LTC4442IMS8E-TRPBF

LTC4442/LTC4442-1 High Speed Synchronous N-Channel MOSFET Drivers FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTION The LTC®4442 is a high frequency gate driver designed to drive two N-channel MOSFETs in a synchronous buck DC/DC converter topology. The powerful driver capability reduces switching losses in MOSFETs with high gate capacitance. The LTC4442 features a separate supply for the input logic to match the signal swing of the controller IC. If the input signal is not being driven, the LTC4442 activates a shutdown mode that turns off both external MOSFETs. The input logic signal is internally level-shifted to the bootstrapped supply, which may function at up to 42V above ground. The LTC4442 contains undervoltage lockout circuits on both the driver and logic supplies that turn off the external MOSFETs when an undervoltage condition is present. The LTC4442 and LTC4442-1 have different undervoltage lockout thresholds to accommodate a wide variety of applications. An adaptive shoot-through protection feature is also built-in to prevent power loss resulting from MOSFET cross-conduction current. The LTC4442/LTC4442-1 are available in the thermally enhanced 8-lead MSOP package. , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Wide VCC Range: 6V to 9.5V 38V Maximum Input Supply Voltage Adaptive Shoot-Through Protection 2.4A Peak Pull-Up Current 5A Peak Pull-Down Current 8ns TG Fall Time Driving 3000pF Load 12ns TG Rise Time Driving 3000pF Load Separate Supply to Match PWM Controller Drives Dual N-Channel MOSFETs Undervoltage Lockout Thermally Enhanced MSOP Package APPLICATIONS ■ ■ Distributed Power Architectures High Density Power Modules TYPICAL APPLICATION Synchronous Buck Converter Driver VCC 6V BOOST LTC4442 VLOGIC VCC PWM IN GND 4442 TA01a LTC4442 Driving 3000pF Capacitive Loads VIN 32V INPUT (IN) 5V/DIV TG TS BG VOUT BOTTOM GATE (BG) 5V/DIV TOP GATE (TG-TS) 5V/DIV 10ns/DIV 4442 TA01b 4442fa 1 LTC4442/LTC4442-1 ABSOLUTE MAXIMUM RATINGS (Note 1) PIN CONFIGURATION TOP VIEW TG TS BG GND 1 2 3 4 8 7 6 5 BOOST VCC VLOGIC IN 9 Supply Voltage VCC......................................................... –0.3V to 10V VLOGIC .................................................... –0.3V to 10V BOOST – TS ........................................... –0.3V to 10V IN Voltage .................................................. –0.3V to 10V BOOST Voltage .......................................... –0.3V to 42V TS Voltage..................................................... –5V to 38V TS + VCC ...................................................................42V Driver Output TG (with Respect to TS)....... –0.3V to 10V Driver Output BG........................................ –0.3V to 10V Operating Temperature Range (Note 2) ... –40°C to 85°C Junction Temperature (Note 3) ............................. 125°C Storage Temperature Range................... –65°C to 150°C Lead Temperature (Soldering, 10 sec) .................. 