VR11.1, VR12 Compatible Synchronous Rectified Buck MOSFET Driver ISL6627 Features The ISL6627 is a high frequency MOSFET driver designed to drive upper and lower power N-Channel MOSFETs in a synchronous rectified buck converter topology. The advanced PWM protocol of ISL6627 is specifically designed to work with Intersil VR11.1, VR12 controllers and combined with N-Channel MOSFETs to form a complete core-voltage regulator solution for advanced microprocessors. When ISL6627 detects a PSI protocol sent by an Intersil VR11.1, VR12 controller, it activates Diode Emulation (DE) operation; otherwise, it operates in normal Continuous Conduction Mode (CCM) PWM mode. • Intersil VR11.1 and VR12 Compatible To further enhance light load efficiency, the ISL6627 enables diode emulation operation during PSI mode. This allows Discontinuous Conduction Mode (DCM) by detecting when the inductor current reaches zero and subsequently turning off the low side MOSFET to prevent it from sinking current. When ISL6627 detects Diode Braking command from the PWM, it turns off both gates and reduces overshoot in load transient situations. An advanced adaptive shoot-through protection is integrated to prevent both the upper and lower MOSFETs from conducting simultaneously and to minimize dead time. The user also has the option to program the driver working in fixed propagation delay mode to optimize the regulator efficiency. The ISL6627 has a 20kΩ integrated high-side gate-to-source resistor to prevent self turn-on due to high input bus dV/dt. • Dual MOSFET Driver for Synchronous Rectified Bridge • Advanced Adaptive Zero Shoot-through Protection • Programmable Fixed Deadtime for Efficiency Optimization • Low Standby Bias Current • 36V Internal Bootstrap Diode • Bootstrap Capacitor Overcharge Prevention • Supports High Switching Frequency - 4A Sinking Current Capability - Fast Rise/Fall Times and Low Propagation Delays • Integrated High-Side Gate-to-Source Resistor to Prevent Self Turn-on Due to High Input Bus dV/dt • Power Rails Undervoltage Protection • Expandable Bottom Copper Pad for Enhanced Heat Sinking • Dual Flat 10 Ld (3x3 DFN) Package - Near Chip-Scale Package Footprint; Improves PCB Efficiency and Thinner in Profile • Pb-Free (RoHS Compliant) Applications • High Light Load Efficiency Voltage Regulators • Core Regulators for Advanced Microprocessors Related Literature • High Current DC/DC Converters • Technical Brief TB363 “Guidelines for Handling and Processing Moisture Sensitive Surface Mount Devices (SMDs)” • High Frequency and High Efficiency VRM and VRD • Technical Brief TB417 “Designing Stable Compensation Networks for Single Phase Voltage Mode Buck Regulators” BOOT TD UGATE VCC EN 20kΩ +5V POR/ 33.6k PWM CONTROL LOGIC SHOOTTHROUGH PROTECTION/ DELAY PROGRAMMING PHASE LGATE 28.8k GND FIGURE 1. ISL6627 BLOCK DIAGRAM September 22, 2011 FN6992.0 1 CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. 1-888-INTERSIL or 1-888-468-3774 | Copyright Intersil Americas Inc. 2011. All Rights Reserved Intersil (and design) is a trademark owned by Intersil Corporation or one of its subsidiaries. All other trademarks mentioned are the property of their respective owners. ISL6627 Typical Application Circuit VINF +5V +5V BOOT EN UGATE VCC ISL6627 DRIVER DVC FB COMP PWM VCC PWM1 PSICOMP ISEN1- HFCOMP ISEN1+ VINF BOOT EN RGND EN_VTT VTT LGATE +5V VSEN VCC SVDATA SVALERT# SVCLK PWM2 VR_RDY ISEN2- VR_RDYS ISEN2+ PHASE GND UGATE ISL6627 DRIVER PWM PHASE GND LGATE PWM3-5 VR_HOT# ISEN3-5ISEN3-5+ VINF ISL6367 I2CLK VINF PMALERT# VINF EN_PWR_CFP I2DATA +5V VCTRL VCC CFP RAMP_ADJ BOOT ISL6596 DRIVER PWM PWM6 CPU LOAD UGATE PHASE GND LGATE ISEN6- IMON IMONS FS_DRP FSS_DRPS ISEN6+ VIN ISENIN- +5V RISENIN1 RSENIN RISENIN2 VINF ISENIN+ +5V +5V BTS_DES_TCOMPS +5V BT_FDVID_TCOMP +5V BOOT EN GND VCC ADDR_IMAXS_TMAX PWMS ISL6627 DRIVER GND LGATE GPU LOAD ISENS- NPSI_DE_IMAX +5V PWM UGATE PHASE ISENS+ +5V TMS NTC RGNDS VSENS NTC TM AUTO HFCOMPS/DVCS RSET COMPS FBS NTC: BETA = 3477 2 FN6992.0 September 22, 2011 ISL6627 Pin Configuration ISL6627 (10 LD 3x3 DFN) TOP VIEW UGATE 1 10 PHASE BOOT 2 9 EN TD 3 PWM 4 GND 5 PAD (GND) 8 NC 7 VCC 6 LGATE Functional Pin Descriptions PIN # SYMBOL DESCRIPTION 1 UGATE Upper gate drive output. Connect to gate of high-side power N-Channel MOSFET. 