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LTC4449 High Speed Synchronous N-Channel MOSFET Driver FEATURES
n n n n n n n n n n n n
DESCRIPTION
The LTC(R)4449 is a high frequency gate driver 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 LTC4449 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 LTC4449 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 LTC4449 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 LTC4449 is available in the 2mm x 3mm DFN package.
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) 2mm x 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.
TYPICAL APPLICATION
Synchronous Buck Converter Driver
VCC 4V TO 6.5V VCC VLOGIC BOOST VIN TO 38V INPUT (IN) 5V/DIV
LTC4449 Driving 3000pF Capacitive Loads
LTC4449
TG TS VOUT
TOP GATE (TG - TS) 5V/DIV
PWM
IN
GND
BG
BOTTOM GATE (BG) 5V/DIV
4449 TA01a
10ns/DIV
4449 TA01b
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LTC4449 ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW TG 1 TS 2 BG 3 GND 4 9 8 BOOST 7 VCC 6 VLOGIC 5 IN
Supply Voltage VLOGIC ...................................................... -0.3V to 7V VCC........................................................... -0.3V to 7V BOOST - TS ............................................. -0.3V to 7V BOOST Voltage .......................................... -0.3V to 42V TS ................................................................. -5V to 38V 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 Junction Temperature Range (Notes 2, 3) ............................................-40C to 125C Storage Temperature Range...................-65C to 150C
DCB PACKAGE 8-LEAD (2mm 3mm) PLASTIC DFN JA = 64C/W, JC = 10.6C/W EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH LTC4449EDCB#PBF LTC4449IDCB#PBF TAPE AND REEL LTC4449EDCB#TRPBF LTC4449IDCB#TRPBF PART MARKING* LFKC LFKC PACKAGE DESCRIPTION 8-Lead (2mm x 3mm) Plastic DFN 8-Lead (2mm x 3mm) Plastic DFN TEMPERATURE RANGE -40C to 85C -40C to 125C
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
SYMBOL VLOGIC IVLOGIC UVLO PARAMETER Operating Range DC Supply Current Undervoltage Lockout Threshold Logic Supply (VLOGIC)
The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25C. VCC = VLOGIC = VBOOST = 5V, VTS = GND = 0V, unless otherwise noted.
CONDITIONS MIN 3 IN = Floating VLOGIC Rising VLOGIC Falling Hysteresis
l l
TYP
MAX 6.5
UNITS V A V V mV V A V V mV A
730 2.5 2.4 2.75 2.65 100
900 3 2.9
Gate Driver Supply (VCC) VCC IVCC UVLO Operating Range DC Supply Current Undervoltage Lockout Threshold IN = Floating VCC Rising VCC Falling Hysteresis IN = Floating
l l
4 300 2.75 2.60 3.20 3.04 160 300
6.5 400 3.65 3.50 400
IBOOST
DC Supply Current
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LTC4449 ELECTRICAL CHARACTERISTICS
SYMBOL 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 Risetime TG Output Falltime BG Output Risetime BG Output Falltime 10% to 90%, CL = 3nF 10% to 90%, CL = 3nF 10% to 90%, CL = 3nF 10% to 90%, CL = 3nF IBG = -100mA, VOH(BG) = VCC - VBG IBG = 100mA
l l
The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25C. VCC = VLOGIC = VBOOST = 5V, VTS = GND = 0V, unless otherwise noted.
PARAMETER CONDITIONS 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 = -100mA, VOH(TG) = VBOOST - VTG ITG = 100mA, VOL(TG) = VTG - VTS
l l l l l l l l l l
MIN 3 1.9 2.75 1.8 0.8 0.8 1.05 0.9 150 75
TYP 3.5 2.2 3.25 2.09 1.25 1.1 1.5 1.21 300 150 140 80
MAX 4 2.6 3.75 2.5 1.6 1.4 1.85 1.5
UNITS V V V V V V V V A A mV mV A A mV mV A A ns ns ns ns ns ns ns ns
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) tf(BG) 14 13 13 11 8 7 7 4
2 1.5
3.2 2.4 100 100
Low Side Gate Driver Output (BG)
2 3
3.2 4.5
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 LTC4449I is guaranteed to meet specifications over the full -40C to 125C operating junction temperature range. The LTC4449E is guaranteed to meet specifications from 0C to 85C with specifications over the -40C to 85C operating junction temperature range assured by design, characterization and correlation with statistical process controls.
