® RT8079 2.95V to 6V Input, 3A Output, 2MHz, Synchronous Step-Down Converter General Description Features The RT8079 is a high efficiency step-down converter and capable of delivering 3A output current over a wide input voltage range from 2.95V to 6V. z The RT8079 provides accurate regulation for a variety of loads with ±3% accuracy. For reducing inductor size, it provides up to 2MHz switching frequency. The efficiency is maximized through the integrated 45mΩ MOSFETs and 550μA typical supply current. z z z z z z z z Under voltage lockout voltage of the RT8079 is 2.7V, and it also provides external setting by a resistor network on the enable pin. z z z The RT8079 provides protections such as inductor current limit under voltage lockout and thermal shutdown. The over temperature threshold is 145°C. z The RT8079 is available in WQFN-16L 3x3 package. z Applications z Ordering Information Ω MOSFETs Integrated 45mΩ Input Range : 2.95V to 6V Adjustable PWM Frequency : 300kHz to 2MHz Output Current : 3A 95% Efficiency Adjustable Soft-Start Power Good Indicator Enable Control Under Voltage Lockout Current Limit Thermal Shutdown 16-Lead WQFN Package RoHS Compliant and Halogen Free z Low-Voltage, High-Density Power Systems Distributed Power Systems Point-of-Load Conversions RT8079 Package Type QW : WQFN-16L 3x3 (W-Type) Lead Plating System G : Green (Halogen Free and Pb Free) Marking Information 62= : Product Code 62=YM DNN Note : YMDNN : Date Code Richtek products are : ` RoHS compliant and compatible with the current require- ` Suitable for use in SnPb or Pb-free soldering processes. ments of IPC/JEDEC J-STD-020. Simplified Application Circuit VIN VIN RT8079 EN BOOT PGOOD FB COMP GND AGND SS/TR RT/SYNC Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8079-01 February 2013 SW VOUT is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT8079 Pin Configurations VIN EN PGOOD BOOT (TOP VIEW) 16 15 14 13 VIN VIN GND GND 1 12 2 11 GND 3 10 17 4 9 6 7 8 AGND FB COMP RT/SYNC 5 SW SW SW SS/TR WQFN-16L 3x3 Functional Pin Description Pin No. 1, 2, 16 3, 4, 17 (Exposed Pad) 5 6 7 8 9 10 to 12 Pin Name VIN GND AGND FB COMP RT/SYNC SS/TR SW 13 BOOT 14 PGOOD 15 EN Pin Function Power Input. Power Ground. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. Analog Ground. Feedback Input. Compensation Node for Converter Stability. Frequency Setting and External Synchronous. Clock input. Soft-Start and Tracking. Switch Node. Connect this pin to external L-C filter. Bootstrap Supply for High Side Gate Driver. Connect a capacitor between the BOOT and SW pin. Output of Power Good Indicator. Chip Enable. Externally pulled high to enable and pulled low to disable this chip. It is internally pulled up to high when the pin is floating. Function Block Diagram VIN Internal pull up current Over Temperature Protection UVLO Enable Comparator EN EN Threshold Shutdown Control Current Sense BOOT RT/SYNC Oscillator Control Logic Slope Compensation Driver SW PWM Comparator SS/TR GND Soft-Start VREF Error Amplifier FB PGOOD Threshold PGOOD Comparator PGOOD Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 COMP AGND GND is a registered trademark of Richtek Technology Corporation. DS8079-01 February 2013 RT8079 Operation The RT8079 is a synchronous step-down DC/DC converter with two integrated power MOSFETs. It can deliver up to 3A output current from a 2.95V to 6V input supply. The RT8079's current mode architecture allows the transient response to be optimized over a wider input voltage and load range. Cycle-by-cycle current limit provides protection against shorted outputs and soft-start eliminates input current surge during start-up. The RT8079 is synchronizable to an external clock with frequency ranging from 300kHz to 2MHz. The RT8079 is available in WQFN-16L 3x3 package. High side MOSFET peak current is measured by internal sensing resistor. The Current