® RT7238B/C/D/E 8A, 23V, 500kHz Synchronous Step-Down Converter with 3.3V/5V LDO General Description Features The RT7238B/C/D/E is an advanced constant on-time (ACOTTM) mode synchronous step-down converter. The main control loop of RT7238B/C/D/E using an advanced constant on-time (ACOTTM) mode control which provides a very fast transient response. The RT7238B/C/D/E operates from 8V to 23V input voltage. For the RT7238D, the output voltage can be adjusted between 0.9V to 5V. Ordering Information RT7238 Package Type QUF : UQFN-10L 3x3 (FC) (U-Type) Lead Plating System G : Green (Halogen Free and Pb Free) Output Voltage B : 3.35V C : 5.1V D : Adjustable E : 5V Note : Applications Richtek products are : RoHS compliant and compatible with the current require- ments of IPC/JEDEC J-STD-020. Advanced Constant On-Time (ACOT) Control 8V to 23V (RT7238B/C/D/E) Input Voltage Range @ 8A Output Current ACOTTM Mode Performs Fast Transient Response ACOTTM Architecture to Enable all MLCC Output Capacitor Usage Fixed 500kHz Switching Frequency High Efficient Internal Power MOSFET Switch 27mΩ Ω (High-Side) and 10mΩ Ω (Low-Side) Adjustable Output Voltage from 0.9V to 5V (RT7238D) Fixed 3.3V (RT7238B/D) or 5V (RT7238C/E) LDO Output Supplies 70mA Pre-biased Soft-Start Cycle-by-Cycle Over-Current Protection Input Under-Voltage Lockout Thermal Shutdown Output Over/Under-Voltage Protection Suitable for use in SnPb or Pb-free soldering processes. Industrial and Commercial Low Power Systems Computer Peripherals LCD Monitors and TVs Green Electronics/Appliances Point of Load Regulation for High-Performance DSPs, FPGAs, and ASICs Simplified Application Circuit RT7238B VIN PGOOD VIN CIN GND VLDO VEN1 VEN2 LDO CLDO BOOT VIN VPGOOD CIN CBOOT RT7238C/E VIN PGOOD BOOT GND VOUT EN1 EN2 VOUT COUT LX VLDO VEN LDO CLDO EN Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7238B/C/D/E-01 April 2015 VOUT VIN CBOOT L1 L1 LX VPGOOD CIN GND VOUT COUT RT7238D PGOOD VIN BOOT VLDO VILMT VEN L1 FB ILMT EN VOUT LX LDO CLDO VPGOOD CBOOT BYP CFF(opt) VBYP CBYP R1 COUT R2 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT7238B/C/D/E Marking Information Pin Configurations (TOP VIEW) RT7238BGQUF YMDNN : Date Code RT7238CGQUF 4R= : Product Code 6 7 5 8 VIN 9 GND 8 VIN 9 GND 8 VIN 9 GND 4 3 2 10 1 YMDNN : Date Code RT7238B LDO 4R=YM DNN BOOT LDO VOUT NC PGOOD EN1 LX YB=YM DNN EN2 YB= : Product Code RT7238DGQUF 4V= : Product Code YMDNN : Date Code 6 7 5 4 3 2 10 1 LX 4V=YM DNN BOOT NC VOUT NC PGOOD EN RT7238C/E BYP RT7238EGQUF 6L= : Product Code YMDNN : Date Code BOOT LDO FB ILMT PGOOD EN 6 7 5 4 3 2 1 10 LX 6L=YM DNN RT7238D UQFN-10L 3x3 (FC) Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS7238B/C/D/E-01 April 2015 RT7238B/C/D/E Functional Pin Description RT7238B Pin No. Pin Name Pin Function 1 EN1 Enable Control Input of the DC/DC Regulator. Pull this pin high to turn on the regulator. Do not leave this pin floating. 2 PGOOD Power Good Indicator. Open-drain output when the output voltage is within 91% to 120% of regulation point. 3 NC No Internal Connection. 4 VOUT Output. Connect to the Output of DC/DC Regulator. The pin also provide the bypass input for internal LDO. 5 LDO Internal 3.3V LDO Output. Power supply for internal analog circuits and driving circuit. Bypass a 2.2F capacitor to GND. This pin is also capable of sourcing 70mA current for external load. 6 BOOT Bootstrap Supply for High-Side Gate Driver. Decouple this pin to LX pin with a 0.1F ceramic capacitor. 7 EN2 Enable Control Input of the IC and Internal LDO. Pull this pin high to turn on the IC and internal LDO. Do not leave this pin floating. 8 VIN Power Input. Decouple this pin to GND pin with a at least 10F ceramic capacitor. 9 GND Ground. 10 LX Switch Node. Connect this pin to the external inductor. RT7238C/E Pin No. Pin Name Pin Function 1 EN Enable Control of the DC/DC Regulator. Pull this pin high to turn on the regulator. Do not leave this pin floating. 2 PGOOG Power Good Indicator. Open-drain output when the output voltage is within 91% to 120% of regulation point. NC No Internal Connection. 4 VOUT Output. Connect to the output of DC/DC regulator. The pin also provide the bypass input for internal LDO. 6 BOOT Bootstrap Supply for High-Side Gate Driver. Decouple this pin to LX pin with a 0.1F ceramic capacitor. 7 LDO Internal 5V LDO Output. Power supply for internal analog circuits and driving circuit. Bypass a 2.2F capacitor to GND. This pin is also capable of sourcing 70mA current for external load. 8 VIN Power Input. Decouple this pin to GND pin with a at least 10F ceramic cap. 9 GND Ground. 10 LX Switch Node. Connect this pin to the external inductor. 3, 5 Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7238B/C/D/E-01 April 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT7238B/C/D/E RT7238D Pin No. Pin Name Pin Function 1 EN Enable Control Input. Pull this pin high to turn on the IC. Do not leave this pin floating. 2 PGOOD Power Good Indicator. Open-drain output when the output voltage is within 91% to 120% of regulation point. 3 ILMT Current Limit Setting. The current limit is set to 8A, 12A or 16A when this pin is pulled low, floating or pulled high, respectively. 4 FB Feedback Voltage Input. Connect this pin to the center point of the output resistor divider to program the output voltage. 5 LDO Internal 3.3V LDO Output. Power supply for internal analog circuits and driving circuit. Bypass a 2.2F capacitor to GND. This pin is also capable sourcing 70mA current for external load. 6 BOOT Decouple this pin to LX pin with a 0.1F Ceramic Capacitor. 