The junction temperature TJ is calculated from the ambient temperature TA and power dissipation PD according to the following formula: TJ = TA + (PD * 64C/W) Note 3: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 125C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature may impair device reliability.
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LTC4449 TYPICAL PERFORMANCE CHARACTERISTICS
Input Thresholds vs VLOGIC Supply Voltage
4.0 VIH(TG) 3.5 INPUT THRESHOLD (V) INPUT THRESHOLD (V) INPUT THRESHOLD (V) 3.0 2.5 2.0 VIL(BG) 1.5 1.0 0.5 0 3.0 3.5 4.0 4.5 5.0 5.5 VLOGIC SUPPLY (V) 6.0 6.5 0.5 -40 -10 VIH(BG) VIL(TG) 2.5 VIH(TG) VIL(TG) 4 VIH(TG) VIL(TG) 3.0
Input Thresholds for VLOGIC = 3.3V vs Temperature
5 VLOGIC = 3.3V
Input Thresholds for VLOGIC 5V vs Temperature
VLOGIC 5V
2.0
3
1.5 VIL(BG) 1.0 VIH(BG)
2
VIL(BG) VIH(BG)
1
20 50 80 TEMPERATURE (C)
110
4449 G02
0 -40
-10
20 80 50 TEMPERATURE (C)
110
4449 G03
4449 G01
BG or TG Input Threshold Hysteresis vs VLOGIC Supply Voltage
BG OR TG INPUT THRESHOLD HYSTERESIS (V) BG OR TG INPUT THRESHOLD HYSTERESIS (V) 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0 3.0 3.5 0.40 0.35
BG or TG Input Threshold Hysteresis vs Temperature
1.0
Quiescent Supply Current vs Supply Voltage
IN FLOATING 0.9 TS = GND 0.8 SUPPLY CURRENT (mA) IVLOGIC
0.30 VLOGIC = 5V 0.25 0.20 0.15 0.10 0.05 0 -40 -10 20 50 80 TEMPERATURE (C) 110
4449 G05
0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 3.0 3.5
VLOGIC = 3.3V
IBOOST IVCC
4.0 4.5 5.0 5.5 VLOGIC SUPPLY (V)
6.0
6.5
4.0 4.5 5.0 5.5 6.0 SUPPLY VOLTAGE (V)
6.5
7.0
4449 G04
4449 G06
VLOGIC Undervoltage Lockout Thresholds vs Temperature
2.9 3.3
VCC Undervoltage Lockout Thresholds vs Temperature
250 UVLO THRESHOLD HYSTERESIS (V)
Undervoltage Lockout Threshold Hysteresis vs Temperature
VLOGIC UVLO THRESHOLD (V)
2.8 RISING THRESHOLD
VCC UVLO THRESHOLD (V)
200 VCC UVLO 150
3.2 RISING THRESHOLD
2.7 FALLING THRESHOLD 2.6
3.1 FALLING THRESHOLD 3.0
100 VLOGIC UVLO 50
2.5 -40
-10
20 80 50 TEMPERATURE (C)
110
4449 G08
2.9 -40
-10
20 80 50 TEMPERATURE (C)
110
4449 G09a
0 -40
-10
20 80 50 TEMPERATURE (C)
110
4449 G09b
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LTC4449 TYPICAL PERFORMANCE CHARACTERISTICS
Supply Current vs Input Frequency
6 NO LOAD VLOGIC = VCC = 5V 5 TS = GND SUPPLY CURRENT (mA) 100
Switching Supply Current vs Load Capacitance
VLOGIC = VCC = 5V TS = GND ICC fIN = 500kHz 10 ICC fIN = 100kHz ILOGIC fIN = 500kHz 15
Rise and Fall Time vs VCC (Boost) Supply Voltage
CLOAD = 3.3nF TS = GND RISE/FALL TIME (ns)
SUPPLY CURRENT (mA)
4 IVCC 3 2 1 0 0 200k 400k 600k 800k 1M
4449 G12
10 tr(TG) tr(BG) 5 tf(BG)
tf(TG)
1
IVLOGIC
0.1 1 3 10 LOAD CAPACITANCE (nF) 30
4449 G13
0 3.5
FREQUENCY (Hz)
5.5 5.0 6.0 4.0 4.5 VCC (BOOST) SUPPLY VOLTAGE (V)
6.5
4449 G14
Rise and Fall Time vs Load Capacitance
100 VCC = 5V TS = GND tr(TG) PROPAGATION DLEAY (ns) RISE/FALL TIME (ns) 20 25
Propagation Delay vs VLOGIC Supply Voltage
20 NO LOAD VCC = BOOST = 5V TS = GND PROPAGATION DLEAY (ns) tpLH(TG) tpLH(BG) 15 tpHL(TG) 10 15
Propagation Delay vs VCC (Boost) Supply Voltage
NO LOAD VLOGIC = 5V TS = GND tpLH(TG) tpLH(BG)
tf(TG) 10 tr(BG) tf(BG)
tpHL(TG) 10 tpHL(BG)
tpHL(BG)
1 1 10 3 LOAD CAPACITANCE (nF) 30
4449 G15
5 3.0
3.5
5.0 5.5 6.0 4.5 VLOGIC SUPPLY VOLTAGE (V) 4.0
6.5
5 4.0
5.5 5.0 6.0 4.5 VCC (BOOST) SUPPLY VOLTAGE (V)
6.5
4449 G17
4449 G16
Propagation Delay vs Temperature
25 NO LOAD VCC = VLOGIC = 5V TS = GND tpHL(TG)
PROPAGATION DELAY (ns)
20
15
tpLH(TG) tpLH(BG)
10
tpHL(BG)
5
0 -40
-10
20 50 80 TEMPERATURE (C)
110
4449 G18