300°C MS8E PACKAGE 8-LEAD PLASTIC MSOP TJMAX = 125°C, θJA = 160°C/W EXPOSED PAD (PIN #) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH LTC4442EMS8E#PBF LTC4442IMS8E#PBF LTC4442EMS8E-1#PBF LTC4442IMS8E-1#PBF TAPE AND REEL LTC4442EMS8E#TRPBF LTC4442IMS8E#TRPBF PART MARKING* LTCTJ LTCTJ PACKAGE DESCRIPTION 8-Lead Plastic MSOP 8-Lead Plastic MSOP 8-Lead Plastic MSOP 8-Lead Plastic MSOP TEMPERATURE RANGE –40°C to 85°C –40°C to 85°C –40°C to 85°C –40°C to 85°C LTC4442EMS8E-1#TRPBF LTCXR LTC4442IMS8E-1#TRPBF LTCXR Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ ELECTRICAL CHARACTERISTICS SYMBOL VLOGIC IVLOGIC UVLO PARAMETER Operating Range DC Supply Current Undervoltage Lockout Threshold Logic Supply (VLOGIC) The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = VBOOST = 7V, VTS = GND = 0V, VLOGIC = 5V, unless otherwise noted. CONDITIONS MIN 3 IN = Floating VLOGIC Rising VLOGIC Falling Hysteresis ● ● TYP MAX 9.5 UNITS V μA V V mV V μA 730 2.5 2.4 2.75 2.65 100 850 3.0 2.9 Gate Driver Supply (VCC) VCC IVCC Operating Range DC Supply Current IN = Floating 6 300 9.5 380 4442fa 2 LTC4442/LTC4442-1 ELECTRICAL CHARACTERISTICS SYMBOL UVLO PARAMETER Undervoltage Lockout Threshold The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = VBOOST = 7V, VTS = GND = 0V, VLOGIC = 5V, unless otherwise noted. CONDITIONS VCC Rising (LTC4442) VCC Falling (LTC4442) Hysteresis (LTC4442) VCC Rising (LTC4442-1) VCC Falling (LTC4442-1) Hysteresis (LTC4442-1) ● ● ● ● MIN 2.75 2.60 5.6 4.7 TYP 3.20 3.04 160 6.2 5.3 850 325 MAX 3.65 3.50 6.7 5.8 UNITS V V mV V V mV μA V V V V Bootstrapped Supply (BOOST – TS) IBOOST Input Signal (IN) VIH(TG) VIL(TG) VIH(BG) VIL(BG) IIN(SD) TG Turn-On Input Threshold TG Turn-Off Input Threshold BG Turn-On Input Threshold BG Turn-Off Input Theshold Maximum Current Into or Out of IN in Shutdown Mode TG High Output Voltage TG Low Output Voltage TG Peak Pull-Up Current TG Peak Pull-Down Current BG High Output Voltage BG Low Output Voltage BG Peak Pull-Up Current BG Peak Pull-Down Current BG Low to TG High Propagation Delay IN Low to TG Low Propagation Delay TG Low to BG High Propagation Delay IN High to BG Low Propagation Delay TG Output Rise Time TG Output Fall Time BG Output Rise Time BG Output Fall Time 10% – 90%, CL = 3nF 10% – 90%, CL = 3nF 10% – 90%, CL = 3nF 10% – 90%, CL = 3nF IBG = –10mA, VOH(BG) = VCC – VBG IBG = 100mA ● ● DC Supply Current IN = Floating VLOGIC ≥ 5V, IN Rising VLOGIC = 3.3V, IN Rising VLOGIC ≥ 5V, IN Falling VLOGIC = 3.3V, IN Falling VLOGIC ≥ 5V, IN Falling VLOGIC = 3.3V, IN Falling VLOGIC ≥ 5V, IN Rising VLOGIC = 3.3V, IN Rising VLOGIC ≥ 5V, IN Floating VLOGIC = 3.3V, IN Floating ITG = –10mA, VOH(TG) = VBOOST – VTG ITG = 100mA, VOL(TG) = VTG – VTS ● ● ● ● ● ● 400 4.0 2.6 3.0 1.9 3.5 2.2 3.25 2.09 0.8 0.8 1.25 1.10 1.50 1.21 1.6 1.4 V V V V μA μA V mV A A V mV A A ns ns ns ns ns ns ns ns 200 100 300 150 0.7 100 High Side Gate Driver Output (TG) VOH(TG) VOL(TG) IPU(TG) IPD(TG) VOH(BG) VOL(BG) IPU(BG) IPD(BG) Switching Time tPLH(TG) tPHL(TG) tPLH(BG) tPHL(BG) tr(TG) tf(TG) tr(BG) tr(BG) 20 12 20 12 12 8 12 5 1.5 1.5 2.4 2.4 0.7 100 Low Side Gate Driver Output (BG) 1.4 3.5 2.4 5.0 Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LTC4442I/LTC4442I-1 are guaranteed to meet specifications from –40°C to 85°C. The LTC4442E/LTC4442E-1 are guaranteed to meet specifications from 0°C to 85°C with specifications over the –40°C to 85°C operating temperature range assured by design, characterization and correlation with statistical process controls. TJ is calculated from the ambient temperature TA and power dissipation PD according to the following formula: TJ = TA + (PD • θJA°C/W) Note 3: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 125°C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature may impair device reliability. 