ISL6431 TM Data Sheet June 2001 Advanced Pulse-Width Modulation (PWM) Controller for Home Gateways The ISL6431 is a high efficiency, fixed frequency, synchronous buck PWM controller. It is designed for use in applications that convert 5V to lower distributed voltages required for set-top box, cable modem, DSL modem and residential home gateway core processor, memory and peripheral power supplies. This device makes simple work out of implementing a complete control and protection scheme for a DC-DC stepdown converter. Designed to drive N-channel MOSFETs in a synchronous buck topology, the ISL6431 integrates the control, output adjustment, monitoring and protection functions into a single 8-pin package. The ISL6431 provides simple, single feedback loop, voltagemode control with fast transient response. The output voltage can be precisely regulated to as low as 0.8V, with a maximum tolerance of ±1.5% over temperature and line voltage variations. A fixed frequency oscillator reduces design complexity, while balancing typical application cost and efficiency. The error amplifier features a 15MHz gain-bandwidth product and 6V/µs slew rate which enables high converter bandwidth for fast transient performance. The resulting PWM duty cycles range from 0% to 100%. Protection from overcurrent conditions is provided by monitoring the rDS(ON) of the upper MOSFET to inhibit PWM operation appropriately. This approach simplifies the implementation and improves efficiency by eliminating the need for a current sense resistor. TEMP. RANGE (oC) PACKAGE PKG. NO. ISL6431CB 0 to 70 8 Ld SOIC M8.15 ISL6431IB -40 to 85 8 Ld SOIC M8.15 ISL6431EVAL1 Evaluation Board Features • Operates from +5V Input • 0.8V to VIN Output Range - 0.8V Internal Reference - ±1.5% Over Line Voltage and Temperature • Drives N-Channel MOSFETs • Simple Single-Loop Control Design - Voltage-Mode PWM Control • Fast Transient Response • Lossless, Programmable Overcurrent Protection - Uses Upper MOSFET’s rDS(ON) • Small Converter Size - 300kHz Fixed Frequency Oscillator - Internal Soft Start - 8 Lead SOIC Package • High Conversion Efficiency • Synchronous/Standard Buck Configuration Applications • Cable Modems, Set Top Boxes, and DSL Modems • DSP and Core Communications Processor Supplies • Power Supplies for Microprocessors and Embedded Controllers • Memory Supplies • Personal Computer Peripherals • Industrial Power Supplies • Low-Voltage Distributed Power Supplies Pinout BOOT 1 UGATE 2 GND 3 LGATE 4 1 9018 • 5V-Input DC-DC Regulators Ordering Information PART NUMBER File Number 8 PHASE 7 COMP/OCSET 6 FB 5 VCC CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. 1-888-INTERSIL or 321-724-7143 | Intersil and Design is a trademark of Intersil Americas Inc. Copyright © Intersil Americas Inc. 2001, All Rights Reserved ISL6431 Block Diagram VCC POR AND SOFTSTART + SAMPLE AND HOLD - BOOT OC COMPARATOR UGATE PHASE + - INHIBIT PWM COMPARATOR ERROR AMP + 0.8V GATE CONTROL LOGIC PWM + - - VCC FB LGATE COMP/OCSET 20µA OSCILLATOR FIXED 300kHz GND Typical Application VCC C3 C4 C5 DBOOT VCC R1 5 1 ISL6431 COMP/OCSET BOOT UGATE C6 2 7 8 R2 LOUT PHASE +VO = 0.8 to VIN C2 6 C1 FB 4 3 LGATE C7 GND R3 R4 2 ISL6431 Absolute Maximum Ratings Thermal Information Supply Voltage, VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +6.0V Absolute Boot Voltage, VBOOT . . . . . . . . . . . . . . . . . . . . . . . +15.0V Upper Driver Supply Voltage, VBOOT - VPHASE . . . . . . . . . . . +6.0V Input, Output or I/O Voltage . . . . . . . . . . . GND -0.3V to VCC +0.3V ESD Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Class 2 Thermal Resistance (Typical, Note 1) θJA ( oC/W) SOIC Package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 Maximum Junction Temperature . . . . . . . . . . . . . . . . . . . . . . 150oC Maximum Storage Temperature Range . . . . . . . . . . -65oC to 150oC Maximum Lead Temperature (Soldering 10s) . . . . . . . . . . . . 