MPQ8616 High Efficiency, 6A/12A, 6V Synchronous Step-Down Converter DESCRIPTION FEATURES The MPQ8616 is fully integrated high frequency synchronous rectified step-down switch mode converter. It offers very compact solutions to achieve 6A/12A output current from a 3V to 6V input with excellent load and line regulation. Constant-On-Time (COT) control mode provides fast transient response and eases loop stabilization. The MPQ8616 can operate with a low-cost electrolytic capacitor and can support ceramic output capacitor with external slope compensation. Operating frequency is programmed by an external resistor and is compensated for variations in VIN. It is almost constant with all the input voltage and output load conditions. Under voltage lockout is internally set at 2.8 V, but can be increased by programming the threshold with a resistor network on the enable pin. The output voltage startup ramp is controlled by the soft start pin. A power good signal indicates the output is within its nominal voltage range. Wide 3V to 6V Operating Input Range 6A/12A Output Current Low RDS(ON) Internal Power MOSFETs Proprietary Switching Loss Reduction Technique Adaptive COT for Ultrafast Transient Response 1% Reference Voltage Over -20C to +85C Junction Temperature Range Programmable Soft Start Time Pre-Bias Start up Programmable Switching Frequency from 300kHz to 1MHz. Minimum On Time TON_MIN=60ns Minimum Off Time TOFF_MIN=100ns Non-latch OCP, non-latch OVP Protection and Thermal Shutdown Output Adjustable from 0.61V to 4.5V APPLICATIONS Full fault protection including OCP, SCP, OVP UVP and OTP is provided by internal comparators. The MPQ8616 requires a minimum number of readily available standard external components and are available in QFN3x4 packages. Telecom System Base Stations Networking Systems Server Personal Video Recorders Flat Panel Television and Monitors Distributed Power Systems All MPS parts are lead-free and adhere to the RoHS directive. For MPS green status, please visit MPS website under Products, Quality Assurance page. “MPS” and “The Future of Analog IC Technology” are registered trademarks of Monolithic Power Systems, Inc. TYPICAL APPLICATION VIN BST IN C3 RFREQ C1 FREQ EN ON/OFF VCC VOUT R4 C4 R1 MPQ8616 C2 FB VCC C5 L1 SW SS R3 R2 C6 PG PGND AGND MPQ8616 Rev. 1.01 www.MonolithicPower.com 8/4/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 1 MPQ8616, 6A/12A, 6V, SYNCHRONOUS STEP-DOWN CONVERTER ORDERING INFORMATION Part Number* Package Top Marking MPQ8616GL-6 QFN (3x4mm) MP8616 6 MPQ8616GL-12 QFN (3x4mm) MP8616 12 * For Tape & Reel, add suffix –Z (e.g. MPQ8616GL-6/12–Z); PACKAGE REFERENCE TOP VIEW TOP VIEW 1 FB 2 SS 3 EN IN IN 12 11 10 2 SS 3 4 EN 4 VCC 5 VCC 5 PG 6 PG 6 7 BST 8 13 14 9 GND GND IN IN 12 11 10 13 14 SW FB SW 1 SW AGND FREQ SW AGND FREQ 7 8 9 BST GND GND EXPOSED PAD ON BACKSIDE EXPOSED PAD ON BACKSIDE Part Number** Package Part Number** Package MPQ8616GL-6 QFN14 (3x4mm) MPQ8616GL-12 QFN14 (3x4mm) ** For Tape & Reel, add suffix –Z (eg. MPQ8616GL-6–Z) *** For Tape & Reel, add suffix –Z (eg. MPQ8616GL-12–Z) MPQ8616 Rev. 1.01 www.MonolithicPower.com 8/4/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 2 MPQ8616, 6A/12A, 6V, SYNCHRONOUS STEP-DOWN CONVERTER ABSOLUTE MAXIMUM RATINGS (1) Supply Voltage VIN ......................................6.5V VSW ....................................... -0.3V to VIN + 0.3V VSW (30ns) ..................................-3V to VIN + 3V VIN -VSW ................................ -0.3V to VIN + 0.3V VIN -VSW (30ns) ............................-3V to VIN + 3V VBST .....................................................VSW + 6V All Other Pins ................................. -0.3V to +6V (2) Continuous Power Dissipation (TA=+25) …… QFN(3x4mm)…………………...……………2.6W Junction Temperature .............................. 150C Lead Temperature ................................... 260C Storage Temperature ............... -65C to +150C Recommended Operating Conditions Thermal Resistance (4) θJA θJC QFN (3x4mm) ........................ 48 ...... 10 ... C/W Notes: 1) Exceeding these ratings may damage the device. 2) The maximum allowable power dissipation is a function of the maximum junction temperature TJ(MAX), the junction-toambient thermal resistance θJA, and the ambient temperature TA. The maximum allowable continuous power dissipation at any ambient temperature is calculated by PD(MAX)=(TJ(MAX)TA)/θJA. Exceeding the maximum allowable power dissipation will cause excessive die temperature, and the regulator will go into thermal shutdown. Internal thermal shutdown circuitry protects the device from permanent damage. 3) The device is not guaranteed to function outside of its operating conditions. 4) Measured on JESD51-7, 4-layer PCB. (3) Supply Voltage VIN ............................... 