LTC4447 High Speed Synchronous N-Channel MOSFET Driver FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTION Integrated Schottky Diode 4V to 6.5V VCC Operating Voltage 38V Maximum Input Supply Voltage Adaptive Shoot-Through Protection Rail-to-Rail Output Drivers 3.2A Peak Pull-Up Current 4.5A Peak Pull-Down Current 8ns TG Risetime Driving 3000pF Load 7ns TG Falltime Driving 3000pF Load Separate Supply to Match PWM Controller Drives Dual N-Channel MOSFETs Undervoltage Lockout Low Profile (0.75mm) 3mm × 3mm DFN Package APPLICATIONS ■ ■ Distributed Power Architectures High Density Power Modules , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. The LTC®4447 is a high frequency gate driver with integrated bootstrap Schottky diode that is designed to drive two N-Channel MOSFETs in a synchronous DC/DC converter. The powerful rail-to-rail driver capability reduces switching losses in MOSFETs with high gate capacitance. The LTC4447 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 LTC4447 activates a shutdown mode that turns off both external MOSFETs. The input logic signal is internally level-shifted to the bootstrapped supply, which functions at up to 42V above ground. The Schottky diode required for the bootstrapped supply is integrated to simplify layout and reduce parts count. The LTC4447 contains undervoltage lockout circuits on both the driver and logic supplies that turn off the external MOSFETs when an undervoltage condition is present. An adaptive shoot-through protection feature is also built-in to prevent the power loss resulting from MOSFET crossconduction current. The LTC4447 is available in the 3mm × 3mm DFN package. TYPICAL APPLICATION Synchronous Buck Converter Driver LTC4447 Driving 3000pF Capacitive Loads VCC 4V TO 6.5V VCC BOOST VLOGIC LTC4447 IN GND TOP GATE (TG - TS) 5V/DIV TG TS PWM INPUT (IN) 5V/DIV VIN TO 38V VOUT BOTTOM GATE (BG) 5V/DIV BG 4447 TA01a 10ns/DIV 4447 TA01b 4447f 1 LTC4447 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) Supply Voltage VLOGIC ...................................................... –0.3V to 7V VCC........................................................... –0.3V to 7V BOOST – TS ............................................. –0.3V to 7V BOOST Voltage .......................................... –0.3V to 42V BOOST – VCC ............................................................38V TS + VCC....................................................................42V IN Voltage .................................................... –0.3V to 7V Driver Output TG (with Respect to TS)......... –0.3V to 7V Driver Output BG.......................................... –0.3V to 7V Operating Temperature Range (Note 2).... –40°C to 85°C Junction Temperature (Note 3) ............................. 