LTC4442/LTC4442-1
High Speed Synchronous
N-Channel MOSFET Drivers
FEATURES
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DESCRIPTION
The LTC®4442 is a high frequency gate driver designed
to drive two N-channel MOSFETs in a synchronous buck
DC/DC converter topology. The powerful driver capability reduces switching losses in MOSFETs with high gate
capacitance.
Wide VCC Range: 6V to 9.5V
38V Maximum Input Supply Voltage
Adaptive Shoot-Through Protection
2.4A Peak Pull-Up Current
5A Peak Pull-Down Current
8ns TG Fall Time Driving 3000pF Load
12ns TG Rise Time Driving 3000pF Load
Separate Supply to Match PWM Controller
Drives Dual N-Channel MOSFETs
Undervoltage Lockout
Thermally Enhanced MSOP Package
The LTC4442 features a separate supply for the input
logic to match the signal swing of the controller IC. If the
input signal is not being driven, the LTC4442 activates a
shutdown mode that turns off both external MOSFETs.
The input logic signal is internally level-shifted to the
bootstrapped supply, which may function at up to 42V
above ground.
APPLICATIONS
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The LTC4442 contains undervoltage lockout circuits on
both the driver and logic supplies that turn off the external
MOSFETs when an undervoltage condition is present.
The LTC4442 and LTC4442-1 have different undervoltage
lockout thresholds to accommodate a wide variety of applications. An adaptive shoot-through protection feature is
also built-in to prevent power loss resulting from MOSFET
cross-conduction current.
Distributed Power Architectures
High Density Power Modules
The LTC4442/LTC4442-1 are available in the thermally
enhanced 8-lead MSOP package.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
LTC4442 Driving 3000pF Capacitive Loads
Synchronous Buck Converter Driver
INPUT (IN)
5V/DIV
VIN
32V
VCC
6V
BOOST
LTC4442
PWM
VLOGIC
TG
VCC
TS
IN
BG
BOTTOM
GATE (BG)
5V/DIV
VOUT
TOP GATE
(TG-TS)
5V/DIV
GND
4442 TA01a
10ns/DIV
4442 TA01b
4442fb
1
LTC4442/LTC4442-1
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
Supply Voltage
VCC......................................................... –0.3V to 10V
VLOGIC .................................................... –0.3V to 10V
BOOST – TS ........................................... –0.3V to 10V
IN Voltage .................................................. –0.3V to 10V
BOOST Voltage .......................................... –0.3V to 42V
TS Voltage..................................................... –5V to 38V
TS + VCC....................................................................42V
Driver Output TG (with Respect to TS)....... –0.3V to 10V
Driver Output BG........................................ –0.3V to 10V
Operating Temperature Range (Note 2).... –40°C to 85°C
Junction Temperature (Note 3) ............................. 125°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec) .................. 300°C
TOP VIEW
TG
TS
BG
GND
1
2
3
4
9
GND
8
7
6
5
BOOST
VCC
VLOGIC
IN
MS8E PACKAGE
8-LEAD PLASTIC MSOP
TJMAX = 125°C, θJA = 40°C/W
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC4442EMS8E#PBF
LTC4442EMS8E#TRPBF
LTCTJ
