Is Now Part of To learn more about ON Semiconductor, please visit our website at www.onsemi.com Please note: As part of the Fairchild Semiconductor integration, some of the Fairchild orderable part numbers will need to change in order to meet ON Semiconductor's system requirements. Since the ON Semiconductor product management systems do not have the ability to manage part nomenclature that utilizes an underscore (_), the underscore (_) in the Fairchild part numbers will be changed to a dash (-). This document may contain device numbers with an underscore (_). Please check the ON Semiconductor website to verify the updated device numbers. The most current and up-to-date ordering information can be found at www.onsemi.com. Please email any questions regarding the system integration to Fairchild_questions@onsemi.com. ON Semiconductor and the ON Semiconductor logo are trademarks of Semiconductor Components Industries, LLC dba ON Semiconductor or its subsidiaries in the United States and/or other countries. ON Semiconductor owns the rights to a number of patents, trademarks, copyrights, trade secrets, and other intellectual property. A listing of ON Semiconductor's product/patent coverage may be accessed at www.onsemi.com/site/pdf/Patent-Marking.pdf. ON Semiconductor reserves the right to make changes without further notice to any products herein. ON Semiconductor makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does ON Semiconductor assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. Buyer is responsible for its products and applications using ON Semiconductor products, including compliance with all laws, regulations and safety requirements or standards, regardless of any support or applications information provided by ON Semiconductor. "Typical" parameters which may be provided in ON Semiconductor data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including "Typicals" must be validated for each customer application by customer's technical experts. ON Semiconductor does not convey any license under its patent rights nor the rights of others. ON Semiconductor products are not designed, intended, or authorized for use as a critical component in life support systems or any FDA Class 3 medical devices or medical devices with a same or similar classification in a foreign jurisdiction or any devices intended for implantation in the human body. Should Buyer purchase or use ON Semiconductor products for any such unintended or unauthorized application, Buyer shall indemnify and hold ON Semiconductor and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that ON Semiconductor was negligent regarding the design or manufacture of the part. ON Semiconductor is an Equal Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner. FAN2106 -- 3-24 V Input, 6 A, High-Efficiency, Integrated Synchronous Buck Regulator Features Description 6 A Output Current The FAN2106 is a highly efficient, small-footprint, constant-frequency, 6 A, integrated synchronous buck regulator. Fully Synchronous Operation with Integrated Schottky Diode on Low-Side MOSFET Boosts Efficiency Wide Input Range: 3 V - 24 V Output Voltage Range: 0.8 V to 80% VIN Over 95% Peak Efficiency 1% Reference Accuracy Over Temperature Programmable Frequency Operation: 200 KHz to 600 KHz Internal Bootstrap Diode 5x6 mm, 25-Pin, 3-Pad MLP Package Internal Soft-Start Power-Good Signal The FAN2106 provides for external loop compensation, programmable switching frequency, and current limit. These features allow design flexibility and optimization. High-frequency operation allows for all-ceramic solutions. The summing current-mode modulator uses lossless current sensing for current feedback and over-current protection. Voltage feedforward helps operation