3V to 6V Output Voltage VOUT..................... 0.61V to 4.5V Operating Junction Temp. (TJ). -40°C to +125°C MPQ8616 Rev. 1.01 www.MonolithicPower.com 8/4/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 3 MPQ8616, 6A/12A, 6V, SYNCHRONOUS STEP-DOWN CONVERTER ELECTRICAL CHARACTERISTICS VIN = 5V, TJ = -40 to +125C, unless otherwise noted. Parameters Symbol Condition Min Typ Max Units 0.6 1 1.05 2 1.3 μA mA Supply Current Supply Current (Shutdown) Supply Current (Quiescent) MOSFET High-side Switch On Resistance Low-side Switch On Resistance Switch Leakage IIN IIN HSRDS-ON LSRDS-ON SW LKG VEN = 0V VEN = 2V, VFB = 1V MPQ8616-6, TJ =25C 19.8 MPQ8616-12, TJ =25C 16 mΩ MPQ8616-6 TJ =25C 15.3 MPQ8616-12, TJ =25C 8.4 VEN = 0V, VSW = 0V or 5V 0.01 3 mΩ μA Current Limit High-side Current Limit ILIMIT MPQ8616-6 9.5 12 14.5 MPQ8616-12 17 23 27 50 200 100 2.5 A Timer One-Shot On Time tON Minimum Off Time tOFF (5) Fold back Timer tFOLDBACK Over-voltage and Under-voltage Protection OVP Threshold (5) OVP Delay (5) UVP Threshold Reference And Soft Start VOVP tOVP VUVP Reference Voltage VREF Feedback Current Soft Start Charging Current IFB ISS RFREQ=165kΩ,VOUT=1.2V OCP happens 150 110% 120% 1 50% 130% TJ = -20C to +85C 604 610 616 TJ = -40C to +125C VFB = 610mV VSS=0V 601 610 619 5 0.001 7.5 150 10 MPQ8616 Rev. 1.01 www.MonolithicPower.com 8/4/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. ns ns μs V μs VREF mV nA μA 4 MPQ8616, 6A/12A, 6V, SYNCHRONOUS STEP-DOWN CONVERTER ELECTRICAL CHARACTERISTICS (continued) VIN = 5V, TJ = -40 to +125C, unless otherwise noted. Parameters Symbol Condition Min Typ Max Units 1.8 V mV Enable And UVLO Enable Input Low Voltage Enable Hysteresis Enable Input Current VILEN VEN-HYS IEN 1.4 VEN = 2V VEN = 0V 890 1.5 0.01 2 1 μA 2.8 2.95 V VCC UVLO VCC Under Voltage Lockout Threshold Rising VCC Under Voltage Lockout Threshold Hysteresis Power Good VCCVth 2.3 VCCHYS 300 Power Good Rising Threshold Power Good Falling Threshold Power Good Deglitch Timer Power Good Sink Current Capability Power Good Leakage Current Thermal Protection PGVth-Hi PGVth-Lo PGTd 84% 63% TSS=1ms, VPG Sink 4mA IPG_LEAK VPG = 3.3V Thermal Shutdown Thermal Shutdown Hysteresis TSD Note 5 90% 70% 2000 50 150 mV 96% 73% 5000 VREF VREF μs 0.4 V 150 nA 160 25 °C °C Note: 5) Guaranteed by design. MPQ8616 Rev. 1.01 www.MonolithicPower.com 8/4/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 5 MPQ8616, 6A/12A, 6V, SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL CHARACTERISTICS MPQ8616, Performance waveforms are tested on the evaluation board of the Design Example section. MPQ8616 Rev. 1.01 www.MonolithicPower.com 8/4/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 6 MPQ8616, 6A/12A, 6V, SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL CHARACTERISTICS (continued) MPQ8616GL, Performance waveforms are tested on the evaluation board of the Design Example section. MPQ8616 Rev. 1.01 www.MonolithicPower.com 8/4/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 7 MPQ8616, 6A/12A, 6V, SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS Performance waveforms are tested on the evaluation board of the Design Example section. MPQ8616GL-6, VIN=5V, VOUT=1.2V, L=1.0µH, TA=+25°C, unless otherwise noted. MPQ8616 Rev. 1.01 www.MonolithicPower.com 8/4/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 8 MPQ8616, 6A/12A, 6V, SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS (continued) Performance waveforms are tested on the evaluation board of the Design Example section. MPQ8616GL-6, VIN=5V, VOUT=1.2V, L=1.0µH, TA=+25°C, unless otherwise noted. MPQ8616 Rev. 1.01 www.MonolithicPower.com 8/4/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 9 MPQ8616, 6A/12A, 6V, SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS (continued) Performance waveforms are tested on the evaluation board of the Design Example section. MPQ8616GL-6, VIN=5V, VOUT=1.2V, L=1.0µH, TA=+25°C, unless otherwise noted. MPQ8616 Rev. 1.01 www.MonolithicPower.com 8/4/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 10 MPQ8616, 6A/12A, 6V, SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS (continued) Performance waveforms are tested on the evaluation board of the Design Example section. MPQ8616GL-6, VIN=5V, VOUT=1.2V, L=1.0µH, TA=+25°C, unless otherwise noted. MPQ8616 Rev. 1.01 www.MonolithicPower.com 8/4/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 11 MPQ8616, 6A/12A, 6V, SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS (continued) Performance waveforms are tested on the evaluation board of the Design Example section. MPQ8616GL-6, VIN=5V, VOUT=1.2V, L=1.0µH, TA=+25°C, unless otherwise noted. MPQ8616 Rev. 1.01 www.MonolithicPower.com 8/4/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 