DATASHEET ISL6420 FN9151 Rev 5.00 Feb 13, 2008 Advanced Single Synchronous Buck Pulse-Width Modulation (PWM) Controller The ISL6420 makes simple work out of implementing a complete control and protection scheme for a highperformance DC/DC buck converter. Designed to drive N-channel MOSFETs in a synchronous rectified buck topology, the ISL6420 integrates control, output adjustment, monitoring and protection functions into a single package. Additionally, the IC features an external reference voltage tracking mode for externally referenced buck converter applications and DDR termination supplies, as well as a voltage margining mode for system testing in networking DC/DC converter applications. Features The ISL6420 provides simple, single feedback loop, voltage mode control with fast transient response. The output voltage of the converter can be precisely regulated to as low as 0.6V. • Lossless, Programmable Overcurrent Protection - Uses Upper MOSFET‘s rDS(ON) The operating frequency is fully adjustable from 100kHz to 1.4MHz. High frequency operation offers cost and space savings. The error amplifier features a 15MHz gain-bandwidth product and 6V/µs slew rate that enables high converter bandwidth for fast transient response. The PWM duty cycle ranges from 0% to 100% in transient conditions. Selecting the capacitor value from the ENSS pin to ground sets a fully adjustable PWM soft-start. Pulling the ENSS pin LOW disables the controller. The ISL6420 monitors the output voltage and generates a PGOOD (power good) signal when soft-start sequence is complete and the output is within regulation. A built-in overvoltage protection circuit prevents the output voltage from going above typically 115% of the set point. Protection from overcurrent conditions is provided by monitoring the rDS(ON) of the upper MOSFET to inhibit the PWM operation appropriately. This approach simplifies the implementation and improves efficiency by eliminating the need for a current sensing resistor. • Operates from 4.5V to 16V Input • 0.6V Internal Reference Voltage - ±1.0% Reference Voltage Accuracy • Resistor-Selectable Switching Frequency - 100kHz to 1.4MHz • Voltage Margining and External Reference Tracking Modes • Output Can Sink or Source Current • Programmable Soft-Start • Drives N-Channel MOSFETs • Simple Single-Loop Control Design - Voltage-Mode PWM Control • Fast Transient Response - High-Bandwidth Error Amplifier - Full 0% to 100% Duty Cycle • Extensive Circuit Protection Functions - PGOOD, overvoltage, overcurrent, Shutdown • QFN (4x4) Package - QFN Compliant to JEDEC PUB95 MO-220 QFN - Quad Flat No Leads - Product Outline - QFN Near Chip Scale Package Footprint; Improves PCB Efficiency, Thinner in Profile • Also Available in QSOP Package • Pb-Free Available (RoHS Compliant) Applications • Power Supplies for Microprocessors/ASICs - Embedded Controllers - DSP and Core Processors - DDR SDRAM Bus Termination • Ethernet Routers and Switchers • High-Power DC/DC Regulators • Distributed DC/DC Power Architecture • Personal Computer Peripherals • Externally Referenced Buck Converters FN9151 Rev 5.00 Feb 13, 2008 Page 1 of 20 ISL6420 Pinouts ISL6420 (20 LD QSOP) TOP VIEW 19 PVCC PHASE 18 17 LGATE 20 UGATE BOOT ISL6420 (20 LD QFN) TOP VIEW CDEL 1 PGND 2 19 ENSS 16 LGATE 3 18 COMP GPIO2 1 15 PGND GPIO1/REFIN 2 14 CDEL 12 ENSS VMSET/MODE 5 11 COMP 6 7 8 9 10 FB 4 RT REFOUT SGND 13 PGOOD VIN 3 VCC5 OCSET 20 PGOOD PVCC 4 17 FB PHASE 5 16 RT UGATE 6 15 SGND BOOT 7 14 VIN GPIO2 8 13 VCC5 GPIO1/REFIN 9 12 VMSET/MODE OCSET 10 11 REFOUT Ordering Information PART NUMBER PART MARKING TEMP. RANGE (°C) -40 to +85 PACKAGE 20 Ld 4x4 QFN PKG. DWG. # ISL6420IR ISL 6420IRZ ISL6420IR-T* ISL 6420IRZ ISL6420IRZ (Note) 64 20IRZ ISL6420IRZ-T* (Note) 64 20IRZ 20 Ld 4x4 QFN Tape and Reel (Pb-free) L20.4x4 ISL6420IRZ-TK* (Note) 64 20IRZ 20 Ld 4x4 QFN Tape and Reel (Pb-free) L20.4x4 ISL6420IA ISL 6420IA -40 to +85 ISL6420IA-TK* ISL 6420IA 20 Ld QSOP Tape and Reel ISL6420IAZ (Note) ISL 6420IAZ ISL6420IAZ-TK* (Note) ISL 6420IAZ 20 Ld 4x4 QFN Tape and Reel -40 to +85 -40 to +85 20 Ld 4x4 QFN (Pb-free) 20 Ld QSOP L20.4x4 L20.4x4 L20.4x4 M20.15 M20.15 20 Ld QSOP (Pb-free) 20 Ld QSOP Tape and Reel (Pb-free) M20.15 M20.15 *Please refer to TB347 for details on reel specifications. NOTE: These Intersil Pb-free plastic packaged products employ special Pb-free material sets; molding compounds/die attach materials and 100% matte tin plate PLUS ANNEAL - e3 termination finish, which is RoHS compliant and compatible with both SnPb and Pb-free soldering operations. Intersil Pb-free products are MSL classified at Pb-free peak reflow temperatures that meet or exceed the Pb-free requirements of IPC/JEDEC J STD-020. FN9151 Rev 5.00 Feb 13, 2008 Page 2 of 20 ISL6420 Functional Block Diagram VIN VCC5 OCSET SGND LDO OVERCURRENT COMP + OCFLT PHASE REFERENCE 0.6V SS + OVFLT UVFLT UGATE FAULT LOGIC PHASE ERROR AMP - FB BOOT + - COMP PHASE LOGIC PWM LOGIC PWM COMP PVCC GPIO1/REFIN LGATE RAMP GENERATOR GPIO2 REFOUT VOLTAGE MARGINING VMSET/MODE OV/UV VOLTAGE MONITOR FB PGND OVFLT UVFLT OSC EN/SS RT ENSS PGOOD CDEL Typical 5V Input DC/DC Application Schematic 5V C6 C1 C3 C2 PVCC VIN VCC5 D1 OCSET MONITOR AND PROTECTION ENSS Q1 PGOOD C8 C9 UGATE OSC R2 CDEL R1 BOOT RT C7 0.1µF C5 C4 L1 PHASE REF 3.3V SGND ++ -- FB R3 C11 COMP Q2 C10 PGND GPIO1/REFIN R6 R5 LGATE -+ + C12 REFOUT GPIO2 C13 R4 FN9151 Rev 5.00 Feb 13, 2008 VMSET/MODE Page 3 of 20 ISL6420 Typical 12V Input DC/DC Application Schematic 12V C6 C1 C3 C2 PVCC VIN VCC5 D1 OCSET MONITOR AND