300oC (SOIC - Lead Tips Only) Operating Conditions Supply Voltage, VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . +5V ±10% Ambient Temperature Range . . . . . . . . . . . . . . . . . . . -40oC to 85oC Junction Temperature Range. . . . . . . . . . . . . . . . . . -40oC to 125oC CAUTION: Stresses above those listed in “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress only rating and operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. NOTE: 1. θJA is measured with the component mounted on a low effective thermal conductivity test board in free air. See Tech Brief TB379 for details. Recommended Operating Conditions, Unless Otherwise Noted VCC = 5.0V±5% and TA = 25oC Electrical Specifications PARAMETER SYMBOL TEST CONDITIONS MIN TYP MAX UNITS VCC SUPPLY CURRENT Nominal Supply IVCC ISL6431CB; UGATE and LGATE Open - 3.2 - mA ISL6431IB; UGATE and LGATE Open 2.5 3.2 3.8 mA ISL6431CB - 4.30 - V ISL6431IB 4.17 4.30 4.50 V ISL6431CB - 0.20 - V ISL6431IB 0.01 0.20 0.85 V ISL6431CB; VCC = 5V - 300 - kHz ISL6431IB; VCC = 5V 230 300 340 kHz ISL6431CB - 1.5 - VP-P ISL6431IB - 1.5 - VP-P ISL6431CB - - 1.5 % POWER-ON RESET Rising VCC POR Threshold POR VCC POR Threshold Hysteresis OSCILLATOR Frequency fOSC ∆VOSC Ramp Amplitude REFERENCE Reference Voltage Tolerance Nominal Reference Voltage VREF ISL6431IB - - 1.5 % ISL6431CB - 0.800 - V ISL6431IB - 0.800 - V ERROR AMPLIFIER DC Gain Gain-Bandwidth Product GBWP Slew Rate SR ISL6431CB - 82 - dB ISL6431IB - 82 - dB ISL6431CB 14 - - MHz ISL6431IB 14 - - MHz ISL6431CB; COMP = 10pF - 8.0 - V/µs ISL6431IB; COMP = 10pF 4.5 8.0 9.2 V/µs ISL6431CB; VBOOT - VPHASE = 5V, VUGATE = 4V - 1.0 - A ISL6431IB; VBOOT - VPHASE = 5V, VUGATE = 4V - 1.0 - A ISL6431CB - 1.0 - A GATE DRIVERS Upper Gate Source Current IUGATE-SRC Upper Gate Sink Current IUGATE-SNK Lower Gate Source Current ILGATE-SRC 3 ISL6431IB - 1.0 - A ISL6431CB; VCC = 5V, VLGATE = 4V - 1.0 - A ISL6431IB; VCC = 5V, VLGATE = 4V - 1.0 - A ISL6431 Recommended Operating Conditions, Unless Otherwise Noted VCC = 5.0V±5% and TA = 25oC (Continued) Electrical Specifications PARAMETER Lower Gate Sink Current SYMBOL MIN TYP MAX UNITS ISL6431CB - 2.0 - A ISL6431IB - 2.0 - A IOCSET ISL6431CB 17 20 22 µA ISL6431IB 14 20 24 µA VDISABLE ISL6431CB - - 0.8 V ISL6431IB - - 0.8 V ILGATE-SNK TEST CONDITIONS PROTECTION / DISABLE OCSET Current Source Disable Threshold Functional Pin Descriptions VCC (Pin 5) (IOCSET), and the upper MOSFET on-resistance (rDS(ON)) set the converter overcurrent (OC) trip point according to the following equation: This is the main bias supply for the ISL6431, as well as the lower MOSFET’s gate. Connect a well-decoupled 5V supply to this pin. IOCSET xR OC SET I PEAK = ------------------------------------------------r DS ( ON ) FB (Pin 6) This pin is the inverting input of the internal error amplifier. Use this pin, in combination with the COMP/OCSET pin, to compensate the voltage-control feedback loop of the converter. GND (Pin 3) This pin represents the signal and power ground for the IC. Tie this pin to the ground island/plane through the lowest impedance connection available. PHASE (Pin 8) Connect this pin to the upper MOSFET source. This pin is used to monitor the voltage drop across the upper MOSFET for overcurrent protection. This pin is also monitored by the continuously adaptive shoot-through protection circuitry to determine when the upper MOSFET has turned off. UGATE (Pin 2) Connect this pin to the upper MOSFET’s gate. This pin provides the PWM-controlled gate drive for the upper MOSFET. This pin is also monitored by the adaptive shootthrough protection circuitry to determine when the upper MOSFET has turned off. Do not insert any circuitry between this pin and the gate of the upper MOSFET, as it may interfere with the internal adaptive shoot-through protection circuitry and render it ineffective. BOOT (Pin 1) This pin provides ground referenced bias voltage to the upper MOSFET driver. A bootstrap circuit is used to create a voltage suitable to drive a logic-level N-channel MOSFET. COMP/OCSET (Pin 7) This is a multiplexed pin. During a short period of time following power-on reset (POR), this pin is used to determine the overcurrent threshold of the converter. Connect a resistor (R OCSET) from this pin to the drain of the upper MOSFET (VCC ). ROCSET, an internal 20µA current source 4 Internal circuitry of the ISL6431 will not recognize a voltage drop across ROCSET larger than 0.5V. Any voltage drop across ROCSET that is greater than 0.5V will set the overcurrent trip point to: 0.5V I PEAK = ---------------------r DS ( ON ) An overcurrent trip cycles the soft-start function. Pulling OCSET to a level below 0.8V will disable the controller. Disabling the ISL6431 causes the oscillator to stop, the LGATE and UGATE outputs to be held low, and the softstart circuitry to re-arm. During soft-start, and all the time during normal converter operation, this pin represents the