LTC4442EMS8E-1-PBF [Linear]
High Speed Synchronous N-Channel MOSFET Drivers; 高速同步N沟道MOSFET驱动器
| 型号： | LTC4442EMS8E-1-PBF |
| 厂家： | 
Linear |
| 描述： | High Speed Synchronous N-Channel MOSFET Drivers |
| 文件： | 总12页 (文件大小：159K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC4442/LTC4442-1
High Speed Synchronous
N-Channel MOSFET Drivers
FEATURES
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 capabil-
ity reduces switching losses in MOSFETs with high gate
capacitance.
■
Wide V Range: 6V to 9.5V
CC
■
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
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.
■
12ns TG Rise Time Driving 3000pF Load
■
Separate Supply to Match PWM Controller
■
Drives Dual N-Channel MOSFETs
■
Undervoltage Lockout
■
Thermally Enhanced MSOP Package
APPLICATIONS
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 ap-
plications.Anadaptiveshoot-throughprotectionfeatureis
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.
, LT, LTC and LTM 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
V
V
IN
CC
32V
6V
BOOST
LTC4442
BOTTOM
GATE (BG)
5V/DIV
V
V
TG
TS
LOGIC
CC
TOP GATE
(TG-TS)
5V/DIV
V
OUT
PWM
IN
BG
GND
4442 TA01a
4442 TA01b
10ns/DIV
4442fa
1
LTC4442/LTC4442-1
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
Supply Voltage
TOP VIEW
TG
TS
BG
1
2
3
4
8 BOOST
V ......................................................... –0.3V to 10V
CC
7 V
6 V
CC
LOGIC
9
V
LOGIC
.................................................... –0.3V to 10V
5 IN
GND
BOOST – TS........................................... –0.3V to 10V
IN Voltage .................................................. –0.3V to 10V
BOOST Voltage .......................................... –0.3V to 42V
TS Voltage..................................................... –5V to 38V
MS8E PACKAGE
8-LEAD PLASTIC MSOP
T
= 125°C, θ = 160°C/W
JMAX
JA
EXPOSED PAD (PIN #) IS GND, MUST BE SOLDERED TO PCB
TS + V ...................................................................42V
CC
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
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
LTCTJ
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC4442EMS8E#PBF
LTC4442IMS8E#PBF
LTC4442EMS8E-1#PBF
LTC4442IMS8E-1#PBF
LTC4442EMS8E#TRPBF
LTC4442IMS8E#TRPBF
8-Lead Plastic MSOP
8-Lead Plastic MSOP
8-Lead Plastic MSOP
8-Lead Plastic MSOP
–40°C to 85°C
–40°C to 85°C
–40°C to 85°C
–40°C to 85°C
LTCTJ
LTC4442EMS8E-1#TRPBF LTCXR
LTC4442IMS8E-1#TRPBF LTCXR
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
Logic Supply (V
)
LOGIC
V
Operating Range
3
9.5
V
LOGIC
I
DC Supply Current
IN = Floating
730
850
μA
VLOGIC
●
●
UVLO
Undervoltage Lockout Threshold
V
V
Rising
Falling
2.5
2.4
2.75
2.65
100
3.0
2.9
V
V
mV
LOGIC
LOGIC
Hysteresis
Gate Driver Supply (V
)
CC
V
Operating Range
6
9.5
V
CC
I
DC Supply Current
IN = Floating
300
380
μA
VCC
4442fa
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
V
V