PROTECTION ENSS Q1 PGOOD R2 C9 UGATE OSC L1 PHASE CDEL C8 R1 BOOT RT C7 C5 C4 REF 3.3V SGND R3 C11 C10 PGND COMP GPIO1/REFIN R6 C12 R5 Q2 LGATE -+ + ++ -- FB REFOUT GPIO2 C13 R4 VMSET/MODE Typical 5V Input DC/DC Application Schematic 5V C6 C1 C3 C2 VIN PVCC C4 D1 VCC5 OCSET MONITOR AND PROTECTION SS/EN Q1 CDEL R2 R1 BOOT RT C7 C5 C8 UGATE OSC L1 PHASE PGOOD REF 2.5V/1.25V SGND R3 C10 C11 LGATE -+ + ++ -- FB COMP R5 C9 GPIO1/REFIN <-- VREF = VDDQ/2 GPIO2 REFOUT C12 R4 Q2 PGND 1.25V VREF TO REFIN OF VTT SUPPLY VMSET/MODE VCC5 CONFIGURATION FOR DDR TERMINATION/EXTERNALLY REFERENCED TRACKING APPLICATIONS FN9151 Rev 5.00 Feb 13, 2008 Page 4 of 20 ISL6420 Typical 12V Input DC/DC Application Schematic 12V C6 C1 C2 C3 VIN PVCC VCC5 MONITOR AND PROTECTION SS/EN RT D1 OCSET R1 BOOT Q1 CDEL R2 C7 C5 C4 UGATE OSC C8 L1 PHASE PGOOD REF 2.5V/1.25V VDDQ/VTT SGND R3 -+ + ++ -- FB C10 LGATE Q2 C9 PGND COMP GPIO1/REFIN <-- VREF = VDDQ/2 GPIO2 C11 R5 REFOUT C12 R4 1.25V VREF TO REFIN OF VTT SUPPLY VMSET/MODE VCC5 CONFIGURATION FOR DDR TERMINATION/EXTERNALLY REFERENCED TRACKING APPLICATIONS FN9151 Rev 5.00 Feb 13, 2008 Page 5 of 20 ISL6420 Absolute Maximum Ratings (Note 1) Thermal Information Bias Voltage, VIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .+18V BOOT and Ugate Pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +24V Thermal Resistance (Typical) JA (°C/W) JC (°C/W) QFN Package (Notes 2, 3). . . . . . . . . . 47 8.5 QSOP Package (Note 2) . . . . . . . . . . . 90 NA Maximum Junction Temperature (Plastic Package) . . . . . . . +150°C Maximum Storage Temperature Range . . . . . . . . . .-65°C to +150°C Ambient Temperature Range. . . . . . . . -40°C to +85°C (for “I” suffix) Junction Temperature Range. . . . . . . . . . . . . . . . . .-40°C to +125°C Pb-free reflow profile . . . . . . . . . . . . . . . . . . . . . . . . . .see link below http://www.intersil.com/pbfree/Pb-FreeReflow.asp CAUTION: Do not operate at or near the maximum ratings listed for extended periods of time. Exposure to such conditions may adversely impact product reliability and result in failures not covered by warranty. NOTES: 1. All voltages are with respect to GND. 2. JA is measured in free air with the component mounted on a high effective thermal conductivity test board with “direct attach” features. See Tech Brief TB379. 3. For JC, the “case temp” location is the center of the exposed metal pad on the package underside. Electrical Specifications PARAMETER Operating Conditions, Unless Otherwise Noted: VIN = 12V, PVCC shorted with VCC5, TA = +25°C SYMBOL TEST CONDITIONS MIN TYP MAX UNITS 5.6 12 16 V - 1.4 - mA - 2.0 3.0 mA VIN SUPPLY Input Voltage Range VIN SUPPLY CURRENT Shutdown Current (Note 4) ENSS = GND Operating Current (Notes 4, 5) VCC5 SUPPLY (Notes 5, 6) Input Voltage Range VIN = VCC5 for 5V configuration 4.5 5.0 5.5 V Output Voltage VIN = 5.6V to 16V, IL = 3mA to 50mA 4.5 5.0 5.5 V Maximum Output Current VIN = 12V 50 - - mA 4.32 4.4 4.45 V Falling VCC5 Threshold 4.09 4.1 4.25 V UVLO Threshold Hysteresis 0.16 - - V POWER-ON RESET Rising VCC5 Threshold VIN connected to VCC5, 5V input operation PWM CONVERTERS Maximum Duty Cycle FSW = 300kHz 90 96 - % Minimum Duty Cycle FSW = 300kHz - - 0 % - 80 - nA FB pin bias current Undervoltage Protection VUV1 Fraction of the set point; ~3s noise filter 75 - 85 % Overvoltage Protection VOVP1 Fraction of the set point; ~1s noise filter 112 - 120 % Free Running Frequency RT = VCC5, TA = -40°C to +85°C 270 300 330 kHz Total Variation TA = -40°C to +85°C, with freq. set by external resistor at RT -10 - +10 % Frequency Range (Set by RT) VIN = 12V 100 - 1400 kHz - 1.25 - VP-P OSCILLATOR Ramp Amplitude (Note 7) FN9151 Rev 5.00 Feb 13, 2008 VOSC Page 6 of 20 ISL6420 Electrical Specifications Operating Conditions, Unless Otherwise Noted: VIN = 12V, PVCC shorted with VCC5, TA = +25°C (Continued) PARAMETER SYMBOL TEST CONDITIONS MIN TYP MAX UNITS 0.606 V REFERENCE AND SOFT-START/ENABLE Internal Reference Voltage Soft-Start Current Soft-Start Threshold VREF 0.594 ISS - 10 - A VSOFT 1.0 - - V - - 1.0 V - 0.7 - A Enable Low (Converter disabled) PWM CONTROLLER GATE DRIVERS Gate Drive Peak Current Rise Time Co = 1000pF - 20 - ns Fall Time Co = 1000pF - 20 - ns - 20 - ns - 88 - dB GBW - 15 - MHz SR - 6 - V/s Vocset = 4.5V 80 100 120 A Dead Time Between Drivers ERROR AMPLIFIER DC Gain (Note 7) Gain-Bandwidth Product (Note 7) Slew Rate (Note 7) PROTECTION OCSET Current Source IOCSET POWER GOOD AND CONTROL FUNCTIONS Power-Good Lower Threshold VPG- Fraction of the set point; ~3s noise filter -14 -10 -8 % Power-Good Higher Threshold VPG+ Fraction of the set point; ~3s noise filter 10 - 16 % VPULLUP = 5.5V - - 1 A PGOOD Voltage Low IPGOOD = 4mA - - 0.5 V PGOOD Delay CDEL = 0.1µF - 125 - ms CDEL Current for PGOOD CDEL threshold = 2.5V - 2 - A - 2.5 - V VMSET/MODE = H, CREFOUT = 2.2µF 0.6 - 1.25 V PGOOD Leakage Current IPGLKG CDEL Threshold EXTERNAL REFERENCE External Reference Input Range at GPIO1/REFIN. REFERENCE BUFFER Buffered Output Voltage - Internal Reference VREFOUT IREFOUT = 20mA, VMSET/MODE = HIGH, CREFOUT = 2.2µF, TA = -40°C to +85°C 0.585 0.6V 0.615 V Buffered Output Voltage - External Reference VREFOUT VREFIN = 1.25V, IREFOUT = 20mA, VMSET/MODE = HIGH, CREFOUT = 2.2µF Vrefin -0.01 - Vrefin +0.01 V 20 - - mA +10 % Current Drive Capability CREFOUT = 2.2µF VOLTAGE MARGINING Voltage Margining Range (Note 7) -10 CDEL Current for Voltage Margining Slew Time FN9151 Rev 5.00 Feb 13, 2008 CDEL = 0.1µF, VMSET/MODE = 330k - 100 - A - 2.5 - ms Page 7 of 20 ISL6420 Electrical Specifications Operating Conditions, Unless Otherwise Noted: VIN = 12V, PVCC shorted with VCC5, TA = +25°C (Continued) PARAMETER SYMBOL TEST CONDITIONS MIN TYP MAX UNITS ISET1 on FB Pin VMSET/MODE = 330k, GPIO1/REFIN = L GPIO2 = H - 7.48 - A ISET2 on FB Pin VMSET/MODE = 330k, GPIO1/REFIN = H GPIO2 = L - 7.48 - A Shutdown Temperature (Note 7) - 150 - °C Thermal Shutdown Hysteresis (Note 7) - 20 - °C THERMAL SHUTDOWN NOTES: 4. The operating supply current and shutdown current specifications for 5V input are the same as VIN supply current specifications, i.e., 5.6V to 16V input conditions. These should also be tested with part configured for 5V input configuration, i.e., VIN = VCC5 = PVCC = 5V. 5. This is the VCC current consumed when the device is active but not switching. Does not include gate drive current. 