output of the error amplifier. Use this pin, in combination with the FB pin, to compensate the voltage-control feedback loop of the converter. LGATE (Pin 4) Connect this pin to the lower MOSFET’s gate. This pin provides the PWM-controlled gate drive for the lower MOSFET. This pin is also monitored by the adaptive shootthrough protection circuitry to determine when the lower MOSFET has turned off. Do not insert any circuitry between this pin and the gate of the lower MOSFET, as it may interfere with the internal adaptive shoot-through protection circuitry and render it ineffective. Functional Descriptions Initialization The ISL6431 automatically initializes upon receipt of power. The Power-On Reset (POR) function continually monitors the bias voltage at the VCC pin. The POR function initiates the Overcurrent Protection (OCP) sampling and hold operation after the supply voltage exceeds its POR threshold. Upon ISL6431 completion of the OCP sampling and hold operation, the POR function initiates the Soft Start operation. in the normal operating load range, find the R OCSET resistor from the equation above with: 1. The maximum rDS(ON) at the highest junction temperature. 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. 2. The minimum IOCSET from the specification table. OUTPUT INDUCTOR Over Current Protection ( ∆I ) IPEAK > IOUT ( MAX ) + ---------- , 2 3. Determine IPEAK for where ∆I is the output inductor ripple current. For an equation for the ripple current see the section under component guidelines titled ‘Output Inductor Selection’. 14A Soft Start 12A The POR function initiates the soft start sequence after the overcurrent set point has been sampled. Soft start clamps the error amplifier output (COMP pin) and reference input (noninverting terminal of the error amp) to the internally generated Soft Start voltage. Figure 2 shows a typical soft start interval. Initially the clamp on the error amplifier (COMP/OCSET pin) controls the converter’s output voltage. The oscillator’s triangular waveform is compared to the ramping error amplifier voltage. This generates PHASE pulses of increasing width that charge the output capacitor(s). With sufficient output voltage, the clamp on the reference input controls the output voltage. When the internally generated Soft Start voltage exceeds the feedback (FB pin) voltage, the output voltage is in regulation. This method provides a rapid and controlled output voltage rise. 10A 8A 6A 4A 2A 0A TIME (50µs/DIV.) FIGURE 1. OVERCURRENT OPERATION The overcurrent function cycles the soft-start function in a hiccup mode to provide fault protection. A resistor (ROCSET) programs the overcurrent trip level (see Typical Application diagram). Immediately following POR, the ISL6431 initiates the Overcurrent Protection sampling and hold operation. First, the internal error amplifier is disabled. This allows an internal 20µA current sink to develop a voltage across ROCSET. The ISL6431 then samples this voltage at the COMP pin. This sampled voltage, which is referenced to the VCC pin, is held internally as the Overcurrent Set Point. VOUT 500mV/DIV. 0V When the voltage across the upper MOSFET, which is also referenced to the VCC pin, exceeds the Overcurrent Set Point, the overcurrent function initiates a soft-start sequence. Figure 1 shows this operation with an overload condition. This current is repeated with a 21ms period. Note that the inductor current increases to over 14A during the Soft Start interval and causes an overcurrent trip. The converter dissipates very little power with this method. The measured input power for the conditions of Figure 1 is only 0.25W. The overcurrent function will trip at a peak inductor current (IPEAK) determined by: IOCSET x R OCSET I PEAK = ----------------------------------------------------r DS ( ON ) where IOCSET is the internal OCSET current source (20µA typical). The OC trip point varies mainly due to the MOSFET’s rDS(ON) variations. To avoid overcurrent tripping 5 TIME (1ms/DIV.) FIGURE 2. SOFT START INTERVAL 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. ISL6431 width modulated (PWM) wave with an amplitude of V IN at the PHASE node. The PWM wave is smoothed by the output filter (LO and CO). VIN ISL6431 Q1 PHASE CIN Q2 LGATE VOUT CO VIN DRIVER OSC LO PWM COMPARATOR LO + ∆ VOSC LOAD UGATE DRIVER PHASE VE/A FIGURE 3. PRINTED CIRCUIT BOARD POWER AND GROUND PLANES OR ISLANDS Figure 4 