2 BOOT Floating bootstrap supply pin for the upper gate drive. Connect the bootstrap capacitor between this pin and the PHASE pin. The bootstrap capacitor provides the charge to turn on the upper MOSFET. See “Internal Bootstrap Device” on page 7 for guidance in choosing the capacitor value. 3 TD 4 PWM Control input for the driver. The PWM signal can enter three distinct states during operation; see “Advanced PWM Protocol (Patent Pending)” on page 6 for further details. Connect this pin to the PWM output of the controller. 5 GND Bias and reference ground. All signals are referenced to this node. It is also the power ground return of the driver. 6 LGATE 7 VCC Connect to 5V bias supply. This pin supplies power to the gate drives and small-signal circuitry. Place a high quality low ESR ceramic capacitor from this pin to GND. 8 NC No connection. 9 EN Enable input pin. Connect this pin high to enable the driver and low to disable the driver. - PAD Deadtime programming pin. Connect to ground or VCC via resistor to program fixed time delay from LGATE fall to UGATE rise or UGATE fall to LGATE rise. Open pin sets the adaptive mode. See Table 1 for more details. Lower gate drive output. Connect to gate of the low-side power N-Channel MOSFET. EPAD at ground potential. Soldering it directly to GND plane is required for thermal considerations. Ordering Information PART NUMBER (Notes 1, 2, 3) PART MARKING TEMP. RANGE (°C) PACKAGE (Pb-Free) PKG. DWG. # ISL6627CRZ 6627 0 to +70 10 Ld 3x3 DFN L10.3X3 ISL6627IRZ 627I -40 to +85 10 Ld 3x3 DFN L10.3X3 NOTES: 1. Add “-T*” suffix for tape and reel. Please refer to TB347 for details on reel specifications. 2. 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 Pbfree products are MSL classified at Pb-free peak reflow temperatures that meet or exceed the Pb-free requirements of IPC/JEDEC J STD-020. 3. For Moisture Sensitivity Level (MSL), please see device information page for ISL6627. For more information on MSL please see techbrief TB363. 3 FN6992.0 September 22, 2011 ISL6627 Absolute Maximum Ratings Thermal Information Supply Voltage (VCC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 7V Input Voltage (VEN, VPWM). . . . . . . . . . . . . . . . . . . . . . . -0.3V to VCC + 0.3V BOOT Voltage (VBOOT-GND) . . . . . . . . . . -0.3V to 25V (DC) or 36V (<200ns) BOOT to PHASE Voltage (VBOOT-PHASE) . . . . . . . . . . . . . . . . -0.3V to 7V (DC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 9V (<10ns) PHASE Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . GND - 0.3V to 25V (DC) . . . . . . . . . . . . . . . GND -8V (<20ns Pulse Width, 10μJ) to 30V (<100ns) UGATE Voltage. . . . . . . . . . . . . . . . . . . . . . . . . . VPHASE - 0.3V (DC) to VBOOT . . . . . . . . . . . . . . . . . . .VPHASE - 5V (<20ns Pulse Width, 10μJ) to VBOOT LGATE Voltage . . . . . . . . . . . . . . . . . . . . . . . . .GND - 0.3V (DC) to VCC + 0.3V . . . . . . . . . . . . . . . . GND - 2.5V (<20ns Pulse Width, 5μJ) to VCC + 0.3V Ambient Temperature Range . . . . . . . . . . . . . . . . . . . . . . .-40°C to +125°C ESD Rating Human Body Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.5kV Charged Device Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1kV Latch Up (Tested per JESD78C; Class II, Level A) . . . . . . . . . . . . . . . 100mA Thermal Resistance θJA (°C/W) θJC (°C/W) 10 Ld 3x3 DFN Package (Notes 4, 5). . . . . 