over a wide input voltage range. Starts on Pre-Biased Outputs Accepts Ceramic Capacitors on Output External Compensation for Flexible Design Programmable Current Limit Under-Voltage, Over-Voltage, and Thermal Protections Applications Servers & Telecom Graphics Cards & Displays Computing Systems Point-of-Load Regulation Set-Top Boxes & Game Consoles The FAN2106 contains both synchronous MOSFETs and a controller/driver with optimized interconnects in one package, which enables designers to solve highcurrent requirements in a small area with minimal external components. Integration helps to minimize critical inductances, making component layout simpler and more efficient compared to discrete solutions. Fairchild's advanced BiCMOS power process, combined with low-RDS(ON) internal MOSFETs and a thermally efficient MLP package, provide the ability to dissipate high power in a small package. Output over-voltage, under-voltage, over-current, and thermal shutdown protections help protect the device from damage during fault conditions. FAN2106 prevents pre-biased output discharge during startup in point-of-load applications. Related Resources AN-8022 -- TinyCalcTM Calculator User Guide TinyCalcTM Calculator Design Tool Ordering Information Part Number FAN2106MPX FAN2106EMPX Operating Temperature Range -40C to 85C (c) 2009 Fairchild Semiconductor Corporation FAN2106 * Rev. 1.25 Package Molded Leadless Package (MLP) 5 x 6 mm Packing Method Tape and Reel www.fairchildsemi.com FAN2106 -- 3-24V Input, 6A, High-Efficiency, Integrated Synchronous Buck Regulator September 2015 Figure 1. Typical Application Block Diagram FAN2106 -- 3-24V Input, 6A, High-Efficiency, Integrated Synchronous Buck Regulator Typical Application Diagram Figure 2. Block Diagram (c) 2009 Fairchild Semiconductor Corporation FAN2106 * Rev. 1.25 www.fairchildsemi.com 2 VIN VIN SW SW SW 4 5 6 7 8 15 14 EN 16 AGND VCC 17 ILIM 9 VIN 3 18 R(T) 10 VIN 2 19 FB 11 BOOT 1 20 COMP 22 PGND P3 GND SW SW 12 24 PGND 21 PGND P1 SW SW SW PGOOD 13 25 NC P2 VIN 23 RAMP Figure 3. MLP 5 x 6 mm Pin Configuration (Bottom View) Pin Definitions Pin # Name Description P1, 6-12 SW Switching Node. Junction of high-side and low-side MOSFETs. P2, 2-5 VIN Power Input Voltage. Connect to the main input power source. P3, 21-23 PGND Power Ground. Power return and Q2 source. 1 BOOT High-Side Drive BOOT Voltage. Connect through capacitor (CBOOT) to SW. The IC includes an internal synchronous bootstrap diode to recharge the capacitor on this pin to VCC when SW is LOW. 13 PGOOD 14 EN 15 VCC 16 AGND 17 ILIM Current Limit. A resistor (RILIM) from this pin to AGND can be used to program the currentlimit trip threshold lower than the default setting. 18 R(T) Oscillator Frequency. A resistor (RT) from this pin to AGND sets the PWM switching frequency. 19 FB Output Voltage Feedback. Connect through a resistor divider to the output voltage. 20 COMP Compensation. Error amplifier output. Connect the external compensation network between this pin and FB. 24 NC 25 RAMP Power-Good Flag. An open-drain output that pulls LOW when FB is outside the limits specified in electrical specs. PGOOD does not assert HIGH until the fault latch is enabled. ENABLE. Enables operation when pulled to logic HIGH or left open. Toggling EN resets the regulator after a latched fault condition. This input has an internal pull-up when the IC is functioning normally. When a latched fault occurs, EN is discharged by a current sink. Input Bias Supply for IC. The IC's logic and analog circuitry are powered from this pin. This pin should be decoupled to AGND through a >1 F X5R/X7R capacitor. FAN2106 -- 3-24V Input, 6A, High-Efficiency, Integrated Synchronous Buck Regulator Pin Configuration Analog Ground. The signal ground