RT8015BGQW

RT8015B 3A, 2MHz, Synchronous Step-Down Converter General Description Features The RT8015B is a high efficiency synchronous, step down DC/DC converter. Its input voltage range is from 2.6V to 5.5V and provides an adjustable regulated output voltage from 0.8V to 5V while delivering up to 3A of output current. z z z z z z z z Applications z z The RT8015B is operated in forced continuous PWM Mode which minimizes ripple voltage and reduces the noise and RF interference. The 100% duty cycle in Low Dropout Operation further maximize battery life. The RT8015B is available in the WDFN-10L 3x3 and SOP8 (Exposed Pad) packages. Ordering Information RT8015B Package Type QW : WDFN-10L 3x3 SP : SOP-8 (Exposed Pad-Option 2) Lead Plating System G : Green (Halogen Free and Pb Free) Note : Low RDS(ON) Internal Switches : 110mΩ Ω Programmable Frequency : 300kHz to 2MHz No Schottky Diode Required 0.8V Reference Allows for Low Output Voltage Forced Continuous Mode Operation Low Dropout Operation : 100% Duty Cycle Power Good Output Voltage Indicator RoHS Compliant and Halogen Free z z z z Portable Instruments Battery-Powered Equipment Notebook Computers Distributed Power Systems IP Phones Digital Cameras Pin Configurations (TOP VIEW) SHDN/RT GND LX LX PGND 1 2 3 4 5 10 9 8 7 11 9 The internal synchronous low on resistance power switches increase efficiency and eliminate the need for an external Schottky diode. The switching frequency is set by an external resistor. The 100% duty cycle provides low dropout operation extending battery life in portable systems. Current mode operation with external compensation allows the transient response to be optimized over a wide range of loads and output capacitors. z High Efficiency : Up to 95% WDFN-10L 3x3 8 SHDN/RT GND 2 LX PGND 3 4 GND 9 RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. ` Suitable for use in SnPb or Pb-free soldering processes. COMP 7 FB 6 VDD 5 PVDD Richtek products are : ` COMP FB PGOOD VDD PVDD SOP-8 (Exposed Pad) Marking Information For marking information, contact our sales representative directly or through a Richtek distributor located in your area. DS8015B-04 March 2011 www.richtek.com 1 RT8015B Typical Application Circuit RT8015B VIN 5V 6 PVDD CIN 22µF R3 1 R4 100k 7 VDD 8 ROSC 332k L1 2.2µH VOUT 2.5V/3A CF 22pF R1 510k COUT 22µF x 2 FB 9 C1 0.1µF PGOOD LX 3, 4 PGOOD 1 SHDN/RT COMP 10 GND PGND RCOMP CCOMP 1nF 27k R2 240k 2 5 Note : Using all Ceramic Capacitors Table 1. Recommended Component Selection VOUT (V) R1 (kΩ) R2 (kΩ) RCOMP (kΩ) CCOMP (nF) L1 (μH) COUT (μF) 3.3 750 240 30 1 2.2 22 x 2 2.5 510 240 27 1 2.2 22 x 2 1.8 300 240 22 1 2.2 22 x 2 1.5 210 240 18 1 2.2 22 x 2 1.2 120 240 15 1 1.0 22 x 2 1.0 60 240 13 1 1.0 22 x 2 Functional Pin Description Pin No. WDFN SOP-8 -10L 3x3 (Exposed Pad) Pin Name 1 1 SHDN/RT 2 2 GND 3, 4 3 LX 5 4 PGND 6 5 PVDD 7 6 8 -- 9 7 10 8 11 -- -- 9 www.richtek.com 2 Pin Function Oscillator Resistor Input. Connecting a resistor to ground from this pin sets the switching frequency. Forcing this pin to VDD causes the device to be shut down. Signal Ground. All small signal components and compensation components should connect to this ground, which in turn connects to PGND at one point. Internal Power MOSFET Switches Output. Connect this pin to the inductor. Power Ground. Connect this pin close to the negative terminal of CIN and COUT. Power Input Supply. Decouple this pin to PGND with a capacitor. Signal Input Supply. Decouple this pin to GND with a capacitor. Normally VDD is equal to PVDD. Power Good Indicator. This pin is open drain logic output that is PGOOD pulled to ground when the output voltage is not within ±12.5% of regulation point. Feedback Pin. This pin receives the feedback voltage from a FB resistive divider connected across the output. Error Amplifier Compensation Point. The current comparator COMP threshold increases with this control voltage. Connect external compensation elements to this pin to stabilize the control loop. No Internal Connection. The exposed pad must