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LTC4443/LTC4443-1 High Speed Synchronous N-Channel MOSFET Drivers FEATURES
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DESCRIPTION
The LTC(R)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. 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 x 3mm DFN package.
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 x 3mm DFN Package
APPLICATIONS
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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
VIN 32V BOOST VCC 6V VLOGIC TG VOUT INPUT (IN) 5V/DIV
LTC4443 Driving 3000pF Capacitive Loads
VCC LTC4443 TS PWM IN GND BG
BOTTOM GATE (BG) 5V/DIV TOP GATE (TG-TS) 5V/DIV
4443 TA01a
10ns/DIV
4443 TA01b
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LTC4443/LTC4443-1 ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW NC NC TG TS BG GND 1 2 3 4 5 6 12 BOOST 11 BOOST 10 BOOST 9 VCC 8 VLOGIC 7 IN
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).... -40C to 85C Junction Temperature (Note 3) ............................. 125C Storage Temperature Range................... -65C to 150C
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DDMA PACKAGE 12-LEAD (3mm 3mm) PLASTIC DFN JA = 43C/W, JC = 3C/W EXPOSED PAD (PIN 13) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH LTC4443EDD#PBF LTC4443IDD#PBF LTC4443EDD-1#PBF LTC4443IDD-1#PBF TAPE AND REEL LTC4443EDD#TRPBF LTC4443IDD#TRPBF LTC4443EDD-1#TRPBF LTC4443IDD-1#TRPBF PART MARKING* LCXH LCXH LCYN LCYN PACKAGE DESCRIPTION 12-Lead (3mm x 3mm) Plastic DFN 12-Lead (3mm x 3mm) Plastic DFN 12-Lead (3mm x 3mm) Plastic DFN 12-Lead (3mm x 3mm) Plastic DFN TEMPERATURE RANGE -40C to 85C -40C to 85C -40C to 85C -40C to 85C
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/
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 7V, VTS = GND = 0V, VLOGIC = 5V, unless otherwise noted.
SYMBOL VLOGIC IVLOGIC UVLO PARAMETER Operating Range DC Supply Current Undervoltage Lockout Threshold IN = Floating VLOGIC Rising VLOGIC Falling Hysteresis
l l
ELECTRICAL CHARACTERISTICS
Logic Supply (VLOGIC)
CONDITIONS
MIN 3
TYP
MAX 9.5
UNITS V A V V mV V A V V mV V V mV
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730 2.5 2.4 2.75 2.65 100
850 3.0 2.9
Gate Driver Supply (VCC) VCC IVCC UVLO Operating Range DC Supply Current Undervoltage Lockout Threshold IN = Floating VCC Rising (LTC4443) VCC Falling (LTC4443) Hysteresis (LTC4443) VCC Rising (LTC4443-1) VCC Falling (LTC4443-1) Hysteresis (LTC4443-1)
l l l l
6 600 2.75 2.60 5.6 4.7 3.20 3.04 160 6.2 5.3 850
9.5 800 3.65 3.50 6.7 5.8
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LTC4443/LTC4443-1 ELECTRICAL CHARACTERISTICS
SYMBOL VD 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
l l
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 7V, VTS = GND = 0V, VLOGIC = 5V, unless otherwise noted.