4442fa 3 LTC4442/LTC4442-1 TYPICAL PERFORMANCE CHARACTERISTICS Input Thresholds vs VLOGIC Supply Voltage 5 3.0 2.5 INPUT THRESHOLD (V) 2.0 1.5 1.0 VIH(BG) 0.5 0 –40 Input Thresholds for VLOGIC = 3.3V vs Temperature VLOGIC = 3.3V VIH(TG) VIL(TG) INPUT THRESHOLD (V) 5 Input Thresholds for VLOGIC ≥ 5V vs Temperature VLOGIC ≥ 5V VIH(TG) VIL(TG) 4 INPUT THRESHOLD (V) VIH(TG) VIL(TG) 4 3 3 2 VIL(BG) VIL(BG) VIH(BG) 2 VIL(BG) VIH(BG) 1 1 0 3 4 7 6 5 8 VLOGIC SUPPLY (V ) 9 10 4442 G01 –10 20 50 80 TEMPERATURE (°C) 110 4442 G02 0 –40 –10 20 80 50 TEMPERATURE (°C) 110 4442 G03 BG or TG Input Threshold Hysteresis vs VLOGIC Supply Voltage BG OR TG INPUT THRESHOLD HYSTERESIS (V) BG OR TG INPUT THRESHOLD HYSTERSIS (V) 0.5 0.40 0.35 BG or TG Input Threshold Hysteresis vs Temperature 1.0 0.9 0.8 SUPPLY CURRENT (mA) 0.30 VLOGIC = 5V 0.25 0.20 0.15 0.10 0.05 0 –40 –10 20 50 80 TEMPERATURE (°C) 110 4442 G05 Quiescent Supply Current vs Supply Voltage IN FLOATING IVLOGIC 0.4 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 3 4 7 6 5 8 SUPPLY VOLTAGE (V) 9 10 4442 G06 0.3 0.2 VLOGIC = 3.3V IVCC IBOOST 0.1 0 3 4 7 6 5 8 VLOGIC SUPPLY (V) 9 10 4442 G04 Quiescent Supply Current vs Temperature 1.0 IN FLOATING 0.9 VLOGIC = 5V V = BOOST-TS = 7V 0.8 CC SUPPLY CURRENT (mA) 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 –40 –10 20 80 50 TEMPERATURE (°C) 110 4442 G07 VLOGIC Undervoltage Lockout Thresholds vs Temperature 3.0 7.0 6.5 VLOGIC UVLO THRESHOLD (V) VCC UVLO THRESHOLD (V) VCC Undervoltage Lockout Thresholds vs Temperature LTC4442-1 RISING THRESHOLD LTC4442-1 FALLING THRESHOLD IVLOGIC 2.9 RISING THRESHOLD 2.8 FALLING THRESHOLD 2.7 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 IBOOST IVCC LTC4442 RISING THRESHOLD LTC4442 FALLING THRESHOLD 2.6 2.5 –40 –10 20 80 50 TEMPERATURE (°C) 110 4442 G08 2.0 –40 –10 20 80 50 TEMPERATURE (°C) 110 4442 G09 4442fa 4 LTC4442/LTC4442-1 TYPICAL PERFORMANCE CHARACTERISTICS Undervoltage Lockout Threshold Hysteresis vs Temperature 1000 UVLO THRESHOLD HYSTERESIS (mV) 900 800 700 600 500 400 300 200 100 0 –40 –10 LTC4442 VCC UVLO VLOGIC UVLO 20 80 50 TEMPERATURE (°C) 110 4442 G10 Switching Supply Current vs Input Frequency 4 NO LOAD VLOGIC = 5V VCC = BOOST-TS = 7V IVCC 2 IBOOST 1 IVLOGIC SUPPLY CURRENT (mA) 100 Switching Supply Current vs Load Capacitance VLOGIC = 5V VCC = BOOST-TS = 7V ICC OR IBOOST fIN = 500kHz LTC4442-1 VCC UVLO SUPPLY CURRENT (mA) 3 10 ICC OR IBOOST fIN = 100kHz 1 ILOGIC fIN = 500kHz 0 0.1 0.3 1 10 3 LOAD CAPACITANCE (nF) 30 4442 G12 0 0 200k 600k 400k FREQUENCY (Hz) 800k 1M 4442 G11 Propagation Delay vs VLOGIC Supply Voltage 40 35 30 PROPAGATION DELAY (ns) 25 20 15 10 5 0 3 4 7 8 9 6 VLOGIC SUPPLY VOLTAGE (V) 5 10 4442 G13 Propagation Delay vs VCC Supply Voltage 40 NO LOAD