SP7652EB

SP7652 6A 28V 600KHz Synchronous Step Down Regulator January 2020 Rev. 2.0.1 GENERAL DESCRIPTION APPLICATIONS • Distributed Power Architectures The SP7652 is a synchronous voltage mode PWM step down (buck) regulator capable of a constant output current up to 6Amps. A wide 2.5V to 28V power input voltage range, with the required 5V biasing voltage, allows conversions from industry standard 5V, 12V, 18V and 24V power rails. • Point of Load Converters • Power Supply Modules • FPGAs, DSPs and Processors Supplies FEATURES With a 600kHz constant operating frequency and integrated high and low side switch, the SP7652 reduces the overall component count and solution footprint. In addition to a 1% output setpoint accuracy, this device provides high efficiency, low ripple and excellent line and load regulation. An enable function and soft start feature allow for controlled power up sequencing implementation. • 6A Continuous Current • 2.5V-28V Power Input Voltage Rail − 5V Biasing voltage − 0.8V Min. Output Voltage – 1% Accuracy • PWM Voltage Mode Control − 600kHz Fixed Synchronous Operations − Low RDSON Power Switches Built-in Under voltage lockout (VLO) on both VCC and VIN, outputs short-circuit and over temperature protection insure safe operation under abnormal operating conditions. − Greater than 92% Efficiency • Type II & III Compensations Support • Programmable Soft Start The SP7652 is offered in a RoHS compliant, lead free 26-pin 7mmx4mm DFN package. • UVLO on both VIN and VCC • Pre-biased Output Start-Up • Over Temperature & Short Circuit Protection/Auto-Restart • RoHS Compliant Lead Free 26-Pin DFN • US Patent #6,922,041 TYPICAL APPLICATION DIAGRAM Fig. 1: SP7652 Application Diagram 1/15 Rev. 2.0.1 SP7652 6A 28V 600KHz Synchronous Step Down Regulator ABSOLUTE MAXIMUM RATINGS OPERATING RATINGS These are stress ratings only and functional operation of the device at these ratings or any other above those indicated in the operation sections of the specifications below is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability. Input Voltage Range VCC .............................. 4.5V to 5.5V Input Voltage Range VIN .................................. 3V to 28V Junction Temperature Range ................. -40°C to +125°C Thermal Resistance θJC ........................................ 5°C/W Thermal Resistance θJA ...................................... 36°C/W VIN ........................................................................ 30V VCC ......................................................................... 7V ILX ........................................................................ 10A BST ...................................................................... 35V LX-BST........................................................ -0.3V to 7V LX ............................................................... -1V to 30V All other pins ................................... -0.3V to (VCC+0.3)V Storage Temperature .............................. -65°C to 150°C Power Dissipation ................................ Internally Limited Lead Temperature (Soldering, 10 sec) ................... 300°C ESD Rating (HBM - Human Body Model) ............. 2kV HBM ELECTRICAL SPECIFICATIONS Specifications with standard type are for an Operating Junction Temperature of TJ = TA = 25°C only; limits applying over the full Operating Junction Temperature range are denoted by a “•”. Minimum and Maximum limits are guaranteed through test, design, or statistical correlation. Typical values represent the most likely parametric norm at TJ = TA = 25°C, and are provided for reference purposes only. Unless otherwise indicated, VCC = 4.5V to 5.5V, VIN = 3.0V to 28V, BST = LX + 5V, LX = GND = 0V, UVIN = 3V, CVCC = 1µF, CCOMP = 0.1µF, CSS = 50nF, TA= –40°C to 85°C, TJ = –40°C to 125°C. Parameter Min. Typ. Max. Units VCC Supply Current (No