6. When the input voltage is 5.6V to 16V at VIN pin, the VCC5 pin provides a 5V output capable of 50mA (max) total from the internal LDO. When the input voltage is 5V, VCC5 pin will be used as a 5V input, the internal LDO regulator is disabled and the VIN must be connected to the VCC5. In both cases the PVCC pin should always be connected to VCC5 pin. (Refer to the Pin Descriptions sections for more details.) 7. Limits established by characterization and are not production tested. FN9151 Rev 5.00 Feb 13, 2008 Page 8 of 20 ISL6420 0.604 320 0.602 310 VSW (kHz) VREF (V) Typical Performance Curves 0.6 0.598 0.596 0.594 -40 300 290 280 -15 10 35 TEMPERATURE (°C) 60 270 -40 85 -15 FIGURE 1. VREF vs. TEMPERATURE 10 35 TEMPERATURE (°C) 60 85 FIGURE 2. VSW vs. TEMPERATURE 98 94 EFFICIENCY (%) IOCSET NORMALIZED VIN = 5V 96 1.15 1.05 0.95 VIN = 12V 92 90 88 86 84 82 0.85 -40 80 -15 10 35 TEMPERATURE (°C) 60 85 0 1 2 3 4 5 6 LOAD (A) 7 8 9 10 FIGURE 3. IOCSET vs. TEMPERATURE FIGURE 4. EFFICIENCY vs. LOAD CURRENT (VOUT = 3.3V) FIGURE 5. PWM WAVEFORMS FIGURE 6. LOAD TRANSIENT RESPONSE FN9151 Rev 5.00 Feb 13, 2008 Page 9 of 20 ISL6420 Pin Descriptions VIN This pin powers the controller and must be closely decoupled to ground using a ceramic capacitor as close to the VIN pin as possible. TABLE 1. INPUT SUPPLY CONFIGURATION INPUT PIN CONFIGURATION 5.6V to 16V Connect the input to the VIN pin. The VCC5 pin will provide a 5V output from the internal LDO. Connect PVCC to VCC5. 5V +±10% Connect the input to the VCC5 pin. Connect the PVCC and VIN pins to VCC5. frequency of 300kHz. By placing a resistor from this pin to GND, the oscillator frequency can be programmed from 100kHz to 1.4MHz. Figure 7 shows the oscillator frequency vs. the RT resistance. CDEL The PGOOD signal can be delayed by a time proportional to a CDEL current of 2µA and the value of the capacitor connected between this pin and ground. A 0.1µF will typically provide 125ms delay. When in the Voltage Margining mode the CDEL current is 100µA typical and provides the delay for the output voltage slew rate, 2.5ms typical for the 0.1µF capacitor. This pin provides the signal and power ground for the IC. Tie this pin to the ground plane through the lowest impedance connection. LGATE This pin provides the PWM-controlled gate drive for the lower MOSFET. PHASE This pin is the junction point of the output filter inductor, the upper MOSFET source and the lower MOSFET drain. This pin is used to monitor the voltage drop across the upper MOSFET for overcurrent protection. This pin also provides a return path for the upper gate drive. UGATE This pin provides the PWM-controlled gate drive for the upper MOSFET. BOOT This pin powers the upper MOSFET driver. Connect this pin to the junction of the bootstrap capacitor and the cathode of the bootstrap diode. The anode of the bootstrap diode is connected to the VCC5 pin. FB This pin is connected to the feedback resistor divider and provides the voltage feedback signal for the controller. This pin sets the output voltage of the converter. FREQUENCY (kHz) SGND 1400 1300 1200 1100 1000 900 800 700 600 500 400 300 200 100 0 0 25 50 75 RT (k) 100 125 150 FIGURE 7. OSCILLATOR FREQUENCY vs. RT PGND This pin provides the power ground for the IC. Tie this pin to the ground plane through the lowest impedance connection. PVCC This pin is the power connection for the gate drivers. Connect this pin to the VCC5 pin. VCC5 This pin is the output of the internal 5V LDO. Connect a minimum of 4.7µF ceramic decoupling capacitor as close to the IC as possible at this pin. Refer to Table 1. ENSS COMP This pin provides enable/disable function and soft-start for the PWM output. The output drivers are turned off when this pin is held below 1V. This pin is the error amplifier output pin. It is used as the compensation point for the PWM error amplifier. OCSET PGOOD This pin provides a power good status. It is an open collector output used to indicate the status of the output voltage. RT Connect a resistor (ROCSET) and a capacitor from this pin to the drain of the upper MOSFET. ROCSET, an internal 100µA current source (IOCSET), and the upper MOSFET on resistance rDS(ON) set the converter overcurrent (OC) trip point. This is the oscillator frequency selection pin. Connecting this pin directly to VCC5 will select the oscillator free running FN9151 Rev 5.00 Feb 13, 2008 Page 10 of 20 ISL6420 GPIO1/REFIN reference tracking mode are not needed, this pin can be tied directly to ground. This is a dual function pin. If VMSET/MODE is not connected to VCC5 then this pin serves as GPIO1. Refer to Table 2 for GPIO1 commands interpretation. GPIO2 If VMSET/MODE is connected to VCC5 then this pin will serve as REFIN. As