XR76121ELTR-F

XR76121 20A Synchronous Step-Down COT Regulators Description FEATURES ■■ 20A step-down regulator 4.5V to 5.5V low VIN operation 5V to 22V wide single input voltage 3V to 22V operation with external 5V bias ≥0.6V adjustable output voltage ■■ Proprietary constant on-time control No loop compensation required Ceramic output capacitor stable operation Programmable 70ns-1µs on-time Constant 200kHz-1MHz frequency Selectable CCM or CCM/DCM operation ■■ Power-good flag with low impedance when power removed ■■ Precision enable ■■ Programmable soft-start ■■ 5mm x 6mm QFN package The XR76121 is a synchronous step-down regulator combining the controller, drivers, bootstrap diode and MOSFETs in a single package for point-of-load supplies. The XR76121 has a load current rating of 20A. A wide 5V to 22V input voltage range allows for single supply operation from industry standard 5V, 12V and 19.6V rails. With a proprietary emulated current mode constant on-time (COT) control scheme, the XR76121 provides extremely fast line and load transient response using ceramic output capacitors. They require no loop compensation, simplifying circuit implementation and reducing overall component count. The control loop also provides 0.1% load and 0.1% line regulation and maintains constant operating frequency. A selectable power saving mode, allows the user to operate in discontinuous mode (DCM) at light current loads thereby significantly increasing the converter efficiency. A host of protection features, including overcurrent, over temperature, overvoltage, short-circuit, open feedback detect and UVLO, helps achieve safe operation under abnormal operating conditions. APPLICATIONS ■■ Servers ■■ Distributed power architecture ■■ Point-of-load converters ■■ FPGA, DSP and processor supplies ■■ Base stations, switches/routers The XR76121 is available in a RoHS compliant, green/halogen-free space-saving 5mm x 6mm QFN package. Typical Application VIN EN BST VIN SW PVIN ILIM RLIM POWER GOOD VCC XR76121 SS FCCM TON VSNS AGND PGND CSS COUT VOUT R1 CVCC R1 FB R RON VOUT CFF RFF PGOOD CIN L1 R2 R2 Efficiency (%) CBST ENABLE 100 98 96 94 92 90 88 86 84 82 80 78 76 74 72 70 600kHz 800kHz 5.0V 3.3V 2.5V 1.8V 1.5V 1.2V 1.0V 0.1 5.1 10.1 15.1 20.1 IOUT (A) Figure 1. Typical Application Figure 2. Efficiency REV1D 1/18 XR76121 Absolute Maximum Ratings Operating Conditions 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. Stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. Exposure to any absolute maximum rating condition for extended periods may affect device reliability and lifetime. PVIN.......................................................................3V to 22V PVIN, VIN.......................................................................... -0.3V to 25V Junction temperature range (TJ).................. -40°C to 125°C VCC...................................................................................-0.3V to 6.0V Package power dissipation max at 25°C...................... 4.1W BST.................................................................-0.3V to 31V Package thermal resistance θJA..................................... 24°C/W(4) BST-SW.............................................................. -0.3V to 6V NOTES: 1. No external voltage applied. 2. SW pin’s DC range is -1V, transient is -5V for less than 50ns. 3. Recommended. 4. Measured on MaxLinear evaluation board. (1) SW, ILIM......................................................... -1V to 25V(1)(2) All other pins.......................................... -0.3V to VCC + 0.3V VIN......................................................................4.5V to 22V VCC....................................................................4.5V to 5.5V SW, ILIM ...........................................................