Switching) 1.5 3 mA VCC Supply Current (Switching) 11 15 mA BST Supply Current (No Switching) 0.2 0.4 mA 8 12 mA Conditions Quiescent Current BST Supply Current (Switching) VFB = 0.9V • VFB = 0.9V • Protection: UVLO VCC UVLO Start Threshold 4.00 4.25 4.5 v VCC UVLO Hysteresis 100 200 300 mV UVIN Start Threshold 2.3 2.5 2.65 V 200 300 400 mV 1 µA UVIN Hysteresis UVIN Input Current • UVIN = 3.0V Error Amplifier Reference Error Amplifier Reference 0.792 0.800 0.808 V Error Amplifier Reference Over Line and Temperature 0.788 0.800 0.812 V Error Amplifier Transconductance 2x Gain Config., Measure VFB; VCC=5V, T=25°C • 6 mA/V Error Amplifier Gain 60 dB No Load COMP Sink Current 150 µA VFB = 0.9V, COMP = 0.9V COMP Source Current 150 µA VFB = 0.7V, COMP = 2.2V VFB Input Bias Current 50 nA VFB = 0.8V 200 Internal Pole 4 MHz COMP Clamp 2.5 V COMP Clamp Temp. Coefficient -2 mV/°C 2/15 VFB = 0.7V, TA=25°C Rev. 2.0.1 SP7652 6A 28V 600KHz Synchronous Step Down Regulator Parameter Min. Typ. Max. Units Conditions Control Loop: PWM Comparator, Ramp & Loop Delay Path Ramp Amplitude 0.92 1.1 1.28 V Ramp Offset 1.1 V Ramp Offset Temp. Coefficient -2 mV/°C GH Minimum Pulse width 90 Maximum Controllable Duty Ratio 92 Maximum Duty Ratio 100 Internal Oscillator Ratio 420 180 97 ns • • Maximum Duty Ratio measured just before pulsing begins % % 600 720 kHz TA=25°C, Ramp COMP Valid for 20 cycles • Timers: Soft Start SS Charge Current 10 µA SS Discharge Current 1 Protection: Short Circuit & Thermal Short Circuit Threshold Voltage 0.2 0.25 0.3 mA • Fault Present, SS = 0.2V V • Measured (VREF(0.8V)-VFB) 200 ms Number of Allowable Clock Cycles at 100% Duty Cycle 20 Cycles Minimum GL Pulse After 20 Cycles 0.5 Cycles VFB = 0.7V Thermal Shutdown Temperature 145 °C VFB = 0.7V Thermal Recovery Temperature 135 °C 10 °C High Side RDSON 15 mΩ VCC = 5V ; IOUT= 6A, TA = 25°C Synchronous FET RDSON 15 mΩ VCC = 5V ; IOUT= 6A, TA = 25°C Hiccup Timeout Thermal Hysteresis VFB = 0.5V Output: Power Stage Maximum Output Current A 6 PIN ASSIGNMENT Fig. 2: SP7652 Pin Assignment 3/15 Rev. 2.0.1 SP7652 6A 28V 600KHz Synchronous Step Down Regulator PIN DESCRIPTION Name Pin Number PGND 1, 2, 3 GND 4, 8, 19, 20, 21 Ground Pin. The control circuitry of the IC and lower power driver are referenced to this pin. Return separately from other ground traces to the (-) terminal of COUT. VFB 5 Feedback Voltage and Short Circuit Detection pin. The inverting input of the Error Amplifier and serves as the output voltage feedback point for the Buck Converter. The output voltage is sensed and can be adjusted through an external resistor divider. Whenever VFB drops 0.25V below the positive reference, a short circuit fault is detected and the IC enters hiccup mode. COMP 6 Output of the Error Amplifier. Internally connected to the inverting input of the PWM comparator. An optimal filter combination is chosen and connected to this pin and either ground or VFB to stabilize the voltage mode loop. UVIN 7 UVLO input for VIN voltage. Connect a resistor divider between VIN and UVIN to set minimum operating voltage. SS 9 Soft Start. Connect an external capacitor between SS and GND to set the soft start rate based on the 10μA source current. The SS pin is held low via a 1mA (min.) current during all fault conditions. VIN 10, 11, 12, 13 LX NC Input connection to the high-side N-channel MOSFET. Place a decoupling capacitor between this pin and PGND. 14, 15, 16, Connect an inductor between this pin and VOUT. 23, 24, 25, 26 17 No Connect. BST 18 VCC 22 - Description Ground connection for the synchronous rectifier. High-side driver supply pin. Connect BST to the external boost diode and capacitor as shown in the Typical Application Circuit on page one. High-side driver is connected between BST and SWN pin. Input for external 5V bias supply Exposed Pad 1 Exposed Pad 1 Connect to LX through PCB. - Exposed Pad 2 Exposed Pad 1 Connect to GND through PCB. - Exposed Pad 3 Exposed Pad 1 Connect to VIN through PCB. ORDERING INFORMATION(1) Part Number SP7652ER-L/TR SP7652EB Junction Temperature Range -40°C ≤ TJ ≤ +125°C Package Packing Method 7mm x 4mm 26-pin DFN SP7652 Evaluation Board Tape & Reel Lead Free(2) Yes Notes: 1. Refer to www.maxlinear.com/SP7652 for most up-to-date Ordering Information. 