125°C Storage Temperature Range................... –65°C to 150°C TOP VIEW NC NC TG TS BG GND 12 BOOST 11 BOOST 10 BOOST 9 VCC 8 VLOGIC 7 IN 1 2 3 13 4 5 6 DDMA PACKAGE 12-LEAD (3mm ´ 3mm) PLASTIC DFN θJA = 43°C/W, θJC = 3°C/W EXPOSED PAD (PIN 13) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC4447EDD#PBF LTC4447EDD#TRPBF LDHD 12-Lead (3mm × 3mm) Plastic DFN –40°C to 85°C LTC4447IDD#PBF LTC4447IDD#TRPBF LDHD 12-Lead (3mm × 3mm) Plastic DFN –40°C to 85°C Consult LTC Marketing for parts specified with wider operating temperature ranges. *Temperature grades are identified by a label on the shipping container. Consult LTC Marketing for information on 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 The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = VLOGIC = 5V, VTS = GND = 0V, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Logic Supply (VLOGIC) VLOGIC Operating Range 3 IVLOGIC DC Supply Current IN = Floating UVLO Undervoltage Lockout Threshold VLOGIC Rising VLOGIC Falling Hysteresis ● ● 2.5 2.4 6.5 V 730 900 μA 2.75 2.65 100 3 2.9 V V mV 6.5 V 600 800 μA 3.20 3.04 160 3.65 3.50 V V mV Gate Driver Supply (VCC) VCC Operating Range 4 IVCC DC Supply Current IN = Floating UVLO Undervoltage Lockout Threshold VCC Rising VCC Falling Hysteresis VD Schottky Diode Forward Voltage ID = 10mA ID = 100mA ● ● 2.75 2.60 0.38 0.48 V V 4447f 2 LTC4447 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = VLOGIC = 5V, VTS = GND = 0V, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX VIH(TG) TG Turn-On Input Threshold VLOGIC ≥ 5V, IN Rising VLOGIC = 3.3V, IN Rising VIL(TG) TG Turn-Off Input Threshold VIH(BG) UNITS ● ● 3 1.9 3.5 2.2 4 2.6 V V VLOGIC ≥ 5V, IN Falling VLOGIC = 3.3V, IN Falling ● ● 2.75 1.8 3.25 2.09 3.75 2.5 V V BG Turn-On Input Threshold VLOGIC ≥ 5V, IN Falling VLOGIC = 3.3V, IN Falling ● ● 0.8 0.8 1.25 1.1 1.6 1.4 V V VIL(BG) BG Turn-Off Input Theshold VLOGIC ≥ 5V, IN Rising VLOGIC = 3.3V, IN Rising ● ● 1.05 0.9 1.5 1.21 1.85 1.5 V V IIN(SD) Maximum Current Into or Out of IN in Shutdown Mode VLOGIC ≥ 5V, IN Floating VLOGIC = 3.3V, IN Floating 150 75 300 150 Input Signal (IN) μA μA High Side Gate Driver Output (TG) VOH(TG) TG High Output Voltage ITG = –100mA, VOH(TG) = VBOOST – V TG 140 mV VOL(TG) TG Low Output Voltage ITG = 100mA, VOL(TG) = V TG – V TS 80 mV IPU(TG) TG Peak Pull-Up Current ● 2 3.2 A IPD(TG) TG Peak Pull-Down Current ● 1.5 2.4 A Low Side Gate Driver Output (BG) VOH(BG) BG High Output Voltage IBG = –100mA, VOH(BG) = VCC – VBG 100 mV VOL(BG) BG Low Output Voltage IBG = 100mA 100 mV IPU(BG) BG Peak Pull-Up Current ● 2 3.2 A IPD(BG) BG Peak Pull-Down Current ● 3 4.5 A Switching Time tPLH(TG) BG Low to TG High Propagation Delay 14 ns tPHL(TG) IN Low toTG Low Propagation Delay 13 ns tPLH(BG) TG Low to BG High Propagation Delay 13 ns tPHL(BG) IN High to BG Low Propagation Delay 11 ns tr(TG) TG Output Risetime 10% to 90%, CL = 3nF 8 ns t f(TG) TG Output Falltime 10% to 90%, CL = 3nF 7 ns tr(BG) BG Output Risetime 10% to 90%, CL = 3nF 7 ns t f(BG) BG Output Falltime 10% to 90%, CL = 3nF 4 ns 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 LTC4447I is guaranteed to meet specifications from –40°C to 85°C. The LTC4447E is guaranteed to meet specifications from 0°C to 85°C with specifications over the –40°C to 85°C 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 • 43°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. 