for the IC. All internal control voltages are referred to this pin. Tie this pin to the ground island/plane through the lowest impedance connection. No Connect. This pin is not used. Ramp Amplitude. A resistor (RRAMP) connected from this pin to VIN sets the ramp amplitude and provides voltage feedforward functionality. (c) 2009 Fairchild Semiconductor Corporation FAN2106 * Rev. 1.25 www.fairchildsemi.com 3 Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be operable above the recommended operating conditions and stressing the parts to these levels is not recommended. In addition, extended exposure to stresses above the recommended operating conditions may affect device reliability. The absolute maximum ratings are stress ratings only. Parameter Conditions Min. VIN to PGND VCC to AGND AGND = PGND 28 V 6 V V -0.3 6.0 V Continuous -0.5 24.0 Transient (t < 20 ns, f < 600 KHz) -5.0 30.0 -0.3 VCC+0.3 BOOT to SW All other pins ESD Unit 35 BOOT to PGND SW to PGND Max. Human Body Model, JEDEC JESD22-A114 2.0 Charged Device Model, JEDEC JESD22-C101 2.5 V V kV Recommended Operating Conditions The Recommended Operating Conditions table defines the conditions for actual device operation. Recommended operating conditions are specified to ensure optimal performance to the datasheet specifications. Fairchild does not recommend exceeding them or designing to absolute maximum ratings. Symbol Parameter Conditions Min. Typ. Max. Unit 5.0 5.5 V 24 V VCC Bias Voltage VCC to AGND 4.5 VIN Supply Voltage VIN to PGND 3 TA Ambient Temperature TJ Junction Temperature fSW Switching Frequency -40 200 +85 C +125 C 600 KHz Max. Unit +150 C +300 C Thermal Information Symbol TSTG TL JC J-PCB PD Parameter Min. Storage Temperature Typ. -65 Lead Soldering Temperature, 10 Seconds P1 (Q2) 4 P2 (Q1) 7 P3 4 Thermal Resistance: Junction-to-Mounting Surface 35 Thermal Resistance: Junction-to-Case Power Dissipation, TA = 25C FAN2106 -- 3-24V Input, 6A, High-Efficiency, Integrated Synchronous Buck Regulator Absolute Maximum Ratings C/W (1) C/W 2.8 (1) W Note: 1. Typical thermal resistance when mounted on a four-layer, two-ounce PCB, as shown in Figure 26. Actual results are dependent on mounting method and surface related to the design. (c) 2009 Fairchild Semiconductor Corporation FAN2106 * Rev. 1.25 www.fairchildsemi.com 4 Electrical specifications are the result of using the circuit shown in Figure 1 with VIN = 12 V, unless otherwise noted. Parameter Conditions Min. Typ. Max. Unit SW = Open, FB = 0.7 V, VCC = 5 V, fSW = 600 KHz 8 12 mA Shutdown: EN = 0, VCC = 5 V 7 10 A 4.3 4.5 V Power Supplies VCC Current Rising VCC VCC UVLO Threshold 4.1 Hysteresis 300 mV Oscillator Frequency Minimum On-Time 255 300 345 KHz RT = 24 K 540 600 660 KHz 50 65 ns (2) Ramp Amplitude, Peak-to-Peak Minimum Off-Time RT = 50 K 16 VIN, 1.8 VOUT, RT = 30 K, RRAMP = 200 K 0.53 (2) V 100 150 ns 795 800 805 mV 80 85 dB 12 15 MHz Reference Reference Voltage (VFB) (3) Error Amplifier DC Gain (2) Gain Bandwidth Product (2) VCC = 5 V Output Voltage (VCOMP) 0.4 3.2 V Output Current, Sourcing VCC = 5 V, VCOMP = 2.2 V 1.5 2.2 mA Output Current, Sinking VCC = 5 V, VCOMP = 1.2 V 0.8 1.2 mA FB Bias Current VFB = 0.8 V, TA = 25C -850 -650 -450 nA 6 8 10 A -11 -10 -9 A Protection and Shutdown Current Limit RILIM Open, fSW = 500 KHz, VOUT = 1.8 V, RRAMP = 200 K16 Consecutive Cycles ILIM Current VCC = 5 V, TA = 25C Over-Temperature Shutdown Over-Temperature Hysteresis +155 Internal IC Temperature C +30 C Over-Voltage Threshold 2 Consecutive Clock Cycles 110 115 120 %VOUT Under-Voltage Shutdown 16 Consecutive Clock Cycles 68 73 78 %VOUT Fault Discharge Threshold Measured at FB Pin 250 mV Fault Discharge Hysteresis Measured at FB Pin (VFB ~500 mV) 250 mV 5.3 ms 6.7 ms FAN2106 -- 3-24V