7 BYP Bypass Input for the Internal LDO. BYP is externally connected to the output of switching regulator. When the BYP voltage rises above the bypass switch turn-on threshold, the LDO regulator shuts down and the LDO pin is connected to the BYP pin through an internal switch. 8 VIN Power Input. Decouple this pin to GND with a at least 10F ceramic capacitor. 9 GND Ground. 10 LX Switch Node. Connect this pin to the external inductor. Function Block Diagram RT7238B VIN BOOT Input UVLO 3.9V LX EN1 EN2 PWM Control & Protect Logic Internal SST Thermal Protection 0.6V VOUT - Current Sense + GND - PGOOD + LDO VIN 3.1V + EN2 3.3V LDO - Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 is a registered trademark of Richtek Technology Corporation. DS7238B/C/D/E-01 April 2015 RT7238B/C/D/E RT7238C/E VIN BOOT Input UVLO 3.9V LX EN Internal SST PWM Control & Protect Logic Thermal Protection 0.6V VOUT - Current Sense + - GND + PGOOD VIN RT7238C : 4.8V RT7238E : 4.7V 5V LDO + - LDO RT7238D VIN Input UVLO 3.9V BOOT ILMT LX EN + 0.8V PWM Control & Protect Logic - Internal SST - Current Sense Thermal Protection 0.6V FB + GND PGOOD + VIN 3.1V + LDO 3.3V LDO - BYP Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7238B/C/D/E-01 April 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT7238B/C/D/E Absolute Maximum Ratings (Note 1) Supply Voltage, VIN -------------------------------------------------------------------------------------------Enable Pin Voltage, VEN, EN1, EN2 --------------------------------------------------------------------------Switch Voltage, VLX -------------------------------------------------------------------------------------------Boot Voltage, VBOOT ------------------------------------------------------------------------------------------Other I/O Pin Voltages ---------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C UQFN-10L 3x3 (FC) -------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) UQFN-10L 3x3 (FC), θJA -------------------------------------------------------------------------------------Junction Temperature -----------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------Storage Temperature Range --------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Model) ----------------------------------------------------------------------------------- Recommended Operating Conditions −0.3V to 27V −0.3V to 27V −0.3V to (VIN + 0.3V) (VLX − 0.3V) to (VLX + 6V) −0.3V to 6 V 3.33W 30°C/W 150°C 260°C −65°C to 150°C 2kV (Note 4) Supply Input Voltage, VIN (RT7238B/C/D/E) -------------------------------------------------------------- 8V to 23V Junction Temperature Range ---------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range ---------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VIN = 12V, TA = 25°C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max VEN1 = 0, VEN2 = 0 (RT7238B) -- 5 15 VEN = 0 (RT7238D) -- 5 15 VEN = 0 (RT7238C/E) IOUT = 0, VOUT = 3.35V x 105% VEN1 = VEN2 = 2V (RT7238B) IOUT = 0, VFB = VREF x 105% VEN = 2V (RT7238D) IOUT = 0, VOUT = 5.1V x 105% VEN = 2V (RT7238C/E) -- 35 45 -- -- 110 -- -- 110 -- -- 110 0.8 -- -- -- -- 0.3 VEN > 4.5V -- 140 -- VEN 4.5V -- 1 -- (RT7238B) 3.316 3.35 3.383 (RT7238C) 5.049 5.1 5.151 (RT7238E) 4.95 5 5.05 Unit Supply Current Supply Current (Shutdown) Supply Current (Quiescent) ISHDN IQ A A Logic Threshold EN Input Voltage Logic-High VIH Logic-Low EN Input Current VIL IEN V A Output Voltage Output Voltage Setpoint VOUT Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 V is a registered trademark of Richtek Technology Corporation. DS7238B/C/D/E-01 April 2015 RT7238B/C/D/E Parameter Symbol Test Conditions Min Typ Max Unit 0.594 0.6 0.606 V 50 -- 50 nA Feedback Voltage Feedback Reference Voltage VREF (RT7238D) Feedback Current VFB = 4V (RT7238D) IFB On-Resistance High-Side Switch On-Resistance Low-Side RDS(ON)_H -- 27 -- RDS(ON)_L -- 10 -- Discharge FET RON RDis -- 50 -- (RT7238B/C/E) 9 -- -- A ILMT = ”0” 8 -- -- 12 -- -- 16 -- -- m Current Limit Bottom FET Current limit ILIM ILMT = Floating (RT7238D) ILMT = ”1” A ILMT Rising Threshold VILMTH VLDO 0.8 -- VLDO V ILMT Falling Threshold VILMTL -- -- 0.8 V 0.45 0.5 0.55 MHz Oscillator Frequency Oscillator Frequency fOSC On-Time Timer Control Minimum On-Time TON(MIN) -- 50 -- ns Minimum Off-Time TOFF(MIN) -- 200 -- ns Soft-Start Soft-Start Time TSS From EN/EN1 High to PGOOD High -- 1.5 -- ms Input UVLO Threshold VUVLO Wake up -- -- 3.9 V UVLO Hysteresis VHYS -- 0.35 -- V 115 120 125 % Output Over-Voltage Hysteresis -- 3 -- % Output Over-Voltage Delay Time -- 20 -- s UVLO Output Over-Voltage Protection Output Over-Voltage Threshold VFB Rising Output Under-Voltage Protection Output Under-Voltage Threshold VFB Falling 56 59 62 % Output Under-Voltage Delay Time FB Forced Below UV Threshold -- 2 -- s UV Blank Time From EN/EN1 High -- 1.5 -- ms Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7238B/C/D/E-01 April 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT7238B/C/D/E Parameter Symbol Test Conditions Min Typ Max Unit 88 91 94 % -- 6 -- % -- 10 -- s (RT7238B/D) 3.267 3.3 3.333 (RT7238C/E) 4.95 5 5.05 100 120 160 mA -- 3 5 (RT7238B/D) -- 3.1 -- (RT7238C) -- 4.8 -- (RT7238E) -- 4.7 -- (RT7238B/D) -- 0.2 -- (RT7238C/E) -- 0.1 -- TSD -- 150 -- C TSD -- 25 -- C Power Good Power Good Threshold VFB Rising (Good) Power Good Hysteresis Power Good Delay Time VFB Rising (Good) LDO Regulator LDO Output Voltage VLDO LDO Output Current Limit ILMTLDO V Bypass Switch Bypass Switch RON Bypass Switch Turn-on Voltage Rbyp Vbyp_on Bypass Switch Switchover Hysteresis Thermal Shutdown Thermal Shutdown Threshold Thermal Shutdown Hysteresis V V 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. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 is a registered trademark of Richtek Technology Corporation. DS7238B/C/D/E-01 April 2015 RT7238B/C/D/E Typical Application Circuit VIN 8V to 23V VLDO 3.3V RT7238B 2 PGOOD CIN 10µF x 2 9 BOOT 6 GND 8 CLDO 2.2µF VEN1 VEN2 VIN 8V to 23V VLDO 5V VLDO 3.3V VILMT VEN 5 LDO LX 1 EN1 7 EN2 VOUT 7 CLDO 2.2µF LDO VOUT 1 EN 8 CIN 10µF x 2 9 CLDO 2.2µF LX RT7238D VIN GND 5 LDO 3 ILMT 1 EN PGOOD FB BYP CBOOT 0.1µF L1 VOUT 3.35V/8A COUT 22µF x 4 4 10 VPGOOD CBOOT 0.1µF L1 VOUT 5.1V/8A COUT 22µF x 4 2.2µH 4 2 BOOT 6 LX VPGOOD 2.2µH RT7238C/E 2 VIN PGOOD CIN 10µF x 2 9 BOOT 6 GND Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7238B/C/D/E-01 April 2015 10 8 VEN VIN 8V to 23V VIN 10 VPGOOD CBOOT 0.1µF L1 1µH CFF(opt) 4 7 CBYP 4.7µF VBYP R1 15k VOUT 1.05V/8A COUT 22µF x 4 R2 20k is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT7238B/C/D/E Typical Operating Characteristics Efficiency vs. Output Current 100.0 Efficiency vs. Output Current 100.0 RT7238B 95.0 Efficiency (%) 95.0 Efficiency (%) RT7238C VIN = 8V VIN = 12V VIN = 19V 90.0 VIN = 8V VIN = 12V VIN = 19V 90.0 85.0 85.0 EN = 2V EN1 = EN2 = 2V 80.0 0.001 0.010 0.100 1.000 80.0 0.001 10.000 0.010 Output Current (A) Efficiency (%) Switching Frequency (kHz)1 RT7238D VIN = 8V VIN = 12V VIN = 19V 90.0 85.0 80.0 RT7238B 500.0 400.0 VIN = 8V VIN = 12V VIN = 19V 300.0 200.0 100.0 EN1 = EN2 = 2V EN = 2V, VOUT = 1.05V 75.0 0.001 0.010 0.100 1.000 0.0 0.001 10.000 0.010 Output Current (A) Switching Frequency (kHz)1 Switching Frequency (kHz)1 RT7238C 500.0 VIN = 8V VIN = 12V VIN = 19V 300.0 200.0 100.0 0.010 0.100 1.000 Output Current (A) Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 10.000 RT7238D 500.0 VIN = 8V VIN = 12V VIN = 19V 400.0 300.0 200.0 100.0 EN = 2V 0.0 0.001 1.000 Switching Frequency vs. Output Current 600.0 400.0 0.100 Output Current (A) Switching Frequency vs. Output Current 600.0 10.000 Switching Frequency vs. Output Current 600.0 95.0 1.000 Output Current (A) Efficiency vs. Output Current 100.0 0.100 10.000 EN = 2V, VOUT = 1.05V 0.0 0.001 0.010 0.100 1.000 10.000 Output Current (A) is a registered trademark of Richtek Technology Corporation. DS7238B/C/D/E-01 April 2015 RT7238B/C/D/E Quiescent Current vs. Input Voltage Quiescent Current vs. Input Voltage 120 RT7238B 110 Quiescent Current (μA) Quiescent Current (μA) 120 100 90 80 RT7238C 110 100 90 80 VIN = 12V, EN1 = EN2 = 2V, No Switching VIN = 12V, EN = 2V, No Switching 70 70 5 7 9 11 13 15 17 19 21 23 5 7 9 Input Voltage (V) Shutdown Current (μA)1 Quiescent Current (μA) 110 100 90 80 9 11 13 15 17 21 23 19 21 11 10 9 8 7 5 23 7 9 11 13 15 17 19 21 23 Input Voltage (V) Shutdown Current vs. Input Voltage Shutdown Current vs. Input Voltage 12 RT7238C RT7238D 11 37 Shutdown Current (μA)1 Shutdown Current (μA)1 19 RT7238B Input Voltage (V) 38 17 VIN = 12V, EN1 = EN2 = GND VIN = 12V, EN = 2V, No Switching 70 7 15 Shutdown Current vs. Input Voltage 12 RT7238D 5 13 Input Voltage (V) Quiescent Current vs. Input Voltage 120 11 36 35 34 33 10 9 8 7 6 VIN = 12V, EN = GND 32 VIN = 12V, EN = GND 5 5 7 9 11 13 15 17 19 21 Input Voltage (V) Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7238B/C/D/E-01 April 2015 23 5 7 9 11 13 15 17 19 21 23 Input Voltage (V) is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT7238B/C/D/E Output Voltage vs. Output Current 3.4 Output Voltage vs. Output Current 5.4 RT7238B 3.4 VIN = 19V VIN = 12V VIN = 8V 3.3 Output Voltage (V) Output Voltage (V) RT7238C 5.3 3.3 3.2 5.2 5.1 VIN = 19V VIN = 12V VIN = 8V 5.0 4.9 4.8 4.7 3.2 4.6 EN1 = EN2 = 2V 3.1 0.001 0.01 0.1 1 EN = 2V 4.5 0.001 10 0.01 Output Current (A) LDO Output Voltage (V) Output Voltage (V) VIN = 19V VIN = 12V VIN = 8V 1.05 RT7238B 3.40 3.35 3.30 VIN = 8V VIN = 12V VIN = 19V 3.25 3.20 EN1 = GND, EN2 = 2V EN = 2V, R1 = 15.4k, R2 = 20k 3.15 0.01 0.1 1 10 0 0.02 Output Current (A) RT7238C 5.15 5.10 5.05 5.00 4.95 VIN = 8V VIN = 12V VIN = 19V 4.90 4.85 0.06 0.08 LDO Output Voltage vs. Output Current 3.45 LDO Output Voltage (V) LDO Output Voltage (V) 5.20 0.04 Output Current (A) LDO Output Voltage vs. Output Current 5.25 10 LDO Output Voltage vs. Output Current 3.45 RT7238D 1.00 0.001 1 Output Current (A) Output Voltage vs. Output Current 1.10 0.1 4.80 RT7238D 3.40 3.35 3.30 VIN = 8V VIN = 12V VIN = 19V 3.25 3.20 EN = GND EN = 2V 3.15 4.75 0.00 0.02 0.04 0.06 Output Current (A) Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 0.08 0 0.02 0.04 0.06 0.08 Output Current (A) is a registered trademark of Richtek Technology Corporation. DS7238B/C/D/E-01 April 2015 RT7238B/C/D/E Start-Up through EN2 Start-Up through EN1 RT7238B RT7238B VOUT (2V/Div) VOUT (2V/Div) IL (2A/Div) IL (2A/Div) PGOOD (2V/Div) VLDO (2V/Div) EN1 (9V/Div) EN2 (9V/Div) VIN = 12V, EN2 = 2V, No Load VIN = 12V, EN1 = 2V, No Load Time (500μs/Div) Time (500μs/Div) Start-Up through EN Start-Up through EN RT7238C RT7238D VOUT (2V/Div) IL (2A/Div) VOUT (400mV/Div) EN (9V/Div) PGOOD (5V/Div) EN (9V/Div) IL (2A/Div) VIN = 12V, No Load PGOOD (3V/Div) VIN = 12V, No Load Time (500μs/Div) Time (500μs/Div) Power-Off through EN1 Power-Off through EN2 RT7238B RT7238B VOUT (2V/Div) VOUT (2V/Div) IL (2A/Div) IL (2A/Div) PGOOD (2V/Div) VLDO (2V/Div) EN1 (9V/Div) VIN = 12V, EN2 = 2V, No Load Time (5ms/Div) Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7238B/C/D/E-01 April 2015 EN2 (9V/Div) VIN = 12V, EN1 = 2V, No Load Time (10ms/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 13 RT7238B/C/D/E Power-Off through EN Power-Off through EN RT7238C VOUT (2V/Div) VOUT (500mV/Div) PGOOD (2V/Div) IL (2A/Div) IL (2A/Div) PGOOD (5V/Div) EN (9V/Div) RT7238D VIN = 12V, No Load EN (9V/Div) VIN = 12V, No Load Time (2ms/Div) Time (2ms/Div) Load Transient Response Load Transient Response RT7238C RT7238B VOUT (100mV/Div) VOUT (100mV/Div) IL (6A/Div) IL (6A/Div) LX (9V/Div) LX (9V/Div) VIN = 12V, EN1 = EN2 = 2V VIN = 12V, EN = 2V Time (100μs/Div) Time (100μs/Div) Load Transient Response Over Voltage Protection RT7238D VOUT (60mV/Div) VOUT (2V/Div) IL (6A/Div) LX (9V/Div) PGOOD (2V/Div) IL (6A/Div) VIN = 12V, EN = 2V Time (100μs/Div) Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 14 RT7238B LX (9V/Div) VIN = 12V, VOUT = 5V, EN1 = EN2 = 2V Time (100μs/Div) is a registered trademark of Richtek Technology Corporation. DS7238B/C/D/E-01 April 2015 RT7238B/C/D/E Over Voltage Protection Over Voltage Protection RT7238C RT7238D VOUT (4V/Div) VOUT (1V/Div) PGOOD (5V/Div) IL (6A/Div) LX (9V/Div) PGOOD (2V/Div) IL (2A/Div) LX (9V/Div) VIN = 12V, VOUT = 7V, EN = 2V VIN = 12V, VOUT = 2V, EN = 2V Time (50μs/Div) Time (50μs/Div) Under Voltage Protection Under Voltage Protection RT7238B RT7238C VOUT (2V/Div) VOUT (4V/Div) PGOOD (2V/Div) IL (6A/Div) PGOOD (5V/Div) IL (6A/Div) LX (9V/Div) VIN = 12V, EN1 = EN2 = 2V Time (20μs/Div) LX (9V/Div) VIN = 12V, EN = 2V Time (20μs/Div) Under Voltage Protection RT7238D VOUT (1V/Div) IL (6A/Div) PGOOD (2V/Div) LX (9V/Div) VIN = 12V, EN = 2V Time (50μs/Div) Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7238B/C/D/E-01 April 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 15 RT7238B/C/D/E Application Information The RT7238B/C/D/E are high-performance 500kHz 8A stepdown regulators with internal power switches and synchronous rectifiers. They feature an Advanced Constant On-Time (ACOTTM) control architecture that provides stable operation for ceramic output capacitors without complicated external compensation, among other benefits. The input voltage range are from 8V to 23V (RT7238B/C/ D/E). The output voltage are fixed 3.35V (RT7238B), 5.1V (RT7238C), 5V (RT7238E) or adjustable from 0.9V to 5V (RT7238D). The proprietary ACOT TM control scheme improves conventional constant on-time architectures, achieving nearly constant switching frequency over line, load, and output voltage ranges. Since there is no internal clock, response to transients is nearly instantaneous and inductor current can ramp quickly to maintain output regulation without large bulk output capacitance. The RT7238B/C/D/E includes 5V (RT7238C) and 3.3V (RT7238B/D) linear regulators (LDO). The linear regulator steps down input voltage to supply both internal circuitry and gate drivers. The synchronous switch gate drivers are directly powered by LDO. When VOUT rises above 3.1V (RT7238B/D), 4.8V (RT7238C), 4.7V (RT7238E) an automatic circuit disconnects the linear regulator and allows the device to be powered by VOUT (RT7238B/C/ E) or via the BYP pin (RT7238D). ACOTTM Control Architecture Making the on-time proportional to VOUT and inversely proportional to VIN is not sufficient to achieve good constant-frequency behavior for several reasons. First, voltage drops across the MOSFET switches and inductor cause the effective input voltage to be less than the measured input voltage and the effective output voltage to be greater than the measured output voltage as sensing input and output voltage from LX pin. When the load change, the switch voltage drops change causing a switching frequency variation with load current. Also, at light loads if the inductor current goes negative, the switch dead-time between the synchronous rectifier turn-off and the high-side switch turn-on allows the switching node to rise to the input voltage. This increases the effective onCopyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 16 time and causes the switching frequency to drop noticeably. One way to reduce these effects is to measure the actual switching frequency and compare it to the desired range. This has the added benefit eliminating the need to sense the actual output voltage, potentially saving one pin connection. ACOTTM uses this method, measuring the actual switching frequency and modifying the on-time with a feedback loop to keep the average switching frequency in the desired range. In order to achieve good stability with low-ESR ceramic capacitors, ACOTTM uses a virtual inductor current ramp generated inside the IC. This internal ramp signal replaces the ESR ramp normally provided by the output capacitor's ESR. The ramp signal and other internal compensations are optimized for low-ESR ceramic output capacitors. ACOTTM One-shot Operation The RT7238B/C/D/E control algorithm is simple to understand. The feedback voltage, with the virtual inductor current ramp added, is compared to the reference voltage. When the combined signal is less than the reference, the on-time one-shot is triggered, as long as the minimum off-time one-shot is clear and the measured inductor current (through the synchronous rectifier) is below the current limit. The on-time one-shot turns on the high-side switch and the inductor current ramps up linearly. After the on-time, the high-side switch is turned