REFIN, this pin is the non-inverting input to the error amplifier. Connect the desired reference voltage to this pin in the range of 0.6V to 1.25V. Exposed Thermal Pad Connect this pin to VCC5 to use internal reference. This is general purpose IO pin for voltage margining. Refer to Table 2. This pad is electrically isolated. Connect this pad to the signal ground plane using at least five vias for a robust thermal conduction path. REFOUT TABLE 2. VOLTAGE MARGINING CONTROLLED BY GPIO1/REFIN AND GPIO2 It provides buffered reference output for REFIN. Connect 2.2µF decoupling capacitor to this pin. GPIO1/REFIN GPIO2 VOUT L L No Change L H + Delta VOUT H L - Delta VOUT H H Ignored VMSET/MODE This pin is a dual function pin. Tie this pin to VCC5 to disable voltage margining. When not tied to VCC5, this pin serves as VMSET. Connect a resistor from this pin to ground to set the delta for voltage margining. If voltage margining and external TABLE 3. VOLTAGE MARGINING/DDR OR TRACKING SUPPLY PIN CONFIGURATION PIN CONFIGURATIONS FUNCTION/MODES VMSET/MODE REFOUT GPIO1/REFIN Enable Voltage Margining Pin Connected to GND with resistor. It is used as VMSET. Connect a 2.2µF capacitor for Serves as a general bypass of external reference. purpose I/O. Refer to Table 2 No Voltage Margining. Normal operation with internal reference. Buffered VREFOUT = 0.6V. H Connect a 2.2µF capacitor to GND. No Voltage Margining. External reference. Buffered VREFOUT = VREFIN H Connect a 2.2µF capacitor to Connect to an external GND. reference voltage source (0.6V to 1.25V) H (Note 9) GPIO2 Serves as a general purpose I/O. Refer to Table 2 L L NOTES: 8. The GPIO1/REFIN and GPIO2 pins cannot be left floating. 9. Ensure that GPIO1/REFIN is tied high prior to the logic change at VMSET/MODE. FN9151 Rev 5.00 Feb 13, 2008 Page 11 of 20 ISL6420 Functional Description Initialization The ISL6420 automatically initializes upon receipt of power. The Power-On Reset (POR) function monitors the internal bias voltage generated from LDO output (VCC5) and the ENSS pin. The POR function initiates the soft-start operation after the VCC5 exceeds the POR threshold. The POR function inhibits operation with the chip disabled (ENSS pin <1V). The device can operate from an input supply voltage of 5.6V to 16V connected directly to the VIN pin using the internal 5V linear regulator to bias the chip and supply the gate drivers. For 5V ±10% applications, connect VIN to VCC5 to bypass the linear regulator. Soft-Start/Enable The ISL6420 soft-start function uses an internal current source and an external capacitor to reduce stresses and surge current during startup. When the output of the internal linear regulator reaches the POR threshold, the POR function initiates the soft-start sequence. An internal 10µA current source charges an external capacitor on the ENSS pin linearly from 0V to 3.3V. When the ENSS pin voltage reaches 1V typically, the internal 0.6V reference begins to charge following the dv/dt of the ENSS voltage. As the soft-start pin charges from 1V to 1.6V, the reference voltage charges from 0V to 0.6V. Figure 8 shows a typical soft-start sequence. The overcurrent function cycles the soft-start function in a hiccup mode to provide fault protection. A resistor connected to the drain of the upper FET and the OCSET pin programs the overcurrent trip level. The PHASE node voltage will be compared against the voltage on the OCSET pin, while the upper FET is on. A current (100µA typically) is pulled from the OCSET pin to establish the OCSET voltage. If PHASE is lower than OCSET while the upper FET is on then an overcurrent condition is detected for that clock cycle. The upper gate pulse is immediately terminated, and a counter is incremented. If an overcurrent condition is detected for 8 consecutive clock cycles, and the circuit is not in soft-start, the ISL6420 enters into the soft-start hiccup mode. During hiccup, the external capacitor on the ENSS pin is discharged. After the capacitor is discharged, it is released and a soft-start cycle is initiated. There are three dummy softstart delay cycles to allow the MOSFETs to cool down, to keep the average power dissipation in hiccup mode at an acceptable level. At the forth soft-start cycle, the output starts a normal soft-start cycle, and the output tries to ramp. During soft-start, pulse termination current limiting is enabled, but the 8-cycle hiccup counter is held in reset until soft-start is completed. Figure 9 shows the overcurrent hiccup mode. VOUT IOUT PHASE ENSS FIGURE 9. TYPICAL OVER-CURRENT HICCUP MODE The overcurrent function will trip at a peak inductor current (IOC) determined from Equation 1, where IOCSET is the internal OCSET current source. I OCSET R OCSET I OC = -------------------------------------------------R DS ON FIGURE 8. TYPICAL SOFT-START WAVEFORM Overcurrent Protection The overcurrent function protects the converter from a shorted output by using the upper MOSFET’s on-resistance, rDS(ON) to monitor the current. This method enhances the converter’s efficiency and reduces cost by eliminating a current sensing resistor. FN9151 Rev 5.00 Feb 13, 2008 (EQ. 1) The OC trip point varies mainly due to the upper MOSFETs rDS(ON) variations. To avoid overcurrent tripping in the normal operating load range, find the ROCSET resistor from the equation above with: 1. The maximum rDS(ON) at the highest junction temperature. 