VLOGIC = 5V BOOST-TS = VCC tPLH(TG) tPLH(BG) tPHL(TG) tPHL(BG) 35 PROPAGATION DELAY (ns) 30 Propagation Delay vs Temperature NO LOAD VLOGIC = 5V VCC = BOOST-TS = 7V tPLH(TG) 25 tPLH(BG) 20 15 10 5 tPHL(BG) tPHL(TG) NO LOAD 35 VCC = BOOST-TS = 7V PROPAGATION DELAY (ns) 30 25 20 tPHL(TG) 15 10 5 0 tPHL(BG) tPLH(TG) tPLH(BG) 4 5 8 7 9 6 VCC SUPPLY VOLTAGE (V) 10 4442 G14 0 –40 –10 20 50 80 TEMPERATURE (°C) 110 4442 G15 Output High Voltage vs VCC Supply Voltage 10 BG OR TG HIGH OUTPUT VOLTAGE (V) 9 8 7 6 5 4 3 2 1 0 4 5 7 8 9 6 VCC SUPPLY VOLTAGE (V) 10 4442 G16 Rise and Fall Time vs VCC Supply Voltage 20 100 CLOAD = 3.3nF BOOST-TS = VCC RISE/FALL TIME (ns) Rise and Fall Time vs Load Capacitance VCC = BOOST-TS = 7V tr(BG) tr(TG) BOOST-TS = VCC –10mA –1mA –100mA RISE/FALL TIME (ns) 15 tr(BG) 10 tr(TG) tf(TG) 5 tf(BG) 10 tf(TG) tf(BG) 0 4 5 8 9 6 7 VCC SUPPLY VOLTAGE (V) 10 4442 G17 1 1 10 3 LOAD CAPACITANCE (nF) 30 4442 G18 4442fa 5 LTC4442/LTC4442-1 PIN FUNCTIONS TG (Pin 1): High Side Gate Driver Output (Top Gate). This pin swings between TS and BOOST. TS (Pin 2): High Side MOSFET Source Connection (Top Source). BG (Pin 3): Low Side Gate Driver Output (Bottom Gate). This pin swings between VCC and GND. GND (Pin 4): Chip Ground. IN (Pin 5): Input Signal. Input referenced to an internal supply powered by VLOGIC (Pin 6) and referenced to GND (Pin 4). If this pin is floating, an internal resistive divider triggers a shutdown mode in which both BG (Pin 3) and TG (Pin 1) are pulled low. Trace capacitance on this pin should be minimized to keep the shutdown time low. VLOGIC (Pin 6): Logic Supply. This pin powers the input buffer and logic. Connect this pin to the power supply of the controller that is driving IN (Pin 5) to match input thresholds or to VCC (Pin 7) to simplify PCB routing. VCC (Pin 7): Output Driver Supply. This pin powers the low side gate driver output directly and the high side gate driver output through an external diode connected between this pin and BOOST (Pin 8). A low ESR ceramic bypass capacitor should be tied between this pin and GND (Pin 4). BOOST (Pin 8): High Side Bootstrapped Supply. An external capacitor should be tied between this pin and TS (Pin 2). Normally, a bootstrap diode is connected between VCC (Pin 7) and this pin. Voltage swing at this pin is from VCC – VD to VIN + VCC – VD, where VD is the forward voltage drop of the bootstrap diode. Exposed Pad (Pin 9): Ground. Must be electrically connected to GND (Pin 4) and soldered to PCB ground for optimal thermal performance. BLOCK DIAGRAM 7 VCC UNDERVOLTAGE LOCKOUT BOOST VLOGIC LEVEL SHIFTER TG TS INTERNAL SUPPLY 8 1 2 6 UNDERVOLTAGE LOCKOUT SHOOTTHROUGH PROTECTION VCC THREE-STATE INPUT BUFFER BG 3 7k IN 7k 4 GND 5 9 GND 4442 BD 4442fa 6 LTC4442/LTC4442-1 TIMING DIAGRAM IN VIL(TG) VIL(BG) TG 90% 10% BG 90% 10% tr(TG) tpLH(TG) tf(BG) tpHL(BG) tf(TG) tpHL(TG) tr(BG) tpLH(BG) 4442 TD OPERATION Overview The LTC4442 receives a ground-referenced, low voltage digital input signal to drive two N-channel power MOSFETs in a synchronous buck power supply configuration. The gate of the low side MOSFET is driven either to VCC or GND, depending on the state of the input. Similarly, the