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 COMP/OCSET pin and locate the resistor, ROSCET close to the COMP/OCSET pin because the internal current source is only 20µA. Provide local VCC decoupling between VCC and GND pins. Locate the capacitor, CBOOT as close as practical to the BOOT and PHASE pins. All components used for feedback compensation should be located as close to the IC a practical. CBOOT ISL6431 Q1 LO VOUT PHASE VCC +5V Q2 CO COMP/OCSET CVCC GND FIGURE 4. PRINTED CIRCUIT BOARD SMALL SIGNAL LAYOUT GUIDELINES Feedback Compensation Figure 5 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 oscillator (OSC) triangular wave to provide a pulse6 ERROR AMP REFERENCE DETAILED COMPENSATION COMPONENTS ZFB C2 C1 VOUT ZIN C3 R2 R3 R1 COMP FB + ISL6431 REFERENCE FIGURE 5. VOLTAGE-MODE BUCK CONVERTER COMPENSATION DESIGN 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 F LC and a zero at FESR . The DC Gain of the modulator is simply the input voltage (VIN ) divided by the peak-to-peak oscillator voltage ∆VOSC . Modulator Break Frequency Equations +VIN LOAD ROCSET +5V D1 ZIN + Figure 3 shows the critical power components of the converter. To minimize the voltage overshoot, the interconnecting wires indicated by heavy lines should be part of a ground or power plane in a printed circuit board. The components shown in Figure 3 should be located as close together as possible. Please note that the capacitors CIN and CO may each represent numerous physical capacitors. Locate the ISL6431 within 3 inches of the MOSFETs, Q1 and Q2 . The circuit traces for the MOSFETs’ gate and source connections from the ISL6431 must be sized to handle up to 1A peak current. BOOT CO ESR (PARASITIC) ZFB RETURN VOUT 1 F LC = -----------------------------------------2π x L O x C O 1 F ESR = ------------------------------------------2π x ESR x C O The compensation network consists of the error amplifier (internal to the ISL6431) 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 180 degrees. The equations below relate the compensation network’s poles, zeros and gain to the components (R 1 , R2 , R3 , C1 , C2 , and C 3) in Figure 7. Use these guidelines for locating the poles and zeros of the compensation network: 1. Pick Gain (R2/R1) for desired converter bandwidth. 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. 5. Place 2ND Pole at Half the Switching Frequency. ISL6431 6. Check Gain against Error Amplifier’s Open-Loop Gain. 7. Estimate Phase Margin - Repeat if Necessary. Compensation Break Frequency Equations 1 F Z1 = -----------------------------------2π x R 2 x C 1 1 FP1 = -------------------------------------------------------- C 1 x C 2 2π x R 2 x ---------------------- C1 + C2 1 FP2 = -----------------------------------2π x R 3 x C 3 1 F Z2 = ------------------------------------------------------2π x ( R 1 + R 3 ) x C 3 Figure 6 shows an asymptotic plot of the DC-DC converter’s gain vs frequency. The actual Modulator Gain has a high gain peak due to the high Q factor of the output filter and is not shown in Figure 6. 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 Closed Loop Gain is constructed on the graph of Figure 6 by adding the Modulator Gain (in dB) to the Compensation Gain (in dB). This is equivalent to multiplying the modulator transfer function to the compensation transfer function and plotting the 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 degrees. Include worst case component variations when determining phase margin. Refer to the evaluation board application note (available soon) for a complete reference design schematic and bill of materials for a typical Residential Gateway application. 100 FZ1 FZ2 FP1 FP2 80 OPEN LOOP ERROR AMP GAIN GAIN (dB) 60 40 20 20LOG (R2/R1) 0 COMPENSATION GAIN CLOSED LOOP GAIN -40 FLC FESR -60 10 100 1K 10K 100K 1M 10M FREQUENCY (Hz) FIGURE 6. ASYMPTOTIC BODE PLOT OF CONVERTER GAIN 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. 7 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. 