51 10 Maximum Junction Temperature (Plastic Package) . . . . . . . . . . . .+150°C Maximum Storage Temperature Range . . . . . . . . . . . . . .-65°C to +150°C Pb-Free Reflow Profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . see link below http://www.intersil.com/pbfree/Pb-FreeReflow.asp Recommended Operating Conditions Ambient Temperature Range(ISL6627IRZ) . . . . . . . . . . . . -40°C to +85°C Ambient Temperature Range (ISL6627CRZ) . . . . . . . . . . . . .0°C to +70°C Maximum Operating Junction Temperature . . . . . . . . . . . . . . . . . . +125°C Supply Voltage, VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5V ±10% 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: 4. θJA 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. 5. For θJC, the “case temp” location is the center of the exposed metal pad on the package underside. Electrical Specifications Recommended Operating Conditions, Unless Otherwise Noted. Boldface limits apply over the operating temperature range. PARAMETER SYMBOL TEST CONDITIONS MIN (Note 7) TYP MAX (Note 7) UNITS VCC SUPPLY CURRENT No Load Switching Supply Current IVCC f_PWM = 300kHz, VCC = 5V, EN = High 1.27 mA Standby Supply Current IVCC VCC = 5V, PWM 0V to 2.5V transition, EN = High 1.85 mA VCC = 5V, PWM 0V to 2.5V transition, EN = Low 1.15 mA POWER-ON RESET AND ENABLE VCC Rising POR Threshold 3.20 3.85 4.40 V VCC Falling POR Threshold 3.00 3.52 4.00 V VCC POR Hysteresis 130 300 530 mV EN High Threshold 1.40 1.65 1.90 V EN Low Threshold 1.20 1.35 1.55 V PWM INPUT (See “TIMING DIAGRAM” on page 6) Input Current IPWM VPWM = 5V 155 µA VPWM = 0V -133 µA Three-State Lower Gate Falling Threshold VCC = 5V 1.6 V Three-State Lower Gate Rising Threshold VCC = 5V 1.1 V Three-State Upper Gate Rising Threshold VCC = 5V 3.2 V Three-state Upper Gate Falling Threshold VCC = 5V 2.8 V UGATE Rise Time (Note 6) t_RU VCC = 5V, 3nF load, 10% to 90% 8 ns LGATE Rise Time (Note 6) t_RL VCC = 5V, 3nF load, 10% to 90% 8 ns UGATE Fall Time (Note 6) t_FU VCC = 5V, 3nF load, 10% to 90% 8 ns tFL LGATE Fall Time (Note 6) VCC = 5V, 3nF load, 10% to 90% 4 ns UGATE Turn-On Propagation Delay (Note 6) tPDHU VCC = 5V, 3nF load, adaptive 28 ns LGATE Turn-On Propagation Delay (Note 6) tPDHL VCC = 5V, 3nF load, adaptive 16 ns UGATE Turn-Off Propagation Delay (Note 6) tPDLU VCC = 5V, 3nF load 15 ns 4 FN6992.0 September 22, 2011 ISL6627 Electrical Specifications Recommended Operating Conditions, Unless Otherwise Noted. Boldface limits apply over the operating temperature range. (Continued) PARAMETER SYMBOL LGATE Turn-Off Propagation Delay (Note 6) Minimum LGATE on Time at Diode Emulation tPDLL tLG_ON_DM TEST CONDITIONS MIN (Note 7) VCC = 5V, 3nF load VCC = 5V TYP MAX (Note 7) UNITS 14 230 330 ns 450 ns PROPAGATION DELAY PROGRAMMING UGATE Fall to LGATE Rise Time tPDUFLR LGATE Fall to UGATE Rise Time tPDLFUR VCC = 5V, 3nF Load, 90% to 10%, short resistor from TD to VCC 23 ns VCC = 5V, 3nF Load, 90% to 10%, 100kΩ resistor from TD to VCC 18 ns VCC = 5V, 3nF Load, 90% to 10%, 330kΩ resistor from TD to VCC 15 ns VCC = 5V, 3nF Load, 90% to 10%, 910kΩ resistor from TD to VCC 7 ns VCC = 5V, 3nF Load, 90% to 10%, short resistor from TD to GND 18 ns VCC = 5V, 3nF Load, 90% to 10%, short resistor from TD to GND 40 ns VCC = 5V, 3nF Load, 90% to 10%, 100kΩ resistor from TD to GND 25 ns VCC = 5V, 3nF Load, 90% to 10%, 360kΩ resistor from TD to GND 17 ns VCC = 5V, 3nF Load, 90% to 10%, short resistor from TD to VCC 27 ns OUTPUT (Note 6) Upper Drive Source Current I_U_SOURCE VCC = 5V, 3nF load 2 A Upper Drive Source Impedance R_U_SOURCE 20mA source current 1 Ω I_U_SINK VCC = 5V, 3nF load 2 A Upper Drive Sink Impedance R_U_SINK 20mA sink current 1 Ω Lower Drive Source Current I_L_SOURCE VCC = 5V, 3nF load 2 A Lower Drive Source Impedance R_L_SOURCE 20mA source current 1 Ω Upper Drive Sink Current Lower Drive Sink Current I_L_SINK VCC = 5V, 3nF load 4 A Lower Drive Sink Impedance R_L_SINK 20mA sink current 0.4 Ω NOTES: 6. Limits established by characterization and are not production tested. 