-1V to 22V(2) PGOOD, TON, SS, EN..................................-0.3V to 5.5V(2) Switching frequency.................................... 200kHz-1MHz(3) Storage temperature..................................... -65°C to 150°C Junction temperature.................................................. 150°C Power dissipation....................................... Internally limited Lead temperature (soldering, 10 second)................... 300°C ESD rating (HBM – human body model)........................ 2kV ESD rating (CDM – charged device model)................... 1kV ESD rating (MM – machine model).............................. 200V Electrical Characteristics Specifications are for operating junction temperature of TJ = 25°C only; limits applying over the full operating junction temperature range are denoted by a •. Typical values represent the most likely parametric norm at TJ = 25°C, and are provided for reference purposes only. Unless otherwise indicated, VIN = 12V, SW = AGND = PGND = 0V, CVCC = 4.7uF. Symbol Parameter Conditions • Min Typ Max 5 12 22 4.5 5.0 5.5 Units Power Supply Characteristics VCC regulating VIN Input voltage range • IVIN VIN supply current Not switching, VIN = 12V, VFB = 0.7V • 0.8 1.3 mA IVCC VCC quiescent current Not switching, VCC = VIN = 5V, VFB = 0.7V • 0.8 1.3 mA IVIN VIN supply current f = 600kHz, RON = 49.9k, VFB = 0.58V 17 mA IOFF Shutdown current Enable = 0V, PVIN = VIN = 12V 1 μA VCC tied to VIN V Enable and Undervoltage Lock-Out UVLO VIH_EN EN pin rising threshold VEN_HYS EN pin hysteresis • 1.8 1.9 2.0 60 VCC UVLO start threshold, rising edge • 4.00 4.25 VCC UVLO hysteresis • 100 170 REV1D V mV 4.40 V mV 2/18 XR76121 Electrical Characteristics (Continued) Specifications are for operating junction temperature of TJ = 25°C only; limits applying over the full operating junction temperature range are denoted by a •. Typical values represent the most likely parametric norm at TJ = 25°C, and are provided for reference purposes only. Unless otherwise indicated, VIN = 12V, SW = AGND = PGND = 0V, CVCC = 4.7uF. Symbol Parameter Conditions • Min Typ Max Units VIN = 5V - 22V, VCC regulating 0.597 0.600 0.603 V VIN = 4.5V - 5.5V, VCC tied to VIN 0.596 0.600 0.604 V 0.594 0.600 0.606 V Reference Voltage VREF Reference voltage VIN = 5V - 22V, VCC regulating VIN = 4.5V - 5.5V, VCC tied to VIN DC load regulation DC line regulation • CCM operation, closed loop, applies to any COUT ±0.1 % ±0.1 % Programmable Constant On-Time On-time 1 RON = 5.90kΩ, VIN = 12V f corresponding to on-time 1 VOUT = 1.0V On-time 2 RON = 16.2kΩ, VIN = 12V f corresponding to on-time 2 VOUT = 3.3V On-time 3 RON = 3.01kΩ, VIN = 12V Minimum off-time • • • 170 200 230 ns 360 415 490 kHz 425 500 575 ns 478 550 647 kHz 90 110 135 ns 250 350 ns • Diode Emulation Mode Zero crossing threshold DC value measured during test -2 mV Soft-Start ISS_CHARGE Charge current ISS_DISCHARGE Discharge current • -14 -10 -6 µA Fault present • 1 3 VIN = 6V to 22V, ILOAD = 0 to 30mA • 4.8 5.0 VIN = 5V, RON = 16.2kΩ, fSW = 678kHz • 4.6 4.8 -10 -7.5 -5 % 1 4 % mA VCC Linear Regulator VCC Output voltage 5.2 V Power Good Output Power good threshold Power good hysteresis Power good Minimum ISINK = 1mA 0.2 V Power good, unpowered ISINK = 1mA 0.5 V Power good assertion delay, FB rising 2 ms Power good de-assertion delay, FB falling 65 µs REV1D 3/18 XR76121 Electrical Characteristics (Continued) Specifications are for operating junction temperature of TJ = 25°C only; limits applying over the full operating junction temperature range are denoted by a •. Typical values represent the most likely parametric norm at TJ = 25°C, and are provided for reference purposes only. Unless otherwise indicated, VIN = 12V, SW = AGND = PGND = 0V, CVCC = 4.7uF. Symbol Parameter Conditions • Min FCCM mode logic high threshold FCCM rising • 2.4 FCCM mode