12 MPQ8616, 6A/12A, 6V, SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS MPQ8616GL-12, VIN=5V, VOUT=1.2V, L=1.0µH, TA=+25°C, unless otherwise noted. MPQ8616 Rev. 1.01 www.MonolithicPower.com 8/4/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 13 MPQ8616, 6A/12A, 6V, SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS (continued) MPQ8616GL-12, VIN=5V, VOUT=1.2V, L=1.0µH, TA=+25°C, unless otherwise noted. MPQ8616 Rev. 1.01 www.MonolithicPower.com 8/4/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 14 MPQ8616, 6A/12A, 6V, SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS (continued) MPQ8616GL-12, VIN=5V, VOUT=1.2V, L=1.0µH, TA=+25°C, unless otherwise noted. MPQ8616 Rev. 1.01 www.MonolithicPower.com 8/4/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 15 MPQ8616, 6A/12A, 6V, SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS (continued) MPQ8616GL-12, VIN=5V, VOUT=1.2V, L=1.0µH, TA=+25°C, unless otherwise noted. MPQ8616 Rev. 1.01 www.MonolithicPower.com 8/4/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 16 MPQ8616, 6A/12A, 6V, SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS (continued) MPQ8616GL-12, VIN=5V, VOUT=1.2V, L=1.0µH, TA=+25°C, unless otherwise noted. MPQ8616 Rev. 1.01 www.MonolithicPower.com 8/4/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 17 MPQ8616, 6A/12A, 6V, SYNCHRONOUS STEP-DOWN CONVERTER PIN FUNCTIONS MPQ8616GL-6, MPQ8616GL-12 PIN # Name Description 1 AGND 2 FB 3 SS 4 EN Analog ground. Feedback. An external resistor divider from the output to GND, tapped to the FB pin, sets the output voltage. It is recommended to place the resistor divider as close to FB pin as possible. Vias should be avoided on the FB traces. Soft Start. Connect on external capacitor to program the soft start time for the switch mode regulator. Enable pin. Pull this pin higher than 1.8V to enable the chip. For automatic start-up, connect EN pin to VIN with 100KΩ resistor. Can be used to set the on/off threshold (adjust UVLO) with two additional resistors. 5 VCC 6 PG 7 BST 8-9 GND 10-11 IN 12 FREQ 13-14 SW Supply Voltage for driver and control circuits. Decouple with a minimum 4.7µF ceramic capacitor as close to the pin as possible. X7R or X5R grade dielectric ceramic capacitors are recommended for their stable temperature characteristics. Power good output. It is high if the output voltage is higher than 90% of the nominal voltage. There is a delay from FB ≥ 90% to PG goes high. Bootstrap. A capacitor connected between SW and BS pins is required to form a floating supply across the high-side switch driver. System Ground. This pin is the reference ground of the regulated output voltage. For this reason care must be taken in PCB layout. Supply Voltage. The IN pin supplies power for internal MOSFET and regulator. The MPQ8616 operate from a +3V to +6V input rail. An input capacitor is needed to decouple the input rail. Use wide PCB traces and multiple vias to make the connection. Frequency setting pin. A resistor connected between FREQ and IN is required to set the switching frequency. The ON time is determined by the input voltage and the resistor connected to the FREQ pin. IN connect through a resistor is used for line feed-forward and makes the frequency basically constant during input voltage’s variation. An optional 1nF decoupling capacitor can be added to improve any switching frequency jitter that may be present. Switch Output. Connect this pin to the inductor and bootstrap capacitor. This pin is driven up to the VIN voltage by the high-side switch during the on-time of the PWM duty cycle. The inductor current drives the SW pin negative during the off-time. The on-resistance of the low-side switch and the internal Schottky diode fixes the negative voltage. Use wide PCB traces to make the connection. MPQ8616 Rev. 1.01 www.MonolithicPower.com 8/4/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 18 MPQ8616, 6A/12A, 6V, SYNCHRONOUS STEP-DOWN CONVERTER BLOCK DIAGRAM IN FREQ Current Sense Amplifer RSEN Over-Current OC Timer VCC Refresh Timer ILIM EN REFERENCE HS Limit Comparator xS Q 0.3V 1MEG 0.75V 0.61V BST BSTREG OFF Timer HS Driver PWM HS-FET xR LOGIC SS SOFT START/STOP VCC START FB SW Loop Comparator ON Timer LS Driver LS-FET Current Modulator PG UV PGOOD Comparator UV Detect Comparator GND AGND OV OV Detect Comparator Figure 1—Functional Block Diagram MPQ8616 Rev. 1.01 www.MonolithicPower.com 8/4/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 19 MPQ8616, 6A/12A, 6V, SYNCHRONOUS STEP-DOWN CONVERTER OPERATION PWM Operation The MPQ8616 is fully integrated synchronous rectified step-down switch mode converter. Constant-on-time (COT) control is employed to provide fast transient response and easy loop stabilization. At the beginning of each