7. Parameters with MIN and/or MAX limits are 100% tested at +25°C, unless otherwise specified. Temperature limits established by characterization and are not production tested. 5 FN6992.0 September 22, 2011 ISL6627 1.6V<PWM<3.2V 1.1V<PWM<2.8V PWM tPDHU tPDLU tPDTS tUG_OFF_DB tPDTS UGATE tFU tRU tPDHL LGATE tRL tFL tTSSHD tPDLL tPDLFUR tPDUFLR FIGURE 2. TIMING DIAGRAM Operation and Adaptive Shoot-Through Protection Designed for high speed switching, the ISL6627 MOSFET driver controls both high-side and low-side N-Channel FETs from one externally-provided PWM signal. A rising transition on PWM initiates the turn-off of the lower MOSFET (see “Timing Diagram”). After a short propagation delay [tPDLL], the lower gate begins to fall. Typical fall times [tFL] are provided in the “Electrical Specifications” on page 4. Adaptive shoot-through circuitry monitors the LGATE voltage and turns on the upper gate following a short delay time [tPDHU] after the LGATE voltage drops below ~1V. The user also has the option to program the propagation delay as described in “Deadtime Programming” on page 6. The upper gate drive then begins to rise [tRU] and the upper MOSFET turns on. A falling transition on PWM indicates the turn-off of the upper MOSFET and the turn-on of the lower MOSFET. A short propagation delay [tPDLU] is encountered before the upper gate begins to fall [tFU]. The adaptive shoot-through circuitry monitors the UGATEPHASE voltage and turns on the lower MOSFET a short delay time [tPDHL], after the upper MOSFET’s gate voltage drops below 1V. The lower gate then rises [tRL], turning on the lower MOSFET. These methods prevent both the lower and upper MOSFETs from conducting simultaneously (shoot-through), while adapting the dead time to the gate charge characteristics of the MOSFETs being used. The user also has the option to program the propagation delay as described in “Deadtime Programming” on page 6. This driver is optimized for voltage regulators with a large step down ratio. The lower MOSFET is usually sized larger compared to the upper MOSFET because the lower MOSFET conducts for a longer time during a switching period. The lower gate driver is therefore sized much larger to meet this application requirement. The 0.4Ω ON-resistance and 4A sink current capability enable the lower gate driver to absorb the charge injected into the lower gate through the drain-to-gate capacitor of the lower MOSFET and help prevent shoot through caused by the self turn-on of the lower MOSFET due to high dV/dt of the switching node. 6 Advanced PWM Protocol (Patent Pending) The advanced PWM protocol of ISL6627 is specifically designed to work with Intersil VR11.1 and VR12 controllers. When ISL6627 detects a PSI# protocol sent by an Intersil VR11.1/VR12 controller, it turns on diode emulation operation; otherwise, it remains in normal CCM PWM mode. Note that for a PWM low to tri-level (2.5V) transition, the LGATE will not turn off until the its diode emulation minimum ON-time of 330ns (typically) passes. Diode Emulation Diode emulation allows for higher converter efficiency under light-load situations. With diode emulation active, the ISL6627 detects the zero current crossing of the output inductor and turns off LGATE, preventing the low side MOSFET from sinking current and ensuring discontinuous conduction mode (DCM) is achieved. In DCM mode, LGATE has a minimum ON-time of 330ns (typically). Deadtime Programming The part provides the user with the option to program either of the two gate propagation delays (as defined in Figure 3) in order to optimize the deadtime and maximize the efficiency of the circuit. Tying the TD pin to either GND or VCC through a specified-value resistor