logic low threshold FCCM falling • Typ Max Units Mode Control (FCCM) V 0.4 Input leakage current 100 V nA Open Feedback/OVP Detect (VSNS) OVP trip high threshold VSNS rising. Specified as % of VREF • OVP trip low threshold VSNS falling. Specified as % of VREF • OVP comparator delay VSNS rising • Delay to turn off power stage from an overvoltage event VSNS rising • 115 120 125 115 0.5 1 % % 3.5 µs 3.5 µs Protection: OCP, OTP, Short-Circuit Hiccup timeout 110 ILIM/RDS 14.5 ILIM current temperature coefficient ILIM comparator offset • 4.7 mV -8.0 0 8.0 mV Thermal hysteresis • %/°C 0 Rising temperature Percent of VREF, short circuit is active. After PGOOD asserts high. µA/mΩ -4.7 Current limit blanking Feedback pin short-circuit threshold 18.0 0.4 ILIM comparator offset Thermal shutdown threshold 16.2 ms 50 100 ns 138 °C 15 °C 60 70 % Output Power Stage High-side MOSFET RDS(ON) IDS = 2A 7.7 10 mΩ Low-side MOSFET RDS(ON) IDS = 2A 3.1 3.5 mΩ Maximum output current • REV1D 20 A 4/18 XR76121 AGND TON ILIM PGOOD 1 2 3 4 5 6 7 BST 14 12 PVIN AGND SW FCCM BOTTOM VIEW FB TOP VIEW Pin Configuration 13 11 PGND 8 VS 17 AGND EN 15 9 VIN SS 16 BST 14 10 VC 10 VCC 17 AGND EN 15 9 VIN SS 16 PVIN 13 8 VSNS 12 7 PGOOD 6 ILIM 5 TON 4 AGND 3 AGND 2 FCCM FB 1 11 SW Pin Functions Pin Number Pin Name Type 1 FB A Feedback input to feedback comparator. 2 FCCM I Forcing this pin logic level high forces CCM operation. AGND A Signal ground for control circuitry. Connect to AGND pad with a short trace. 5 TON A Constant on-time programming pin. Connect with a resistor to AGND. 6 ILIM A Overcurrent protection programming. Connect with a resistor to SW. 7 PGOOD OD 8 VSNS A Sense pin for output OVP and open FB. 9 VIN A Supply input for the regulator’s LDO. Normally connected to PVIN. 10 VCC A The output of regulators LDO. It requires a 4.7µF VCC bypass capacitor. For operation using a 5V rail, VCC should be tied to VIN. 11 PGND PWR Ground of the power stage. Internally connected to source of the low-side MOSFET. 12 SW PWR Switch node. Internally it connects source of the high-side MOSFET to drain of the low-side MOSFET. 13 PVIN PWR Input voltage for power stage. Internally connected to drain of the high-side MOSFET. 14 BST A High-side driver supply pin. Connect a 0.1µF bootstrap capacitor between BST and SW. 15 EN I Precision enable pin. Pulling this pin above 2V will enable the regulator. 16 SS A Soft-start pin. Connect an external capacitor between SS and AGND to program the softstart rate based on the 10µA internal source current. 17 AGND PAD A Signal ground for control circuitry. 3 4 Description Power-good output. Open drain to AGND. Low Z when IC unpowered. NOTE: A = Analog, I = Input, O = Output, OD = Open Drain, PWR = Power. REV1D 5/18 PG XR76121 Typical Performance Characteristics 100 98 96 94 92 90 88 86 84 82 80 78 76 74 72 70 600kHz L = 0.4µH (1.0V, 1.2V, 1.5V, 1.8V) L = 1µH (2.5V, 3.3V, 5.0V) 5.0V DCM 3.3V DCM 2.5V DCM 1.8V DCM 1.5V DCM 1.2V DCM 1.0V DCM 5.0V CCM 3.3V CCM 2.5V CCM 1.8V CCM 1.5V CCM 1.2V CCM 1.0V CCM 10.0 1.0 IOUT (A) 0.1 Efficiency (%) Efficiency (%) Efficiency and Package Thermal Derating Unless otherwise specified: TAMBIENT = 25°C, no airflow, f = 800kHz. Efficiency data includes inductor losses, schematic from the Application Information section of this datasheet. 