PARAMETER Schottky Diode Forward Voltage CONDITIONS ID = 10mA ID = 100mA 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
l l l l l l
MIN
TYP 0.38 0.48
MAX
UNITS V V
3.0 1.9
3.5 2.2 3.25 2.09
4.0 2.6
V V V V
0.8 0.8
1.25 1.10 1.50 1.21
1.6 1.4
V V V V A A 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) tf(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 LTC4443I/LTC4443I-1 are guaranteed to meet specifications from -40C to 85C. The LTC4443E/LTC4443E-1 are guaranteed to meet specifications from 0C to 85C with specifications over the -40C to 85C 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 * 43C/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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LTC4443/LTC4443-1 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
4443 G01
-10
20 50 80 TEMPERATURE (C)
110
4443 G02
0 -40
-10
20 80 50 TEMPERATURE (C)
110
4443 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
Quiescent Supply Current vs Supply Voltage
IN FLOATING 0.9 BOOST > VCC 0.8 SUPPLY CURRENT (mA) 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 IVCC IBOOST
0.4
0.30 VLOGIC = 5V 0.25 0.20 0.15 0.10 0.05 0 -40 -10 20 50 80 TEMPERATURE (C) 110
4443 G05
IVLOGIC
0.3
0.2
VLOGIC = 3.3V
0.1
0 3 4 6 5 7 8 VLOGIC SUPPLY (V) 9 10
4443 G04
3
4
7 6 5 8 SUPPLY VOLTAGE (V)
9
10
4443 G06
Schottky Diode Forward Voltage vs Diode Current
0.60 0.50 0.40 0.30 0.20 0.10 0 0 50 100 150 DIODE CURRENT (mA) 200
4443 G07
VLOGIC Undervoltage Lockout Thresholds vs Temperature
3.0 7.0 6.5
VCC Undervoltage Lockout Thresholds vs Temperature
LTC4443-1 RISING THRESHOLD LTC4443-1 FALLING THRESHOLD
DIODE FORWARD VOLTAGE (V)
VLOGIC UVLO THRESHOLD (V)
VCC UVLO THRESHOLD (V)
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
LTC4443 RISING THRESHOLD LTC4443 FALLING THRESHOLD
2.6
2.5 -40
-10
20 80 50 TEMPERATURE (C)
110
4443 G08
2.0 -40
-10
20 80 50 TEMPERATURE (C)
110
4443 G09
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LTC4443/LTC4443-1 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 LTC4443 VCC UVLO VLOGIC UVLO 20 80 50 TEMPERATURE (C) 110
4443 G10
Switching Supply Current vs Input Frequency
7 NO LOAD = 5V V 6 VLOGIC CC = 7V TS = GND 5 IVCC 100
Switching Supply Current vs Load Capacitance
VLOGIC = 5V VCC = 7V TS = GND ICC fIN = 500kHz
LTC4443-1 VCC UVLO SUPPLY CURRENT (mA)
SUPPLY CURRENT (mA)
10 ICC fIN = 100kHz 1 ILOGIC fIN = 500kHz 0
4 3 2 1 0 0 200k
IVLOGIC
400k
600k
800k
1M
4443 G11
0.1
0.3
FREQUENCY (Hz)
1 10 3 LOAD CAPACITANCE (nF)
30
4443 G12
Propagation Delay vs VLOGIC Supply Voltage
40 35 PROPAGATION DELAY (ns) 30 25 20 tPHL(TG) 15 10 5 0 3 4 8 9 7 6 VLOGIC SUPPLY VOLTAGE (V) 5 10
4443 G13
Propagation Delay vs VCC Supply Voltage
NO LOAD VCC = 7V TS = GND PROPAGATION DELAY (ns) 35 30 25 20 15 10 5 0 4 5 tPHL(BG) tPLH(TG) tPLH(BG) tPHL(TG) NO LOAD VLOGIC = 5V TS = GND PROPAGATION DELAY (ns) 40 35 30 25
Propagation Delay vs Temperature
NO LOAD VLOGIC = 5V VCC = 7V TS = GND tPLH(TG) tPLH(BG) 20 15 10 5 tPHL(BG) tPHL(TG)
tPLH(TG) tPLH(BG)
tPHL(BG)
8 7 9 6 VCC SUPPLY VOLTAGE (V)
10
4443 G14
0 -40
-10
20 50 80 TEMPERATURE (C)
110
4443 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 6 VCC SUPPLY VOLTAGE (V) 9 10
4443 G16
Rise and Fall Time vs VCC Supply Voltage
20 100 CLOAD = 3.3nF TS = GND
Rise and Fall Time vs Load Capacitance
VCC = 7V TS = GND tr(TG) tr(BG)
TS = GND
-1mA
-100mA
RISE/FALL TIME (ns)
tr(BG) 10 tr(TG) tf(TG) 5 tf(BG)
RISE/FALL TIME (ns)
-10mA
15
10
tf(TG) tf(BG)
0 4 5 8 9 6 7 VCC SUPPLY VOLTAGE (V) 10
4443 G17
1 1 10 3 LOAD CAPACITANCE (nF) 30
4443 G18
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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
BOOST UNDERVOLTAGE LOCKOUT BOOST BOOST VLOGIC LEVEL SHIFTER TG TS INTERNAL SUPPLY
9
VCC
12 11 10 3 4
8
UNDERVOLTAGE LOCKOUT
SHOOTTHROUGH PROTECTION VCC THREE-STATE INPUT BUFFER BG 5
7k IN 7k 6 GND
7
13 GND
4443 BD
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LTC4443/LTC4443-1 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)
4443 TD
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). 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).