2. Visit www.maxlinear.com for additional information on Environmental Rating. 4/15 Rev. 2.0.1 SP7652 6A 28V 600KHz Synchronous Step Down Regulator TYPICAL PERFORMANCE CHARACTERISTICS All data taken at VIN = 2.7V to 5.5V, TJ = TA = 25°C, unless otherwise specified - Schematic and BOM from Application Information section of this datasheet. Fig. 4: Output Voltage versus Output Current VIN=8V, 12V and 15V Fig. 3: Efficiency versus Output Current VIN=8V, 12V and 15V, VOUT=5V Fig. 5: Efficiency versus Output Current VIN=5V, VOUT=3.3V Fig. 6: Output Voltage versus Output Current VIN=5V, VOUT=3.3V Fig. 8: Output Voltage versus Output Current VIN=3.3V, VOUT=0.8V Fig. 7: Efficiency versus Output Current VIN=3.3V, VOUT=0.8V 5/15 Rev. 2.0.1 SP7652 6A 28V 600KHz Synchronous Step Down Regulator Fig. 10: Efficiency versus Output Current VIN=5V Fig. 9: Efficiency versus Output Current VIN=12V Fig. 11: Efficiency versus Output Current VIN=3.3V 6/15 Rev. 2.0.1 SP7652 6A 28V 600KHz Synchronous Step Down Regulator THEORY OF OPERATION SOFT START Soft start is achieved when a power converter ramps up the output voltage while controlling the magnitude of the input supply source current. In a modern step down converter, ramping up the positive terminal of the error amplifier controls soft start. As a result, excess source current can be defined as the current required to charge the output capacitor. GENERAL OVERVIEW The SP7652 is a fixed frequency, voltage mode, synchronous PWM regulator optimized for high efficiency. The part has been designed to be especially attractive for split plane applications utilizing 5V to power the controller and 3V to 20V for step down conversion. The heart of the SP7652 is a wide bandwidth transconductance amplifier designed to accommodate Type II and Type III compensation schemes. A precision 0.8V reference, present on the positive terminal of the error amplifier, permits the programming of the output voltage down to 0.8V via the VFB pin. The output of the error amplifier, COMP, which is compared to a 1.1V peak-to-peak ramp, is responsible for trailing edge PWM control. This voltage ramp and PWM control logic are governed by the internal oscillator that accurately sets the PWM frequency to 600kHz. IVIN = COUT * (ΔVOUT / ΔTSOFT-START) The SP7652 provides the user with the option to program the soft start rate by tying a capacitor from the SS pin to GND. The selection of this capacitor is based on the 10μA pull up current present at the SS pin and the 0.8V reference voltage. Therefore, the excess source can be redefined as: IVIN = COUT * (ΔVOUT *10μA / (CSS * 0.8V) UNDER VOLTAGE LOCK OUT (UVLO) The SP7652 contains two separate UVLO comparators to monitor the internal bias (VCC) and conversion (VIN) voltages independently. The VCC UVLO threshold is internally set to 4.25V, whereas the VIN UVLO threshold is programmable through the UVIN pin. When the UVIN pin is greater than 2.5V, the SP7652 is permitted to start up pending the removal of all other faults. Both the VCC and VIN UVLO comparators have been designed with hysteresis to prevent noise from resetting a fault. The SP7652 contains two unique control features that are very powerful in distributed applications. First, asynchronous driver control is enabled during start up, to prohibit the low side NFET from pulling down the output until the high side NFET has attempted to turn on. Second, a 100% duty cycle timeout ensures that the low side NFET is periodically enhanced