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 transient. The inductor value determines the converter’s ripple current and the ripple voltage is a function of the ripple current. The ripple voltage and current are approximated by the following equations: ∆I = 20LOG (VIN/DVOSC) MODULATOR GAIN -20 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. VIN - VOUT Fs x L x VOUT VIN ∆VOUT = ∆I x ESR Increasing the value of inductance reduces the ripple current and voltage. However, the large 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 ISL6431 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. ISL6431 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: tRISE = L x ITRAN VIN - VOUT tFALL = L x ITRAN VOUT 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. The worst case response time can be either at the application or removal of load. Be sure to check both of these equations at the minimum and maximum output levels for the worst case response time. across the lower MOSFET clamps the switching node before the synchronous rectifier turns on. These equations assume linear voltage-current transitions and do not adequately model power loss due the reverse-recovery of the lower MOSFET’s body diode. The gate-charge losses are dissipated by the ISL6431 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. 1 Io x VIN x tSW x FS 2 Input Capacitor Selection PUPPER = Io2 x rDS(ON) x D + 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 . PLOWER = Io2 x rDS(ON) x (1 - D) 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. Where: D is the duty cycle = VOUT / VIN , tSW is the switch ON time, and FS is the switching frequency. Given the reduced available gate bias voltage (5V), logiclevel or sub-logic-level transistors have to be used for both N-MOSFETs. Caution should be exercised with devices exhibiting very low VGS(ON) characteristics, as the low gate threshold could be conducive to some shoot-through (due to the Miller effect), in spite of the counteracting circuitry present aboard the ISL6431. +5V DBOOT VCC For a through hole design, several electrolytic capacitors 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 surge-current at power-up. Some capacitor series available from reputable manufacturers are surge current tested. MOSFET Selection/Considerations The ISL6431 requires two N-Channel power MOSFETs for use in a synchronous buck configuration. 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 lower MOSFETs body diode or an external Schottky rectifier 8 +5V + VD BOOT CBOOT ISL6431 Q1 UGATE PHASE + LGATE NOTE: VG-S ≈ VCC -VD Q2 NOTE: VG-S ≈ VCC GND FIGURE 7. UPPER GATE DRIVE BOOTSTRAP Figure 7 shows the upper gate drive (BOOT pin) supplied by a bootstrap circuit from VCC. The boot capacitor, CBOOT, develops a floating supply voltage referenced to the PHASE pin. The supply is refreshed to a voltage of VCC less the boot diode drop (VD) each time the lower MOSFET, Q2 , turns on. ISL6431 ISL6431 DC-DC Converter Application Circuit Figure 8 shows an application circuit of a DC-DC Converter. Detailed information on the circuit, including a complete Billof-Materials and circuit board description is available. +5V + CIN VCC 5 ISL6431 D1 MONITOR AND PROTECTION 1 BOOT 2 UGATE COMP/OCSET 7 REF 8 PHASE Q1 L1 + - VOUT + FB - 6 OSC U1 4 LGATE 3 GND FIGURE 8. DC-DC CONVERTER 9 Q2 COUT + ISL6431 Small Outline Plastic Packages (SOIC) M8.15 (JEDEC MS-012-AA ISSUE C) N INDEX AREA 0.25(0.010) M H 8 LEAD NARROW BODY SMALL OUTLINE PLASTIC PACKAGE B M E INCHES -B- 1 2 SYMBOL 3 L SEATING PLANE -A- h x 45o A D -C- e µα B 0.25(0.010) M C 0.10(0.004) C A M B S MAX MIN MAX NOTES A 0.0532 0.0688 1.35 1.75 - A1 0.0040 0.0098 0.10 0.25 - B 0.013 0.020 0.33 0.51 9 C 0.0075 0.0098 0.19 0.25 - D 0.1890 0.1968 4.80 5.00 3 E 0.1497 0.1574 3.80 4.00 4 e A1 0.050 BSC 1. Symbols are defined in the “MO Series Symbol List” in Section 2.2 of Publication Number 95. 1.27 BSC - H 0.2284 0.2440 5.80 6.20 - h 0.0099 0.0196 0.25 0.50 5 L 0.016 0.050 0.40 1.27 6 8o 0o N NOTES: MILLIMETERS MIN α 8 0o 8 7 8o Rev. 0 12/93 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. 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. The lead width “B”, as measured 0.36mm (0.014 inch) or greater above the seating plane, shall not exceed a maximum value of 0.61mm (0.024 inch). 10. Controlling dimension: MILLIMETER. Converted inch dimensions are not necessarily exact. All Intersil products are manufactured, assembled and tested utilizing ISO9000 quality systems. Intersil Corporation’s quality certifications can be viewed at website www.intersil.com/design/quality Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design and/or specifications at any time without notice. Accordingly, the reader is cautioned to verify that data sheets 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. 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