gate of the high side MOSFET is driven to either BOOST or TS by a supply bootstrapped off of the switch node (TS). Input Stage The LTC4442 employs a unique three-state input stage with transition thresholds that are proportional to the VLOGIC supply. The VLOGIC supply can be tied to the controller IC’s power supply so that the input thresholds will match those of the controller’s output signal. Alternatively, VLOGIC can be tied to VCC to simplify routing. An internal voltage regulator in the LTC4442 limits the input threshold values for VLOGIC supply voltages greater than 5V. The relationship between the transition thresholds and the three input states of the LTC4442 is illustrated in Figure 1. When the voltage on IN is greater than the threshold VIH(TG), TG is pulled up to BOOST, turning the high side MOSFET on. This MOSFET will stay on until IN falls below VIL(TG). Similarly, when IN is less than VIH(BG), BG is pulled up to VCC, turning the low side (synchronous) MOSFET on. BG will stay high until IN increases above the threshold VIL(BG). VIH(TG) TG HIGH TG LOW TG HIGH TG LOW IN VIL(TG) VIL(BG) BG LOW BG HIGH BG LOW BG HIGH VIH(BG) 4442 F01 Figure 1. Three-State Input Operation The thresholds are positioned to allow for a region in which both BG and TG are low. An internal resistive divider will pull IN into this region if the signal driving the IN pin goes into a high impedance state. One application of this three-state input is to keep both of the power MOSFETs off while an undervoltage condition exists on the controller IC power supply. This can be accomplished by driving the IN pin with a logic buffer that has an enable pin. With the enable pin of the buffer tied to the power good pin of the controller IC, the logic buffer output will remain in a high impedance state until the controller confirms that its supply is not in an undervoltage state. The three-state input of the LTC4442 will therefore pull IN into the region where TG and BG are low until the controller has enough voltage to operate predictably. 4442fa 7 LTC4442/LTC4442-1 OPERATION The hysteresis between the corresponding VIH and VIL voltage levels eliminates false triggering due to noise during switch transitions; however, care should be taken to keep noise from coupling into the IN pin, particularly in high frequency, high voltage applications. Undervoltage Lockout The LTC4442 contains undervoltage lockout detectors that monitor both the VCC and VLOGIC supplies. When VCC falls below 3.04V or VLOGIC falls below 2.65V, the output pins BG and TG are pulled to GND and TS, respectively. This turns off both of the external MOSFETs. When VCC and VLOGIC have adequate supply voltage for the LTC4442 to operate reliably, normal operation will resume. Adaptive Shoot-Through Protection Internal adaptive shoot-through protection circuitry monitors the voltages on the external MOSFETs to ensure that they do not conduct simultaneously. The LTC4442 does not allow the bottom MOSFET to turn on until the gate-source voltage on the top MOSFET is sufficiently low, and vice-versa. This feature improves efficiency by eliminating cross-conduction current from flowing from the VIN supply through