8-Lead Plastic MSOP
–40°C to 85°C
LTC4442IMS8E#PBF
LTC4442IMS8E#TRPBF
LTCTJ
8-Lead Plastic MSOP
–40°C to 85°C
LTC4442EMS8E-1#PBF
LTC4442EMS8E-1#TRPBF LTCXR
8-Lead Plastic MSOP
–40°C to 85°C
LTC4442IMS8E-1#PBF
LTC4442IMS8E-1#TRPBF LTCXR
8-Lead Plastic MSOP
–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 ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = VBOOST = 7V, VTS = GND = 0V, VLOGIC = 5V, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
9.5
V
730
850
μA
2.75
2.65
100
3.0
2.9
V
V
mV
9.5
V
300
380
μA
Logic Supply (VLOGIC)
VLOGIC
Operating Range
IVLOGIC
DC Supply Current
IN = Floating
UVLO
Undervoltage Lockout Threshold
VLOGIC Rising
VLOGIC Falling
Hysteresis
3
●
●
2.5
2.4
Gate Driver Supply (VCC)
VCC
Operating Range
IVCC
DC Supply Current
6
IN = Floating
4442fb
2
LTC4442/LTC4442-1
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = VBOOST = 7V, VTS = GND = 0V, VLOGIC = 5V, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
UVLO
Undervoltage Lockout Threshold
VCC Rising (LTC4442)
VCC Falling (LTC4442)
Hysteresis (LTC4442)
●
●
2.75
2.60
3.20
3.04
160
3.65
3.50
V
V
mV
VCC Rising (LTC4442-1)
VCC Falling (LTC4442-1)
Hysteresis (LTC4442-1)
●
●
5.6
4.7
6.2
5.3
850
6.7
5.8
V
V
mV
325
400
μA
3.5
2.2
4.0
2.6
V
V
Bootstrapped Supply (BOOST – TS)
IBOOST
DC Supply Current
IN = Floating
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 Threshold
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
Input Signal (IN)
●
●
3.0
1.9
3.25
2.09
●
●
0.8
0.8
200
100
1.25
1.10
V
V
1.6
1.4
V
V
1.50
1.21
V
V
300
150
μA
μA
High Side Gate Driver Output (TG)
VOH(TG)
TG High Output Voltage
ITG = –10mA, VOH(TG) = VBOOST – VTG
0.7
V
VOL(TG)
TG Low Output Voltage
ITG = 100mA, VOL(TG) = VTG – VTS
100
mV
IPU(TG)
TG Peak Pull-Up Current
●
1.5
2.4
A
IPD(TG)
TG Peak Pull-Down Current
●
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
●
1.4
2.4
A
IPD(BG)
BG Peak Pull-Down Current
●
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
tr(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 LTC4442I/LTC4442I-1 are guaranteed to meet specifications
from –40°C to 85°C. The LTC4442E/LTC4442E-1 are guaranteed to meet
specifications from 0°C to 85°C with specifications over the –40°C to
85°C operating temperature range assured by design, characterization and
correlation with statistical process controls.
TJ is calculated from the ambient temperature TA and power dissipation PD
according to the following formula:
TJ = TA + (PD • θJA°C/W)
Note 3: This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may impair device reliability.
4442fb
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LTC4442/LTC4442-1
TYPICAL PERFORMANCE CHARACTERISTICS
Input Thresholds for VLOGIC = 3.3V
vs Temperature
5
3.0
INPUT THRESHOLD (V)
VIL(BG)
VIH(BG)
1
4
VIL(TG)
1.5
VIL(BG)
1.0
VIH(BG)
7
6
5
8
VLOGIC SUPPLY (V )
0
–40
10
9
–10
20
50
80
TEMPERATURE (°C)
4442 G01
0.3
0.2
0.1
0
3
4
7
6
5
8
VLOGIC SUPPLY (V)
10
9
VLOGIC UVLO THRESHOLD (V)
SUPPLY CURRENT (mA)
0.5
IBOOST
0.3
IVLOGIC
0.8
0.30
VLOGIC = 5V
0.25
0.20
VLOGIC = 3.3V
0.15
0.10
0.7
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
IVCC
7
6
5
8
