHDN/RT and GND pins. An equation for calculating a resistor value for a target frequency is given the Application Information section. 100% DUTY CYCLE AND LDO OPERATION The XRP6670 switching FET is a P-channel device and therefore can operate at 100% duty cycle. In battery operated applications where VIN will droop, XRP6670 can seamlessly transition from PWM to LDO mode. OVER -TEMPERATURE PROTECTION OTP If the junction temperature exceeds 160°C the OTP circuit is triggered, turning off the internal control circuit and FETs. When junction temperature drops below 140°C the XRP6670 will restart. Although thermal shutdown is built-in in the XRP6670 to protect the device from thermal damage, the total power dissipation that the XRP6670 can sustain is based on the package thermal capability. Equation 1 shown on page two, can be used to calculate junction temperature and ensure operation within the recommended maximum temperature of 125°C. APPLICATION INFORMATION PROGRAMMING THE OUTPUT VOLTAGE Use an external resistor divider to set the output voltage based on the following equation: 2 1 0.800 1 Where: R1 is the resistor between VOUT and FB (nominally set at 100kΩ) |
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