Signal is where Slope Compensator works together with sensing voltage sensing resistor. The error amplifier adjusts COMP voltage by comparing the feedback signal (VFB) from the output voltage with the internal 0.827V reference. When the load current increases, it causes a drop in the feedback voltage relative to the reference, the COMP voltage then rises to allow higher inductor current to match the load current. EN Comparator The RT8079 is enable when EN pin is higher than 1.25V. It is disable when EN pin lower than 1.18V. There is an internal pull-high current source to charge the EN pin to high when the EN pin is floating. PGOOD Comparator When the feedback voltage (VFB) rises above 93% or falls below 107% of reference voltage the PGOOD open drain output will be high impedance. The PGOOD open drain output will be internally pulled low when the feedback voltage (VFB) falls below 88% or rises above 113% of reference voltage. Soft-Start (SS) An internal current source (2.2μA) charges an external capacitor to build the soft-start ramp voltage (VSS). The VFB voltage will track the VSS during soft-start interval. The Soft-Start setting capacitor (CSS) for the Soft-Start time (TSS) can be easily calculated by the following equation : CSS (nF) = TSS (ms) × 2.2 (μA) 0.827 (V) Over Temperature Protection (OTP) The RT8079 implement an internal over temperature protection. When junction temperature is higher than 145°C, it will stop switching. Until the junction temperature decreases below 125°C, the RT8079 will re-soft-start from initial condition. Oscillator (OSC) The internal oscillator that provides switching frequency from 300kHz to 2MHz. It is adjusted using an external timing resistor. It also can be synchronized by an external clock in the range between 300kHz and 2MHz from RT/ SYNC pin. Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8079-01 February 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT8079 Absolute Maximum Ratings z z z z z z z z z z (Note 1) Supply Input Voltage, VIN ----------------------------------------------------------------------------------------Switch Note Voltage, SW ----------------------------------------------------------------------------------------BOOT to SW --------------------------------------------------------------------------------------------------------Other Pins ------------------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C WQFN-16L 3x3 -----------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) WQFN-16L 3x3, θJA ------------------------------------------------------------------------------------------------WQFN-16L 3x3, θJC -----------------------------------------------------------------------------------------------Junction Temperature ----------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Model) ---------------------------------------------------------------------------------------- Recommended Operating Conditions z z z −0.3V to 7V −0.3V to (VIN + 0.3V) −0.3V to 7V −0.3V to (VIN + 0.3V) 2.128W 47°C/W 7.5°C/W 150°C 260°C −65°C to 150°C 2kV (Note 4) Supply Input Voltage ------------------------------------------------------------------------------------------------ 2.95V to 6V Junction Temperature Range -------------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range -------------------------------------------------------------------------------------- −40°C t o 85°C Electrical Characteristics (VIN = 5V, CIN = 10μF, TA = 25°C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit -- 2.7 2.8 V -- 200 -- mV -- 550 800 μA -- 2 5 μA 0.802 0.827 0.852 V Input Power Supply Under Voltage Lockout Threshold VUVLO Under Voltage Lockout Hysteresis ΔVUVLO Quiescent Current IQ Shutdown Current ISHDN VIN Rising Active, VFB = 1V, Not Switching Feedback Voltage Feedback Voltage VFB Enable EN Input Voltage Threshold Logic-High VIH Rising -- 1.25 -- Logic-Low