SUPPLY VOLTAGE (V)
4
10
9
4442 G06
VCC Undervoltage Lockout
Thresholds vs Temperature
7.0
2.9
RISING THRESHOLD
2.8
FALLING THRESHOLD
2.7
2.6
0.1
0
–40
IN FLOATING
0.9
6.5
0.6
110
1.0
3.0
0.7
20
80
50
TEMPERATURE (°C)
Quiescent Supply Current vs
Supply Voltage
VLOGIC Undervoltage Lockout
Thresholds vs Temperature
IVLOGIC
–10
4442 G05
1.0
0.2
VIH(BG)
4442 G03
0.35
Quiescent Supply Current vs
Temperature
0.4
VIL(BG)
0
–40
110
0.40
4442 G04
IN FLOATING
0.9 VLOGIC = 5V
V = BOOST-TS = 7V
0.8 CC
2
BG or TG Input Threshold
Hysteresis vs Temperature
BG OR TG INPUT THRESHOLD HYSTERSIS (V)
BG OR TG INPUT THRESHOLD HYSTERESIS (V)
0.4
VIL(TG)
3
4442 G02
BG or TG Input Threshold Hysteresis
vs VLOGIC Supply Voltage
0.5
VIH(TG)
1
0.5
0
3
2.0
VLOGIC ≥ 5V
4
SUPPLY CURRENT (mA)
2
VIH(TG)
VCC UVLO THRESHOLD (V)
INPUT THRESHOLD (V)
VIL(TG)
3
5
VLOGIC = 3.3V
2.5
VIH(TG)
4
Input Thresholds for VLOGIC ≥ 5V
vs Temperature
INPUT THRESHOLD (V)
Input Thresholds vs
VLOGIC Supply Voltage
6.0
LTC4442-1 RISING THRESHOLD
LTC4442-1 FALLING THRESHOLD
5.5
5.0
4.5
4.0
3.5
3.0
LTC4442 RISING THRESHOLD
LTC4442 FALLING THRESHOLD
2.5
–10
20
80
50
TEMPERATURE (°C)
110
4442 G07
2.5
–40
–10
20
80
50
TEMPERATURE (°C)
110
4442 G08
2.0
–40
–10
20
80
50
TEMPERATURE (°C)
110
4442 G09
4442fb
4
LTC4442/LTC4442-1
TYPICAL PERFORMANCE CHARACTERISTICS
Undervoltage Lockout Threshold
Hysteresis vs Temperature
Switching Supply Current vs
Input Frequency
4
800
700
600
500
400
300
LTC4442
VCC UVLO
200
100
0
–40
VLOGIC UVLO
–10
20
80
50
TEMPERATURE (°C)
3
IVCC
2
IBOOST
1
0
110
IVLOGIC
0
200k
600k
400k
FREQUENCY (Hz)
800k
4442 G10
tPLH(BG)
tPHL(TG)
15
tPHL(BG)
10
NO LOAD
VLOGIC = 5V
BOOST-TS = VCC
tPLH(TG)
25
tPLH(BG)
20
tPHL(TG)
15
tPHL(BG)
10
7
8
9
6
VLOGIC SUPPLY VOLTAGE (V)
5
8
7
9
6
VCC SUPPLY VOLTAGE (V)
Output High Voltage vs
VCC Supply Voltage
RISE/FALL TIME (ns)
BG OR TG HIGH OUTPUT VOLTAGE (V)
–10mA
–100mA
6
5
4
3
tPHL(BG)
15
tPHL(TG)
10
0
–40
10
–10
20
50
80
TEMPERATURE (°C)
110
4442 G15
Rise and Fall Time vs
Load Capacitance
100
20
VCC = BOOST-TS = 7V
CLOAD = 3.3nF
BOOST-TS = VCC
9
–1mA
tPLH(BG)
20
Rise and Fall Time vs
VCC Supply Voltage
BOOST-TS = VCC
7
tPLH(TG)
25
4442 G14
4442 G13
8
30
5
4
10
30
NO LOAD
VLOGIC = 5V
VCC = BOOST-TS = 7V
35
tr(BG)
tr(TG)
15
RISE/FALL TIME (ns)
5
1
10
3
LOAD CAPACITANCE (nF)
Propagation Delay vs Temperature
0
0
4
0.3
4442 G12
5
5
3
ILOGIC
fIN = 500kHz
0.1
PROPAGATION DELAY (ns)
20
1
40
30
PROPAGATION DELAY (ns)
PROPAGATION DELAY (ns)
NO LOAD
35 VCC = BOOST-TS = 7V
tPLH(TG)
ICC OR IBOOST
fIN = 100kHz
0
1M
35
40
25
ICC OR IBOOST
fIN = 500kHz
10
Propagation Delay vs
VCC Supply Voltage
30
VLOGIC = 5V
VCC = BOOST-TS = 7V
4442 G11
Propagation Delay vs VLOGIC
Supply Voltage
10
SUPPLY CURRENT (mA)
900
100
NO LOAD
VLOGIC = 5V
VCC = BOOST-TS = 7V
LTC4442-1
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
9
6
VCC SUPPLY VOLTAGE (V)
10
4442 G16
4
5
8
9
6
7
VCC SUPPLY VOLTAGE (V)
10
4442 G17
1
10
3
LOAD CAPACITANCE (nF)
30
4442 G18
4442fb
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LTC4442/LTC4442-1
PIN FUNCTIONS
TG (Pin 1): High Side Gate Driver Output (Top Gate). This
pin swings between TS and BOOST.
