LTC4443/LTC4443-1 High Speed Synchronous N-Channel MOSFET Drivers FEATURES DESCRIPTION n The LTC®4443 is a high frequency gate driver with integrated bootstrap Schottky diode 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. n n n n n n n n n n n Integrated Schottky Diode 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 Low Profile (0.75mm) 3mm × 3mm DFN Package APPLICATIONS n n Distributed Power Architectures High Density Power Modules L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. The LTC4443 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 LTC4443 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 Schottky diode required for the bootstrapped supply is integrated to simplify layout and reduce parts count. The LTC4443 contains undervoltage lockout circuits on both the driver and logic supplies that turn off the external MOSFETs when an undervoltage condition is present. The LTC4443 and LTC4443-1 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 LTC4443/LTC4443-1 are available in a tiny 3mm × 3mm DFN package. TYPICAL APPLICATION Synchronous Buck Converter Driver LTC4443 Driving 3000pF Capacitive Loads VIN 32V INPUT (IN) 5V/DIV BOOST VCC 6V TG VLOGIC VCC LTC4443 TS PWM IN VOUT BG GND 4443 TA01a BOTTOM GATE (BG) 5V/DIV TOP GATE (TG-TS) 5V/DIV 10ns/DIV 4443 TA01b 4443fa 1 LTC4443/LTC4443-1 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) Supply Voltage VLOGIC .................................................... –0.3V to 10V VCC......................................................... –0.3V to 10V BOOST – TS ........................................... –0.3V to 10V BOOST Voltage .......................................... –0.3V to 42V BOOST – VCC ............................................................38V TS Voltage..................................................... –5V to 38V TS + VCC....................................................................42V IN Voltage .................................................. –0.3V to 10V 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 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 s 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 LTC4443EDD#PBF LTC4443EDD#TRPBF LCXH 12-Lead (3mm × 3mm) Plastic DFN –40°C to 85°C LTC4443IDD#PBF LTC4443IDD#TRPBF LCXH 12-Lead (3mm × 3mm) Plastic DFN –40°C to 85°C LTC4443EDD-1#PBF LTC4443EDD-1#TRPBF LCYN 12-Lead (3mm × 3mm) Plastic DFN –40°C to 85°C LTC4443IDD-1#PBF LTC4443IDD-1#TRPBF LCYN 12-Lead (3mm × 3mm) Plastic DFN –40°C to 85°C 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 The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 7V, VTS = GND = 0V, VLOGIC = 5V, 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 l l 2.5 2.4 9.5 V 730 850 μA 2.75 2.65 100 3.0 2.9 V V mV 9.5 V 600 800 μA Gate Driver Supply (VCC) VCC Operating Range 6 IVCC DC Supply Current IN = Floating UVLO Undervoltage Lockout Threshold VCC Rising (LTC4443) VCC Falling (LTC4443) Hysteresis (LTC4443) l l 2.75 2.60 3.20 3.04 160 3.65 3.50 V V mV VCC Rising (LTC4443-1) VCC Falling (LTC4443-1) Hysteresis (LTC4443-1) l l 5.6 4.7 6.2 5.3 850 6.7 5.8 V V mV 4443fa 2 LTC4443/LTC4443-1 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 7V, VTS = GND = 0V, VLOGIC = 5V, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN VD Schottky Diode Forward Voltage ID = 10mA ID = 100mA VIH(TG) TG Turn-On Input Threshold VLOGIC ≥ 5V, IN Rising VLOGIC = 3.3V, IN