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LTC4449 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, Exposed Pad Pin 9): Chip Ground. The exposed pad must be soldered to PCB ground for optimal electrical and thermal performance. IN (Pin 5): 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 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 7) to match input thresholds or to VCC (Pin 9) 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 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 (Pin 8): High Side Bootstrapped Supply. An external capacitor should be tied between this pin and TS (Pin 4). Normally an external Schottky diode is connected between VCC (Pin 9) 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 Schottky diode.
BLOCK DIAGRAM
7 VCC UNDERVOLTAGE LOCKOUT BOOST 8 VLOGIC UNDERVOLTAGE LOCKOUT LEVEL SHIFTER TG TS INTERNAL SUPPLY 1 2
6
SHOOTTHROUGH PROTECTION VCC THREE-STATE INPUT BUFFER BG 3
7k IN 7k 4 GND
5
9 GND
4449 BD
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LTC4449 TIMING DIAGRAM
IN VIL(TG) VIL(BG) VIL(BG)
TG
90% 10% tr(TG) 90% tf(TG)
BG
10% tpLH(TG) tf(BG) tpHL(BG) tpHL(TG) tr(BG) tpLH(BG)
4449 TD
OPERATION
Overview The LTC4449 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). Input Stage The LTC4449 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 LTC4449 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 LTC4449 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)
4449 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 LTC4449 will therefore pull IN into the region where TG and BG are low until the controller has enough voltage to operate predictably.
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LTC4449 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 LTC4449 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 LTC4449 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 LTC4449 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 LTC4449'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 - VTH). 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 LTC4449's peak pullup 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.
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VIN LTC4449 Q1 BOOST P1 TG N1 TS LOAD INDUCTOR CGS CGD HIGH SIDE POWER MOSFET
VCC Q2 P2 BG Q3 N2 GND CGS CGD
LOW SIDE POWER MOSFET
4449 F02
Figure 2. Capacitance Seen by BG and TG During Switching
8
LTC4449 OPERATION
The LTC4449'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 0.8 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 LTC4449 must not operate beyond its maximum temperature rating. Package junction temperature can be calculated by: TJ = TA + (PD)(JA) where: TJ = junction temperature TA = ambient temperature PD = power dissipation JA = 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 LTC4449 consumes very little quiescent current. The DC power loss at VLOGIC = 5V and VCC = 5V is only (730A + 600A)(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 external 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 LTC4449 includes a temperature monitor that will pull BG and TG low if the junction temperature exceeds 160C. Normal operation will resume when the junction temperature cools to less than 135C.
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LTC4449 APPLICATIONS INFORMATION
Bypassing and Grounding The LTC4449 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 LTC4449: * 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 LTC4449 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 LTC4449 packages to the board. Correctly soldered to a double-sided copper board, the LTC4449 has a thermal resistance of approximately 64C/W. Failure to make good thermal contact between the exposed back side and the copper board will result in thermal resistances far greater.