the MOSFETs to ground during a switch transition. Output Stage A simplified version of the LTC4442’s output stage is shown in Figure 2. The pull-up device on both the BG and TG outputs is an NPN bipolar junction transistor (Q1 and Q2). The BG and TG outputs are pulled up to within an NPN VBE (~0.7V) of their positive rails (VCC and BOOST, respectively). Both BG and TG have N-channel MOSFET pulldown devices (N1 and N2) which pull BG and TG down to their negative rails, GND and TS. An additional NPN bipolar junction transistor (Q3) is present on BG to increase its pull-down drive current capacity. The large voltage swing of the BG and TG output pins is important in driving external power MOSFETs, whose RDS(ON) is inversely proportional to its gate overdrive voltage (VGS – VTH). 8 LTC4442 BOOST Q1 TG N1 TS 2 1 CGS CGD HIGH SIDE POWER MOSFET LOAD INDUCTOR VIN UP TO 38V VCC Q2 BG Q3 N2 GND 7 CGD 3 CGS 4 LOW SIDE POWER MOSFET 4442 F02 Figure 2. Capacitance Seen by BG and TG During Switching Rise/Fall Time Since the power MOSFET generally accounts for the majority of power loss in a converter, it is important to quickly turn it on and off, thereby minimizing the transition time and power loss. The LTC4442’s peak pull-up current of 2.4A for both BG and TG (Q1 and Q2) produces a rapid turn-on transition for the MOSFETs. This high current is capable of driving a 3nF load with a 12ns rise time. It is also important to turn the power MOSFETs off quickly to minimize power loss due to transition time; however, an additional benefit of a strong pull-down on the driver outputs is the prevention of cross-conduction current. For example, when BG turns the low-side power MOSFET off and TG turns the high-side power MOSFET on, the voltage on the TS pin will rise to VIN very rapidly. This high frequency positive voltage transient will couple through the CGD capacitance of the low side power MOSFET to the BG pin. If the BG pin is not held down sufficiently, the voltage on the BG pin will rise above the threshold voltage of the low side power MOSFET, momentarily turning it back on. As a result, both the high side and low side MOSFETs will be conducting, which will cause significant cross-conduction current to flow through the MOSFETs from VIN to ground, thereby introducing substantial power loss. A similar effect occurs on TG due to the CGS and CGD capacitances of the high side MOSFET. 4442fa 8 LTC4442/LTC4442-1 OPERATION The LTC4442’s powerful parallel combination of the N-channel MOSFET (N2) and NPN (Q3) on the BG pull-down generates a phenomenal 5ns fall time on BG while driving a 3nF load. Similarly, the 1Ω pull-down MOSFET (N1) on TG results in a rapid 8ns fall time with a 3nF load. These powerful pull-down devices minimize the power loss associated with MOSFET turn-off time and cross-conduction current. APPLICATIONS INFORMATION Power Dissipation To ensure proper operation and long-term reliability, the LTC4442 must not operate beyond its maximum temperature rating. Package junction temperature can be calculated by: TJ = TA + (PD)(θJA) where: TJ = Junction temperature TA = Ambient temperature PD = Power dissipation θJA = Junction-to-ambient thermal