Rising VIL(TG) TG Turn-Off Input Threshold VLOGIC ≥ 5V, IN Falling VLOGIC = 3.3V, IN Falling VIH(BG) BG Turn-On Input Threshold VLOGIC ≥ 5V, IN Falling VLOGIC = 3.3V, IN Falling VIL(BG) BG Turn-Off Input Theshold VLOGIC ≥ 5V, IN Rising VLOGIC = 3.3V, IN Rising IIN(SD) Maximum Current Into or Out of IN in Shutdown Mode VLOGIC ≥ 5V, IN Floating VLOGIC = 3.3V, IN Floating TYP MAX 0.38 0.48 UNITS V V Input Signal (IN) l l 3.0 1.9 3.5 2.2 4.0 2.6 3.25 2.09 l l 0.8 0.8 200 100 1.25 1.10 V V V V 1.6 1.4 V V 1.50 1.21 V V 300 150 μA μA 0.7 V High Side Gate Driver Output (TG) VOH(TG) TG High Output Voltage ITG = –10mA, VOH(TG) = VBOOST – VTG ITG = 100mA, VOL(TG) = VTG – VTS VOL(TG) TG Low Output Voltage 100 mV IPU(TG) TG Peak Pull-Up Current l 1.5 2.4 A IPD(TG) TG Peak Pull-Down Current l 1.5 2.4 A 0.7 V Low Side Gate Driver Output (BG) VOH(BG) BG High Output Voltage IBG = –10mA, VOH(BG) = VCC – VBG VOL(BG) BG Low Output Voltage IBG = 100mA 100 mV IPU(BG) BG Peak Pull-Up Current l 1.4 2.4 A IPD(BG) BG Peak Pull-Down Current l 3.5 5.0 A Switching Time tPLH(TG) BG Low to TG High Propagation Delay 20 ns tPHL(TG) IN Low to TG Low Propagation Delay 12 ns tPLH(BG) TG Low to BG High Propagation Delay 20 ns tPHL(BG) IN High to BG Low Propagation Delay 12 ns tr(TG) TG Output Rise Time 10% – 90%, CL = 3nF 12 ns tf(TG) TG Output Fall Time 10% – 90%, CL = 3nF 8 ns tr(BG) BG Output Rise Time 10% – 90%, CL = 3nF 12 ns tf(BG) BG Output Fall Time 10% – 90%, CL = 3nF 5 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 LTC4443I/LTC4443I-1 are guaranteed to meet specifications from –40°C to 85°C. The LTC4443E/LTC4443E-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 • 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. 4443fa 3 LTC4443/LTC4443-1 TYPICAL PERFORMANCE CHARACTERISTICS Input Thresholds for VLOGIC = 3.3V vs Temperature 3.0 5 VIL(TG) 3 2 VIL(BG) VIH(BG) 1 0 3 4 7 6 5 8 VLOGIC SUPPLY (V) 5 VLOGIC = 3.3V 2.5 VIH(TG) 2.0 VIL(TG) 1.5 VIL(BG) 1.0 VIH(BG) 0 –40 10 –10 20 50 80 TEMPERATURE (°C) BG OR TG INPUT THRESHOLD HYSTERSIS (V) BG OR TG INPUT THRESHOLD HYSTERESIS (V) 0.3 0.2 0.1 0 3 4 6 5 7 8 VLOGIC SUPPLY (V) 9 2 VIL(BG) VIH(BG) 0 –40 110 10 IN FLOATING 0.9 BOOST > VCC 0.8 0.30 VLOGIC = 5V 0.25 0.20 VLOGIC = 3.3V 0.15 0.10 0.7 IVLOGIC 0.6 0.5 0.4 IVCC 0.3 IBOOST 0.2 0.05 0.1 0 –40 0 –10 20 50 80 TEMPERATURE (°C) 3 110 VCC Undervoltage Lockout Thresholds vs Temperature 7.0 2.9 VCC UVLO THRESHOLD (V) VLOGIC UVLO THRESHOLD (V) DIODE FORWARD VOLTAGE (V) 6.5 0.10 10 9 4443 G06 3.0 0.60 0.20 7 6 5 8 SUPPLY VOLTAGE (V) 4 4443 G05 VLOGIC Undervoltage Lockout Thresholds vs Temperature 0.30 110 1.0 0.35 Schottky Diode Forward Voltage vs Diode Current 0.40 20 80 50 TEMPERATURE (°C) Quiescent Supply Current vs Supply Voltage 0.40 4443 G04 0.50 –10 4443 G03 BG or TG Input Threshold Hysteresis vs Temperature BG or TG Input Threshold Hysteresis vs VLOGIC Supply Voltage 0.4 VIL(TG) 3 4443 G02 4443 G01 0.5 VIH(TG) 1 0.5 9 VLOGIC ≥ 5V 4 SUPPLY CURRENT (mA) INPUT THRESHOLD (V) INPUT THRESHOLD (V) VIH(TG) 4 Input Thresholds for VLOGIC ≥ 5V vs Temperature INPUT THRESHOLD (V) Input Thresholds vs VLOGIC Supply Voltage RISING THRESHOLD 2.8 FALLING THRESHOLD 2.7 2.6 6.0 LTC4443-1 RISING THRESHOLD LTC4443-1 FALLING THRESHOLD 5.5 5.0 4.5 4.0 3.5 3.0 LTC4443 RISING THRESHOLD LTC4443 FALLING THRESHOLD 2.5 0 0 50 100 150 DIODE CURRENT (mA) 200 4443 G07 2.5 –40 –10 20 80 50 TEMPERATURE (°C) 