Input, 6A, High-Efficiency, Integrated Synchronous Buck Regulator Electrical Specifications Soft-Start VOUT to Regulation (T0.8) Fault Enable/SSOK (T1.0) Frequency = 600 KHz Continued on the following page... (c) 2009 Fairchild Semiconductor Corporation FAN2106 * Rev. 1.25 www.fairchildsemi.com 5 Electrical specifications are the result of using the circuit shown in Figure 1 with VIN= 12 V, unless otherwise noted. Parameter Conditions Min. Typ. Max. Unit 2.00 V Control Functions EN Threshold, Rising VCC = 5 V 1.35 EN Hysteresis VCC = 5 V 250 mV EN Pull-Up Resistance VCC = 5 V 800 K EN Discharge Current Auto-Restart Mode, VCC = 5 V 1 A FB OK Drive Resistance 800 PGOOD Threshold (Compared to VREF) FB < VREF, 2 Consecutive Clock Cycles -14 -11 -8 %VREF FB > VREF, 2 Consecutive Clock Cycles +7 +10 +13 %VREF PGOOD Output Low IOUT < 2 mA 0.4 V Notes: 2. Specifications guaranteed by design and characterization; not production tested. 3. See Figure 4 for Temperature Coefficient (c) 2009 Fairchild Semiconductor Corporation FAN2106 * Rev. 1.25 FAN2106 -- 3-24V Input, 6A, High-Efficiency, Integrated Synchronous Buck Regulator Electrical Specifications (Continued) www.fairchildsemi.com 6 1.20 1.005 1.10 I FB V FB 1.010 1.000 0.995 1.00 0.90 0.990 0.80 -50 0 50 100 150 -50 0 o 150 Figure 5. Reference Bias Current (IFB) vs. Temperature, Normalized 1500 1.02 1200 1.01 Frequency Frequency (KHz) 100 Temperature ( C) Figure 4. Reference Voltage (VFB) vs. Temperature, Normalized 900 600 600 kHz 1.00 300 kHz 0.99 300 0.98 0 0 20 40 60 80 100 120 -50 140 0 50 100 150 o RT (K) Temperature ( C) Figure 6. Frequency vs. RT Figure 7. Frequency vs. Temperature, Normalized 1.04 1.60 1.40 1.02 1.20 I ILIM RDS 50 o Temperature ( C) 1.00 FAN2106 -- 3-24V Input, 6A, High-Efficiency, Integrated Synchronous Buck Regulator Typical Characteristics 1.00 o Q1 ~0.32 %/ C 0.80 0.98 o Q2 ~0.35 %/ C 0.96 0.60 -50 0 50 100 150 -50 50 100 150 Temperature ( C) Temperature ( C) Figure 9. Figure 8. RDS vs. Temperature, Normalized (VCC = VGS = 5 V) (c) 2009 Fairchild Semiconductor Corporation FAN2106 * Rev. 1.25 0 o o ILIM Current (IILIM) vs. Temperature, Normalized www.fairchildsemi.com 7 VCC +5V 1.0 P2 15 VIN 8-20 VIN 10K X5R PGOOD 200K 13 3.3n 2 x 4.7 VOUT X7R NC 24 2.49K 62 COMP 2.49K 4.7n 25 RAMP 20 56p FB 1 19 * Inter-Technical SC7232-2R2M BOOT 4.7n ILIM 0.1 17 VOUT EN 200K 14 P1 SW 2.2 * R(T) 18 1.5 30.1K 2.00K 4 x 22 AGND P3 PGND 16 X5R 390p 4.7n Figure 10. Application Circuit: 1.8 VOUT, 500 KHz Typical Performance Characteristics 100 1400 95 1200 Dissipation (mW) Efficiency (%) Typical operating characteristics using the circuit shown in Figure 10. VIN=12 V, VCC=5 V, unless otherwise specified. 90 85 8 VIN 12 VIN 18 VIN 80 75 1000 8 VIN 12 VIN 18 VIN 800 600 400 200 70 0 0 1 2 3 4 5 6 0 1 2 Load (A) 4 5 6 Load (A) 1.8 VOUT Efficiency Over VIN vs. Load Figure 12. 1.8 VOUT Dissipation Over VIN vs. Load 100 100 95 95 Efficiency (%) Efficiency (%) Figure 11. 3 90 85 VIN=12V 80 FAN2106 -- 3-24V Input, 6A, High-Efficiency, Integrated Synchronous Buck Regulator FAN2106 Application Circuit 90 8VIN, 300 kHz 85 12VIN, 500 kHz 80 18VIN, 700 kHz 300 kHz 500 kHz 700 kHz 75 75 70 70 0 1 2 3 4 5 0 6 Figure 13. 1.8 VOUT Efficiency Over Frequency vs. Load (Circuit Value Changes) (c) 2009 Fairchild Semiconductor Corporation FAN2106 * Rev. 1.25 1 2 3 4 5 6 Load (A) Load (A) Figure 14. 