leads the driver to operate in fixed gate propagation delay mode. Leaving the TD pin floating results in the driver operating in adaptive deadtime mode. Refer to Table 1 for typical programming resistor value options. Propagation delay has a typical tolerance of 30%. As actual deadtime depends on FET switching transition characteristics, while operating in fixed propagation delay mode, the user needs to monitor the gate transitions under worst-case operating conditions and use appropriate design margin to prevent eventual shoot-through due to insufficient dead time. FN6992.0 September 22, 2011 ISL6627 where QG1 is the amount of gate charge per upper MOSFET at VGS1 gate-source voltage and NQ1 is the number of control (upper) MOSFETs. The ΔVBOOT_CAP term is defined as the allowable droop in the rail of the upper gate drive. Select results are exemplified in Figure 4. PWM 1.6 LG 1.4 1.2 LG FALL TO UG RISE PROPAGATION DELAY UG FALL TO LG RISE PROPAGATION DELAY FIGURE 3. PROGRAMMABLE PROPAGATION DELAY ILLUSTRATION CBOOT_CAP (µF) UG 1. 0.8 0.6 QGATE = 100nC 0.4 50nC TABLE 1. TYPICAL DELAY PROGRAMMING RESISTOR VALUE LG FALL TO RESISTOR FROM RESISTOR FROM TD TO GND UG RISE DELAY TD TO VCC (kΩ) (ns) (kΩ) UG FALL TO LG RISE DELAY (ns) - 27 23 100 - 27 18 330 - 27 15 910 - 27 7 - Short 40 18 - 100 25 18 - 360 17 18 Floating Floating Adaptive Adaptive 0.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 FIGURE 4. BOOTSTRAP CAPACITANCE vs BOOT RIPPLE VOLTAGE Power Dissipation Power-On Reset (POR) Function VCC voltage level is monitored at all times. Once the VCC voltage exceeds 3.85V (typically), operation of the driver is enabled and the PWM input signal takes control of the gate drivers. If VCC drops below the falling threshold of 3.52V (typically), operation of the driver is disabled. Internal Bootstrap Device ISL6627 features an internal bootstrap schottky diode. Simply adding an external capacitor across the BOOT and PHASE pins completes the bootstrap circuit. The bootstrap function is also designed to prevent the bootstrap capacitor from overcharging due to the large negative swing at the trailing-edge of the PHASE node excursion. This reduces the potential for overstressing the upper driver. The bootstrap capacitor must have a voltage rating above the maximum VCC voltage. Its capacitance value can be estimated from Equation 1: Q GATE C BOOT_CAP ≥ --------------------------------ΔV BOOT_CAP (EQ. 1) 7 20nC ΔVBOOT_CAP (V) short Q G1 • VCC Q GATE = --------------------------- • N Q1 V GS1 0.2 Package power dissipation is mainly a function of the switching frequency (FSW), the output drive impedance, the layout resistance, the selected MOSFET’s internal gate resistance and its total gate charge (QG). Calculating the power dissipation in the driver for a desired application is critical to ensure safe operation. Exceeding the maximum allowable power dissipation level may push the IC beyond the maximum recommended operating junction temperature. The DFN package is more suitable for high frequency applications. See “Layout Considerations” on page 8 for thermal impedance improvement suggestions. The total driver power loss, essentially MOSFETs’ gate charge and driver internal circuitry losses, can be estimated using Equations 2 and 3, respectively. P Qg_TOT = P Qg_Q1 + P Qg_Q2 + I Q • VCC Q G1 • UVCC 2 P Qg_Q1 = ----------------------------------- • F SW • N Q1 V GS1 (EQ. 2) Q G2 • LVCC 2 P Qg_Q2 = ---------------------------------- • F SW • N Q2 V GS2 ⎛ Q G1 • UVCC • N Q1 Q G2 • LVCC • N Q2⎞ I DR = ⎜ ------------------------------------------------ + ------------------------------------------------⎟ • F SW + I Q V GS1 V GS2 ⎝ ⎠ (EQ. 3) where the gate charge (QG1 and QG2) is defined at a particular gate to source voltage (VGS1 and VGS2) in the corresponding MOSFET datasheet; IQ is the driver’s total quiescent current