110 4443 G08 2.0 –40 –10 20 80 50 TEMPERATURE (°C) 110 4443 G09 4443fa 4 LTC4443/LTC4443-1 TYPICAL PERFORMANCE CHARACTERISTICS Undervoltage Lockout Threshold Hysteresis vs Temperature Switching Supply Current vs Input Frequency 100 7 800 700 600 500 400 300 LTC4443 VCC UVLO 200 100 0 –40 IVCC 3 2 0 20 80 50 TEMPERATURE (°C) 110 200k 400k 600k tPLH(TG) 20 tPLH(BG) tPHL(TG) tPHL(BG) 8 9 7 6 VLOGIC SUPPLY VOLTAGE (V) 5 40 tPHL(TG) 15 tPHL(BG) 10 10 5 4443 G13 tPLH(TG) 25 tPLH(BG) 20 8 7 9 6 VCC SUPPLY VOLTAGE (V) 0 –40 10 6 5 4 3 –10 20 50 80 TEMPERATURE (°C) 4443 G14 110 4443 G15 Rise and Fall Time vs Load Capacitance VCC = 7V TS = GND CLOAD = 3.3nF TS = GND tr(BG) tr(TG) 15 RISE/FALL TIME (ns) RISE/FALL TIME (ns) –100mA tPHL(TG) 10 100 20 –10mA tPHL(BG) 15 Rise and Fall Time vs VCC Supply Voltage 9 –1mA 30 5 4 TS = GND 30 NO LOAD VLOGIC = 5V VCC = 7V TS = GND 35 tPLH(BG) 20 Output High Voltage vs VCC Supply Voltage 7 1 10 3 LOAD CAPACITANCE (nF) Propagation Delay vs Temperature tPLH(TG) 25 0 0 8 0.3 4443 G12 5 5 BG OR TG HIGH OUTPUT VOLTAGE (V) 0.1 NO LOAD VLOGIC = 5V TS = GND 30 15 10 ILOGIC fIN = 500kHz 1M 800k 35 PROPAGATION DELAY (ns) PROPAGATION DELAY (ns) 25 4 1 Propagation Delay vs VCC Supply Voltage 30 3 ICC fIN = 100kHz 4443 G11 NO LOAD VCC = 7V TS = GND 10 10 FREQUENCY (Hz) Propagation Delay vs VLOGIC Supply Voltage 35 ICC fIN = 500kHz 0 0 4443 G10 40 VLOGIC = 5V VCC = 7V TS = GND IVLOGIC 1 VLOGIC UVLO –10 4 PROPAGATION DELAY (ns) 900 NO LOAD = 5V V 6 VLOGIC CC = 7V TS = GND 5 SUPPLY CURRENT (mA) LTC4443-1 VCC UVLO SUPPLY CURRENT (mA) UVLO THRESHOLD HYSTERESIS (mV) 1000 Switching Supply Current vs Load Capacitance tr(BG) tr(TG) 10 tf(TG) 5 tf(TG) tf(BG) 10 tf(BG) 2 1 0 1 0 4 5 7 8 6 VCC SUPPLY VOLTAGE (V) 9 10 4443 G16 4 5 8 9 6 7 VCC SUPPLY VOLTAGE (V) 10 4443 G17 1 10 3 LOAD CAPACITANCE (nF) 30 4443 G18 4443fa 5 LTC4443/LTC4443-1 PIN FUNCTIONS 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 powered by VLOGIC (Pin 8) and referenced to 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 bootstrap diode. Exposed Pad (Pin 13): Ground. The Exposed Pad must be soldered to PCB ground for optimal electrical and thermal performance. BLOCK DIAGRAM 9 BOOST VCC UNDERVOLTAGE LOCKOUT BOOST BOOST 8 VLOGIC UNDERVOLTAGE LOCKOUT TG LEVEL SHIFTER TS INTERNAL SUPPLY 10 3 4 VCC THREE-STATE INPUT BUFFER IN 11 SHOOTTHROUGH PROTECTION 7k 7 12 BG 5 7k 6 GND 13 GND 4443 BD 4443fa 6 LTC4443/LTC4443-1 TIMING DIAGRAM IN TG BG VIL(TG) VIL(BG) 90% 10% 90% 4443 TD 10% tr(TG) tpLH(TG) tr(BG) tpLH(BG) tf(BG) tpHL(BG) tf(TG) tpHL(TG) OPERATION Overview The LTC4443 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). 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) 4443 F01 Input Stage The LTC4443 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 LTC4443 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 LTC4443 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 LTC4443 will therefore pull IN into the region where TG and BG are low until the controller has enough voltage to operate predictably. 4443fa 7 LTC4443/LTC4443-1 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. VIN LTC4443 BOOST CGD Q1 TG N1 CGS HIGH SIDE POWER MOSFET TS Undervoltage Lockout The LTC4443 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 LTC4443 to operate reliably, normal operation will resume. LOAD INDUCTOR VCC Q2 CGD BG Q3 N2 CGS LOW SIDE POWER MOSFET GND 4443 F02 Figure 2. Capacitance Seen by BG and TG During Switching Adaptive Shoot-Through Protection Rise/Fall Time Internal adaptive shoot-through protection circuitry monitors the voltages on the external MOSFETs to ensure that they do not conduct simultaneously. The LTC4443 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. 