4447f 3 LTC4447 TYPICAL PERFORMANCE CHARACTERISTICS Input Thresholds vs VLOGIC Supply Voltage Input Thresholds for VLOGIC ≥ 5V vs Temperature Input Thresholds for VLOGIC = 3.3V vs Temperature 4.0 3.0 VIH(TG) 5 VLOGIC = 3.3V VLOGIC ≥ 5V 2.5 2.0 VIL(BG) 1.5 VIH(BG) 1.0 2.0 VIL(TG) 1.5 VIL(BG) 1.0 3.5 4.0 4.5 5.0 5.5 VLOGIC SUPPLY (V) 6.0 0.5 –40 6.5 –10 20 50 80 TEMPERATURE (°C) 0.25 0.20 0.15 0.10 0.05 0 3.0 3.5 4.0 4.5 5.0 5.5 VLOGIC SUPPLY (V) 6.0 6.5 0.35 IN FLOATING 0.9 TS = GND VLOGIC = 5V 0.25 0.20 0.15 VLOGIC = 3.3V 0.10 VCC UVLO THRESHOLD (V) VLOGIC UVLO THRESHOLD (V) 2.5 –40 –10 20 80 50 TEMPERATURE (°C) 0.7 0.6 110 4447 G08 IVCC 0.5 0.4 0.3 0.2 0.05 0.1 0 –40 –10 20 50 80 TEMPERATURE (°C) 0 110 3.0 3.5 4.0 4.5 5.0 5.5 6.0 SUPPLY VOLTAGE (V) 7.0 Undervoltage Lockout Threshold Hysteresis vs Temperature 250 3.2 RISING THRESHOLD 3.1 FALLING THRESHOLD 3.0 2.9 –40 6.5 4447 G06 3.3 2.6 110 IVLOGIC 0.8 0.30 4447 G05 2.9 FALLING THRESHOLD 20 80 50 TEMPERATURE (°C) Quiescent Supply Current vs Supply Voltage VCC Undervoltage Lockout Thresholds vs Temperature 2.7 –10 1.0 VLOGIC Undervoltage Lockout Thresholds vs Temperature RISING THRESHOLD VIH(BG) 0.40 4447 G04 2.8 VIL(BG) 4447 G03 BG or TG Input Threshold Hysteresis vs Temperature BG OR TG INPUT THRESHOLD HYSTERESIS (V) BG OR TG INPUT THRESHOLD HYSTERESIS (V) BG or TG Input Threshold Hysteresis vs VLOGIC Supply Voltage 0.30 2 4447 G02 4447 G01 0.35 VIL(TG) 3 0 –40 110 UVLO THRESHOLD HYSTERESIS (V) 3.0 VIH(TG) 1 VIH(BG) 0.5 0 INPUT THRESHOLD (V) 2.5 4 VIH(TG) SUPPLY CURRENT (mA) VIL(TG) 3.0 INPUT THRESHOLD (V) INPUT THRESHOLD (V) 3.5 –10 20 80 50 TEMPERATURE (°C) 110 4447 G09a 200 VCC UVLO 150 100 VLOGIC UVLO 50 0 –40 –10 20 80 50 TEMPERATURE (°C) 110 4447 G09b 4447f 4 LTC4447 TYPICAL PERFORMANCE CHARACTERISTICS Schottky Diode Forward Voltage vs Diode Current Schottky Diode Forward Voltage vs Temperature 6 0.6 0.5 0.4 0.3 0.2 0.1 0 50 100 150 DIODE CURRENT (mA) ID = 100mA 0.4 ID = 10mA 0.3 ID = 1mA 0.2 0 –40 200 RISE/FALL TIME (ns) ILOGIC fIN = 500kHz 600k 1M 800k Rise and Fall Time vs Load Capacitance 100 VCC = 5V TS = GND tr(TG) 10 tf(TG) tr(TG) tr(BG) 5 tf(TG) 10 tr(BG) tf(BG) tf(BG) 3 10 LOAD CAPACITANCE (nF) 1 0 3.5 30 1 4.0 5.5 5.0 6.0 4.5 VCC SUPPLY VOLTAGE (V) 4447 G13 Propagation Delay vs VCC Supply Voltage 25 PROPAGATION DLEAY (ns) tpLH(BG) 15 tpHL(TG) 10 tpHL(BG) 3.5 25 NO LOAD VLOGIC = 5V TS = GND tpLH(TG) 5 3.0 Propagation Delay vs Temperature 20 NO LOAD VCC = 5V TS = GND 5.0 5.5 6.0 4.5 VLOGIC SUPPLY VOLTAGE (V) 4.0 6.5 4447 G16 30 4447 G15 4447 G14 Propagation Delay vs VLOGIC Supply Voltage 20 10 3 LOAD CAPACITANCE (nF) 1 6.5 15 tpLH(TG) PROPAGATION DELAY (ns) SUPPLY CURRENT (mA) ICC fIN = 100kHz 400k 4447 G12 CLOAD = 3.3nF TS = GND ICC fIN = 500kHz 200k FREQUENCY (Hz) 15 0.1 PROPAGATION DLEAY (ns) IVLOGIC 0 110 Rise and Fall Time vs VCC Supply Voltage VLOGIC = VCC = 5V TS = GND 1 2 4447 G11 Switching Supply Current vs Load Capacitance 10 IVCC 3 0 20 80 50 TEMPERATURE (°C) –10 4447 G10 100 4 1 0.1 RISE/FALL TIME (ns) 0 0.5 NO LOAD VLOGIC = VCC = 5V 5 TS = GND SUPPLY CURRENT (mA) SCHOTTKY DIODE