3.3 VOUT Efficiency vs. Load (Circuit Value Changes) www.fairchildsemi.com 8 (Continued) Typical operating characteristics using the circuit shown in Figure 10. VIN=12 V, VCC=5 V, unless otherwise specified. VOUT VOUT SW SW Figure 15. SW and VOUT Ripple, 6 A Load Figure 16. Startup with 1 V Pre-Bias on VOUT VOUT EN IOUT SW Figure 17. Transient Response, 2-6 A Load Figure 18. VOUT Re-Start on Fault VOUT FAN2106 -- 3-24V Input, 6A, High-Efficiency, Integrated Synchronous Buck Regulator Typical Performance Characteristics PGOOD PGOOD EN EN Figure 19. Startup, 3 A Load (c) 2009 Fairchild Semiconductor Corporation FAN2106 * Rev. 1.25 Figure 20. Shutdown, 3 A Load www.fairchildsemi.com 9 Soft-start time is a function of switching frequency. PWM Generation Refer to Figure 2 for the PWM control mechanism. FAN2106 uses the summing-mode method of control to generate the PWM pulses. An amplified current-sense signal is summed with an internally generated ramp and the combined signal is compared with the output of the error amplifier to generate the pulsewidth to drive the high-side MOSFET. Sensed current from the previous cycle is used to modulate the output of the summing block. The output of the summing block is also compared against a voltage threshold set by the RLIM resistor to limit the inductor current on a cycle-by-cycle basis. The RRAMP resistor helps set the charging current for the internal ramp and provides input voltage feedforward function. The controller facilitates external compensation for enhanced flexibility. EN 1.35V 2400 CLKs 0.8V FB Fault Latch Enable 1.0V 0.8V SS 3200 CLKs T0.8 Initialization 4000 CLKs Once VCC exceeds the UVLO threshold and EN is HIGH, the IC checks for a shorted FB pin before releasing the internal soft-start ramp (SS). T1.0 Figure 22. Soft-Start Timing Diagram If the parallel combination of R1 and R BIAS is 1 K, the internal SS ramp is not released and the regulator does not start. Cycling VCC or the EN pin discharges the internal SS and resets the IC. In applications where external EN signal is used, VIN and VCC should be established before the EN signal comes up to prevent skipping the soft-start function. Enable FAN2106 has an internal pull-up to the ENABLE (EN) pin so that the IC is enabled once V CC exceeds the UVLO threshold. Connecting a small capacitor across EN and AGND delays the rate of voltage rise on the EN pin. The EN pin also serves for the restart whenever a fault occurs (refer to the Auto-Restart section). If the regulator is enabled externally, the external EN signal should go HIGH only after VCC is established. For applications where such sequencing is required, FAN2106 can be enabled (after the VCC comes up) with external control, as shown in Figure 21. Startup on Pre-Bias The regulator does not allow the low-side MOSFET to operate in full synchronous rectification mode until internal SS ramp reaches 95% of VREF (~0.76 V). This helps the regulator start on a pre-biased output and ensures that the pre-biased outputs are not discharged during soft-start. Protections The converter output is monitored and protected against extreme overload, short-circuit, over-voltage, under-voltage, and over-temperature conditions. FAN2106 14 EN FAN2106 -- 3-24V Input, 6A, High-Efficiency, Integrated Synchronous Buck Regulator Circuit Description Under-Voltage Shutdown If the voltage on the FB pin remains below the undervoltage threshold for 16 consecutive clock cycles, the fault latch is set and the converter shuts down. This protection is not active until the internal SS ramp reaches 1.0 V during soft-start. 