100 98 96 94 92 90 88 86 84 82 80 78 76 74 72 70 600kHz 3.3V DCM 2.5V DCM 1.8V DCM 1.5V DCM 1.2V DCM 1.0V DCM 120 120 110 110 100 100 90 90 80 70 50 5.0V, CCM, 600kHz 2.5V, CCM, 800kHz 40 1.0V, CCM, 800kHz 80 70 60 3.3V, CCM, 600kHz 1.8V, CCM, 800kHz 1.0V, CCM, 800kHz 50 40 30 20 10.0 Figure 4. Efficiency, VIN = 5V, L = 0.4µH TAMBIENT (ºC) TAMBIENT (ºC) Figure 3. Efficiency, VIN = 12V 60 1.0 IOUT (A) 0.1 3.3V CCM 2.5V CCM 1.8V CCM 1.5V CCM 1.2V CCM 1.0V CCM 30 4 6 8 10 12 14 16 18 20 20 IOUT (A) 12 IOUT (A) Figure 5. Maximum TAMBIENT vs. IOUT, VIN = 12V, No Airflow Figure 6. Maximum TAMBIENT vs. IOUT, VIN = 5V, No Airflow REV1D 4 6 8 10 14 16 18 20 6/18 XR76121 Typical Performance Characteristics (Continued) All data taken at VIN = 12V, VOUT = 1.8V, f = 800kHz, TA = 25°C, no airflow, forced CCM. (Unless otherwise specified). Schematic from the Applications Information section of this datasheet. SW SW 13mVp-p 27mVp-p VOUT AC-coupled 20MHz VOUT AC-coupled 20MHz IOUT IOUT Figure 7. Steady State, IOUT = 20A Figure 8. Steady State, DCM, IOUT = 0A VIN VIN EN EN VOUT VOUT IOUT IOUT Figure 9. Power-Up, IOUT = 20A Figure 10. Power-Up, IOUT = 0A SW SW VOUT AC-coupled 20MHz -64mV IOUT 4ms/div 4ms/div 90mV VOUT AC-coupled 20MHz 82mV -82mV Di/Dt = 2.5A/μs Di/Dt = 2.5A/μs IOUT 10μs/div Figure 11. Load Transient, Forced CCM, 0A-10A-0A 40μs/div Figure 12. Load Transient, DCM, 1.8A-11.8A-1.8A REV1D 7/18 XR76121 Typical Performance Characteristics (Continued) All data taken at VIN = 12V, VOUT = 1.8V, f = 800kHz, TA = 25°C, no airflow, forced CCM. (Unless otherwise specified). Schematic from the Applications Information section of this datasheet. SW EN 88mV VOUT AC-coupled 20MHz -62mV VOUT PGOOD Di/Dt = 2.5A/μs IOUT 10μs/div IOUT Figure 13. Load Transient, DCM or Forced CCM, 10A-20A-10A 4ms/div Figure 14. Enable Functionality, VIN = 12V Pre-bias = 1.2V VOUT VOUT PGOOD IOUT 1ms/div Figure 15. Power-Up with Pre-Bias Voltage, IOUT = 0A 40ms/div Figure 16. Short-Circuit Recovery, IOUT = 20A REV1D 8/18 XR76121 Typical Performance Characteristics (Continued) 1.850 1.850 1.840 1.840 1.830 1.830 1.820 1.820 1.810 1.810 VOUT (V) VOUT (V) All data taken at VIN = 12V, VOUT = 1.8V, f = 800kHz, TA = 25°C, no airflow, forced CCM. (Unless otherwise specified). Schematic from the Applications Information section of this datasheet. 1.800 1.790 1.800 1.790 1.780 1.780 1.770 1.770 1.760 1.760 1.750 0 2 4 6 8 10 12 14 16 18 1.750 20 12 14 16 18 Figure 18. Line Regulation 20 22 20 22 20 22 Calculated Typical 400 350 600 300 tON (ns) 700 500 400 300 250 200 200 150 100 0 10 5 15 20 RON (kΩ) 25 30 100 35 4 6 Figure 19. tON vs. RON 900 900 800 800 700 700 600 600 500 500 400 300 200 200 100 100 2 4 6 8 10 IOUT (A) 12 14 10 12 14 VIN (V) 16 18 400 300 0 8 Figure 20. tON vs. VIN, RON = 5.9kΩ f (kHz) f (kHz) 10 Figure 17. Load Regulation Calculated Typical 800 0 8 450 900 tON (ns) 6 VIN (V) 1,000 0 4 IOUT (A) 16 18 0 20 4 Figure 21. Frequency vs. IOUT 6 8 10 12 VIN (V) 14 16 18 Figure 22. Frequency vs. VIN REV1D 9/18 XR76121 Typical Performance Characteristics (Continued) All data taken at VIN = 12V, VOUT = 1.8V, f = 800kHz, TA = 25°C, no airflow, forced CCM. (Unless otherwise specified). Schematic from the Applications Information section of this datasheet. 35 610 30 605 20 VREF (mV) IOCP (A) 25 15 10 600 595 Calculated worst case Typical 5 0 1 1.2 1.4 1.6 RLIM (kΩ) 1.8 2 590 -40 2.2 -20 0 20 40 60 TJ (°C) 80 100 120 Figure 24. VREF vs. Temperature Figure 23. IOCP vs. RLIM 300 tON (ns) 250 200 150 100 -40 -20 0 20 40 TJ (˚C) 60 80 100 120 Figure 25. tON vs. Temperature, RON = 5.9k REV1D 10/18 XR76121 Functional Block Diagram VIN VCC PGOOD VCC UVLO 4.25V VCC XR76121 LDO 10µA VCC THERMAL SHUTDOWN SS 0.6V POWER GOOD PVIN HS DRV LEVEL ENABLING SWITCHING BST SHIFT AND SW NON FB VSNS VH = 1.2 x VREF VL = 1.15 x VREF OVERLAP COT CONTROL LOOP 0.555V CONTROL DELAY SW OVP ZC FB 0.36V PGND 1.9V EN LS DRV VCC SCCOMP VCC FCCM PGND HICCUP ILIM PGND TON EN ILIM AGND Figure 26. Functional Block Diagram REV1D 11/18 XR76121 Applications Information Detailed Operation The XR76121 uses a synchronous step-down proprietary emulated current-mode Constant On-Time (COT) control scheme. The on-time, which is programmed via RON, is inversely proportional to VIN and maintains a nearly constant frequency. The emulated current-mode control allows the use of