off and the synchronous rectifier is turned on and the inductor current ramps down linearly. At the same time, the minimum off-time one-shot is triggered to prevent another immediate on-time during the noisy switching time and allow the feedback voltage and current sense signals to settle. The minimum off-time is kept short (200ns typical) so that rapidly-repeated ontimes can raise the inductor current quickly when needed. Bypass Function The RT7238B/C/D/E provide bypass function to improve power conversion efficiency. When the bypass pin voltage(RT7238D) or output voltage (RT7238B/C/E) rises is a registered trademark of Richtek Technology Corporation. DS7238B/C/D/E-01 April 2015 RT7238B/C/D/E above bypass switch turn-on threshold, the LDO regulator will shut down and the LDO pin will be connected to the bypass pin (RT7238D) or output pin (RT7238B/C/E) through an internal switch. Because the internal switch has turnon resistor, there will be a naturally voltage drop of LDO pin as bypass function working. In practical application, the voltage drop of LDO pin should be considered. Diode Emulation Mode In diode emulation mode, the RT7238B/C/D/E automatically reduces switching frequency at light load conditions to maintain high efficiency. This reduction of frequency is achieved smoothly. As the output current decreases from heavy load condition, the inductor current is also reduced, and eventually comes to the point that its current valley touches zero, which is the boundary between continuous conduction and discontinuous conduction modes. To emulate the behavior of diodes, the low-side MOSFET allows only partial negative current to flow when the inductor free wheeling current becomes negative. As the load current is further decreased, it takes longer and longer time to discharge the output capacitor to the level that requires the next “ON” cycle. In reverse, when the output current increases from light load to heavy load, the switching frequency increases to the preset value as the inductor current reaches the continuous conduction. The transition load point to the light load operation is shown in Figure 1. and can be calculated as follows : IL IPEAK ILOAD = IPEAK / 2 tON t Figure 1. Boundary Condition of CCM/DEM (VIN VOUT ) tON 2L where tON is the on-time. ILOAD(SKIP) The switching waveforms may appear noisy and asynchronous when light load causes diode emulation operation. This is normal and results in high efficiency. Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7238B/C/D/E-01 April 2015 During discontinuous switching, the on-time is immediately increased to add “hysteresis” to discourage the IC from switching back to continuous switching unless the load increases substantially. The IC returns to continuous switching as soon as an on-time is generated before the inductor current reaches zero. The on-time is reduced back to the length needed for 500kHz switching and encouraging the circuit to remain in continuous conduction, preventing repetitive mode transitions between continuous switching and discontinuous switching. Linear Regulators (LDO) The RT7238B/C/D/E includes 5V (RT7238C/E) and 3.3V (RT7238B/D) linear regulators (LDO). The regulators can supply up to 70mA for external loads. When VOUT is higher than the switch over threshold 3.1V (RT7238B/D), 4.8V (RT7238C), 4.7V (RT7238E) an internal 3Ω PMOSFET switch connects VOUT (RT7238B/C/E) or BYP (RT7238D) to the LDO pin while simultaneously disconnects the internal linear regulator. Current Limit Slope = (VIN - VOUT) / L 0 Trade offs in DEM noise vs. light load efficiency is made by varying the inductor value. Generally, low inductor values produce a broader efficiency vs. load curve, while higher values result in higher full load efficiency (assuming that the coil resistance remains fixed) and less output voltage ripple. Penalties for using higher inductor values include larger physical size and degraded load transient response (especially at low input voltage levels). The RT7238B/C/D/E current limit is fixed 9A (RT7238B/ C/E) or adjustable (8A,12A,16A) by ILMT pin (RT7238D) and it is a cycle-by-cycle “valley” type, measuring the inductor current through the synchronous rectifier during the off-time while the inductor current ramps down. The current is determined by measuring the voltage between source and drain of the synchronous rectifier, adding temperature compensation for greater accuracy. If the current exceeds the current limit, the on-time one-shot is inhibited until the inductor current ramps down below the current limit. Thus, only when the inductor current is well below the current limit, another on-time is permitted. If the output current exceeds the available inductor current is a registered trademark of Richtek Technology Corporation. www.richtek.com 17 RT7238B/C/D/E (controlled by the current limit mechanism), the output voltage will drop. If it drops below the output under-voltage protection level (see next section) the IC will stop switching to avoid excessive heat. The RT7238B/C/D/E also includes a negative current limit to protect the IC against sinking excessive current and possibly damaging the IC. If the voltage across the synchronous rectifier indicates the negative current is too high, the synchronous rectifier turns off until after the next high-side on-time. Output Over-voltage Protection and Under-voltage Protection The RT7238B/C/D/E include output over-voltage protection (OVP). If the output voltage rises above the regulation