2. Determine I OC for I OC I OUT MAX + I 2 , where I is the output inductor ripple current. Page 12 of 20 ISL6420 A small ceramic capacitor should be placed in parallel with ROCSET to smooth the voltage across ROCSET in the presence of switching noise on the input voltage. Voltage Margining The ISL6420 has a voltage margining mode that can be used for system testing. The voltage margining percentage is resistor selectable up to ±10%. The voltage margining mode can be enabled by connecting a margining set resistor from VMSET/MODE pin to ground and using the control pins GPIO1/REFIN and GPIO2 to toggle between positive and negative margining (Refer to Table 2). With voltage margining enabled, the VMSET resistor to ground sets a current, which is switched to the FB pin. The current will be equal to 2.468V divided by the value of the external resistor tied to the VMSET/MODE pin. 2.468V I VM = -----------------------R VMSET (EQ. 2) R FB V VM = 2.468V -----------------------R VMSET (EQ. 3) The power supply output increases when GPIO2 is HIGH and decreases when GPIO1/REFIN is HIGH. The amount that the output voltage of the power supply changes with voltage margining, will be equal to 2.468V times the ratio of the external feedback resistor and the external resistor tied to VMSET/MODE pin. Figure 9 shows the positive and negative margining for a 3.3V output, using a 20.5k feedback resistor and using various VMSET resistor values. 3.7 3.5 3.4 VOUT (V) VOUT 100mV/DIV 2ms/DIV FIGURE 11. VOLTAGE MARGINING SLEW TIME The slew time of the current is set by an external capacitor on the CDEL pin, which is charged and discharged with a 100A current source. The change in voltage on the capacitor is 2.5V. This same capacitor is used to set the PGOOD active delay after soft-start. When PGOOD is low, the internal PGOOD circuitry uses the capacitor and when PGOOD is high the voltage margining circuit uses the capacitor. The slew time for voltage margining can be in the range of 300µs to 2ms. External Reference/DDR Supply The voltage margining can be disabled by connecting the VMSET/MODE to VCC5. In this mode the chip can be configured to work with an external reference input and provide a buffered reference output. If VMSET/MODE pin and the GPIO1/REFIN pin are both tied to VCC5, then the internal 0.6V reference is used as the error amplifier non-inverting input. The buffered reference output on REFOUT will be 0.6V ±0.01V, capable of sourcing 20mA and sinking up to 50µA current with a 2.2µF capacitor connected to the REFOUT pin. 3.6 3.3 3.2 3.1 3.0 2.9 2.8 150 VOUT 100m/DIV 175 200 225 250 275 300 325 350 375 400 RVMSET (k) FIGURE 10. VOLTAGE MARGINING vs VMSET RESISTANCE If VMSET/MODE pin is tied to high but GPIO1/REFIN is connected to external voltage source between 0.6V to 1.25V, then this external voltage is used as the reference voltage at the positive input of the error amplifier. The buffered reference output on REFOUT will be Vrefin ±0.01V, capable of sourcing 20mA and sinking up to 50µA current with a 2.2µF capacitor on the REFOUT pin. Power Good The PGOOD pin can be used to monitor the status of the output voltage. PGOOD will be true (open drain) when the FB pin is within ±10% of the reference and the ENSS pin has completed its soft-start ramp. Additionally, a capacitor on the CDEL pin will set a delay for the PGOOD signal. After the ENSS pin completes its softstart ramp, a 2µA current begins charging the CDEL FN9151 Rev 5.00 Feb 13, 2008 Page 13 of 20 ISL6420 capacitor to 2.5V. The capacitor will be quickly discharged before PGOOD goes high. The programmable delay can be used to sequence multiple converters or as a LOW-true reset signal. Application Guidelines Layout Considerations As in any high frequency switching converter, layout is very important. Switching current from one power device to another can generate voltage transients across the impedances of the interconnecting bond wires and circuit traces. These interconnecting impedances should be minimized by using wide, short printed circuit traces. The critical components should be located as close together as possible using ground plane construction or single point grounding. VIN ISL6420 Q1 LO VOUT FIGURE 12. PGOOD DELAY If the voltage on the FB pin exceeds ±10% of the reference, then PGOOD will go low after 3µs of noise filtering. Over-Temperature Protection The IC is protected against over temperature conditions. When the junction temperature exceeds +150°C, the PWM shuts off. Normal operation is resumed when the junction temperature is cooled down to +130°C. Shutdown When ENSS pin is below 1V, the regulator is disabled with the PWM output drivers tri-stated. When disabled, the IC power will be reduced. Under-Voltage If the voltage on the FB pin is less than 15% of the reference voltage for 8 consecutive PWM cycles, then the circuit enters into soft-start hiccup mode. This mode is identical to the overcurrent hiccup mode. Overvoltage Protection If the voltage on the FB pin exceeds the reference voltage by 15%, the lower gate driver is turned on continuously to discharge the output voltage. If the overvoltage condition continues for 32 consecutive PWM cycles, then the chip is turned off with the gate drivers tri-stated. The voltage on the FB pin will fall and reach the 15% undervoltage threshold. After 8 clock cycles, the chip will enter soft-start hiccup mode. This mode is identical to the overcurrent hiccup mode. LGATE Q2 D2 CIN CO LOAD UGATE PHASE GND RETURN FIGURE 13. PRINTED CIRCUIT BOARD POWER AND GROUND PLANES OR ISLANDS Figure 12 shows the critical power components of the converter. To minimize the voltage overshoot the interconnecting wires