with no load at both drive outputs; NQ1 and NQ2 are number of upper and lower MOSFETs, respectively; UVCC and LVCC are the drive voltages for both upper and lower FETs, respectively. The IQ*VCC product is the bias power of the driver without a load. FN6992.0 September 22, 2011 ISL6627 Layout Considerations P DR = P DR_UP + P DR_LOW + I Q • VCC R LO1 R HI1 ⎛ ⎞ P Qg_Q1 P DR_UP = ⎜ ----------------------------------- + -------------------------------------⎟ • ------------------2 ⎝ R HI1 + R EXT1 R LO1 + R EXT1⎠ (EQ. 4) R HI2 R LO2 ⎛ ⎞ P Qg_Q2 P DR_LOW = ⎜ ----------------------------------- + -------------------------------------⎟ • ------------------R + R R + R 2 ⎝ HI2 EXT2 LO2 EXT2⎠ R GI1 R EXT1 = R G1 + -----------N Q1 • Keep decoupling circuit loops (VCC-GND and BOOT-PHASE) as short as possible. R GI2 R EXT2 = R G2 + -----------N Q2 The total gate drive power losses are dissipated among the resistive components along the transition path, as outlined in Equation 4. The drive resistance dissipates a portion of the total gate drive power losses, the rest will be dissipated by the external gate resistors (RG1 and RG2) and the internal gate resistors (RGI1 and RGI2) of MOSFETs. Figures 5 and 6 show the typical upper and lower gate drives turn-on current paths. BOOT VCC D CGD RHI1 RLO1 G RG1 CDS RGI1 CGS Q1 S PHASE FIGURE 5. TYPICAL UPPER-GATE DRIVE TURN-ON PATH VCC D CGD RHI2 RLO2 G RG2 CDS RGI2 CGS Q2 S FIGURE 6. TYPICAL LOWER-GATE DRIVE TURN-ON PATH Application Information MOSFET and Driver Selection The parasitic inductances of the PCB and of the power devices’ packaging (both upper and lower MOSFETs) can cause serious ringing, exceeding absolute maximum rating of the devices. The negative ringing at the edges of the PHASE node could increase the bootstrap capacitor voltage through the internal bootstrap diode, and in some cases, it may overstress the upper MOSFET driver. Careful layout, proper selection of MOSFETs and packaging, as well as the driver can minimize such unwanted stress. 8 A good layout helps reduce the ringing on the switching (PHASE) node and significantly lower the stress applied to the MOSFETs as well as the driver. The following advice is meant to lead to an optimized layout: • Minimize trace inductance, especially on low-impedance lines. All power traces (UGATE, PHASE, LGATE, GND, VCC) should be short and wide, as much as possible. • Minimize the inductance of the PHASE node. Ideally, the source of the upper and the drain of the lower MOSFET should be as close as thermally allowable. • Minimize the current loop of the output and input power trains. Short the source connection of the lower MOSFET to ground as close to the transistor pin as feasible. Input capacitors (especially ceramic decoupling) should be placed as close to the drain of upper and source of lower MOSFETs as possible. In addition, connecting the thermal pad of the DFN package to the power ground through one or several vias is recommended for high switching frequency, high current applications. This is to improve heat dissipation and allow the part to achieve its full thermal potential. Upper MOSFET Self Turn-On Effects at Startup Should the driver have insufficient bias voltage applied, its outputs are floating. If the input bus is energized at a high dV/dt rate while the driver outputs are floating, due to self-coupling via the internal CGD of the MOSFET, the gate of the upper MOSFET could momentarily rise up to a level greater than the threshold voltage of the device, potentially turning on the upper switch. Therefore, if such a situation could conceivably be encountered, it is a common practice to place a resistor (RUGPH) across the gate and source of the upper MOSFET to suppress the Miller coupling effect. The value of the resistor depends mainly on the input voltage’s rate of rise, the CGD/CGS ratio, as well