cycle, the high-side MOSFET (HS-FET) is turned ON when the feedback voltage (VFB) is below the reference voltage (VREF), which indicates insufficient output voltage. The ON period is determined by the input voltage and the frequency-set resistor as follows: t ON (ns) 4.8 RFREQ (k) VIN (V) 0.49 (1) After the ON period elapses, the HS-FET is turned off, or becomes OFF state. It is turned ON again when VFB drops below VREF. By repeating operation this way, the converter regulates the output voltage. The integrated low-side MOSFET (LS-FET) is turned on when the HS-FET is in its OFF state to minimize the conduction loss. There will be a dead short between input and GND if both HS-FET and LS-FET are turned on at the same time. It’s called shoot-through. In order to avoid shoot-through, a dead-time (DT) is internally generated between HS-FET off and LSFET on, or LS-FET off and HS-FET on. the HS-MOSFET is turned off, the LS-MOSFET is turned on until next period. For the MPQ8616 is operated in CCM, the switching frequency is fairly constant and it is called PWM mode. Switching Frequency The selection of switching frequency is a tradeoff between efficiency and component size. Low frequency operation increases efficiency by reducing MOSFET switching losses, but requires larger inductance and capacitance to maintain low output voltage ripple. For MPQ8616 ， the on time can be set using FREQ pin, then the frequency is set in steady state operation at CCM mode. Adaptive constant-on-time (COT) control is used in MPQ8616 and there is no dedicated oscillator in the IC. Connect FREQ pin to IN pin through resistor RFREQ and the input voltage is feedforwarded to the one-shot on-time timer through the resistor RFREQ. When in steady state operation at CCM, the duty ratio is kept as VOUT/VIN. Hence the switching frequency is fairly constant over the input voltage range. The switching frequency can be set as follows: 106 (2) fSW (kHz) 4.8 RFREQ (k) VIN (V) tDELAY (ns) VIN (V) 0.49 VOUT (V) Where tDELAY is the comparator delay. It’s about 40ns. Generally, the MPQ8616 is set for 300kHz to 1MHz application. It is optimized to operate at high switching frequency with high efficiency. High switching frequency makes it possible to utilize small sized LC filter components to save system PCB space. Figure 2—PWM Operation MPQ8616 always operating in continuousconduction-mode (CCM), which means the inductor current can go negative at light load. The CCM mode operation is shown in Figure2. When VFB is below VREF, HS-MOSFET is turned on for a fixed interval which is determined by one- shot on-timer as equation 1 shown. When Jitter and FB Ramp Slope Figure 3 shows jitter occurring in PWM mode. When there is noise in the VFB downward slope, the ON time of HS-FET deviates from its intended location and produces jitter. It is necessary to understand that there is a relationship between a system’s stability and the steepness of the VFB ripple’s downward slope. The slope steepness of the VFB ripple dominates MPQ8616 Rev. 1.01 www.MonolithicPower.com 8/4/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 20 MPQ8616, 6A/12A, 6V, SYNCHRONOUS STEP-DOWN CONVERTER in noise immunity. The magnitude of the VFB ripple doesn’t affect the noise immunity directly. L SW Vo R4 C4 IR4 IC4 R9 R1 I FB Ceramic FB R2 Figure 5—Simplified Circuit in PWM Mode with External Ramp Compensation Figure 3—Jitter in PWM Mode Ramp with Large ESR Capacitor In the case of POSCAP or other types of capacitor with lager ESR is applied as output capacitor, the ESR ripple dominates the output ripple, and the slope on the FB is quite ESR related. Figure 4 shows an equivalent circuit in PWM mode with the HS-FET off and without an external ramp circuit. Turn to application information section for design steps with large ESR capacitors. SW L FB 1 R1 R2 R9 20 R1 R2 (4) Where: IR4 IC4 IFB IC4 VRAMP (5) R1 // R2 VIN VO t ON R 4 C4 R1 // R2 R9 (6) The downward slope of the VFB ripple then follows: POSCAP Figure 4—Simplified Circuit in PWM Mode without External Ramp Compensation To realize the stability when no external ramp is applied, usually the ESR value should be chosen as follow: RESR 2 fSW C4 ESR R2 t SW t ON 0.7 2 COUT 1 And the ramp on the VFB can then be estimated as: Vo R1 In PWM mode, an equivalent circuit with HS-FET off and the use of an external ramp compensation circuit (R4, C4) is simplified in Figure 5. The external ramp is derived from the inductor ripple current. If one chooses C4, R9, R1 and R2 to meet the following condition: (3) TSW is the switching period. Ramp with Small ESR Capacitor When the output capacitors are ceramic ones, the ESR ripple is not high enough to stabilize the system, and external ramp compensation is needed. Skip to application information section