indicated by heavy lines should be part of ground or power plane in a printed circuit board. The components shown in Figure 12 should be located as close together as possible. Please note that the capacitors CIN and CO each represent numerous physical capacitors. Locate the ISL6420 within 3 inches of the MOSFETs, Q1 and Q2. The circuit traces for the MOSFETs’ gate and source connections from the ISL6420 must be sized to handle up to 1A peak current. Figure 13 shows the circuit traces that require additional layout consideration. Use single point and ground plane construction for the circuits shown. Minimize any leakage current paths on the ENSS PIN and locate the capacitor, Css close to the ENSS pin because the internal current source is only 30µA. Provide local VCC decoupling between VCC and GND pins. Locate the capacitor, CBOOT as close as practical to the BOOT and PHASE pins. Feedback Compensation Figure 14 highlights the voltage-mode control loop for a synchronous-rectified buck converter. The output voltage (Vout) is regulated to the Reference voltage level. The error amplifier (Error Amp) output (VE/A) is compared with the FN9151 Rev 5.00 Feb 13, 2008 Page 14 of 20 ISL6420 +VIN BOOT D1 Q1 CBOOT ISL6420 the modulator is simply the input voltage (VIN) divided by the peak-to-peak oscillator voltage VOSC. Modulator Break Frequency Equations LO VOUT ENSS +5V LOAD PHASE CO Q2 VCC CVCC CSS GND FIGURE 14. PRINTED CIRCUIT BOARD SMALL SIGNAL LAYOUT GUIDELINES VIN OSC DRIVER PWM COMPARATOR LO - DRIVER + VOSC VOUT PHASE CO ESR (PARASITIC) ZFB VE/A - REFERENCE ERROR AMP (EQ. 4) 1 F ESR = --------------------------------------------2 ESR C O (EQ. 5) The compensation network consists of the error amplifier (internal to the ISL6420) and the impedance networks ZIN and ZFB. The goal of the compensation network is to provide a closed loop transfer function with the highest 0dB crossing frequency (f0dB) and adequate phase margin. Phase margin is the difference between the closed loop phase at f0dB and 180o. The equations below relate the compensation network’s poles, zeros and gain to the components (R1, R2, R3, C1, C2, and C3) in Figure 14. Use these guidelines for locating the poles and zeros of the compensation network: Compensation Break Frequency Equations 1 F Z1 = ---------------------------------2 R 2 C1 (EQ. 6) 1 F P1 = ------------------------------------------------------C1 C2 2 R2 ---------------------- C1 + C2 ZIN + 1 F LC = --------------------------------------2 L O C O (EQ. 7) 1 F Z2 = -----------------------------------------------------2 R1 + R3 C3 (EQ. 8) 1 F P2 = ---------------------------------2 R3 C3 (EQ. 9) DETAILED COMPENSATION COMPONENTS ZFB C2 C1 VOUT ZIN C3 R2 R3 R1 COMP FB - 2. Place 1ST Zero Below Filter’s Double Pole (~75% FLC) 3. Place 2ND Zero at Filter’s Double Pole 4. Place 1ST Pole at the ESR Zero + ISL6420 1. Pick Gain (R2/R1) for desired converter bandwidth 5. Place 2ND Pole at Half the Switching Frequency REF 6. Check Gain against Error Amplifier’s Open-Loop Gain 7. Estimate Phase Margin - Repeat if Necessary FIGURE 15. VOLTAGE - MODE BUCK CONVERTER COMPENSATION DESIGN oscillator (OSC) triangular wave to provide a pulse-width modulated (PWM) wave with an amplitude of VIN at the PHASE node. The PWM wave is smoothed by the output filter (LO and CO). The modulator transfer function is the small-signal transfer function of Vout/VE/A. This function is dominated by a DC Gain and the output filter (LO and CO), with a double pole break frequency at FLC and a zero at FESR. The DC Gain of FN9151 Rev 5.00 Feb 13, 2008 Figure 15 shows an asymptotic plot of the DC/DC converter’s gain vs. frequency. The actual Modulator Gain has a high gain peak do to the high Q factor of the output filter and is not shown in Figure 15. Using the above guidelines should give a Compensation Gain similar to the curve plotted. The open loop error amplifier gain bounds the compensation gain. Check the compensation gain at FP2 with the capabilities of the error amplifier. The Loop Gain is constructed on the log-log graph of Figure 15 by adding the Modulator Gain (in dB) to the Compensation Gain (in dB). This is equivalent to multiplying the modulator transfer Page 15 of 20 ISL6420 function to the compensation transfer function and plotting the gain. 100 FZ1 FZ2 FP1 FP2 80 OPEN LOOP ERROR AMP GAIN GAIN (dB) 60 40 20 20LOG (R2/R1) 20LOG (VIN/VOSC) 0 -40 -60 COMPENSATION GAIN MODULATOR GAIN -20 LOOP GAIN FLC 10 100 1k FESR 10k 100k 1M 10M FREQUENCY (Hz) FIGURE 16. ASYMPTOTIC BODE PLOT OF CONVERTER GAIN The compensation gain uses external impedance networks ZFB and ZIN to provide a stable, high bandwidth (BW) overall loop. A stable control loop has a gain crossing with 20dB/decade slope and a phase margin greater than 45°. Include worst case component variations when determining phase margin. Component Selection Guidelines Output Capacitor Selection An output capacitor is required to filter the output and supply the load transient current. The filtering requirements are a function of the switching frequency and the ripple current. The load transient requirements are a function of the slew rate (di/dt) and the magnitude of the transient load current. These requirements are generally met with a mix of capacitors and careful layout. Modern microprocessors produce transient load rates above 1A/ns. High frequency capacitors initially supply the transient and slow the current load rate seen by the bulk capacitors. The bulk filter capacitor values are generally determined by