TS (Pin 2): High Side MOSFET Source Connection (Top
Source).
VLOGIC (Pin 6): Logic Supply. This pin powers the input
buffer and logic. Connect this pin to the power supply
of the controller that is driving IN (Pin 5) to match input
thresholds or to VCC (Pin 7) to simplify PCB routing.
GND (Pin 4, Exposed Pad Pin 9): Chip Ground. The exposed
pad must be soldered to the PCB ground for electrical
contact and for rated thermal performance.
VCC (Pin 7): Output Driver Supply. This pin powers the
low side gate driver output directly and the high side
gate driver output through an external diode connected
between this pin and BOOST (Pin 8). A low ESR ceramic
bypass capacitor should be tied between this pin and
GND (Pin 4).
IN (Pin 5): Input Signal. Input referenced to an internal
supply powered by VLOGIC (Pin 6) and referenced to GND
(Pin 4). If this pin is floating, an internal resistive divider
triggers a shutdown mode in which both BG (Pin 3) and
TG (Pin 1) are pulled low. Trace capacitance on this pin
should be minimized to keep the shutdown time low.
BOOST (Pin 8): High Side Bootstrapped Supply. An external capacitor should be tied between this pin and TS
(Pin 2). Normally, a bootstrap diode is connected between
VCC (Pin 7) and this pin. Voltage swing at this pin is from
VCC – VD to VIN + VCC – VD, where VD is the forward voltage drop of the bootstrap diode.
BG (Pin 3): Low Side Gate Driver Output (Bottom Gate).
This pin swings between VCC and GND.
4442fb
6
LTC4442/LTC4442-1
BLOCK DIAGRAM
7
VCC
UNDERVOLTAGE
LOCKOUT
BOOST
6
VLOGIC
TG
LEVEL
SHIFTER
UNDERVOLTAGE
LOCKOUT
TS
INTERNAL
SUPPLY
1
2
SHOOTTHROUGH
PROTECTION
7k
5
8
VCC
THREE-STATE
INPUT
BUFFER
IN
BG
3
7k
4
GND
9 GND
4442 BD
TIMING DIAGRAM
IN
TG
BG
VIL(TG)
VIL(BG)
90%
10%
90%
4442 TD
10%
tr(TG)
tpLH(TG)
tf(BG)
tpHL(BG)
tr(BG)
tpLH(BG)
tf(TG)
tpHL(TG)
4442fb
7
LTC4442/LTC4442-1
OPERATION
Overview
The LTC4442 receives a ground-referenced, low voltage
digital input signal to drive two N-channel power MOSFETs
in a synchronous buck power supply configuration. The
gate of the low side MOSFET is driven either to VCC or GND,
depending on the state of the input. Similarly, the gate of
the high side MOSFET is driven to either BOOST or TS by
a supply bootstrapped off of the switch node (TS).
Input Stage
The LTC4442 employs a unique three-state input stage with
transition thresholds that are proportional to the VLOGIC
supply. The VLOGIC supply can be tied to the controller
IC’s power supply so that the input thresholds will match
those of the controller’s output signal. Alternatively, VLOGIC
can be tied to VCC to simplify routing. An internal voltage
regulator in the LTC4442 limits the input threshold values
for VLOGIC supply voltages greater than 5V.
The relationship between the transition thresholds and the
three input states of the LTC4442 is illustrated in Figure 1.
When the voltage on IN is greater than the threshold VIH(TG),
TG is pulled up to BOOST, turning the high side MOSFET
on. This MOSFET will stay on until IN falls below VIL(TG).
Similarly, when IN is less than VIH(BG), BG is pulled up
to VCC, turning the low side (synchronous) MOSFET on.
BG will stay high until IN increases above the threshold
VIL(BG).
VIH(TG)
One application of this three-state input is to keep both of
the power MOSFETs off while an undervoltage condition
exists on the controller IC power supply. This can be accomplished by driving the IN pin with a logic buffer that
has an enable pin. With the enable pin of the buffer tied
to the power good pin of the controller IC, the logic buffer output will remain in a high impedance state until the
controller confirms that its supply is not in an undervoltage
state. The three-state input of the LTC4442 will therefore
pull IN into the region where TG and BG are low until the
controller has enough voltage to operate predictably.