for design steps with small ESR caps. VSLOPE1 VOUT VRAMP t off R 4 C4 (7) As can be seen from equation 7, if there is instability in PWM mode, we can reduce either R4 or C4. If C4 can not be reduced further due to limitation from equation 4, then we can only reduce R4. For a stable PWM operation, the Vslope1 should be design follow equation 8. VSLOPE1 t SW t ON RESR COUT 0.7 IO 103 0.7 2 VOUT 2 L COUT t sw t on (8) Where Io is the load current. MPQ8616 Rev. 1.01 www.MonolithicPower.com 8/4/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 21 MPQ8616, 6A/12A, 6V, SYNCHRONOUS STEP-DOWN CONVERTER Soft Start/Stop The MPQ8616 employs soft start/stop (SS) mechanism to ensure smooth output during power up and power down. When the EN pin becomes high, an internal current source (8μA) charges up the SS capacitor C6. The SS capacitor voltage takes over the REF voltage to the PWM comparator. The output voltage smoothly ramps up with the SS voltage. Once the SS voltage reaches the same level as the REF voltage, it keeps ramping up while VREF takes over the PWM comparator. At this point, the soft start finishes and it enters into steady state operation. When the EN pin is pulled to low, the SS CAP voltage is discharged through an 8uA internal current source. Once the SS voltage reaches REF voltage, it takes over the PWM comparator. The output voltage will decrease smoothly with SS voltage until zero level. The SS capacitor value can be determined as follows: CSS (nF) t SS (ms) ISS (A) VREF (9) If the output capacitors have large capacitance value, it’s not recommended to set the SS time too small. Otherwise, it’s easy to hit the current limit during SS. A minimum value of 4.7nF should be used if the output capacitance value is larger than 330μF. Pre-Bias Startup If the output is pre-biased to a certain voltage during startup, the MPQ8616 will disable the switching of both high-side and low-side switches until the voltage on the internal soft-start capacitor exceeds the sensed output voltage at the FB pin. Power Good (PG) The MPQ8616 has power-good (PG) output. It can be connected to VCC or other voltage source through a resistor (e.g. 100k). When the MPQ8616 is powered on and FB voltage reaches above 90% of REF voltage, the PG pin is pulled high. When the FB voltage drops to 70% of REF voltage or the part is not powered on, the PG pin will be pulled low. Over-Current Protection (OCP) The MPQ8616 enters over-current protection mode when the inductor current hits the current limit, and tries to recover from over-current fault with hiccup mode. That means in over-current protection, the chip will disable output power stage, discharge soft-start capacitor and then automatically try to soft-start again. If the overcurrent condition still holds after soft-start ends, the chip repeats this operation cycle till overcurrent disappears and output rises back to regulation level. The MPQ8616 also operates in hiccup mode when short circuit happens. Over/Under –Voltage Protection (OVP/UVP) The MPQ8616 has non-latching over voltage protection. It monitors the output voltage through a resistor divider feedback (FB) voltage to detect over-voltage on the output. When the FB voltage is higher than 120% of the REF voltage (0.610V), the LS-FET will be turned on while the HS-FET will be off. The LS-FET keeps on until it hits the negative current limit and turns off for 100ns. If over voltage condition still holds, the chip repeats this operation cycle till the FB voltage drops below 110% of the REF voltage. When the FB voltage is below 50% of the REF voltage (0.610V), it is recognized as undervoltage (UV). Usually, UVP accompanies a hit in current limit and results in OCP. Configuring the EN Control The EN pin provides electrical on/off control of the device. Set EN high to turn on the regulator and low to turn it off. Do not float this pin. For automatic start-up, the EN pin can be pulled up to input voltage through a resistive voltage divider. Choose the values of the pull-up resistor (RUP from VIN pin to EN pin) and the pull-down resistor (RDOWN from EN pin to GND) to determine the automatic start-up voltage: VINSTART 1.4 RUP RDOWN RDOWN MPQ8616 Rev. 1.01 www.MonolithicPower.com 8/4/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. (10) 22 MPQ8616, 6A/12A, 6V, SYNCHRONOUS STEP-DOWN CONVERTER For example, for RUP =100kΩ and RDOWN =51kΩ, the VINSTART is set at 4.15V. To avoid noise, a 10nF ceramic capacitor from EN to GND is recommended. There is an internal zener diode on the EN pin, which clamps the EN pin voltage to prevent it from running away. The maximum pull up current assuming a worst case 6V internal zener clamp should be less than 1mA. Therefore, when EN is driven by an external logic signal, the EN voltage should be