as the gate-source threshold of the upper MOSFET. A higher dV/dt, a lower CGD/CGS ratio, and a lower gate-source threshold upper FET will require a smaller resistor to diminish the effect of the internal capacitive coupling. For most applications, the integrated 20kΩ resistor is sufficient, not measurably affecting normal performance and efficiency. The coupling effect can be roughly estimated with Equation 5, which assumes a fixed linear input ramp and neglects the clamping effect of the body diode of the upper drive and the bootstrap capacitor. Other parasitic components, such as lead inductances and PCB capacitances are also not taken into account. Figure 7 provides a visual reference for this phenomenon and its potential solution. –V DS ⎛ -------------------------------⎞ dV ⎜ -----⋅ R ⋅ C iss⎟ dV ⎟ V GS_MILLER = ------ ⋅ R ⋅ C rss ⎜ 1 – e dt ⎜ ⎟ dt ⎜ ⎟ ⎝ ⎠ R = R UGPH + R GI C rss = C GD (EQ. 5) C iss = C GD + C GS FN6992.0 September 22, 2011 ISL6627 General PowerPAD Design Considerations VCC BOOT VIN D CBOOT CGD DL G RUGPH ISL6627 DU UGATE CDS RGI CGS QUPPER S PHASE Figure 8 shows the recommended use of vias on the thermal pad to remove heat from the IC. This typical array populates the thermal pad footprint with vias spaced three times the radius distance from the center of each via. Small via size is advisable, but not to the extent that solder reflow becomes difficult. All vias should be connected to the pad potential, with low thermal resistance for efficient heat transfer. Complete connection of the plated-through hole to each plane is important. It is not recommended to use “thermal relief” patterns to connect the vias. FIGURE 7. GATE TO SOURCE RESISTOR TO REDUCE UPPER MOSFET MILLER COUPLING FIGURE 8. PCB VIA PATTERN 9 FN6992.0 September 22, 2011 ISL6627 Revision History The revision history provided is for informational purposes only and is believed to be accurate, but not warranted. Please go to web to make sure you have the latest Rev. DATE REVISION 9/22/11 FN6992.0 CHANGE Initial release. Products Intersil Corporation is a leader in the design and manufacture of high-performance analog semiconductors. The Company's products address some of the industry's fastest growing markets, such as, flat panel displays, cell phones, handheld products, and notebooks. Intersil's product families address power management and analog signal processing functions. Go to www.intersil.com/products for a complete list of Intersil product families. For a complete listing of Applications, Related Documentation and Related Parts, please see the respective device information page on intersil.com: ISL6627 To report errors or suggestions for this datasheet, please go to: www.intersil.com/askourstaff FITs are available from our website at: http://rel.intersil.com/reports/sear For additional products, see www.intersil.com/product_tree Intersil products are manufactured, assembled and tested utilizing ISO9000 quality systems as noted in the quality certifications found at www.intersil.com/design/quality Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software 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. 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 10 FN6992.0 September 22, 2011 ISL6627 Package Outline Drawing L10.3x3 10 LEAD DUAL FLAT PACKAGE (DFN) Rev 6, 09/09 3.00 6 PIN #1 INDEX AREA A B 1 6 PIN 1 INDEX AREA (4X) 3.00 2.00 8x 0.50 2 10 x 0.23 4 0.10 1.60 TOP VIEW 10x 0.35 BOTTOM VIEW 4 (4X) 0.10 M C A B 0.415 PACKAGE OUTLINE 0.200 0.23 0.35 (10 x 0.55) SEE DETAIL "X" (10x 0.23) 1.00 MAX 0.10 C BASE PLANE 2.00 0.20 C SEATING PLANE 0.08 C SIDE VIEW (8x 0.50) C 0.20 REF 5 1.60 0.05 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. Lead width applies to the metallized terminal and is measured between 0.18mm 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. 11 FN6992.0 September 22, 2011