ceramic output capacitors. Programming the On-Time The on-time tON is programmed via resistor RON according to following equation: Each switching cycle begins with the high-side (switching) FET turning on for a preprogrammed time. At the end of the on-time, the high-side FET is turned off and the low-side (synchronous) FET is turned on for a preset minimum time (250ns nominal). This parameter is termed the minimum off-time. After the minimum off-time the voltage at the feedback pin FB is compared to an internal voltage ramp at the feedback comparator. When VFB drops below the ramp voltage, the high-side FET is turned on and the cycle repeats. This voltage ramp constitutes an emulated current ramp and allows for the use of ceramic capacitors, in addition to other capacitor types, for output filtering. A graph of tON versus RON, using the above equation, is compared to typical test data in Figure 19. The graph VOUT shows that calculated data matches typical test data – (2.5 × 10-8)] IN × x[tfON within 3%.tON = V xV1.06 x Eff. RONIN= 10-10 The tON corresponding to3.45 a × particular set of operating conditions can be calculated based on empirical data from: Enable The enable input provides precise control for startup. Where bus voltage is well regulated, the enable input can be derived from this voltage with a suitable resistor divider. This ensures that XR76121 does not turn on until bus voltage reaches the desired level. Therefore the enable feature allows implementation of undervoltage lockout for the bus voltage PVIN. Simple sequencing can be implemented by using the PGOOD signal as the enable input of a succeeding XR76121. Sequencing can also be achieved by using an external signal to control the enable pin. Selecting the Forced CCM Mode A voltage higher than 2.4V at the FCCM pin forces the XR76121 to operate in continuous conduction mode (CCM). Note that discontinuous conduction mode (DCM) is always on during soft-start. DCM will persist following soft-start until a sufficient load is applied to transition the regulator to CCM. Magnitude of the load required to transition to CCM is ΔIL/2, where ΔIL is peak-to-peak inductor current ripple. Once the regulator transitions to CCM it will continue operating in CCM regardless of the load magnitude. Selecting the DCM/CCM Mode The DCM will always be available if a voltage less than 0.4V is applied to the FCCM pin. XR76121 will operate in either DCM or CCM depending on the load magnitude. At light loads DCM significantly increases efficiency as seen in Figures 3 and 4. A preload of 10mA is recommended for DCM operation. This helps improve voltage regulation when external load is less then 10mA and may reduce voltage ripple. RON = Where: VIN × [tON – (2.5 × 10-8)] 3.45 × 10-10 VOUT VOUT -8 VIN =× [tON – (2.5 × )]× 10-8) x VIN] tON – 10 [(2.5 1.06VxINf xx 1.06 Eff. x f x Eff. RON = RON = 3.45 ×(3.45 10-10× 10-10) ■■ f is the desired switching frequency at nominal IOUT. VOUT VOUT tON = – [(2.5 × 10-8) x V ] ■■ Eff. is the Vconverter 1.06 xxfEff. x Eff. correspondingINto x 1.06 x fefficiency IN ∆ IL)) (I + (0.5 × RON .OCP = nominal IOUT (3.45 +× 0.16kΩ 10-10) RLIM = ILIM Substituting for tON in the first equation we get: RDS VOUT – [(2.5 × 10-8) x VIN] 1.06 x f x Eff. (IOCP + (0.5 × ∆IL)) RON = (3.45 × 10-10) RLIM = + 0.16kΩ ILIM R DS VOUT – 1in terms of operating = R2 Now RONR1 can bexcalculated 0.6 conditions VIN, VOUT, f and efficiency using the above equation. (I OCP + (0.5 × ∆IL)) 10µA RLIM = + 0.16kΩ CSS f==tSS x ILIMI At VIN = 12V, 800kHz, = 20A and using the OUT 0.6V RDS VOUT 3 we get the following RON: efficiency numbers from –1 R1 = R2 x Figure 0.6 1 VOUT (V) f (kHz) RON (kΩ) CFF = Eff. (%) 2 x π x R1 x 5 x fLC 5.0 0.95 600 23.12 10µA CSS = tSS x 0.6V 3.3 0.93 600 15.30 VOUT 1– 1 R1f= R2 x = 0.6 2.5 LC 0.91 800 8.52 2 x π x √ L x 1COUT CFF = 0.89 1.8 800 6.04 2 x π x R1 x 5 x fLC 10µA 1.5 C 0.87 800 5.02 SS = tSS x 0.6V 1 1.2 RFF = 0.84 800 4.01 2 x=π x f x CFF 1 fLC 1.0 0.81 800 3.35 21x π x √ L x COUT CFF = 2 x π x R1 x 5 x fLC XR76121 RON for common output voltages, VIN = 12V, 1 IOUT = 20A RFF = 1 2 x π x f x CFF fLC = 2 x π x √ L x COUT REV1D 12/18 RON = VIN × [tON – (2.5 × 10-8)] 3.45 × 10-10 RON = VIN × [tON – (2.5 × 10-8)]XR76121 3.45 × 10-10 Applications Information VOUT (Continued) tON = VIN x(OCP) 1.06 x f x Eff. Overcurrent Protection If the load current exceeds the programmed overcurrent threshold IOCP for four consecutive switching cycles, the regulator enters the hiccup mode of operation. In hiccup mode the MOSFET off for 110ms VOUT gates are turned – [(2.5 timeout × 10-8) x VaIN]soft-start (hiccup timeout). Following the hiccup 1.06 x f x Eff. is attempted.RON If = OCP persists, hiccup-10timeout will repeat. (3.45 × mode 10 ) until load current The regulator will remain in hiccup is reduced below the programmed IOCP. In order to program overcurrent protection use the following equation: (IOCP + (0.5 × ∆IL)) RLIM = + 0.16kΩ ILIM RDS Where: ■■ RLIM is resistor value in kΩ for programming IOCP ■■ IOCP is the overcurrent value to be programmed VOUT inductor current ripple is the peak-to-peak –1 R1 = R2 x 0.6 ■■ ILIM/RDS is the minimum value of the parameter specified in the tabulated data Overvoltage Protection (OVP)VOUT tON = The output OVP function overvoltage condition VINdetects x 1.06 x an f x Eff. on VOUT of the regulator. OVP is achieved by comparing VIN × [tON – (2.5 × 10-8)] the voltage at VSNS pin to an OVP threshold voltage RON = 3.45 ×voltage 10-10 set at 1.2 x VREF. When VSNS exceeds the OVP threshold, an internal overvoltage signal asserts after 1us (typical). This OVP signalVOUT latches off the × high-side – [(2.5 10-8) x V FET, ] 1.06and x f xalso Eff. asserts PGOODIN low. turns on the low-side FET VOUT RON = The low-side FET tON remains on (3.45 to discharge = × 10-10) the output VIN x 1.06 x f xbelow Eff. 1.15 x VREF. capacitor until VSNS voltage drops Then low-side FET turns off to prevent complete discharge of VOUT. The high-side and low-side FETs remain latched off until VIN or EN is recycled. In order to use this feature, (IOCP a+Vresistor (0.5 × ∆IL)) connect VSNS to VOUT with divider as shown in OUT – [(2.5 × 10-8) xvalue VIN] the application circuit. the ILIM same resistor divider RLIM = Use 1.06 + 0.16kΩ x f x Eff. RON = that was used for programming OUT. RV DS (3.45 × 10-10) Programming the Output Voltage Use a voltage divider as shown in Figure 1 to program the output voltage VOUT. ■■ ΔIL R1R=LIM R2 =x ■■ ILIM/RDS = 14.5uA/mΩ 10µA CSS = tSS x ■■ 0.16kΩ accounts for 0.6V OCP comparator offset The above equation is for worst-case analysis and 1 safeguards against CFF = premature OCP. Typical value of IOCP, R1 higher x 5 x fLC than that predicted by x π xbe for a given RLIM, 2will the above equation. Graph of calculated IOCP vs. RLIM is compared to typical IOCP in Figures 23. 1 LC = Short-Circuit fProtection (SCP) 2 x π x √ L x COUT If the output voltage drops below 60% of its programmed value (i.e., FB drops below 0.36V), the regulator will enter hiccup mode. Hiccup mode will persist until short-circuit is removed. The SCP circuit becomes active at the end 1 R = of soft-start. FFHiccup mode 2 x π x f x CFF and short-circuit recovery waveform is shown in Figure 16. Over Temperature Protection (OTP) OTP triggers at a nominal controller temperature of 138°C. The gates of the switching FET and the synchronous FET are turned off. When controller temperature cools down to 123°C, soft-start is initiated and regular operation resumes. (IOCP + (0.5 × ∆IL)) VOUT + 0.16kΩ I– 1 0.6 LIM RDS The recommended value for R2 is 2kΩ. 10µA CSS = tSS x Programming the Soft-Start 0.6V Place a capacitor CSS between the SS and AGND pins to program the soft-start. In order to program a soft-start time VOUT 1 –1 R1 ==required R2 x of tSS, calculate Cthe capacitance CSS from the FF 0.6x 5 x fLC 2 x π x R1 following equation: 10µA 1 fLCCSS = = tSS x 0.6V 2 x π x √ L x COUT 1 Pre-Bias Startup C = FF 2 x π x R1 x 5 x f XR76121 has the capability to startup LC into a pre-charged 1 output. Typical pre-bias startup waveforms are shown in RFF = 2 x π x f x CFF Figure 15. 