lower than 6V; when EN is connected with VIN through a pull-up resistor or a resistive voltage divider, the resistance selection should ensure the maximum pull up current less than 1mA. If using a resistive voltage divider and VIN higher than 6V, the allowed minimum pull-up resistor RUP should meet the following equation: VIN (V) 6 6 1(mA) RUP (k) RDOWN (k) (11) As a result, when just the pull-up resistor RUP is applied, the VINSTART is determined by input UVLO. The value of RUP can be got as: RUP (k) VIN (V) 6 1(mA) (12) A typical pull-up resistor is 100kΩ. UVLO protection The MPQ8616 has under-voltage lock-out protection (UVLO). When the VCC voltage is higher than the UVLO rising threshold voltage, the MPQ8616 will be powered up. It shuts off when the VCC voltage is lower than the UVLO falling threshold voltage. This is non-latch protection. The MPQ8616 is disabled when the VCC voltage falls below its UVLO falling threshold (2.45V). If an application requires a higher under-voltage lockout (UVLO), use the EN pin as shown in Figure 6 to adjust the input voltage UVLO by using two external resistors. It is recommended to use the enable resistors to set the UVLO falling threshold (VSTOP) above 2.8 V. The rising threshold (VSTART) should be set to provide enough hysteresis to allow for any input supply variations. IN MPQ8616 VCC RUP EN Comparator EN RDOWN Figure 6—Adjustable UVLO Thermal Shutdown Thermal shutdown is employed in the MPQ8616. The junction temperature of the IC is internally monitored. If the junction temperature exceeds the threshold value (minimum 150ºC), the converter shuts off. This is a non-latch protection. There is about 25ºC hysteresis. Once the junction temperature drops to about 125ºC, it initiates a soft startup. MPQ8616 Rev. 1.01 www.MonolithicPower.com 8/4/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 23 MPQ8616, 6A/12A, 6V, SYNCHRONOUS STEP-DOWN CONVERTER APPLICATION INFORMATION Setting the Output Voltage-Large ESR Caps For applications that electrolytic capacitor or POS capacitor with a controlled output of ESR is set as output capacitors. The output voltage is set by feedback resistors R1 and R2. As figure 7 shows. SW L Vo FB in Figure 8. The VRAMP can be calculated as shown in equation 6. R2 should be chosen reasonably, a small R2 will lead to considerable quiescent current loss while too large R2 makes the FB noise sensitive. It is recommended to choose a value within 5kΩ-100kΩ for R2, using a comparatively larger R2 when VOUT is low, and a smaller R2 when VOUT is high. And the value of R1 then is determined as follow: ESR R1 R1 POSCAP VOUT VFB( AVG) R2 Figure7—Simplified Circuit of POS Capacitor First, choose a value for R2. R2 should be chosen reasonably, a small R2 will lead to considerable quiescent current loss while too large R2 makes the FB noise sensitive. It is recommended to choose a value within 5kΩ100kΩ for R2, using a comparatively larger R2 when VOUT is low, and a smaller R2 when VOUT is high. Then R1 is determined as follow with the output ripple considered: R1 VOUT 1 VOUT VREF 2 R2 VREF (13) VOUT is the output ripple determined by equation Setting the Output Voltage-Small ESR Caps FB L R4 Vo C4 R1 R9 Ceramic R2 Figure8—Simplified Circuit of Ceramic Capacitor When low ESR ceramic capacitor is used in the output, an external voltage ramp should be added to FB through resistor R4 and capacitor C4.The output voltage is influenced by ramp voltage VRAMP besides resistor divider as shown (14) R2 R 4 R9 The VFB(AVG) is the average value on the FB. VFB(AVG) varies with the Vin, Vo, and load condition, etc.. It is means the load regulation is strictly related to the VFB(AVG). Also the line regulation is related to the VFB(AVG) ,if one wants to gets a better load or line regulation, a lower VRAMP is suggested once it meets equation 8. For PWM operation, VFB(AVG) value can be deduced from equation 15. VFB( AVG) VREF R1 // R2 1 VRAMP 2 R1 // R2 R9 (15) Usually, R9 is set to 0Ω, and it can also be set following equation 16 for a better noise immunity. It should be set to be 5 timers smaller than R1//R2 to minimize its influence on Vramp. R9 21. SW R2 VFB( AVG) 1 R1 R2 10 R1 R2 (16) Using equation 14 and 15 to calculate the output voltage can be complicated. To simplify the calculation of R1 in equation 14, a DC-blocking capacitor Cdc can be added to filter the DC influence from R4 and R9. Figure 9 shows a simplified circuit with external ramp compensation and a DC-blocking capacitor. With this capacitor, R1 can easily be obtained by using equation 17 for PWM mode operation. R1 1 VRAMP 2 R2 1 VRAMP 2 VOUT VREF VREF (17) Cdc is suggested to be at least 10 times larger than C4 for better DC blocking performance, and should be not larger than 0.47μF considering startup