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 LTC4443’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. Output Stage A simplified version of the LTC4443’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). 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. 4443fa 8 LTC4443/LTC4443-1 OPERATION The LTC4443’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 LTC4443 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 LTC4443 consumes very little quiescent current. The DC power loss at VLOGIC = 5V and VCC = VBOOST − TS = 7V is only (730μA)(5V) + (600μA)(7V) = 7.85mW. 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 LTC4443 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. 4443fa 9 LTC4443/LTC4443-1 APPLICATIONS INFORMATION Bypassing and Grounding The LTC4443 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. To obtain the optimum performance from the LTC4443: 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 LTC4443 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 trace between the driver output pin and the load short and wide. E. Be sure to solder the Exposed Pad on the back side of the LTC4443 packages to the board. Correctly soldered to a double-sided copper board, the LTC4443 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/LTC4443-1 12V to 1.5V/30A Digital Step-Down DC/DC Converter with PMBus Serial Interface 7V DRIVE 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 LTC4443-1 VCC TS IN 1μF SYNC_IN RCM SYNC_OUT BG GND M1 RJK0305 s2 M2 RJK0301 s2 L1 0.3μH R3 C6 VOUT + 330μF s6 D1 TEMPSEN LOAD FAULT OUTPUTS FAULT1 FAULT2 ISENN RSENSE ISENP VSENP VSENN I-SHARE IOUT/ISH ISH_GND 1k SADDR 1k VSET RTN 4443 TA02 1k FSET 1k RESET_N VTRIM 1k IMAXSET 4443fa 10 LTC4443/LTC4443-1 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 1.07 ±0.05 PACKAGE OUTLINE 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 0.75 ±0.05 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 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 4443fa 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 LTC4443/LTC4443-1 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT 1161 Quad Protected High Side MOSFET Driver 8V to 48V Supply Range, tON = 200μs, tOFF = 28μs LTC1693 Family High Speed Single/Dual N-Channel MOSFET Drivers 1.5A Peak Output Current, 4.5V ≤ VIN ≤ 13.2V 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 LTC4444 High Voltage Synchronous N-Channel MOSFET Driver High Side Source Up to 100V, 3A Peak Output Current, 7.2V ≤ VCC ≤ 13.5V LTC4445/LTC4445-1 Dual High Speed Synchronous N-Channel MOSFET Driver Two Independent Drivers, Internal Schottky Diodes, 38V Maximum Input Supply Voltage, 6V ≤ VCC ≤ 9.5V, LTC4447 High Speed Synchronous N-Channel MOSFET Driver 4.5A Peak Output Current, Rail-to-Rail Drivers, 38V Maximum Input Supply Voltage, 4V ≤ VCC ≤ 6.5V LTC7510 Digital DC/DC Controller with PMBus Interface Digital Controller, PMBus Serial Interface, 150kHz to 2MHz Switching Frequency 4443fa 12 Linear Technology Corporation LT 0608 REV A • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2008