resistance Power dissipation consists of standby, switching and capacitive load power losses: PD = PDC + PAC + PQG where: PDC = Quiescent power loss PAC = Internal switching loss at input frequency fIN PQG = Loss due turning on and off the external MOSFET with gate charge QG at frequency fIN The LTC4442 consumes very little quiescent current. The DC power loss at VLOGIC = 5V and VCC = VBOOST − TS = 7V is only (730μA)(5V) + (625μA)(7V) = 8mW. At a particular switching frequency, the internal power loss increases due to both AC currents required to charge and discharge internal nodal capacitances and cross-conduction currents in the internal logic gates. The sum of the quiescent current and internal switching current with no load are shown in the Typical Performance Characteristics plot of Switching Supply Current vs Input Frequency. The gate charge losses are primarily due to the large AC currents required to charge and discharge the capacitance of the external MOSFETs during switching. For identical pure capacitive loads CLOAD on TG and BG at switching frequency fin, the load losses would be: PCLOAD = (CLOAD)(fIN)[(VBOOST – TS)2 + (VCC)2] In a typical synchronous buck configuration, VBOOST – TS is equal to VCC – VD, where VD is the forward voltage drop across the diode between VCC and BOOST. If this drop is small relative to VCC, the load losses can be approximated as: PCLOAD ≈ 2(CLOAD)(fIN)(VCC)2 Unlike a pure capacitive load, a power MOSFET’s gate capacitance seen by the driver output varies with its VGS voltage level during switching. A MOSFET’s capacitive load power dissipation can be calculated using its gate charge, QG. The QG value corresponding to the MOSFET’s VGS value (VCC in this case) can be readily obtained from the manufacturer’s QG vs VGS curves. For identical MOSFETs on TG and BG: PQG ≈ 2(VCC)(QG)(fIN) To avoid damaging junction temperatures due to power dissipation, the LTC4442 includes a temperature monitor that will pull BG and TG low if the junction temperature exceeds 160°C. Normal operation will resume when the junction temperature cools to less than 135°C. Bypassing and Grounding The LTC4442 requires proper bypassing on the VLOGIC, VCC and VBOOST – TS supplies due to its high speed switching (nanoseconds) and large AC currents (Amperes). Careless component placement and PCB trace routing may cause excessive ringing and undershoot/overshoot. 4442fa 9 LTC4442/LTC4442-1 APPLICATIONS INFORMATION To obtain the optimum performance from the LTC4442: A. Mount the bypass capacitors as close as possible between the VLOGIC and GND pins, the VCC and GND pins, and the BOOST and TS pins. The leads should be shortened as much as possible to reduce lead inductance. B. Use a low inductance, low impedance ground plane to reduce any ground drop and stray capacitance. Remember that the LTC4442 switches greater than 5A peak currents and any significant ground drop will degrade signal integrity. C. Plan the power/ground routing carefully. Know where the large load switching current is coming from and going to. Maintain separate ground return paths for the input pin and the output power stage. D. Keep the copper traces between the driver output