the ESR (effective series resistance) and voltage rating requirements rather than actual capacitance requirements. High frequency decoupling capacitors should be placed as close to the power pins of the load as physically possible. Be careful not to add inductance in the circuit board wiring that could cancel the usefulness of these low inductance components. Consult with the manufacturer of the load on specific decoupling requirements. For example, Intel recommends that the high frequency decoupling for the Pentium Pro be composed of at least forty (40) 1.0µF ceramic capacitors in the 1206 surface-mount package. FN9151 Rev 5.00 Feb 13, 2008 Use only specialized low-ESR capacitors intended for switching-regulator applications for the bulk capacitors. The bulk capacitor’s ESR will determine the output ripple voltage and the initial voltage drop after a high slew-rate transient. An aluminum electrolytic capacitor's ESR value is related to the case size with lower ESR available in larger case sizes. However, the equivalent series inductance (ESL) of these capacitors increases with case size and can reduce the usefulness of the capacitor to high slew-rate transient loading. Unfortunately, ESL is not a specified parameter. Work with your capacitor supplier and measure the capacitor’s impedance with frequency to select a suitable component. In most cases, multiple electrolytic capacitors of small case size perform better than a single large case capacitor. Output Inductor Selection The output inductor is selected to meet the output voltage ripple requirements and minimize the converter’s response time to the load transients. The inductor value determines the converter’s ripple current and the ripple voltage is a function of the ripple current and the output capacitors ESR. The ripple voltage and current are approximated by the following equations: V IN - V OUT V OUT I L = -------------------------------- ---------------Fs x L V IN (EQ. 10) V OUT = I L ESR (EQ. 11) Increasing the value of inductance reduces the ripple current and voltage. However, larger inductance values reduce the converter’s response time to a load transient. One of the parameters limiting the converter’s response to a load transient is the time required to change the inductor current. Given a sufficiently fast control loop design, the ISL6420 will provide either 0% or 100% duty cycle in response to a load transient. The response time is the time required to slew the inductor current from an initial current value to the transient current level. During this interval the difference between the inductor current and the transient current level must be supplied by the output capacitor. Minimizing the response time can minimize the output capacitance required. Page 16 of 20 ISL6420 The response time to a transient is different for the application of load and the removal of load. The following equations give the approximate response time interval for application and removal of a transient load: L O I TRAN t RISE = ------------------------------V IN – V OUT (EQ. 12) L O I TRAN t FALL = -----------------------------V OUT (EQ. 13) where: ITRAN is the transient load current step, tRISE is the response time to the application of load, and tFALL is the response time to the removal of load. With a +5V input source, the worst case response time can be either at the application or removal of load and dependent upon the output voltage setting. Be sure to check both of these equations at the minimum and maximum output levels for the worst case response time. Input Capacitor Selection The important parameters for the bulk input capacitor are the voltage rating and the RMS current rating. For reliable operation, select the bulk capacitor with voltage and current ratings above the maximum input voltage and largest RMS current required by the circuit. The capacitor voltage rating should be at least 1.25 times greater than the maximum input voltage and a voltage rating of 1.5 times is a conservative guideline. The RMS current rating requirement for the input capacitor of a buck regulator is approximately 1/2 the DC load current. A more specific equation for determining the input ripple is the following, I RMS = I MAX D – D (EQ. 14) For a through hole design, several electrolytic capacitors (Panasonic HFQ series or Nichicon PL series or Sanyo MV-GX or equivalent) may be needed. For surface mount designs, solid tantalum capacitors can be used, but caution must be exercised with regard to the capacitor surge current rating. These capacitors must be capable of handling the surgecurrent at power-up. The TPS series available from AVX, and the 593D series from Sprague are both surge current tested. FN9151 Rev 5.00 Feb 13, 2008 The ISL6420 requires 2 N-Channel power MOSFETs. These should be selected based upon rDS(ON), gate supply requirements, and thermal management requirements. In high-current applications, the MOSFET power dissipation, package selection and heatsink are the dominant design factors. The power dissipation includes two loss components; conduction loss and switching loss. The conduction losses are the largest component of power dissipation for both the upper and the lower MOSFETs. These losses are distributed between the two MOSFETs according to duty factor (see the equations below). Only the upper MOSFET has switching losses, since the Schottky rectifier clamps the switching node before the synchronous rectifier turns on. 2 1 P UFET = I O R DS ON D + --- I O V IN t sw f sw 2 2 Use a mix of input bypass capacitors to control the voltage overshoot across the MOSFETs. Use small ceramic capacitors for high frequency decoupling and bulk capacitors to supply the current needed each time Q1 turns on. Place the small ceramic capacitors physically close to the MOSFETs and between the drain of Q1 and the source of Q2. 