FORWARD VOLTAGE (V) DIODE FORWARD VOLTAGE (V) 0.6 Supply Current vs Input Frequency tpLH(BG) tpHL(TG) 10 tpHL(BG) 20 15 NO LOAD VCC = VLOGIC = 5V TS = GND tpHL(TG) tpLH(TG) 10 tpHL(BG) tpLH(BG) 5 5 4.0 5.5 5.0 6.0 4.5 VCC SUPPLY VOLTAGE (V) 6.5 4447 G17 0 –40 –10 20 50 80 TEMPERATURE (°C) 110 4447 G18 4447f 5 LTC4447 PIN FUNCTIONS NC (Pins 1, 2): No Connection Required. TG (Pin 3): High Side Gate Driver Output (Top Gate). This pin swings between TS and BOOST. TS (Pin 4): High Side MOSFET Source Connection (Top Source). BG (Pin 5): Low Side Gate Driver Output (Bottom Gate). This pin swings between VCC and GND. GND (Pin 6): Chip Ground. IN (Pin 7): Input Signal. Input referenced to an internal supply baised off of VLOGIC (Pin 8) and GND (Pin 6). If this pin is floating, an internal resistive divider triggers a shutdown mode in which both BG (Pin 5) and TG (Pin 3) are pulled low. Trace capacitance on this pin should be minimized to keep the shutdown time low. VLOGIC (Pin 8): 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 7) to match input thresholds or to VCC (Pin 9) to simplify PCB routing. VCC (Pin 9): Output Driver Supply. This pin powers the low side gate driver output directly and the high side gate driver output through an internal Schottky diode connected between this pin and BOOST. A low ESR ceramic bypass capacitor should be tied between this pin and GND (Pin 6). BOOST (Pins 10, 11, 12): High Side Bootstrapped Supply. An external capacitor should be tied between these pins and TS (Pin 4). An internal Schottky diode is connected between VCC (Pin 9) and these pins. Voltage swing at these pins is from VCC – VD to VIN + VCC – VD, where VD is the forward voltage drop of the Schottky diode. Exposed Pad (Pin 13): Ground. The exposed pad must be soldered to PCB ground for optimal electrical and thermal performance. BLOCK DIAGRAM 9 VCC 12 UNDERVOLTAGE LOCKOUT 11 BOOST 10 8 VLOGIC UNDERVOLTAGE LOCKOUT TG LEVEL SHIFTER TS INTERNAL SUPPLY VCC THREE-STATE INPUT BUFFER IN 4 SHOOTTHROUGH PROTECTION 7k 7 3 BG 5 7k 6 GND 13 GND 4447 BD 4447f 6 LTC4447 TIMING DIAGRAM IN TG VIL(TG) VIL(BG) VIL(BG) 90% 10% tr(TG) tf(TG) 90% BG 10% tr(BG) tpLH(BG) tpLH(TG) tf(BG) tpHL(BG) 4447 TD tpHL(TG) OPERATION Overview The LTC4447 receives a ground-referenced, low voltage digital input signal to drive two N-channel power MOSFETs in a synchronous 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). VIH(TG) TG HIGH TG LOW TG HIGH TG LOW VIL(TG) IN VIL(BG) BG LOW BG HIGH BG LOW BG HIGH VIH(BG) 4447 F01 Input Stage The LTC4447 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 LTC4447 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 LTC4447 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). 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 LTC4447 will therefore pull IN into the region where TG and BG are low until the controller has enough voltage to operate predictably. 