level, the high-side and low-side switch naturally remain off. If the output voltage exceeds the OVP trip threshold for longer than 20μs (typical), the IC's OVP is triggered. The RT7238B/C/D/E also include output Under-Voltage Protection (UVP). If the output voltage drops below the UVP trip threshold for longer than 2μs (typical) the IC's UVP is triggered. The RT7238B/C/D/E use latch-off mode OVP and UVP. When the protection function is triggered, the IC will shut down. The IC stops switching and is latched off. To restart operation, toggle EN or power the IC off and then on again. Input Under-Voltage Lockout In addition to the enable function, the RT7238B/C/D/E feature an Under-Voltage Lockout (UVLO) function that monitors the input voltage. To prevent operation without fully-enhanced internal MOSFET switches, this function inhibits switching when input voltage drops below the UVLO-falling threshold. The IC resumes switching when input voltage exceeds the UVLO-rising threshold. Over-Temperature Protection The RT7238B/C/D/E includes an Over-Temperature Protection (OTP) circuitry to prevent overheating due to excessive power dissipation. The OTP will shut down switching operation when the junction temperature exceeds 150°C. Once the junction temperature cools down by approximately 25°C the IC will resume normal Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 18 operation with a complete soft-start. For continuous operation, provide adequate cooling so that the junction temperature does not exceed 150°C. Enable and Disable The enable input (EN) has a logic-low level of 0.3V. When VEN is below this level the IC enters shutdown mode and supply current drops to less than 5μA.(typical) When VEN exceeds its logic-high level of 0.8V the IC is fully operational. Soft-Start The RT7238B/C/D/E provides an internal soft-start function to prevent large inrush current and output voltage overshoot when the converter starts up. The soft-start (SS) automatically begins once the chip is enabled. During softstart, it clamps the ramping of internal reference voltage which is compared with FB signal. The typical soft-start duration is 0.8ms. A unique PWM duty limit control that prevents output over-voltage during soft-start period is designed specifically for FB floating. Power Off When EN is low or any protection function is triggered, an internal discharging resistor about 50Ω will discharging the residual charges of output capacitors to make sure next soft start without any remaining charge. Power Good Output (PGOOD) The power good output is an open drain output that requires a pull-up resistor. When the output voltage is 15% (typical) below its set voltage, PGOOD will be pulled low. It is held low until the output voltage returns to 91% of its set voltage once more. During soft-start, PGOOD is actively held low and only allowed to be pulled high after soft-start is over and the output reaches 91% of its set voltage. There is a 2μs delay built into PGOOD circuitry to prevent false transition. External Bootstrap Capacitor (CBOOT) Connect a 0.1μF low ESR ceramic capacitor between BOOT pin and LX pin. This bootstrap capacitor provides the gate driver supply voltage for the high-side N-MOSFET switch. is a registered trademark of Richtek Technology Corporation. DS7238B/C/D/E-01 April 2015 RT7238B/C/D/E The internal power MOSFET switch gate driver is optimized to turn the switch on fast enough for low power loss and good efficiency, but also slow enough to reduce EMI. Switch turn-on is when most EMI occurs since VLX rises rapidly. During switch turn-off, LX is discharged relatively slowly by the inductor current during the deadtime between high-side and low-side switch on-times. In some cases it is desirable to reduce EMI further, at the expense of some additional power dissipation. The switch turn-on can be slowed by placing a small (<10Ω) resistance between BOOT and the external bootstrap capacitor. This will slow the high-side switch turn-on and VLX's rise. Output Voltage Setting (RT7238D) Set the desired output voltage using a resistive divider from the output to ground with the midpoint connected to FB. The output voltage is set according to the following equation : VOUT(valley) 0.6V (1 R1 ) R2 VOUT R1 FB RT7238D R2 GND Figure 2. Output Voltage Setting Place the FB resistors within 5mm of the FB pin. Choose R2 between 10kΩ and 100kΩ to minimize power consumption without excessive noise pick-up and calculate R1 as follows : R2 (VOUT(valley) 0.6V) R1 0.6V For output voltage accuracy, use divider resistors with 1% or better tolerance. Inductor Selection Selecting an inductor involves specifying its inductance and also its required peak current. The exact inductor value is generally flexible and is ultimately chosen to obtain the best mix of cost, physical size, and circuit efficiency. Lower inductor values benefit from reduced size and cost Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7238B/C/D/E-01 April 2015 and they can improve the circuit's transient response, but they increase the inductor ripple current and output voltage ripple and reduce the efficiency due to the resulting higher peak currents. Conversely, higher inductor values increase efficiency, but the inductor will either be physically larger or have higher resistance since more turns of wire are required and transient response will be slower since more time is required to change current (up or down) in the inductor. A good compromise between size, efficiency, and