2 MOSFET Selection/Considerations P LFET = I O R DS ON 1 – D (EQ. 15) (EQ. 16) Where D is the duty cycle = Vo/Vin, tsw is the switching interval, and Fsw is the switching frequency. These equations assume linear voltage-current transitions and do not adequately model power loss due the reverse-recovery of the lower MOSFETs body diode. The gate-charge losses are dissipated by the ISL6420 and don't heat the MOSFETs. However, large gate-charge increases the switching interval, tSW which increases the upper MOSFET switching losses. Ensure that both MOSFETs are within their maximum junction temperature at high ambient temperature by calculating the temperature rise according to package thermal-resistance specifications. A separate heatsink may be necessary depending upon MOSFET power, package type, ambient temperature and air flow. Schottky Selection Rectifier D2 is a clamp that catches the negative inductor swing during the dead time between turning off the lower MOSFET and turning on the upper MOSFET. The diode must be a Schottky type to prevent the parasitic MOSFET body diode from conducting. It is acceptable to omit the diode and let the body diode of the lower MOSFET clamp the negative inductor swing, but efficiency will drop one or two percent as a result. The diode's rated reverse breakdown voltage must be greater than the maximum input voltage. Page 17 of 20 ISL6420 © Copyright Intersil Americas LLC 2004-2008. All Rights Reserved. All trademarks and registered trademarks are the property of their respective owners. For additional products, see www.intersil.com/en/products.html Intersil products are manufactured, assembled and tested utilizing ISO9001 quality systems as noted in the quality certifications found at www.intersil.com/en/support/qualandreliability.html Intersil products are sold by description only. Intersil may modify the circuit design and/or specifications of products at any time without notice, provided that such modification does not, in Intersil's sole judgment, affect the form, fit or function of the product. Accordingly, the reader is cautioned to verify that datasheets are current before placing orders. Information furnished by Intersil is believed to be accurate and reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries. For information regarding Intersil Corporation and its products, see www.intersil.com FN9151 Rev 5.00 Feb 13, 2008 Page 18 of 20 ISL6420 Package Outline Drawing L20.4x4 20 LEAD QUAD FLAT NO-LEAD PLASTIC PACKAGE Rev 1, 11/06 4X 4.00 2.0 16X 0.50 A B 16 6 PIN #1 INDEX AREA 20 6 PIN 1 INDEX AREA 1 15 4.00 2 . 10 ± 0 . 15 11 5 0.15 (4X) 6 10 0.10 M C A B 4 0.25 +0.05 / -0.07 TOP VIEW 20X 0.6 +0.15 / -0.25 BOTTOM VIEW SEE DETAIL "X" 0.10 C 0 . 90 ± 0 . 1 C BASE PLANE ( 3. 6 TYP ) ( 2. 10 ) SEATING PLANE 0.08 C ( 20X 0 . 5 ) SIDE VIEW ( 20X 0 . 25 ) C 0 . 2 REF 5 0 . 00 MIN. 0 . 05 MAX. ( 20X 0 . 8) TYPICAL RECOMMENDED LAND PATTERN DETAIL "X" NOTES: 1. Dimensions are in millimeters. Dimensions in ( ) for Reference Only. 2. Dimensioning and tolerancing conform to AMSE Y14.5m-1994. 3. Unless otherwise specified, tolerance : Decimal ± 0.05 4. Dimension b applies to the metallized terminal and is measured between 0.15mm and 0.30mm from the terminal tip. 5. Tiebar shown (if present) is a non-functional feature. 6. The configuration of the pin #1 identifier is optional, but must be located within the zone indicated. The pin #1 identifier may be either a mold or mark feature. FN9151 Rev 5.00 Feb 13, 2008 Page 19 of 20 ISL6420 Shrink Small Outline Plastic Packages (SSOP) Quarter Size Outline Plastic Packages (QSOP) M20.15 N INDEX AREA H 0.25(0.010) M E GAUGE PLANE -B1 2 INCHES 3 0.25 0.010 SEATING PLANE -A- 20 LEAD SHRINK SMALL OUTLINE PLASTIC PACKAGE (0.150” WIDE BODY) B M A D h x 45° -C- e 0.17(0.007) M A2 A1 B L C 0.10(0.004) C A M B S NOTES: 1. Symbols are defined in the “MO Series Symbol List” in Section 2.2 of Publication Number 95. 2. Dimensioning and tolerancing per ANSI Y14.5M-1982. 3. Dimension “D” does not include mold flash, protrusions or gate burrs. Mold flash, protrusion and gate burrs shall not exceed 0.15mm (0.006 inch) per side. MILLIMETERS SYMBOL MIN MAX MIN MAX NOTES A 0.053 0.069 1.35 1.75 - A1 0.004 0.010 0.10 0.25 - A2 - 0.061 - 1.54 - B 0.008 0.012 0.20 0.30 9 C 0.007 0.010 0.18 0.25 - D 0.337 0.344 8.56 8.74 3 E 0.150 0.157 3.81 3.98 4 e 0.025 BSC 0.635 BSC - H 0.228 0.244 5.80 6.19 - h 0.0099 0.0196 0.26 0.49 5 L 0.016 0.050 0.41 1.27 6 8° 0° N 20 0° 20 7 8° Rev. 1 6/04 4. Dimension “E” does not include interlead flash or protrusions. Interlead flash and protrusions shall not exceed 0.25mm (0.010 inch) per side. 5. The chamfer on the body is optional. If it is not present, a visual index feature must be located within the crosshatched area. 6. “L” is the length of terminal for soldering to a substrate. 7. “N” is the number of terminal positions. 8. Terminal numbers are shown for reference only. 9. Dimension “B” does not include dambar protrusion. Allowable dambar protrusion shall be 0.10mm (0.004 inch) total in excess of “B” dimension at maximum material condition. 10. Controlling dimension: INCHES. Converted millimeter dimensions are not necessarily exact. FN9151 Rev 5.00 Feb 13, 2008 Page 20 of 20