4447f 7 LTC4447 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. VIN LTC4447 Q1 BOOST CGD P1 TG CGS N1 HIGH SIDE POWER MOSFET TS Undervoltage Lockout The LTC4447 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 LTC4447 to operate reliably, normal operation will resume. LOAD INDUCTOR VCC Q2 CGD P2 BG Q3 CGS N2 LOW SIDE POWER MOSFET GND 4447 F02 Figure 2. Capacitance Seen by BG and TG During Switching 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 LTC4447 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 LTC4447’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) in parallel with a low resistance P-channel MOSFET (P1 and P2). This powerful combination rapidly pulls the BG and TG outputs to their positive rails (VCC and BOOST, respectively). Both BG and TG have N-channel MOSFET pull-down 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 rail-to-rail 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 – V TH). Rise/Fall Time Since the power MOSFETs generally account for the majority of power loss in a converter, it is important to quickly turn them on and off, thereby minimizing the transition time and power loss. The LTC4447’s peak pull-up current of 3.2A for both BG and TG produces a rapid turn-on transition for the MOSFETs. This high current is capable of driving a 3nF load with an 8ns risetime. 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. 4447f 8 LTC4447 OPERATION The LTC4447’s powerful parallel combination of the N-channel MOSFET (N2) and NPN (Q3) on the BG pull-down generates a phenomenal 4ns fall time on BG while driving a 3nF load. Similarly, the 0.8Ω pull-down MOSFET (N1) on TG results in a rapid 7ns 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 LTC4447 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 LTC4447 consumes very little quiescent current. The DC power loss at VLOGIC = 5V and VCC = 5V is only (730μA + 600μA)(5V) = 6.65mW. 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 of the internal Schottky 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 LTC4447 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. 4447f 9 LTC4447 APPLICATIONS INFORMATION Bypassing and Grounding The LTC4447 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 under/overshoot. To obtain the optimum performance from the LTC4447: • 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. • Use a low inductance, low impedance ground plane to reduce any ground drop and stray capacitance. Remember that the LTC4447 switches greater than 5A peak currents and any significant ground drop will degrade signal integrity. • 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. • Keep the copper trace between the driver output pin and the load short and wide. • Be sure to solder the Exposed Pad on the back side of the LTC4447 packages to the board. Correctly soldered to a double-sided copper board, the LTC4447 has a thermal resistance of approximately 43°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/LTC4447 12V to 1.5V/30A Digital Step-Down DC/DC Converter with PMBus Serial Interface 12V 5V R1 SDATA PMBus INTERFACE SCLK VD33 SMB_AL_N LTC7510 POWER MANAGEMENT INTERFACE C5 0.22μF V12SEN VCC VD25 C2 OUTEN BOOST R2 + PWRGD C4 C1 C3 GND PWM MULTIPHASE INTERFACE TG VLOGIC LTC4447 VCC TS IN 1μF