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2-Phase 1.2V/50A Step-Down Converter
VIN 7V TO 14V 100pF 22F 2 HAT2167H 2 SW1 0.3H HAT2160H 2 2.74k 0.22F SW1 0.22F 47F 3 5 VIN VOS1P
470F
TYPICAL APPLICATION
TRACK/SS1 VCC 100k 4.7F 50k PWM1 VCC 2.2 6 7 8 0.1F
1F
LTC4449 4 IN GND 3 VLOGIC BG 2 VCC TS 1 BOOST TG
47
VOUT1 1.2V 50A 330F 3
RUN1 VCC 5V
1F 47 VOS1N
1.5nF
20k LTC3860 0.22F VCC VIN 5
1.33k
33pF
20k TRACK/SS2 FREQ CLKIN CLKOUT PHSMD PGOOD2 PWM2
VDIFF1 VOS1N VOS1P
220pF 12.7k 1F
VCC
FB1 COMP1 VSNSOUT VSNSN VSNSP COMP2 FB2
VCC TRACK/SS1 VINSNS IAVG PGOOD1 PWM1 RUN1 ILIM1 ISNS1P ISNS1N ISNS2N ISNS2P ILIM2 RUN2
VDIFF1
22F 2 HAT2167H 2 SW2 HAT2160H 2
2.74k
SS1 45k 4.7F 2.2
PWM2 6 7 8
0.3H
4449 TA02
LTC4449 4 IN GND 3 VLOGIC BG 2 VCC TS 1 BOOST TG
47F 3
330F 3
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. VCC 0.22F SW2
FREQ SET FOR 600kHz
CLKOUT
RUN2
7V TO 14V IN AND 1.2V OUT AT 50A fSW = 600kHz, DCR SENSING
LTC4449
11
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LTC4449 PACKAGE DESCRIPTION
DCB Package 8-Lead Plastic DFN (2mm x 3mm)
(Reference LTC DWG # 05-08-1718 Rev A)
2.00 0.10 (2 SIDES) R = 0.115 TYP R = 0.05 5 TYP 0.40 8 0.70 0.05 0.10
1.35 0.10 3.00 0.10 (2 SIDES) PIN 1 BAR TOP MARK (SEE NOTE 6) 4 0.200 REF 0.75 0.05 1.35 REF 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 1 0.23 0.45 BSC 0.05 1.65 0.10
3.50 0.05 2.10 0.05 PIN 1 NOTCH R = 0.20 OR 0.25 45 CHAMFER
(DCB8) DFN 0106 REV A
1.35 0.05 1.65 0.05
PACKAGE OUTLINE
0.25 0.45 BSC 1.35 REF
0.05
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
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 SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
RELATED PARTS
PART NUMBER LTC4442/LTC4442-1 LTC4444/LTC4444-5 LTC4446 LTC1693-1/-2/-3/-5 LTC4440 LTC4440-5 LTC4441 LTC3900 LTC3901 LTC1154 LTC1155 LT 1161 LTC1163 LTC3860
(R)
DESCRIPTION High Speed Synchronous N-Channel MOSFET Driver High Voltage/High Speed Synchronous N-Channel MOSFET Driver High Voltage High Side/Low Side N-Channel MOSFET Driver High Speed Single/Dual N-Channel MOSFET Drivers High Speed, High Voltage High Side Gate Driver High Speed, High Voltage High Side Gate Driver 6A MOSFET Driver Synchronous Rectifier Driver for Forward Converters Secondary Side Synchronous Driver for Push-Pull and Full-Bridge Converters 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 Dual Phase/Dual Channel Step-Down Voltage Mode Controller
COMMENTS 5A Peak Output Current, Three-State Input, 38V Maximum Input Supply Voltage, 6V VCC 9.5V, MS8E Package 3A Peak Output Current, 100V Maximum Input Supply Voltage, 4.5V VCC 13.5V, with Adaptive Shoot Through Protection 3A Output Current, 100V Input Supply Voltage, 7.2V VCC 13.5V, without Adaptive Shoot Through Protection 1.5A Peak Output Current, 4.5V VIN 13.2V High Side Source Up to 100V, 8V VCC 15V High Side Source Up to 80V, 4V VCC 15V 6A Peak Output Current, Adjustable Gate Drive from 5V to 8V, 5V VIN 25V Pulse Drive Transformer Synchronous Input Gate Drive Transformer Synchronous Input Internal Charge Pump 4.5V to 18V Supply Range Internal Charge Pump 4.5V to 18V Supply Range 8V to 48V Supply Range, tON = 200s, tOFF = 28s 1.8V to 6V Supply Range, tON = 95s, tOFF = 45s Optimized for High Current Outputs, 3V VIN 20V
4449f
12 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 0110 * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2010

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