during extended periods at 100% duty cycle. This guarantees the synchronized refreshing of the BST capacitor during very large duty cycle ratios. THERMAL AND SHORT-CIRCUIT PROTECTION The SP7652 also contains a number of valuable protection features. Programmable UVLO allows the user to set the exact VIN value at which the conversion voltage can safely begin down conversion, and an internal VCC UVLO ensures that the controller itself has enough voltage to operate properly. Other protection features include thermal shutdown and short-circuit detection. In the event that either a thermal, short-circuit, or UVLO fault is detected, the SP7652 is forced into an idle state where the output drivers are held off for a finite period before a re-start is attempted. Because the SP7652 is designed to drive large output current, there is a chance that the power converter will become too hot. Therefore, an internal thermal shutdown (145°C) has been included to prevent the IC from malfunctioning at extreme temperatures. A short-circuit detection comparator has also been included in the SP7652 to protect against an accidental short at the output of the power converter. This comparator constantly monitors the positive and negative terminals of the error amplifier, and if the VFB pin falls more than 250mV (typical) below the positive reference, a short-circuit fault is set. Because 7/15 Rev. 2.0.1 SP7652 6A 28V 600KHz Synchronous Step Down Regulator the SS pin overrides the internal 0.8V reference during soft start, the SP7652 is capable of detecting short-circuit faults throughout the duration of soft start as well as in regular operation. prevents the controller from “dragging down” the output voltage during startup or in fault modes. The second feature is a 100% duty cycle timeout that ensures synchronized refreshing of the BST capacitor at very high duty ratios. In the event that the high-side NFET is on for 20 continuous clock cycles, a reset is given to the PWM flip-flop half way through the 21st cycle. This forces GL to rise for the cycle, in turn refreshing the BST capacitor. HANDLING OF FAULTS Upon the detection of power (UVLO), thermal, or short-circuit faults, the SP7652 is forced into an idle state where the SS and COMP pins are pulled low and the NFETS are held off. In the event of UVLO fault, the SP7652 remains in this idle state until the UVLO fault is removed. Upon the detection of a thermal or short-circuit fault, an internal 200ms timer is activated. In the event of a short-circuit fault, a re-start is attempted immediately after the 200ms timeout expires. Whereas, when a thermal fault is detected, the 200ms delay continuously recycles and a re-start cannot be attempted until the thermal fault is removed and the timer expires. POWER MOSFETS The SP7652 contains a pair of integrated low resistance N-MOSFETs designed to drive up to 6A of output current. Maximum output current could be limited by thermal limitations of a particular application. The SP7652 incorporates a built-in over-temperature protection to prevent internal overheating. ERROR AMPLIFIER AND VOLTAGE LOOP Since the heart of the SP7652 voltage error loop is a high performance, wide bandwidth transconductance amplifier, great care should be taken to select the optimal compensation network. Because of the amplifier’s current limited (±150μA) transconductance, there are many ways to compensate the voltage loop or to control the COMP pin externally. If a simple, single-pole, single-zero response is desired, then compensation can be as simple as an RC circuit to Ground. If a more complex compensation is required, then the amplifier has enough bandwidth (45°C at 4MHz) and enough gain (60dB) to run Type III compensation schemes with adequate gain and phase margins at cross over frequencies greater than 50kHz. The common mode output of the error amplifier is 0.9V to 