The hysteresis between the corresponding VIH and VIL
voltage levels eliminates false triggering due to noise
during switch transitions; however, care should be taken
to keep noise from coupling into the IN pin, particularly
in high frequency, high voltage applications.
Undervoltage Lockout
The LTC4442 contains undervoltage lockout detectors that
monitor both the VCC and VLOGIC supplies. When VCC falls
below 3.04V or VLOGIC falls below 2.65V, the output pins
BG and TG are pulled to GND and TS, respectively. This
turns off both of the external MOSFETs. When VCC and
VLOGIC have adequate supply voltage for the LTC4442 to
operate reliably, normal operation will resume.
TG HIGH
TG LOW
TG HIGH
TG LOW
VIL(TG)
IN
VIL(BG)
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.
BG LOW
BG HIGH
BG LOW
BG HIGH
VIH(BG)
4442 F01
Adaptive Shoot-Through Protection
Internal adaptive shoot-through protection circuitry
monitors the voltages on the external MOSFETs to ensure
that they do not conduct simultaneously. The LTC4442
does not allow the bottom MOSFET to turn on until the
gate-source voltage on the top MOSFET is sufficiently
low, and vice-versa. This feature improves efficiency by
Figure 1. Three-State Input Operation
4442fb
8
LTC4442/LTC4442-1
OPERATION
eliminating cross-conduction current from flowing from
the VIN supply through the MOSFETs to ground during a
switch transition.
Output Stage
A simplified version of the LTC4442’s output stage is
shown in Figure 2. The pull-up device on both the BG and
TG outputs is an NPN bipolar junction transistor (Q1 and
Q2). The BG and TG outputs are pulled up to within an
NPN VBE (~0.7V) of their positive rails (VCC and BOOST,
respectively). Both BG and TG have N-channel MOSFET pulldown devices (N1 and N2) which pull BG and TG down to
their negative rails, GND and TS. An additional NPN bipolar
junction transistor (Q3) is present on BG to increase its
pull-down drive current capacity. The large voltage swing of
the BG and TG output pins is important in driving external
power MOSFETs, whose RDS(ON) is inversely proportional
to its gate overdrive voltage (VGS – VTH).
VIN
UP TO 38V
8
LTC4442
BOOST
CGD
Q1
TG
1
N1
CGS
TS
VCC
2
LOAD
INDUCTOR
7
Q2
CGD
BG
Q3
HIGH SIDE
POWER
MOSFET
3
N2
CGS
GND
4
LOW SIDE
POWER
MOSFET
4442 F02
Figure 2. Capacitance Seen by BG and TG During Switching
Rise/Fall Time
Since the power MOSFET generally accounts for the majority of power loss in a converter, it is important to quickly
turn it on and off, thereby minimizing the transition time
and power loss. The LTC4442’s peak pull-up current of
2.4A for both BG and TG (Q1 and Q2) produces a rapid
turn-on transition for the MOSFETs. This high current is
capable of driving a 3nF load with a 12ns rise time.
It is also important to turn the power MOSFETs off quickly
to minimize power loss due to transition time; however,
an additional benefit of a strong pull-down on the driver
outputs is the prevention of cross-conduction current. For
example, when BG turns the low-side power MOSFET off
and TG turns the high-side power MOSFET on, the voltage on the TS pin will rise to VIN very rapidly. This high
frequency positive voltage transient will couple through
the CGD capacitance of the low side power MOSFET to
the BG pin. If the BG pin is not held down sufficiently, the
voltage on the BG pin will rise above the threshold voltage of the low side power MOSFET, momentarily turning
it back on. As a result, both the high side and low side
MOSFETs will be conducting, which will cause significant
cross-conduction current to flow through the MOSFETs
from VIN to ground, thereby introducing substantial power
loss. A similar effect occurs on TG due to the CGS and CGD
capacitances of the high side MOSFET.
