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RT2660 Datasheet(PDF) 4 Page - Richtek Technology Corporation |
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RT2660 Datasheet(HTML) 4 Page - Richtek Technology Corporation |
4 / 18 page 4 RT2660 www.richtek.com DS2660-00 September 2015 © Copyright 2015 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. Operation The RT2660 is a synchronous low voltage step-down converter that can support the V5IN range from 4.5V to 5.5V and the output current can be up to 6A. The RT2660 uses a constant on-time, current mode architecture. In steady-state operation, the high-side N-MOSFET is turned on when the current feedback reaches COMP level which is the amplified difference between the reference voltage and the feedback voltage. The switching frequency of 600kHz or 1000kHz allows for efficiency and size optimization when selecting the output filter components. The switching frequency is set using the mode pin. The RT2660 reduces the external component count by integrating the boot recharge MOSFET. The bias voltage for the integrated high-side MOSFET is supplied by a capacitor between the BOOT and SW pins. The boot capacitor voltage is monitored by an BOOT detection circuit and turns off the high-side MOSFET when the voltage falls below a threshold voltage. The SS pin is used to minimize inrush currents or provide power supply sequencing during power up. A small value capacitor should be coupled to the pin for slow start. The SS pin is discharged before the output power up to ensure a repeatable restart after an over-temperature fault, UVLO fault or disable condition. The error amplifier EA adjusts COMP voltage by comparing the output voltage to the REFIN voltage. When the load increases, it causes a drop in the feedback voltage relative to the reference, then the COMP voltage rises to allow higher inductor current to match the load current. Bootstrap Voltage (Boot) and Low Dropout Operation The RT2660 has an integrated boot regulator and requires a small ceramic capacitor between the BOOT and SW pins to provide the gate drive voltage for the high-side MOSFET. The value of the ceramic capacitor should be 0.1 μF. A ceramic capacitor with an X7R or X5R grade dielectric with a voltage rating of 10V or higher is recommended because of the stable characteristics over temperature and voltage. When the BOOT voltage is lower than the threshold voltage, low-side MOSFET turns on and built-in bootstrap MOSFET will recharge the BOOT capacitor. The high-side MOSFET is always turned off when BOOT voltage is lower than threshold voltage. PWM Frequency and Adaptive On-Time Control The on-time can be roughly estimated by the equation : OUT ON IN SW V 1 T = Vf Error Amplifier The RT2660 has a transconductance amplifier. The error amplifier compares the VOUT voltage to the REFIN voltage The REFIN voltage can comes from external power source or taps off the voltage divider from the 2V VREF. The transconductance of the error amplifier is 1000 μA/V during normal operation. The frequency compensation components are placed between the COMP pin and ground. Auto-Zero Current Detector The auto-zero current detector circuit senses the SW waveform to adjust the zero current threshold voltage. When the current of low-side MOSFET decreases to the zero current threshold, the low-side MOSFET turns off to prevent negative inductor current. In this way, the zero current threshold can adjust for different conditions to get better efficiency. Protection Features The RT2660 has many features to protect the device. Under-Voltage Protection (UVLO) The RT2660 continuously monitors the voltage on the V5IN pin to ensure that the voltage level is high enough to bias the device properly and to provide sufficient gate drive potential to maintain high efficiency. The converter starts with approximately 4.3V and has a nominal hysteresis of 440mV. If the 5V UVLO limit is reached, the converter transitions the phase node into an off function. And the converter remains in the off state until the device is reset by cycling 5V until the 5V POR is reached (2.3V nominal). The power input does not have an UVLO function. |
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