VIL Falling -- 1.18 -- VEN = VIH + 50mV -- −4.6 -- VEN = VIL − 50mV -- −1.2 -- PGOOD Falling (Fault) -- 88 -- PGOOD Rising (Good) -- 93 -- PGOOD Rising (Fault) -- 113 -- PGOOD Falling (Good) -- 107 -- Input Current Power Good Threshold Voltage Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 V μA %VREF is a registered trademark of Richtek Technology Corporation. DS8079-01 February 2013 RT8079 Parameter Symbol Test Conditions Min Typ Max Unit 300 -- 2000 kHz -- 1000 -- kHz 300 -- 2000 kHz -- 45 -- mΩ -- 42 -- mΩ ILIM 4.2 6.6 -- A Thermal Shutdown Temperature TSD -- 145 -- °C Thermal Shutdown Hysteresis ΔT SD -- 20 -- °C Switching Frequency Setting and External Synchronization (RT/SYNC pin) Switching Frequency Range in RT Mode fOSC Oscillator Frequency Switching Frequency Range in ExtSYNC Mode RRT = 180kΩ fSYNC MOSFET VBOOT − VSW = 5V High Side MOSFET Resistance Low Side MOSFET Resistance Current Limit Current Limit Threshold Over Temperature Protection Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may affect device reliability. Note 2. θJA is measured at TA = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC is measured at the exposed pad of the package. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8079-01 February 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT8079 Typical Application Circuit RT8079 1, 2, 16 VIN C1 10µF R3 100k VIN 15 EN 14 9 C4 10nF PGOOD SS/TR 8 RT/SYNC RRT 180k L 1.5µH 10, 11, 12 SW CBOOT C2 C3 0.1µF 22µF 22µF 13 BOOT 6 FB 7 COMP RC 3, 4, 17(Exposed Pad) GND 7.68k 5 AGND CC 3.3nF VOUT 1.8V R1 11.8k R2 10k Table 1. Recommended Component Selection VOUT (V) R1 (kΩ) R2 (kΩ) RC (kΩ) C C (nF) L (μH) 1.2 4.3 10 11.8 1 1 to 1.5 1.8 11.8 10 7.68 3.3 1 to 1.5 2.5 20.4 10 10.7 2.2 1 to 2.2 3.3 30 10 14 1.8 1 to 2.2 Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 is a registered trademark of Richtek Technology Corporation. DS8079-01 February 2013 RT8079 Typical Operating Characteristics Efficiency vs. Output Current 100 90 90 80 80 70 VIN = 3.3V VIN = 5V 60 Efficiency (%) Efficiency (%) Efficiency vs. Output Current 100 50 40 30 70 60 50 40 30 20 20 10 10 VOUT = 1.8V 0 0.001 0.01 0.1 1 VIN = 5V, VOUT = 3.3V 0 0.001 10 0.01 Output Current (A) 1 10 Output Current (A) Output Voltage vs. Output Current Reference Voltage vs. Temperature 0.85 1.85 0.84 1.84 Output Voltage (V) Reference Voltage (V) 0.1 0.83 0.82 1.83 VIN = 5V VIN = 3.3V 1.82 0.81 1.81 0.80 1.80 VOUT = 1.8V -50 -25 0 25 50 75 100 125 0 0.5 Temperature (°C) 1 1.5 2 2.5 3 Output Current (A) Frequency vs. Input Voltage Frequency vs. Temperature 1000 1.02 1.01 1.00 Frequency (MHz)1 Frequency (kHz)1 980 960 940 920 0.99 0.98 0.97 0.96 0.95 0.94 VIN = 3.3V, VOUT = 1.8V, IOUT = 1A 900 0.93 VOUT = 1.8V, IOUT = 1A 0.92 -50 -25 0 25 50 75 100 Temperature (°C) Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8079-01 February 2013 125 3 3.5 4 4.5 5 5.5 6 Input Voltage (V) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT8079 Current Limit vs. Input Voltage Current Limit vs. Temperature 9.0 9.0 8.4 Current Limit (A) Current Limit (A) 8.5 8.0 7.5 7.0 VIN = 5V VIN = 3.3V 7.8 7.2 6.6 6.5 VOUT = 1.8V VOUT = 1.8V 6.0 6.0 3 3.5 4 4.5 5 5.5 -50 6 -25 0 Input Voltage (V) 50 75 100 125 Temperature (°C) UVLO vs. Temperature Enable Threshold Voltage vs. Temperature 1.40 Enable Threshold Voltage (V)1 2.9 2.8 UVLO (V) 25 2.7 Rising 2.6 2.5 Falling 2.4 2.3 1.32 Rising 1.24 1.16 Falling 1.08 1.00 -50 -25 0 25 50 75 100 125 -50 0 25 50 75 Temperature (°C) Output Ripple Output Ripple VSW (5V/Div) VOUT (10mV/Div) VSW (5V/Div) VOUT (10mV/Div) IL (1A/Div) IL (2A/Div) VIN = 3.3V, VOUT = 1.8V, IOUT = 1A Time (500ns/Div) Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 -25 Temperature (°C) 100 125 VIN = 3.3V, VOUT = 1.8V, IOUT = 3A Time (500ns/Div) is a registered trademark of Richtek Technology Corporation. DS8079-01 February 2013 RT8079 Load