transient response is to use a ripple current (ΔIL) about 20-50% of the desired full output load current. Calculate the approximate inductor value by selecting the input and output voltages, the switching frequency (f SW), the maximum output current (IOUT(MAX)) and estimating a ΔIL as some percentage of that current. V (VIN VOUT ) L OUT VIN fSW IL Once an inductor value is chosen, the ripple current (ΔIL) is calculated to determine the required peak inductor current. VOUT (VIN VOUT ) and VIN fSW L I IL(PEAK) IOUT(MAX) L 2 IL To guarantee the required output current, the inductor needs a saturation current rating and a thermal rating that exceeds IL(PEAK). These are minimum requirements. To maintain control of inductor current in overload and shortcircuit conditions, some applications may desire current ratings up to the current limit value. However, the IC's output under-voltage shutdown feature make this unnecessary for most applications. For best efficiency, choose an inductor with a low DC resistance that meets the cost and size requirements. For low inductor core losses some type of ferrite core is usually best and a shielded core type, although possibly larger or more expensive, will probably give fewer EMI and other noise problems. Input Capacitor Selection High quality ceramic input decoupling capacitor, such as X5R or X7R, with values greater than 20μF are recommended for the input capacitor. The X5R and X7R ceramic capacitors are usually selected for power regulator is a registered trademark of Richtek Technology Corporation. www.richtek.com 19 RT7238B/C/D/E capacitors because the dielectric material has less capacitance variation and more temperature stability. Voltage rating and current rating are the key parameters when selecting an input capacitor. Generally, selecting an input capacitor with voltage rating 1.5 times greater than the maximum input voltage is a conservatively safe design. The input capacitor is used to supply the input RMS current, which can be approximately calculated using the following equation : IRMS VOUT V I 2 (1 OUT ) IOUT 2 L VIN VIN 12 The next step is to select a proper capacitor for RMS current rating. One good design uses more than one capacitor with low Equivalent Series Resistance (ESR) in parallel to form a capacitor bank. The input capacitance value determines the input ripple voltage of the regulator. The input voltage ripple can be approximately calculated using the following equation : VIN IOUT VIN V (1 OUT ) CIN fSW VOUT VIN The typical operating circuit is recommended to use two 10μF and low ESR ceramic capacitors on the input. Output Capacitor Selection The RT7238B/C/D/E are optimized for ceramic output capacitors and best performance will be obtained using them. The total output capacitance value is usually determined by the desired output voltage ripple level and transient response requirements for sag (undershoot on positive load steps) and soar (overshoot on negative load steps). Output ripple at the switching frequency is caused by the inductor current ripple and its effect on the output capacitor's ESR and stored charge. These two ripple components are called ESR ripple and capacitive ripple. Since ceramic capacitors have extremely low ESR and relatively little capacitance, both components are similar in amplitude and both should be considered if ripple is critical. VRIPPLE VRIPPLE(ESR) VRIPPLE(C) In addition to voltage ripple at the switching frequency, the output capacitor and its ESR also affect the voltage sag (undershoot) and soar (overshoot) when the load steps up and down abruptly. The ACOT transient response is very quick and output transients are usually small. However, the combination of small ceramic output capacitors (with little capacitance), low output voltages (with little stored charge in the output capacitors), and low duty cycle applications (which require high inductance to get reasonable ripple currents with high input voltages) increases the size of voltage variations in response to very quick load changes. Typically, load changes occur slowly with respect to the IC's 500kHz switching frequency. But some modern digital loads can exhibit nearly instantaneous load changes and the following section shows how to calculate the worst-case voltage swings in response to very fast load steps. The amplitude of the ESR step up or down is a function of the load step and the ESR of the output capacitor : VESR_STEP IOUT RESR The amplitude of the capacitive sag is a function of the load step, the output capacitor value, the inductor value, the input-to-output voltage differential, and the maximum duty cycle. The maximum duty cycle during a fast transient is a function of the on-time and the minimum off-time since the ACOTTM control scheme will ramp the current using on-times spaced apart with minimum off-times, which is as fast as allowed. Calculate the approximate on-time (neglecting parasitics) and maximum duty cycle for a given input and output voltage as : tON VOUT tON and DMAX VIN fSW tON tOFF(MIN) The actual on-time will be slightly longer as the IC compensates for voltage drops in the circuit, but we can neglect both of these since the on-time increase compensates for the voltage losses. Calculate the output voltage sag as : VSAG L (IOUT )2 2 COUT ( VIN(MIN) DMAX VOUT ) VRIPPLE(ESR) IL RESR VRIPPLE(C) IL 8 COUT fSW Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 20 is a registered trademark of Richtek Technology Corporation. DS7238B/C/D/E-01 