1 = Maximum AllowablefLC Voltage Ripple at FB Pin π x √ L atx COUT The steady-state voltage2 xripple feedback pin FB (VFB,RIPPLE) must not exceed 50mV in order for the regulator to function correctly. If VFB,RIPPLE is larger than 50mV then COUT and/or L should be increased 1 as necessary in order to FF = 2 50mV. keep the VFB,RIPPLERbelow x π x f x CFF REV1D 13/18 RDS× ∆IL)) (IOCP + (0.5 + 0.16kΩ ILIM VOUT R DS tON = VIN x 1.06 x f x Eff. RLIM = XR76121 VOUT (Continued) ApplicationsR1Information –1 = R2 x 0.6 V) Feed-Forward CapacitorV(CFF – [(2.5 × 10-8) x VIN] OUT OUT –fisx1 Eff. R1 =capacitor R2 x 1.06 x The feed-forward C used to set the necessary FF RON = 0.6 10µA phase margin when using ceramic (3.45 × output 10-10) capacitors. CSS = tSS x 0.6V equation: Calculate CFF from the following 10µA CSS = tSS x 0.6V 1 CFF = 2 x π x R1 x 5 x fLC (IOCP + (0.5 × ∆IL)) 1 I R = + 0.16kΩ CFFLIM = LIM Where fLC, the output frequency is 2 x π x filter R1 x 5Rdouble-pole x fLC 1 DS calculated from: f = LC 2 x π x √ L x COUT 1 fLC = 2 x π x √ L x COUT 1 = VOUT You must use RFF manufacturer’s π x f x CFF–DC 2 x 1 derating curves to R1 = R2 x 0.6 determine the effective capacitance corresponding to VOUT. A load step test a1 loop frequency response test) RFF(and/or = x π xiff necessary x CFF should be performed2and CFF can be adjusted 10µAtransient load response. in order to get a critically damped CSS = tSS x 0.6V In applications where output voltage ripple is less than about 3mV, such as when a large number of ceramic COUT are paralleled, it is necessary to use ripple injection 1 CFF = from across the inductor. x R1 xcircuit 5 x fLCand corresponding 2 x πThe calculations are explained in the MaxLinear design note. Thermal Design Proper thermal design is critical in controlling device temperatures and in achieving robust designs. There are a number of factors that affect the thermal performance. One key factor is the temperature rise of the devices in the package, which is a function of the thermal resistances of the devices inside the package and the power being dissipated. The thermal resistance of the XR76121 is specified in the Operating Ratings section of this datasheet. The θJA thermal resistance specification is based on the XR76121 evaluation board operating without forced airflow. Since the actual board design in the final application will be different, the thermal resistances in the final design may be different from those specified. The package thermal derating curves for the XR76121 are shown in Figures 5 and 6. These correspond to input voltage of 12V and 5V, respectively. The package thermal derating curves for the XR76121 are shown in Figures 9 and 10. Feed-Forward Resistor (RFF) 1 fLC =CFF is used. RFF, in conjunction with RFF is required when π x √ Lfrequency x COUT pole and adds CFF, functions similar to 2ax high gain margin to the frequency response. Calculate RFF from: RFF = 1 2 x π x f x CFF Where f is the switching frequency. If RFF is greater than 0.1 x R1, then instead of CFF/RFF, use ripple injection circuit as described in MaxLinear’s design note. REV1D 14/18 XR76121 Applications Information REN2 3.83k REN1 10k VIN = 12V VIN 2 x 0.1µF 13 14 BST 16 15 EN PVIN 12 SW 4 x 0.1µF XR76121 ILIM PGOOD VOUT CFF 470pF PGND 7 RPGOOD 10k 800kHz, 1.8V, 0-20A L1, IHLP-5050FD-01 0.4µH at 44A, 0.9m Ohm