Transient Response Load Transient Response VOUT (100mV/Div) VOUT (100mV/Div) IOUT (1A/Div) IOUT (1A/Div) VIN = 5V, VOUT = 1.8V, IOUT = 1A to 3A VIN = 5V, VOUT = 3.3V, IOUT = 1A to 3A Time (100μs/Div) Time (100μs/Div) Switching Frequency vs. RRT Switching Frequency vs. RRT 2000 Low Frequency Switching Frequency (kHz)1 Switching Frequency (kHz)1 1000 840 680 520 360 200 High Frequency 1760 1520 1280 1040 800 300 400 500 600 700 800 900 RRT (k Ω) Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8079-01 February 2013 1000 60 80 100 120 140 160 180 200 RRT (k Ω) is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT8079 Application Information The basic RT8079 application circuit is shown in Typical Application Circuit. External component selection is determined by the maximum load current and begins with the selection of the inductor value and operating frequency followed by CIN and COUT. The switching frequency range from 300kHz to 2MHz. It is adjusted by using a resistor to ground on the RT/SYNC pin. Output Voltage Setting The resistive divider allows the FB pin to sense the output voltage as shown in Figure 1. VOUT R1 FB RT8079 R2 GND Figure 1. Setting the Output Voltage The output voltage setting range is 0.827V to 3.6V and the set by an external resistive divider is according to the following equation : VOUT = VFB ⎛⎜ 1+ R1 ⎞⎟ ⎝ R2 ⎠ where VFB is the feedback reference voltage 0.827V (typ.). Inductor Selection For a given input and output voltage, the inductor value and operating frequency determine the ripple current. The ripple current ΔIL increases with higher VIN and decreases with higher inductance : V V ΔIL = ⎡⎢ OUT ⎤⎥ × ⎡⎢1− OUT ⎤⎥ VIN ⎦ ⎣ fOSC × L ⎦ ⎣ Having a lower ripple current reduces the ESR losses in the output capacitors and the output voltage ripple. Highest efficiency operation is achieved at low frequency with small ripple current. This, however, requires a large inductor. A reasonable starting point for selecting the ripple current is ΔIL = 0.4 (IMAX). The largest ripple current occurs at the highest VIN. To guarantee that the ripple current stays below a specified maximum, the inductor value should be chosen according to the following equation : ⎡ ⎤ ⎡ VOUT VOUT ⎤ L =⎢ × ⎢1 − ⎥ ⎥ f I V × Δ L(MAX) ⎦ ⎣ IN(MAX) ⎦ ⎣ OSC Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 CIN and COUT Selection The input capacitance, C IN, is needed to filter the trapezoidal current at the source of the top MOSFET. To prevent large ripple voltage, a low ESR input capacitor sized for the maximum RMS current should be used. RMS current is given by : V VIN IRMS = IOUT(MAX) OUT −1 VIN VOUT This formula has a maximum at VIN = 2VOUT, where IRMS = IOUT/2. This simple worst case condition is commonly used for design because even significant deviations do not offer much relief. Note that ripple current ratings from capacitor manufacturers are often based on only 2000 hours of life, which makes it advisable to either further derate the capacitor or choose a capacitor rated at a higher temperature than required. Several capacitors may also be placed in parallel to meet size or height requirements in the design. The selection of COUT is determined by the effective series resistance (ESR) that is required to minimize voltage ripple, load step transients, and the amount of bulk capacitance that is necessary to ensure that the control loop is stable. Loop stability can be examined by viewing the load transient response as described in a later section. The output ripple, ΔVOUT, is determined by : 1 ⎤ ΔVOUT ≤ ΔIL ⎡⎢ESR + 8fOSCCOUT ⎥⎦ ⎣ Using Ceramic Input and Output Capacitors Higher values, lower cost ceramic capacitors are now becoming available in smaller case sizes. Their high ripple current, high voltage rating and low ESR make them ideal for switching regulator applications. However, care must be taken when these capacitors are