April 2015 RT7238B/C/D/E The amplitude of the capacitive soar is a function of the load step, the output capacitor value, the inductor value and the output voltage : VSOAR L ( IOUT ) 2 COUT VOUT 2 The maximum power dissipation depends on the operating ambient temperature for fixed T J(MAX) and thermal resistance, θJA. The derating curve in Figure 3 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. Most applications never experience instantaneous full load steps and the RT7238B/C/D/E's high switching frequency and fast transient response can easily control voltage regulation at all times. Therefore, sag and soar are seldom an issue except in very low-voltage CPU core or DDR memory supply applications, particularly for devices with high clock frequencies and quick changes into and out of sleep modes. In such applications, simply increasing the amount of ceramic output capacitor (sag and soar are directly proportional to capacitance) or adding extra bulk capacitance can easily eliminate any excessive voltage transients. In any application with large quick transients, it should calculate soar and sag to make sure that over-voltage protection and under-voltage protection will not be triggered. Thermal Considerations 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 : Maximum Power Dissipation (W)1 3.6 For recommended operating condition specifications, the maximum junction temperature is 125°C. The junction to ambient thermal resistance, θJA, is layout dependent. For UQFN-10L 3x3 (FC) package, the thermal resistance, θJA, is 30°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 : P D(MAX) = (125°C − 25°C) / (30°C/W) = 3.3W for UQFN-10L 3x3 (FC) package Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7238B/C/D/E-01 April 2015 2.8 2.4 2.0 1.6 1.2 0.8 0.4 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 3. Derating Curve of Maximum Power Dissipation Layout Considerations Layout is very important in high frequency switching converter design. The PCB can radiate excessive noise and contribute to converter instability with improper layout. Certain points must be considered before starting a layout using the RT7238B/C/D/E. Make the traces of the main current paths as short and wide as possible. Put the input capacitor as close as possible to the device pins (VIN and GND). LX node encounters high frequency voltage swings so it should be kept in a small area. Keep sensitive components away from the LX node to prevent stray as possible. The GND pin should be connected to a strong ground plane for heat sinking and noise protection. Avoid using vias in the power path connections that have switched currents (from CIN to GND and CIN to VIN) and the switching node (LX). An example of PCB layout guide is shown in Figure 4 for reference. 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. Four-Layer PCB 3.2 is a registered trademark of Richtek Technology Corporation. www.richtek.com 21 RT7238B/C/D/E EN1 PGOOD NC VOUT LDO BOOT CBOOT 3 4 5 1 EN2 7 LX VIN The output capacitor must be placed near the IC. LX 5 6 BYP 9 8 CIN CIN GND GND The input capacitor must be placed as close to the IC as possible. (RT7238B) (a) For UQFN-10L 3x3 (FC) Package LX should be connected to inductor by wide and short trace. Keep sensitive components away from this trace. The input capacitor must be placed as close to the IC as possible. (RT7238D) (c) For UQFN-10L 3x3 (FC) Package Figure 4. PCB Layout Guide LX The optional compensation Compensation components must be connected as close to the IC as possible. 4 10 COUT 8 GND The output capacitor must be placed near the IC. 3 7 LX 9 2 L 10 COUT CBOOT optional VOUT 6 L CLDO VIN 2 CFF GND 1 R2 EN PGOOD ILMT FB LDO BOOT CLDO VOUT R1 The voltage divider and compensation components must be connected as close to the IC as possible. GND LX GND The optional compensation Compensation components must be connected as close to the IC as possible. LX should be connected to inductor by wide and short trace. Keep sensitive components away from this trace. LX should be connected to inductor by wide and short trace. Keep sensitive components away from this trace. CVCC EN PGOOD NC VOUT NC BOOT CBOOT VOUT 1 2 3 4 5 6 7 L LDO CLDO 10 The output capacitor must be placed near the IC. 9 8 VIN GND COUT GND LX CIN GND The input capacitor must be placed as close to the IC as possible. (RT7238C/E) (b) For UQFN-10L 3x3 (FC) Package Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 22 is a registered trademark of Richtek Technology Corporation. DS7238B/C/D/E-01 April 2015 RT7238B/C/D/E Outline Dimension 1 5 10 Symbol Dimensions In Millimeters Dimensions In Inches Min. Max. Min. Max. A 0.500 0.600 0.020 0.024 A1 0.000 0.050 0.000 0.002 A3 0.100 0.175 0.004 0.007 b 0.150 0.250 0.006 0.010 b1 0.670 0.770 0.026 0.030 b2 0.505 0.605 0.020 0.024 b3 1.680 1.780 0.066 0.070 b4 0.150 0.250 0.006 0.010 b5 0.575 0.675 0.023 0.027 D 2.950 3.050 0.116 0.120 E 2.950 3.050 0.116 0.120 e 0.450 0.018 K 0.250 0.010 K1 0.300 0.012 K2 0.250 0.010 K3 0.175 0.007 K4 0.350 0.014 K5 0.725 0.029 L 0.350 0.450 0.014 0.018 L1 1.800 1.900 0.071 0.075 L2 2.225 2.325 0.088 0.092 L3 1.050 1.150 0.041 0.045 U-Type 10L QFN 3x3 (FC) Package Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7238B/C/D/E-01 April 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 23 RT7238B/C/D/E Richtek Technology Corporation 14F, No. 8, Tai Yuen 1st 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. www.richtek.com 24 DS7238B/C/D/E-01 April 2015