3.3n Figure 21. Enabling with External Control Soft-Start Over-Voltage Protection Once internal SS ramp has charged to 0.8 V (T0.8), the output voltage is in regulation. Until SS ramp reaches 1.0 V (T1.0), the fault latch is inhibited. If voltage on the FB pin exceeds 115% of VREF for two consecutive clock cycles, the fault latch is set and shutdown occurs. To avoid skipping the soft-start cycle, it is necessary to apply VIN before VCC reaches its UVLO threshold. Normal sequence for powering up would be VINVCCEN. (c) 2009 Fairchild Semiconductor Corporation FAN2106 * Rev. 1.25 A shorted high-side MOSFET condition is detected when SW voltage exceeds ~0.7 V while the low-side www.fairchildsemi.com 10 Application Information The OV and high-side short fault protections are active all the time, including during soft-start. Bias Supply The FAN2106 requires a 5 V supply rail to bias the IC and provide gate-drive energy. Connect a 1.0 f X5R or X7R decoupling capacitor between VCC and PGND. Over-Temperature Protection (OTP) The chip incorporates an over-temperature protection circuit that sets the fault latch when a die temperature of about 150C is reached. The IC restarts when the die temperature falls below 125C. Since VCC is used to drive the internal MOSFET gates, supply current is frequency and voltage dependent. Approximate VCC current (ICC) can be calculated using: Auto-Restart ICC (mA ) 4.58 [( After a fault, EN pin is discharged by a 1 A current sink to a 1.1 V threshold before the internal 800 K pull-up is restored. A new soft-start cycle begins when EN charges above 1.35 V. Setting the Output Voltage The output voltage of the regulator can be set from 0.8 V to 80% of VIN by an external resistor divider (R1 and RBIAS in Figure 1). For output voltages > 5 V, output current rating may need to be de-rated depending upon the ambient temperature, power dissipated in the package and the PCB layout. Table 1. Fault / Restart Configurations Controller / Restart State Pull to GND Pull-up to VCC with 100 K Open OFF (Disabled) No Restart - Latched OFF (After VCC Comes Up) Immediate Restart After Fault New Soft-Start Cycle After: tDELAY (ms)=3.9 * C(nf) Cap. to GND The external resistor divider is calculated using: V 0.8V 0.8V OUT 650nA RBIAS R1 (2) Connect RBIAS between FB and AGND. If R1 is open (see Figure 1), the output voltage is not regulated eventually causing a latched fault after the soft start is complete (T1.0) When EN is left open, restart is immediate. If auto-restart is not desired, tie the EN pin to the VCC pin or pull it HIGH after VCC comes up with a logic gate to keep the 1 A current sink from discharging EN to 1.1 V. Figure 23 shows one method to pull up EN to VCC for a latch configuration. If the parallel combination of R1 and R BIAS is 1K, the internal SS ramp is not released and the regulator does not start. Setting the Switching Frequency Switching frequency is determined by an external resistor, RT, connected between the R(T) pin and AGND: 15 VCC 100K (1) where frequency (f) is expressed in KHz. Depending on the external circuit, the FAN2106 can be configured to remain latched-off or to automatically restart after a fault. EN Pin VCC 5 0.013) ( f 128)] 227 R T (K ) FAN2106 (106 / f ) 135 65 (3) FAN2106 -- 3-24V Input, 6A, High-Efficiency, Integrated Synchronous Buck Regulator MOSFET is fully enhanced. The fault latch is set immediately upon detection. where RT is in K and frequency (f) is in KHz. 14 EN The regulator cannot start if RT is left open. Calculating the Inductor Value Typically the inductor value is chosen based on ripple current (IL), which is chosen between 10 to 35% of the maximum DC load. Regulator designs that require fast transient response use a higher ripple-current setting, while regulator designs that require higher efficiency keep ripple current on the low side and operate at a lower switching frequency. The inductor value is calculated by the following formula: 3.3n Figure 23. Enable Control with Latch Option Power-Good (PGOOD) Signal PGOOD is an open-drain output that asserts LOW when VOUT is out of regulation, as measured at the FB pin. Thresholds are specified in the Electrical Specifications section. PGOOD does not assert HIGH until the fault latch is enabled (T1.0) (see Figure 22). (c) 2009 