be soldered to a (Exposed Pad) large PCB and connected to GND for maximum power dissipation. The exposed pad must be soldered to a large PCB and connected to GND GND for maximum power dissipation. VDD DS8015B-04 March 2011 RT8015B Function Block Diagram SHDN/RT SD PVDD ISEN Slope Com OSC COMP 0.8V Output Clamp EA FB OC Limit Driver Int-SS LX 0.9V Control Logic 0.7V NISEN PGND NMOS I Limit POR 0.2V PGOOD V REF OTP GND VDD Layout Guide Place the input and output capacitors as close to the IC as possible. GND VIN R3 C1 R1 RT8015B Bottom Layer R4 GND CF COUT CIN R2 PVDD VDD PGOOD FB COMP 6 5 7 4 8 3 9 2 10 1 LX should be connected to Inductor by wide and short trace, keep sensitive L1 components away from this trace VOUT PGND LX LX GND SHDN/RT ROSC RCOMP CCOMP VOUT GND Place the feedback and compensation components as close to the IC as possible. DS8015B-04 March 2011 www.richtek.com 3 RT8015B Operation Main Control Loop Slope Compensation and Inductor Peak Current The RT8015B is a monolithic, constant-frequency, current mode step-down DC/DC converter. During normal operation, the internal top power switch (P-Channel MOSFET) is turned on at the beginning of each clock cycle. Current in the inductor increases until the peak inductor current reach the value defined by the voltage on the COMP pin. The error amplifier adjusts the voltage on the COMP pin by comparing the feedback signal from a resistor divider on the FB pin with an internal 0.8V reference. When the load current increases, it causes a reduction in the feedback voltage relative to the reference. The error amplifier raises the COMP voltage until the average inductor current matches the new load current. When the top power MOSFET shuts off, the synchronous power switch (N-MOSFET) turns on until either the bottom current limit is reached or the beginning of the next clock cycle. Slope compensation provides stability in constant frequency architectures by preventing sub-harmonic oscillations at duty cycles greater than 50%. It is accomplished internally by adding a compensating ramp to the inductor current signal. Normally, the maximum inductor peak current is reduced when slope compensation is added. In the RT8015B, however, separated inductor current signals are used to monitor over current condition. This keeps the maximum output current relatively constant regardless of duty cycle. The operating frequency is set by an external resistor connected between the RT pin and ground. The practical switching frequency can range from 300kHz to 2MHz. Short Circuit Protection When the output is shorted to ground, the inductor current decays very slowly during a single switching cycle. A current runaway detector is used to monitor inductor current. As current increasing beyond the control of current loop, switching cycles will be skipped to prevent current runaway from occurring. Dropout Operation When the input supply voltage decreases toward the output voltage, the duty cycle increases toward the maximum on-time. Further reduction of the supply voltage forces the main switch to remain on for more than one cycle eventually reaching 100% duty cycle. The output voltage will then be determined by the input voltage minus the voltage drop across the internal P-Channel MOSFET and the inductor. Low Supply Operation The RT8015B is designed to operate down to an input supply voltage of 2.6V. One important consideration at low input supply voltages is that the R DS(ON) of the P-Channel and N-Channel power switches increases. The user should calculate the power dissipation when the RT8015B is used at 100% duty cycle with low input voltages to ensure that thermal limits are not exceeded. www.richtek.com 4 DS8015B-04 March 2011 RT8015B Absolute Maximum Ratings z z z z z z z z z z (Note 1) Supply Input Voltage, VDD, PVDD ---------------------------------------------------------------------------- −0.3V to 6V LX Pin Switch Voltage -------------------------------------------------------------------------------------------- −0.3V to (PVDD + 0.3V)