SYNC_IN RCM SYNC_OUT BG GND M1 RJK0305 ×2 M2 RJK0301 ×2 L1 0.3μH R3 C6 VOUT + 330μF ×6 D1 TEMPSEN LOAD FAULT OUTPUTS FAULT1 FAULT2 ISENN RSENSE ISENP VSENP VSENN I-SHARE IOUT/ISH ISH_GND 1k SADDR 1k VSET RTN 4447 TA02 1k FSET 1k RESET_N VTRIM 1k IMAXSET 4447f 10 LTC4447 PACKAGE DESCRIPTION DDMA Package 12-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1743 Rev A) 0.70 ±0.05 1.19 ±0.05 0.93 ±0.05 2.25 REF 0.57 ±0.05 2.38 ±0.05 1.35 ±0.05 3.50 ±0.05 0.81 ±0.05 2.10 ±0.05 PACKAGE OUTLINE 1.07 ±0.05 0.25 ± 0.05 0.45 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED R = 0.115 TYP 7 3.00 ±0.10 0.11 ± 0.05 12 0.40 ± 0.10 2.38 ±0.10 3.00 ±0.10 0.81 ± 0.10 PIN 1 TOP MARK (SEE NOTE 6) 0.200 REF R = 0.05 TYP 0.63 ± 0.05 1.35 ± 0.10 6 PIN 1 NOTCH R = 0.20 OR 0.25 × 45° CHAMFER 1 0.23 ± 0.05 0.45 BSC 0.75 ±0.05 2.25 REF (DD12MA) DFN 0507 REV A BOTTOM VIEW—EXPOSED PAD 0.00 – 0.05 NOTE: 1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD AND TIE BARS SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 4447f 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 LTC4447 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC1154 High Side Micropower MOSFET Driver Internal Charge Pump 4.5V to 18V Supply Range LTC1155 Dual Micropower High/Low Side Driver Internal Charge Pump 4.5V to 18V Supply Range Quad Protected High Side MOSFET Driver 8V to 48V Supply Range, tON = 200μs, tOFF = 28μs ® LT 1161 LTC1163 Triple 1.8V to 6V High Side MOSFET Driver 1.8V to 6V Supply Range, tON = 95μs, tOFF = 45μs LTC1693 Family High Speed Single/Dual N-Channel MOSFET Drivers 1.5A Peak Output Current, 4.5V ≤ VIN ≤ 13.2V LTC3900 Synchronous Rectifier Driver for Forward Converters Pulse Drive Transformer Synchronous Input LTC3901 Secondary Side Synchronous Driver for Push-Pull and Full-Bridge Converters Gate Drive Transformer Synchronous Input LTC4440 High Speed, High Voltage High Side Gate Driver High Side Source Up to 100V, 8V ≤ VCC ≤ 15V LTC4440-5 High Speed, High Voltage High Side Gate Driver High Side Source Up to 80V, 4V ≤ VCC ≤ 15V LTC4441 6A MOSFET Driver 6A Peak Output Current, Adjustable Gate Drive from 5V to 8V, 5V ≤ VIN ≤ 25V LTC4442/LTC4442-1 High Speed Synchronous N-Channel MOSFET Driver 5A Peak Output Current, Three-State Input, 38V Maximum Input Supply Voltage, 6V ≤ VCC ≤ 9.5V, MS8E Package LTC4443/LTC4443-1 High Speed Synchronous N-Channel MOSFET Driver 5A Peak Output Current, Internal Schottky Diode, 38V Maximum Input Supply Voltage, 6V ≤ VCC ≤ 9.5V, 3mm × 3mm DFN-12 LTC4444/LTC4444-5 High Voltage/High Speed Synchronous N-Channel MOSFET Driver 3A Peak Output Current, 100V Maximum Input Supply Voltage, 4.5V ≤ VCC ≤ 13.5V, with Adaptive Shoot Through Protection LTC4446 High Voltage High Side/Low Side N-Channel MOSFET Driver 3A Output Current, 100V Input Supply Voltage, 7.2V ≤ VCC ≤ 13.5V, without Adaptive Shoot Through Protection LTC7510 Digital DC/DC Controller with PMBus Interface Digital Controller, PMBus Serial Interface, 150kHz to 2MHz Switching Frequency 4447f 12 Linear Technology Corporation LT 0608 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2008