used at the input and output. When a ceramic capacitor is used at the input and the power is supplied by a wall adapter through long wires, a load step at the output can induce ringing at the input, VIN. At best, this ringing can couple with the output and be mistaken as loop instability. At worst, a sudden inrush of current through the long wires can potentially cause a voltage spike at VIN large enough to damage the part. is a registered trademark of Richtek Technology Corporation. DS8079-01 February 2013 RT8079 Thermal Considerations Maximum Power Dissipation (W)1 2.4 For continuous operation, do not exceed absolute maximum junction temperature. The maximum power dissipation depends on the thermal resistance of the IC package, PCB layout, rate of surrounding airflow, and difference between junction and ambient temperature. The maximum power dissipation can be calculated by the following formula : PD(MAX) = (TJ(MAX) − TA) / θJA where TJ(MAX) is the maximum junction temperature, TA is the ambient temperature, and θJA is the junction to ambient thermal resistance. For recommended operating condition specifications, the maximum junction temperature is 125°C. The junction to ambient thermal resistance, θJA, is layout dependent. For WQFN-16L 3x3 package, the thermal resistance, θJA, is 47°C/W on a standard JEDEC 51-7 four-layer thermal test board. The maximum power dissipation at TA = 25°C can be calculated by the following formula : PD(MAX) = (125°C − 25°C) / (47°C/W) = 2.128W for WQFN-16L 3x3 package The maximum power dissipation depends on the operating ambient temperature for fixed T J(MAX) and thermal resistance, θJA. The derating curve in Figure 2 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8079-01 February 2013 Four-Layer PCB 2.0 1.6 1.2 0.8 0.4 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 2. Derating Curve of Maximum Power Dissipation Layout Considerations For the best performance of the RT8079, the following guidelines must be strictly followed. ` The input capacitor should be placed as close as possible to the device pins (VIN and GND). ` The RT/SYNC pin is sensitive. The RT resistor should be located as close as possible to the IC and minimal lengths of trace. ` The SW node is with high frequency voltage swing. It should be kept at a small area. ` Place the feedback components as close as possible to the IC and keep away from the noisy devices. ` The GND and AGND should be connected to a strong ground plane for heat sinking and noise protection. is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT8079 Option R7 R3 SW should be connected to inductor by wide and short trace. Keep sensitive components away from this trace. VIN EN PGOOD BOOT VIN Input capacitor must be placed as close to the IC as possible. 16 15 14 13 C1 VIN VIN GND GND CBOOT 1 12 2 11 GND 3 10 17 4 9 6 7 8 RRT L VOUT C2 C3 CSS AGND FB COMP RT/SYNC 5 SW SW SW SS/TR The feedback components must be connected as close to the device as possible. RC R1 R2 CP CC GND Figure 3. PCB Layout Guide Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 is a registered trademark of Richtek Technology Corporation. DS8079-01 February 2013 RT8079 Outline Dimension D SEE DETAIL A D2 L 1 E E2 e b A A1 1 1 2 2 DETAIL A Pin #1 ID and Tie Bar Mark Options A3 Note : The configuration of the Pin #1 identifier is optional, but must be located within the zone indicated. Dimensions In Millimeters Dimensions In Inches Symbol Min Max Min Max A 0.700 0.800 0.028 0.031 A1 0.000 0.050 0.000 0.002 A3 0.175 0.250 0.007 0.010 b 0.180 0.300 0.007 0.012 D 2.950 3.050 0.116 0.120 D2 1.300 1.750 0.051 0.069 E 2.950 3.050 0.116 0.120 E2 1.300 1.750 0.051 0.069 e L 0.500 0.350 0.020 0.450 0.014 0.018 W-Type 16L QFN 3x3 Package Richtek Technology Corporation 5F, No. 20, Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries. DS8079-01 February 2013 www.richtek.com 13