performance. In case one wants to use larger Cdc for a better FB noise immunity, MPQ8616 Rev. 1.01 www.MonolithicPower.com 8/4/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 24 MPQ8616, 6A/12A, 6V, SYNCHRONOUS STEP-DOWN CONVERTER combined with reduced R1 and R2 to limit Cdc in a reasonable value without affecting system start up. Be noted that even when Cdc is applied, the load and line regulation still Vramp related. SW FB L R4 the the the are The input voltage ripple can be estimated as follows: VIN IOUT V V OUT (1 OUT ) fSW CIN VIN VIN The worst-case condition occurs at VIN = 2VOUT, where: Vo C4 VIN R1 Cdc Ceramic VOUT Input Capacitor The input current to the step-down converter is discontinuous. Therefore, a capacitor is required to supply the AC current to the step-down converter while maintaining the DC input voltage. Ceramic capacitors are recommended for best performance. In the layout, it’s recommended to put the input capacitors as close to the IN pin as possible. The capacitance varies significantly over temperature. Capacitors with X5R and X7R ceramic dielectrics are recommended because they are fairly stable over temperature. The capacitors must also have a ripple current rating greater than the maximum input ripple current of the converter. The input ripple current can be estimated as follows: VOUT V (1 OUT ) VIN VIN (18) The worst-case condition occurs at VIN = 2VOUT, where: IOUT 2 (21) The output capacitor is required to maintain the DC output voltage. Ceramic or POSCAP capacitors are recommended. The output voltage ripple can be estimated as: Figure9—Simplified Circuit of Ceramic Capacitor with DC blocking capacitor ICIN I 1 OUT 4 fSW CIN Output Capacitor R2 ICIN IOUT (20) VOUT V 1 (1 OUT ) (RESR ) (22) fSW L VIN 8 fSW COUT In the case of ceramic capacitors, the impedance at the switching frequency is dominated by the capacitance. The output voltage ripple is mainly caused by the capacitance. For simplification, the output voltage ripple can be estimated as: VOUT VOUT V (1 OUT ) VIN 8 fSW 2 L COUT The output voltage ripple caused by ESR is very small. Therefore, an external ramp is needed to stabilize the system. The external ramp can be generated through resistor R4 and capacitor C4 following equation 4, 7 and 8. In the case of POSCAP capacitors, the ESR dominates the impedance at the switching frequency. The ramp voltage generated from the ESR is high enough to stabilize the system. Therefore, an external ramp is not needed. A minimum ESR value according to equation 3 is required to ensure stable operation of the converter. For simplification, the output ripple can be approximated as: (19) For simplification, choose the input capacitor whose RMS current rating is greater than half of the maximum load current. The input capacitance value determines the input voltage ripple of the converter. If there is input voltage ripple requirement in the system design, choose the input capacitor that meets the specification (23) VOUT VOUT V (1 OUT ) RESR fSW L VIN (24) Inductor The inductor is required to supply constant current to the output load while being driven by the switching input voltage. A larger value inductor will result in less ripple current and lower output ripple voltage. However, a larger value MPQ8616 Rev. 1.01 www.MonolithicPower.com 8/4/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 25 MPQ8616, 6A/12A, 6V, SYNCHRONOUS STEP-DOWN CONVERTER inductor will have a larger physical size, higher series resistance, and/or lower saturation current. A good rule for determining the inductor value is to allow the peak-to-peak ripple current in the inductor to be approximately 10~30% of the maximum output current. Also, make sure that the peak inductor current is below the current limit of the device. The inductance value can be calculated as: VOUT V L (1 OUT ) fSW IL VIN (25) Where ΔIL is the peak-to-peak inductor ripple current. Choose an inductor that will not saturate under the maximum inductor peak current. The peak inductor current can be calculated as: ILP IOUT VOUT V (1 OUT ) 2 fSW L VIN (26) The inductors listed in Table 1 are highly recommended for the high efficiency they can provide. Table 1—Inductor Selection Guide Part Number Manufacturer Inductance (µH) DCR (mΩ) Current Rating (A) Dimensions 3 L x W x H (mm ) FDU1250C-R50M FDU1250C-R56M FDU1250C-R75M FDU1250C-1R0M TOKO TOKO TOKO TOKO 0.50 0.56 0.75 1.0 1.3 1.6 1.7 2.2 46.3 42.6 32.7 31.3 13.3 x 12.1 x5 13.3 x 12.1 x5 13.3 x 12.1 x5 13.3 x 12.1 x5 Typical Design Parameter Tables The following tables include recommended component values for typical output voltages (1.0V, 1.2V, 1.8V, 3.3V) and switching frequencies (600kHz, 800kHz, and 1MHz). Refer to Tables 2-4 for design cases without external ramp compensation and Tables 