The LTC4442’s powerful parallel combination of the
N-channel MOSFET (N2) and NPN (Q3) on the BG pull-down
generates a phenomenal 5ns fall time on BG while driving
a 3nF load. Similarly, the 1Ω pull-down MOSFET (N1) on
TG results in a rapid 8ns fall time with a 3nF load. These
powerful pull-down devices minimize the power loss associated with MOSFET turn-off time and cross-conduction
current.
4442fb
9
LTC4442/LTC4442-1
APPLICATIONS INFORMATION
Power Dissipation
To ensure proper operation and long-term reliability, the
LTC4442 must not operate beyond its maximum temperature rating. Package junction temperature can be
calculated by:
TJ = TA + (PD)(θJA)
where:
TJ = Junction temperature
TA = Ambient temperature
PD = Power dissipation
θJA = Junction-to-ambient thermal resistance
Power dissipation consists of standby, switching and
capacitive load power losses:
PD = PDC + PAC + PQG
where:
PDC = Quiescent power loss
PAC = Internal switching loss at input frequency fIN
PQG = Loss due turning on and off the external MOSFET
with gate charge QG at frequency fIN
The LTC4442 consumes very little quiescent current. The
DC power loss at VLOGIC = 5V and VCC = VBOOST − TS =
7V is only (730μA)(5V) + (625μA)(7V) = 8mW.
At a particular switching frequency, the internal power loss
increases due to both AC currents required to charge and
discharge internal nodal capacitances and cross-conduction currents in the internal logic gates. The sum of the
quiescent current and internal switching current with no
load are shown in the Typical Performance Characteristics
plot of Switching Supply Current vs Input Frequency.
The gate charge losses are primarily due to the large AC
currents required to charge and discharge the capacitance
of the external MOSFETs during switching. For identical
pure capacitive loads CLOAD on TG and BG at switching
frequency fin, the load losses would be:
PCLOAD = (CLOAD)(fIN)[(VBOOST – TS)2 + (VCC)2]
In a typical synchronous buck configuration, VBOOST – TS
is equal to VCC – VD, where VD is the forward voltage
drop across the diode between VCC and BOOST. If this
drop is small relative to VCC, the load losses can be
approximated as:
PCLOAD ≈ 2(CLOAD)(fIN)(VCC)2
Unlike a pure capacitive load, a power MOSFET’s gate
capacitance seen by the driver output varies with its VGS
voltage level during switching. A MOSFET’s capacitive load
power dissipation can be calculated using its gate charge,
QG. The QG value corresponding to the MOSFET’s VGS
value (VCC in this case) can be readily obtained from the
manufacturer’s QG vs VGS curves. For identical MOSFETs
on TG and BG:
PQG ≈ 2(VCC)(QG)(fIN)
To avoid damaging junction temperatures due to power
dissipation, the LTC4442 includes a temperature monitor
that will pull BG and TG low if the junction temperature
exceeds 160°C. Normal operation will resume when the
junction temperature cools to less than 135°C.
Bypassing and Grounding
The LTC4442 requires proper bypassing on the VLOGIC, VCC
and VBOOST – TS supplies due to its high speed switching
(nanoseconds) and large AC currents (Amperes). Careless
component placement and PCB trace routing may cause
excessive ringing and undershoot/overshoot.
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10
LTC4442/LTC4442-1
APPLICATIONS INFORMATION
To obtain the optimum performance from the LTC4442:
A. Mount the bypass capacitors as close as possible
between the VLOGIC and GND pins, the VCC and GND
pins, and the BOOST and TS pins. The leads should
be shortened as much as possible to reduce lead
inductance.
B. Use a low inductance, low impedance ground plane
to reduce any ground drop and stray capacitance.
Remember that the LTC4442 switches greater than
5A peak currents and any significant ground drop will
degrade signal integrity.
C. Plan the power/ground routing carefully. Know where
the large load switching current is coming from and
going to. Maintain separate ground return paths for
the input pin and the output power stage.
D. Keep the copper traces between the driver output pins
and the load short and wide.
E. Be sure to solder the Exposed Pad on the back side of
the LTC4442 packages to the board. Correctly soldered
to a 2500mm2 double-sided 1oz copper board, the
LTC4442 has a thermal resistance of approximately
40°C/W. Failure to make good thermal contact between
the exposed back side and the copper board will result
in thermal resistances far greater.