Rising (LTC4442)
Falling (LTC4442)
2.75
2.60
3.20
3.04
160
3.65
3.50
V
V
mV
CC
CC
Hysteresis (LTC4442)
●
●
V
V
Rising (LTC4442-1)
Falling (LTC4442-1)
5.6
4.7
6.2
5.3
850
6.7
5.8
V
V
mV
CC
CC
Hysteresis (LTC4442-1)
Bootstrapped Supply (BOOST – TS)
I
DC Supply Current
IN = Floating
325
400
μA
BOOST
Input Signal (IN)
●
●
V
V
V
V
TG Turn-On Input Threshold
TG Turn-Off Input Threshold
BG Turn-On Input Threshold
BG Turn-Off Input Theshold
V
V
≥ 5V, IN Rising
3.0
1.9
3.5
2.2
4.0
2.6
V
V
IH(TG)
IL(TG)
IH(BG)
IL(BG)
IN(SD)
LOGIC
LOGIC
= 3.3V, IN Rising
V
LOGIC
V
LOGIC
≥ 5V, IN Falling
= 3.3V, IN Falling
3.25
2.09
V
V
●
●
V
LOGIC
V
LOGIC
≥ 5V, IN Falling
= 3.3V, IN Falling
0.8
0.8
1.25
1.10
1.6
1.4
V
V
V
LOGIC
V
LOGIC
≥ 5V, IN Rising
= 3.3V, IN Rising
1.50
1.21
V
V
I
Maximum Current Into or Out of IN in
Shutdown Mode
V
LOGIC
V
LOGIC
≥ 5V, IN Floating
= 3.3V, IN Floating
200
100
300
150
μA
μA
High Side Gate Driver Output (TG)
V
V
TG High Output Voltage
TG Low Output Voltage
TG Peak Pull-Up Current
TG Peak Pull-Down Current
I
I
= –10mA, V
= V
– V
TG
0.7
100
2.4
2.4
V
mV
A
OH(TG)
OL(TG)
PU(TG)
PD(TG)
TG
OH(TG)
BOOST
= 100mA, V
= V – V
TG
TG
OL(TG)
TS
●
●
I
I
1.5
1.5
A
Low Side Gate Driver Output (BG)
V
V
BG High Output Voltage
BG Low Output Voltage
BG Peak Pull-Up Current
BG Peak Pull-Down Current
I
I
= –10mA, V
= 100mA
= V – V
BG
0.7
100
2.4
5.0
V
mV
A
OH(BG)
OL(BG)
PU(BG)
PD(BG)
BG
OH(BG)
CC
BG
●
●
I
I
1.4
3.5
A
Switching Time
t
t
t
t
t
t
t
t
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
20
12
20
12
12
8
ns
ns
ns
ns
ns
ns
ns
ns
PLH(TG)
PHL(TG)
PLH(BG)
PHL(BG)
r(TG)
10% – 90%, C = 3nF
L
TG Output Fall Time
10% – 90%, C = 3nF
L
f(TG)
BG Output Rise Time
10% – 90%, C = 3nF
12
5
r(BG)
L
BG Output Fall Time
10% – 90%, C = 3nF
L
r(BG)
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.
T is calculated from the ambient temperature T and power dissipation P
according to the following formula:
J
A
D
T = T + (PD • θ °C/W)
J
A
JA
Note 3: This IC includes overtemperature protection that is intended
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.
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.
4442fa
3
LTC4442/LTC4442-1
TYPICAL PERFORMANCE CHARACTERISTICS
Input Thresholds vs
Input Thresholds for VLOGIC = 3.3V
vs Temperature
Input Thresholds for VLOGIC ≥ 5V
vs Temperature
V
LOGIC Supply Voltage
5
4
3
2
1
0
5
4
3
2
1
0
3.0
2.5
2.0
1.5
1.0
0.5
0
V
= 3.3V
V
≥ 5V
LOGIC
LOGIC
V
V
IH(TG)
IH(TG)
V
V
IH(TG)
V
V
V
IL(TG)
IL(TG)
IL(TG)
IL(BG)
V
V
IL(BG)
V
IL(BG)
V
IH(BG)
IH(BG)
V
IH(BG)
3
4
5
6
7
8
9
10
–40
–10
20
50
80
110
–40
–10
20
50
80
110
V
SUPPLY (V )
TEMPERATURE (°C)
TEMPERATURE (°C)
LOGIC
4442 G01
4442 G03
4442 G02
BG or TG Input Threshold Hysteresis
vs VLOGIC Supply Voltage
Quiescent Supply Current vs
Supply Voltage
BG or TG Input Threshold
Hysteresis vs Temperature
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.5
0.4
0.3
0.2
0.1
0
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0