Fairchild Semiconductor Corporation FAN2106 * Rev. 1.25 IL VOUT (1 - D) Lf (4) where f is the switching frequency. www.fairchildsemi.com 11 RRAMP resistor plays a critical role in the design by providing charging current to the internal ramp capacitor and also serving as a means to provide input voltage feedforward. VRILIM = 10A*RILIM To calculate RILIM: RRAMP is calculated by the following formula: RRAMP(K ) (VIN 1.8) VOUT (18) VIN f 106 RILIM = VRILIM/ 10A 2 (5) For wide input operation, first calculate RRAMP for the minimum and maximum input voltage conditions and use larger of the two values calculated. RILIM = {0.96 + (ILOAD * RDSON *KT*8)} + {D*(VIN - 1.8)/(fSW *0.03*10^-3*RRAMP)}/10A (6) VBOT = 0.96 + (ILOAD * RDSON *KT*8); VRMPEAK = D*(VIN - 1.8)/(fSW *0.03*10^-3*RRAMP); ILOAD = the desired maximum load current; RDSON = the nominal RDSON of the low-side MOSFET; KT = the normalized temperature coefficient for the low-side MOSFET (on datasheet graph); D = VOUT/VIN duty cycle; Setting the Current Limit fSW = Clock frequency in kHz; and The current limit system involves two comparators. The MAX ILIMIT comparator is used with a VILIM fixed-voltage reference and represents the maximum current limit allowable. This reference voltage is temperature compensated to reflect the RDSON variation of the lowside MOSFET. The ADJUST ILIMIT comparator is used where the current limit needs to be set lower than the VILIM fixed reference. The 10 A current source does not track the RDSON changes over temperature, so change is added into the equations for calculating the ADJUST ILIMIT comparator reference voltage, as is shown below. Figure 24 shows a simplified schematic of the overcurrent system. VER R VC C VILIM (10) where: If the calculated RRAMP values in Equation (5) result in a current less than 10 A, use the RRAMP value that satisfies Equation (6). In applications with large input ripple voltage, the RRAMP resistor should be adequately decoupled from the input voltage to minimize ripple on the RAMP pin. + _ (9) RILIM = (VBOT + VRMPEAK)/ 10A In all applications, current through the RRAMP pin must be greater than 10 A from the equation below for proper operation: VIN 1.8 10 A RRAMP 2 (8) The voltage VRILIM is made up of two components, VBOT (which relates to the current through the low-side MOSFET) and VRMPEAK (which relates to the peak current through the inductor). Combining those two voltage terms results in: where frequency (f) is expressed in KHz. RAMP (7) RRAMP = chosen ramp resistor value in k. After 16 consecutive, pulse-by-pulse, current-limit cycles, the fault latch is set and the regulator shuts down. Cycling VCC or EN restores operation after a normal soft-start cycle (refer to the Auto-Restart section). The over-current protection fault latch is active during the soft-start cycle. Use 1% resistor for RILIM. PWM COMP FAN2106 -- 3-24V Input, 6A, High-Efficiency, Integrated Synchronous Buck Regulator Since the ILIM voltage is set by a 10 A current source into the RILIM resistor, the basic equation for setting the reference voltage is: Setting the Ramp Resistor Value PWM + _ MAX ILIMI T 10A ILIM + _ ADJUST ILIMI T ILIMTRIP RILI M Figure 24. Current-Limit System Schematic (c) 2009 Fairchild Semiconductor Corporation FAN2106 * Rev. 1.25 www.fairchildsemi.com 12 Recommended PCB Layout The loop is compensated using a feedback network around the error amplifier. Figure 25 shows a complete Type-3 compensation network. For Type-2 compensation, eliminate R3 and C3. Good PCB layout and careful attention to temperature rise is essential for reliable operation of the regulator. Four-layer PCB with two-ounce copper on the top and bottom sides and thermal vias connecting the layers are recommended. Keep power traces