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11
LTC4442/LTC4442-1
PACKAGE DESCRIPTION
MS8E Package
8-Lead Plastic MSOP, Exposed Die Pad
(Reference LTC DWG # 05-08-1662 Rev E)
BOTTOM VIEW OF
EXPOSED PAD OPTION
2.06 p 0.102
(.081 p .004)
1
0.889 p 0.127
(.035 p .005)
2.794 p 0.102
(.110 p .004)
0.29
REF
1.83 p 0.102
(.072 p .004)
0.05 REF
5.23
(.206)
MIN
DETAIL “B”
CORNER TAIL IS PART OF
DETAIL “B” THE LEADFRAME FEATURE.
FOR REFERENCE ONLY
NO MEASUREMENT PURPOSE
2.083 p 0.102 3.20 – 3.45
(.082 p .004) (.126 – .136)
8
0.42 p 0.038
(.0165 p .0015)
TYP
3.00 p 0.102
(.118 p .004)
(NOTE 3)
0.65
(.0256)
BSC
8
7 6 5
0.52
(.0205)
REF
RECOMMENDED SOLDER PAD LAYOUT
0.254
(.010)
3.00 p 0.102
(.118 p .004)
(NOTE 4)
4.90 p 0.152
(.193 p .006)
DETAIL “A”
0o – 6o TYP
GAUGE PLANE
1
0.53 p 0.152
(.021 p .006)
DETAIL “A”
2 3
4
1.10
(.043)
MAX
0.86
(.034)
REF
0.18
(.007)
SEATING
PLANE
0.22 – 0.38
(.009 – .015)
TYP
0.65
(.0256)
BSC
0.1016 p 0.0508
(.004 p .002)
MSOP (MS8E) 0908 REV E
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
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12
LTC4442/LTC4442-1
REVISION HISTORY
(Revision history begins at Rev B)
REV
DATE
DESCRIPTION
B
4/10
Updated Pin Configuration
PAGE NUMBER
2
Updated GND (Pin 4) in Pin Functions
6
Updated Related Parts
14
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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.
13
LTC4442/LTC4442-1
TYPICAL APPLICATION
LTC7510/LTC4442-1 12V to 1.5V/30A Digital Step-Down DC/DC Converter with PMBus Serial Interface
7V VDRIVE
12V
5V
R1
SDATA
PMBus
INTERFACE
SCLK
LTC7510
VD25
C2
BOOST
R2
+
PWRGD
OUTEN
C4
C1 C3
GND
PWM
MULTIPHASE
INTERFACE
C5
0.22μF
VD33
SMB_AL_N
POWER
MANAGEMENT
INTERFACE
D2
CMDSH3
V12SEN
VCC
TG
VLOGIC
LTC4442-1
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
RTN
1k
4442 TA02
VSET
1k
FSET
1k
RESET_N
VTRIM
1k
IMAXSET
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC4449
High Speed Synchronous N-Channel MOSFET Driver
Up to 38V Supply Voltage, 4.5V ≤ VCC ≤ 6.5V, 3.2A Peak Pull-Up/
4.5A Peak Pull-Down
LTC4444/
LTC4444-5
High Voltage Synchronous N-Channel MOSFET Driver with
Shoot Through Protection
Up to 100V Supply Voltage, 4.5V/7.2V ≤ VCC ≤ 13.5V, 3A Peak Pull-Up/
0.55Ω Peak Pull-Down
LTC4446
High Voltage Synchronous N-Channel MOSFET Driver without
Shoot Through Protection
Up to 100V Supply Voltage, 7.2V ≤ VCC ≤ 13.5V, 3A Peak Pull-Up/
0.55Ω Peak Pull-Down
LTC4440/
LTC4440-5
High Speed, High Voltage High Side Gate Driver
Up to 80V Supply Voltage, 8V ≤ VCC ≤ 15V, 2.4A Peak Pull-Up/
1.5Ω Peak Pull-Down
LTC4441/
LTC4441-1
N-Channel MOSFET Gate Driver
Up to 25V Supply Voltage, 5V ≤ VCC ≤ 25V, 6A Peak Output Current
LTC1154
High Side Micropower MOSFET Driver
Up to 18V Supply Voltage, 85μA Quiescent Current, H-Grade Available
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14 Linear Technology Corporation
LT 0410 REV B • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
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