2.2V. Therefore, the PWM voltage ramp has been set between 1.1V and 2.2V to ensure proper 0% to 100% duty cycle capability. The voltage loop also includes two other very important features. One is an asynchronous startup mode. Basically, the synchronous rectifier cannot turn on unless the high-side NFET has attempted to turn on or the SS pin has exceeded 1.7V. This feature SETTING OUTPUT VOLTAGES The SP7652 can be set to different output voltages. The relationship in the following formula is based on a voltage divider from the output to the feedback pin VFB, which is set to an internal reference voltage of 0.80V. Standard 1% metal film resistors of surface mount size 0603 are recommended. 8/15 Rev. 2.0.1 SP7652 6A 28V 600KHz Synchronous Step Down Regulator Furthermore, one could select the value of the R1 and R2 combination to meet the exact output voltage setting by restricting R1 resistance range such that 50kΩ Cp1 and R1 >> RZ3 Output Load Resistance >> RESR and RDC Fig. 14: Type III Error Amplifier Compensation Circuit Fig. 13: Bode Plot of Type III Error Amplifier Compensation beyond the 0.7 square inches did not reduce thermal resistance. SP765X THERMAL RESISTANCE The SP765X family has been tested with a variety of footprint layouts along with different copper area and thermal resistance has been measured. The layouts were done on 4 layer FR4 PCB with the top and bottom layers using 3oz copper and the power and ground layers using 1oz copper. Using a minimum of 0.1 square inches of (3 ounces of) Copper on the top layer with no vias connecting to the 3 other layers produced a thermal resistance of 44°C/W. This thermal impedance is only 22% higher than the medium and large footprint layouts, indicating that space constrained designs can still benefit thermally from the Powerblox family of ICs. This indicates that a minimum footprint of 0.1 square inch, if used on a 4 layer board, can produce 44°C/W thermal resistance. This approach is still very worthwhile if used in a space constrained design. For the Minimum footprint, only about 0.1 square inch (of 3 ounces of) Copper was used on the top or footprint layer, and this layer had no vias to connect to the 3 other layers. For the Medium footprint, about 0.7 square inches (of 3 ounces of) Copper was used on the top layer, but vias were used to connect to the other 3 layers. For the Maximum footprint, about .0 square inch (of 3 ounces of) Copper was used on the top layer and many vias were used to connect to the 3 other layers. The following figures show the footprint layouts from an ORCAD file. The thermal data was taken for still air, not with forced air. If forced air is used, some improvement in thermal resistance would be seen. The results show that only about 0.7 square inches (of 3 ounces of) Copper on the top layer and vias connecting to the 3 other layers are needed to get the best thermal resistance of 36°C/W. Adding area on the top SP765X THERMAL RESISTANCE 4 Layer Board: • Top Layer 3ounces Copper • GND Layer 1ounce Copper 12/15 Rev. 2.0.1 SP7652 6A 28V 600KHz Synchronous Step Down Regulator • Power Layer ounce Copper Medium Footprint: 36°C/W • Bottom Layer 3ounces Copper Top Layer: 0.7 square inch Vias to other 3 Layers Minimum Footprint: 44°C/W Top Layer: 0.1 square inch No Vias to other 3 Layers Fig. 15: Minimum Footprint = 0.10in2 Fig. 16: Medium Footprint = 0.70in2 Maximum Footprint: 36°C/W Top Layer: .0 square inch Vias to other 3 Layers Fig. 17: Maximum Footprint = 1.0in2 13/15 Rev. 2.0.1 SP7652 6A 28V 600KHz Synchronous Step Down Regulator PACKAGE SPECIFICATION 26 PIN DFN 14/15 Rev. 2.0.1 SP7652 6A 28V 600KHz Synchronous Step Down Regulator REVISION HISTORY Revision Date 2.0.0 07/16/2012 Reformat of Datasheet Description 2.0.1 01/24/2020 Updated to MaxLinear logo. Updated Ordering Information. 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