wide and short to minimize losses and ringing. Do not connect AGND to PGND below the IC. Connect the AGND pin to PGND at the output OR to the PGND plane. SW GND Figure 25. Compensation Network Since the FAN2106 employs a summing current-mode architecture, Type-2 compensation can be used for many applications. For applications that require wide loop bandwidth and/or use very low-ESR output capacitors, Type-3 compensation may be required. VOUT Figure 26. Recommended PCB Layout RRAMP also provides feedforward compensation for changes in VIN. With a fixed RRAMP value, the modulator gain increases as VIN is reduced; this could make it difficult to compensate the loop. For low-input-voltagerange designs (3 V to 8 V), RRAMP and the compensation component values are different compared to designs with VIN between 8 V and 24 V. Application note AN-8022 (TinyCalcTM) can be used to calculate the compensation components. (c) 2009 Fairchild Semiconductor Corporation FAN2106 * Rev. 1.25 VIN GND FAN2106 -- 3-24V Input, 6A, High-Efficiency, Integrated Synchronous Buck Regulator Loop Compensation www.fairchildsemi.com 13 ON Semiconductor and are trademarks of Semiconductor Components Industries, LLC dba ON Semiconductor or its subsidiaries in the United States and/or other countries. ON Semiconductor owns the rights to a number of patents, trademarks, copyrights, trade secrets, and other intellectual property. A listing of ON Semiconductor's product/patent coverage may be accessed at www.onsemi.com/site/pdf/Patent-Marking.pdf. ON Semiconductor reserves the right to make changes without further notice to any products herein. ON Semiconductor makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does ON Semiconductor assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. Buyer is responsible for its products and applications using ON Semiconductor products, including compliance with all laws, regulations and safety requirements or standards, regardless of any support or applications information provided by ON Semiconductor. "Typical" parameters which may be provided in ON Semiconductor data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including "Typicals" must be validated for each customer application by customer's technical experts. ON Semiconductor does not convey any license under its patent rights nor the rights of others. ON Semiconductor products are not designed, intended, or authorized for use as a critical component in life support systems or any FDA Class 3 medical devices or medical devices with a same or similar classification in a foreign jurisdiction or any devices intended for implantation in the human body. Should Buyer purchase or use ON Semiconductor products for any such unintended or unauthorized application, Buyer shall indemnify and hold ON Semiconductor and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that ON Semiconductor was negligent regarding the design or manufacture of the part. ON Semiconductor is an Equal Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner. PUBLICATION ORDERING INFORMATION LITERATURE FULFILLMENT: Literature Distribution Center for ON Semiconductor 19521 E. 32nd Pkwy, Aurora, Colorado 80011 USA Phone: 303-675-2175 or 800-344-3860 Toll Free USA/Canada Fax: 303-675-2176 or 800-344-3867 Toll Free USA/Canada Email: orderlit@onsemi.com (c) Semiconductor Components Industries, LLC N. American Technical Support: 800-282-9855 Toll Free USA/Canada Europe, Middle East and Africa Technical Support: Phone: 421 33 790 2910 Japan Customer Focus Center Phone: 81-3-5817-1050 www.onsemi.com 1 ON Semiconductor Website: www.onsemi.com Order Literature: http://www.onsemi.com/orderlit For additional information, please contact your local Sales Representative www.onsemi.com