V OUT 11 6 RLIM 1.82k TON RFF 0.4k VCC RSENS1 4.02k 4 x 22µF/25V/X6T/1206 0.1µF SW AGND VCC VCC 5 8 SW 4 AGND VIN RON 6.19k FCCM 10 3 FB VSENSE 2 9 1 VCC EPAD_AGND FB CBST SS 17 CSS 47nF 5 x 100µF/6.3V/X6T/1206 R1 4.02k FB VIN RSENS2 2k CIN CVCC 0.1µF 4.7µF R2 2k Figure 27. Application Circuit Schematic REV1D 15/18 XR76121 Mechanical Dimensions TOP VIEW BOTTOM VIEW SIDE VIEW TERMINAL DETAILS Drawing No.: POD-00000071 Revision: D Figure 28. Mechanical Dimensions REV1D 16/18 XR76121 Recommended Land Pattern and Stencil TYPICAL RECOMMENDED LAND PATTERN TYPICAL RECOMMENDED STENCIL Drawing No.: POD-00000071 Revision: D Figure 29. Recommended Land Pattern and Stencil REV1D 17/18 XR76121 Ordering Information(1) Part Number Operating Temperature Range Lead-Free Package -40°C ≤ TJ ≤ 125°C Yes(2) 5mm x 6mm QFN XR76121EL-F XR76121ELTR-F XR76121EVB Packaging Method Bulk Tape and Reel XR76121 evaluation board NOTE: 1. Refer to www.exar.com/XR76121 for most up-to-date Ordering Information. 2. Visit www.exar.com for additional information on Environmental Rating. Revision History Revision Date 1A July 2016 1B November 2017 1C May 2018 1D February 2019 Description Initial Release Added MaxLinear logo. Updated format and Ordering Information table. Changed name of Package Description section to Mechanical Dimensions and Recommended Land Pattern and Stencil per updated format. Corrected typo in Package Description / Mechanical Dimensions. Updated Land Pattern and Stencil. Package dimension A updated to align with JEDEC. Update Ordering Information. Corporate Headquarters: 5966 La Place Court Suite 100 Carlsbad, CA 92008 Tel.:+1 (760) 692-0711 Fax: +1 (760) 444-8598 www.maxlinear.com The content of this document is furnished for informational use only, is subject to change without notice, and should not be construed as a commitment by MaxLinear, Inc.. MaxLinear, Inc. assumes no responsibility or liability for any errors or inaccuracies that may appear in the informational content contained in this guide. Complying with all applicable copyright laws is the responsibility of the user. Without limiting the rights under copyright, no part of this document may be reproduced into, stored in, or introduced into a retrieval system, or transmitted in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise), or for any purpose, without the express written permission of MaxLinear, Inc. Maxlinear, Inc. does not recommend the use of any of its products in life support applications where the failure or malfunction of the product can reasonably be expected to cause failure of the life support system or to significantly affect its safety or effectiveness. Products are not authorized for use in such applications unless MaxLinear, Inc. receives, in writing, assurances to its satisfaction that: (a) the risk of injury or damage has been minimized; (b) the user assumes all such risks; (c) potential liability of MaxLinear, Inc. is adequately protected under the circumstances. MaxLinear, Inc. may have patents, patent applications, trademarks, copyrights, or other intellectual property rights covering subject matter in this document. Except as expressly provided in any written license agreement from MaxLinear, Inc., the furnishing of this document does not give you any license to these patents, trademarks, copyrights, or other intellectual property. MaxLinear, the MaxLinear logo, and any MaxLinear trademarks, MxL, Full-Spectrum Capture, FSC, G.now, AirPHY and the MaxLinear logo are all on the products sold, are all trademarks of MaxLinear, Inc. or one of MaxLinear’s subsidiaries in the U.S.A. and other countries. All rights reserved. Other company trademarks and product names appearing herein are the property of their respective owners. © 2016 - 2019 MaxLinear, Inc. All rights reserved XR76121_DS_020819 REV1D 18/18