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)
4443 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 LTC4443 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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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. 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. 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 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. 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).
VCC Q2 BG Q3 N2 GND
4443 F02
VIN LTC4443 BOOST Q1 TG N1 TS LOAD INDUCTOR CGS CGD HIGH SIDE POWER MOSFET
CGD LOW SIDE POWER MOSFET
CGS
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 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. 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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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 1 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)(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 LTC4443 consumes very little quiescent current. The DC power loss at VLOGIC = 5V and VCC = VBOOST - TS = 7V is only (730A)(5V) + (600A)(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 160C. Normal operation will resume when the junction temperature cools to less than 135C.
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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 43C/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 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 FSET 1k RESET_N VTRIM IMAXSET 1k 1k 1k RTN
4443 TA02
R1 V12SEN VCC VD33 VD25 C2 C5 0.22F
+
C1 C3
R2 C4
BOOST TG VLOGIC LTC4443-1 VCC TS IN 1F GND BG
M1 RJK0305 2 M2 RJK0301 2
L1 0.3H R3 C6 VOUT
+
330F 6
RCM
D1
RSENSE
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LTC4443/LTC4443-1 PACKAGE DESCRIPTION
DDMA Package 12-Lead Plastic DFN (3mm x 3mm)
(Reference LTC DWG # 05-08-1743 Rev A)
1.19 0.05 0.93 0.05 0.70 0.05 2.25 REF
0.57 0.05 3.50 0.05 0.81 0.05 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 3.00 0.10 0.40 0.10 2.38 0.10 0.81 0.10 1.35 0.10 R = 0.115 TYP 7 0.11 0.05 12 2.38 0.05 1.35 0.05 2.10 0.05
PACKAGE OUTLINE
3.00 0.10 PIN 1 TOP MARK (SEE NOTE 6) 0.200 REF 0.75 0.05
0.63 0.05 PIN 1 NOTCH R = 0.20 OR 0.25 x 45 CHAMFER
R = 0.05 TYP
6
0.23 0.05 0.45 BSC 2.25 REF
(DD12MA) DFN 0507 REV A
1
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
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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 LT 1161 LTC1693 Family LTC4440 LTC4440-5 LTC4441 LTC4442/LTC4442-1 LTC4444 LTC4445/LTC4445-1 LTC4447 LTC7510
(R)
DESCRIPTION Quad Protected High Side 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 High Speed Synchronous N-Channel MOSFET Driver High Voltage Synchronous N-Channel MOSFET Driver Dual High Speed Synchronous N-Channel MOSFET Driver High Speed Synchronous N-Channel MOSFET Driver Digital DC/DC Controller with PMBus Interface
COMMENTS 8V to 48V Supply Range, tON = 200s, tOFF = 28s 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 5A Peak Output Current, Three-State Input, 38V Maximum Input Supply Voltage, 6V VCC 9.5V, MS8E Package High Side Source Up to 100V, 3A Peak Output Current, 7.2V VCC 13.5V Two Independent Drivers, Internal Schottky Diodes, 38V Maximum Input Supply Voltage, 6V VCC 9.5V, 4.5A Peak Output Current, Rail-to-Rail Drivers, 38V Maximum Input Supply Voltage, 4V VCC 6.5V Digital Controller, PMBus Serial Interface, 150kHz to 2MHz Switching Frequency
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12 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 0608 REV A * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2008

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