pins and the load short and wide. E. Be sure to solder the Exposed Pad on the back side of the LTC4442 packages to the board. Correctly soldered to a 2500mm2 double-sided 1oz copper board, the LTC4442 has a thermal resistance of approximately 40°C/W. Failure to make good thermal contact between the exposed back side and the copper board will result in thermal resistances far greater. TYPICAL APPLICATION LTC7510/LTC4442-1 12V to 1.5V/30A Digital Step-Down DC/DC Converter with PMBus Serial Interface 7V VDRIVE 12V 5V SDATA PMBus INTERFACE SCLK SMB_AL_N LTC7510 POWER MANAGEMENT INTERFACE PWRGD OUTEN GND PWM MULTIPHASE INTERFACE SYNC_IN SYNC_OUT TEMPSEN LOAD FAULT OUTPUTS FAULT1 FAULT2 ISENN ISENP VSENP VSENN I-SHARE IOUT/ISH ISH_GND SADDR 1k VSET 1k FSET 1k RESET_N VTRIM 1k IMAXSET 1k RTN 4442 TA02 R1 V12SEN VCC VD33 VD25 C2 D2 CMDSH3 C5 0.22μF + C1 C3 R2 C4 BOOST TG VLOGIC LTC4442-1 VCC TS IN 1μF GND BG M1 RJK0305 ×2 M2 RJK0301 ×2 L1 0.3μH R3 C6 VOUT + 330μF ×6 RCM D1 RSENSE 4442fa 10 LTC4442/LTC4442-1 PACKAGE DESCRIPTION MS8E Package 8-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1662 Rev D) BOTTOM VIEW OF EXPOSED PAD OPTION 1 2.06 ± 0.102 (.081 ± .004) 1.83 ± 0.102 (.072 ± .004) 2.794 ± 0.102 (.110 ± .004) 0.889 ± 0.127 (.035 ± .005) 5.23 (.206) MIN 2.083 ± 0.102 3.20 – 3.45 (.082 ± .004) (.126 – .136) 8 0.42 ± 0.038 (.0165 ± .0015) TYP 0.65 (.0256) BSC 3.00 ± 0.102 (.118 ± .004) (NOTE 3) 8 7 65 0.52 (.0205) REF RECOMMENDED SOLDER PAD LAYOUT DETAIL “A” 0° – 6° TYP 4.90 ± 0.152 (.193 ± .006) 3.00 ± 0.102 (.118 ± .004) (NOTE 4) 0.254 (.010) GAUGE PLANE 1 0.53 ± 0.152 (.021 ± .006) DETAIL “A” 0.18 (.007) SEATING PLANE 0.22 – 0.38 (.009 – .015) TYP 1.10 (.043) MAX 23 4 0.86 (.034) REF NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX 0.65 (.0256) BSC 0.1016 ± 0.0508 (.004 ± .002) MSOP (MS8E) 0307 REV D 4442fa Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 11 LTC4442/LTC4442-1 RELATED PARTS PART NUMBER LTC1154 LTC1155 LT®1161 LTC1163 LTC1693 LTC3900 LTC3901 LTC4440 LTC4441 LTC7510 DESCRIPTION High Side Micropower MOSFET Driver Dual Micropower High/Low Side Driver Quad Protected High Side MOSFET Driver Triple 1.8V to 6V High Side MOSFET Driver High Speed Single/Dual N-Channel MOSFET Driver Synchronous Rectifier Driver for Forward Converter Secondary Side Synchronous Driver for Push-Pull and Full-Bridge Converter High Speed, High Voltage, High Side Gate Driver 6A MOSFET Driver Digital DC/DC Controller with PMBus Interface COMMENTS Internal Charge Pump, 4.5V to 18V Supply Range Internal Charge Pump, 4.5V to 18V Supply Range 8V to 48V Supply Range, tON = 200μs, tOFF = 28μs 1.8V to 6V Supply Range, tON = 95μs, tOFF = 45μs CMOS Compatible Input, VCC Range: 4.5V to 13.2V Pulse Transformer Synchronization Input Gate Drive Transformer Synchronous Input Wide Operating VIN Range: Up to 80V DC, 100V Transient Adjustable Gate Drive from 5V to 8V, 5V ≤ VIN ≤ 28V Digital Controller, PMBus Serial Interface, 150kHz to 2MHz Switching Frequency 4442fa 12 Linear Technology Corporation (408) 432-1900 ● FAX: (408) 434-0507 ● LT 0108 REV A • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 www.linear.com © LINEAR TECHNOLOGY CORPORATION 2007