5-6 for design cases with external ramp compensation. External ramp is not needed when high-ESR capacitors, such as electrolytic or POSCAPs are used. External ramp is needed when low-ESR capacitors, such as ceramic capacitors are used. For cases not listed in this datasheet, a calculator in excel spreadsheet can also be requested through a local sales representative to assist with the calculation. Table 2—COUT-Poscap, 600kHz, 5VIN VOUT (V) 1.0 1.2 L (μH) 1.0 1.0 R1 (kΩ) 19.8 29.4 R2 (kΩ) 30 30 R7 (kΩ) 300 365 1.5 1.0 29.4 20 453 1.8 1.0 39.2 20 549 3.3 1.0 44.2 10 1000 Switching Frequency (kHz) 1000 800-1000 600-800 600 Table 3—COUT-Poscap, 800kHz, 5VIN VOUT (V) 1.0 L (μH) 0.75 R1 (kΩ) 20 R2 (kΩ) 30 R7 (kΩ) 210 1.2 0.75 20 20 270 1.5 0.75 30 20 330 1.8 3.3 0.75 0.75 39 44.2 20 10 499 750 Table 5—COUT-Ceramic, 600kHz, 5VIN VOUT (V) 1.0 1.2 1.5 L (μH) 1.0 1.0 1.0 R1 (kΩ) 21 33 51 R2 (kΩ) 30 30 30 R4 (kΩ) 240 220 330 C4 (pF) 470 470 390 R7 (kΩ) 309 365 464 1.8 3.3 1.0 1.0 45 62 20 10 270 160 470 680 549 953 Table 6—COUT-Ceramic, 800kHz, 5VIN VOUT (V) 1.0 1.2 1.5 1.8 3.3 L (μH) 0.75 0.75 0.75 0.75 0.75 R1 (kΩ) 21 34 34 47.5 57.6 R2 (kΩ) 30 30 20 20 10 R4 (kΩ) 200 200 220 225 200 MPQ8616 Rev. 1.01 www.MonolithicPower.com 8/4/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. C4 (pF) 470 470 470 470 560 R7 (kΩ) 226 270 324 402 750 26 MPQ8616, 6A/12A, 6V, SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL APPLICATION R3 VIN BST IN C1A C1B C1C C1D 22uF 22uF 22uF 0.1uF 22uF C1E 0 R7 R6 C3 1uF R8 360K 100K FREQ C7 1nF 10 L1 1uH SW VOUT R1 MPQ8616 + 29.4K C2A C2B 220uF/20mΩ 0.1uF EN FB VCC C5 R2 R5 SS 4.7uF 100K 30K C6 33nF PG PGND AGND Figure 13 — Typical Application Circuit with No External Ramp MPQ8616, VIN=5V, VOUT=1.2V, IOUT=6/12A, fSW=600kHz R3 VIN BST IN C1A C1B C1C C1D 22uF 22uF 22uF 0.1uF 22uF C1E R7 R6 360K 100K 0 R8 10 FREQ C7 1nF C3 1uF VOUT C4 R4 MPQ8616 220K EN 470pF R9 0 R1 33K C2A C2B C3C 22uF 22uF 22uF 22uF C2D C2E 0.1uF FB VCC C5 L1 1uH SW R5 R2 30K SS 4.7uF 100K C6 33nF PG PGND AGND Figure 14 — Typical Application Circuit with Low ESR Ceramic Capacitor MPQ8616, VIN=5V, VOUT=1.2V, IOUT=6/12A, fSW=600kHz R3 VIN BST IN C1A 22uF C1B 22uF C1C 22uF C1D C1E 0.1uF 22uF R7 R6 R8 360K 100K 10 FREQ 0 C3 1uF VOUT C7 1nF C4 R4 200K EN MPQ8616 FB VCC C5 L1 1uH SW 560pF Cdc 10nF R1 29.1K C2A C2B C3C 22uF 22uF 22uF 22uF C2D C2E 0.1uF R2 R5 SS 4.7uF 100K C6 33nF PG PGND 30K AGND Figure 15 — Typical Application Circuit with Low ESR Ceramic Capacitor and DC-Blocking Capacitor. MPQ8616, VIN=5V, VOUT=1.2V, IOUT=6/12A, fSW=600kHz MPQ8616 Rev. 1.01 www.MonolithicPower.com 8/4/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 27 MPQ8616, 6A/12A, 6V, SYNCHRONOUS STEP-DOWN CONVERTER LAYOUT RECOMMENDATION 1. The high current paths (GND, IN, and SW) should be placed very close to the device with short, direct and wide traces. 2. Put the input capacitors as close to the IN and GND pins as possible. 3. Put the decoupling capacitor as close to the VCC and GND pins as possible. 4. Keep the switching node SW short and away from the feedback network. 5. The external feedback resistors should be placed next to the FB pin. Make sure that there is no via on the FB trace. 6. Keep the BST voltage path (BST, C3, and SW) as short as possible. 7. Keep the IN and GND pads connected with large copper to achieve better thermal performance. 8. Four-layer layout is strongly recommended to achieve better thermal performance. V IN R5 C3 RFREQ GND EN L1 VOUT SW FREQ C4 R4 R1 MPQ8616 C2 FB VCC C5 Inner1 Layer BST IN C1 R6 GND SS R3 R2 C6 PG PGND AGND Inner2 Layer Schematic for PCB Layout Guide Line SW R3 C1B EN PG SS VCC R3 R3 1 FB BST AG ND FREQ R3 R5 R3 C1A GND R3 R6 R3 RFREQ L1 GND SW IN R3 C3 SW IN R3 C5 R3 R2 R3 C2 R3 C6 R3 R4 R3 R1 VIN R3 C4 VIN GND Top Layer GND VOUT VOUT Bottom Layer Figure 16—PCB Layout MPQ8616 Rev. 1.01 www.MonolithicPower.com 8/4/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 28 MPQ8616, 6A/12A, 6V, SYNCHRONOUS STEP-DOWN CONVERTER PACKAGE INFORMATION PIN 1 ID MARKING PIN 1 ID INDEX AREA BOTTOM VIEW TOP VIEW SIDE VIEW NOTE: 0.1x45 ° 1) ALL DIMENSIONS ARE IN MILLIMETERS. 2) EXPOSED PADDLE SIZE DOES NOT INCLUDE MOLD FLASH. 3) LEAD COPLANARITY SHALL BE0.10 MILLIMETERS MAX. 4) JEDEC REFERENCE IS MO-220. 5) DRAWING IS NOT TO SCALE. RECOMMENDED LAND PATTERN NOTICE: The information in this document is subject to change without notice. Please contact MPS for current specifications. Users should warrant and guarantee that third party Intellectual Property rights are not infringed upon when integrating MPS products into any application. MPS will not assume any legal responsibility for any said applications. MPQ8616 Rev. 1.01 www.MonolithicPower.com 8/4/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 29