IN FLOATING
I
VLOGIC
V
= 5V
LOGIC
V
= 3.3V
LOGIC
I
VCC
I
BOOST
–40
–10
20
50
80
110
3
5
6
7
8
10
7
8
10
4
9
3
4
5
6
9
SUPPLY VOLTAGE (V)
V
SUPPLY (V)
TEMPERATURE (°C)
LOGIC
4442 G05
4442 G06
4442 G04
Quiescent Supply Current vs
Temperature
VLOGIC Undervoltage Lockout
Thresholds vs Temperature
VCC Undervoltage Lockout
Thresholds vs Temperature
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
3.0
2.9
2.8
2.7
2.6
2.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
IN FLOATING
V
V
= 5V
LTC4442-1 RISING THRESHOLD
LOGIC
CC
= BOOST-TS = 7V
I
VLOGIC
LTC4442-1 FALLING THRESHOLD
RISING THRESHOLD
FALLING THRESHOLD
I
BOOST
LTC4442 RISING THRESHOLD
LTC4442 FALLING THRESHOLD
I
VCC
–40
–10
20
50
80
110
–40
–10
20
50
80
110
–40
–10
20
50
80
110
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
4442 G07
4442 G08
4442 G09
4442fa
4
LTC4442/LTC4442-1
TYPICAL PERFORMANCE CHARACTERISTICS
Undervoltage Lockout Threshold
Hysteresis vs Temperature
Switching Supply Current vs
Input Frequency
Switching Supply Current vs
Load Capacitance
1000
900
800
700
600
500
400
300
200
100
0
4
3
2
1
0
100
NO LOAD
V
V
= 5V
LOGIC
= BOOST-TS = 7V
CC
LTC4442-1
V
V
= 5V
LOGIC
CC
V
CC
UVLO
= BOOST-TS = 7V
I
OR I
BOOST
IN
CC
f
= 500kHz
I
I
VCC
10
1
I
f
OR I
BOOST
= 100kHz
CC
IN
BOOST
LTC4442
UVLO
I
VLOGIC
I
LOGIC
V
CC
f
= 500kHz
IN
1
V
UVLO
50
LOGIC
0
–40
–10
20
80
110
0
200k
400k
600k
800k
1M
0.1
0.3
3
10
30
TEMPERATURE (°C)
LOAD CAPACITANCE (nF)
FREQUENCY (Hz)
4442 G12
4442 G10
4442 G11
Propagation Delay vs VLOGIC
Supply Voltage
Propagation Delay vs
VCC Supply Voltage
Propagation Delay vs Temperature
35
30
25
20
15
10
5
40
35
30
25
20
15
10
5
40
NO LOAD
NO LOAD
NO LOAD
= 5V
V
V
= 5V
V
= BOOST-TS = 7V
V
LOGIC
CC
CC
LOGIC
35
30
= BOOST-TS = 7V
BOOST-TS = V
CC
t
t
PLH(TG)
t
PLH(TG)
25
20
15
10
5
t
t
PLH(TG)
PLH(BG)
t
PLH(BG)
t
PLH(BG)
PHL(TG)
t
PHL(TG)
t
PHL(BG)
t
PHL(BG)
t
PHL(TG)
t
PHL(BG)
0
0
0
–40
–10
20
50
80
110
8
SUPPLY VOLTAGE (V)
10
4
5
6
7
9
4
5
7
8
9
10
3
6
TEMPERATURE (°C)
V
V
SUPPLY VOLTAGE (V)
CC
LOGIC
4442 G15
4442 G14
4442 G13
Output High Voltage vs
VCC Supply Voltage
Rise and Fall Time vs
VCC Supply Voltage
Rise and Fall Time vs
Load Capacitance
100
10
1
20
15
10
5
10
9
8
7
6
5
4
3
2
1
0
V
= BOOST-TS = 7V
BOOST-TS = V
CC
C
= 3.3nF
CC
LOAD
BOOST-TS = V
CC
t
r(BG)
t
r(TG)
–10mA
–1mA
–100mA
t
r(BG)
t
f(TG)
t
f(BG)
t
r(TG)
t
f(TG)
f(BG)
t
0
1
3
10
30
4
5
6
7
8
9
10
4
5
7
8
9
10
6
LOAD CAPACITANCE (nF)
V
SUPPLY VOLTAGE (V)
V
SUPPLY VOLTAGE (V)
CC
CC
4442 G18
4442 G17
4442 G16
4442fa
5
LTC4442/LTC4442-1
PIN FUNCTIONS
TG (Pin 1): High Side Gate Driver Output (Top Gate). This
pin swings between TS and BOOST.
V
(Pin 7): Output Driver Supply. This pin powers the
CC
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).
TS (Pin 2): High Side MOSFET Source Connection (Top
Source).
BG (Pin 3): Low Side Gate Driver Output (Bottom Gate).
This pin swings between V and GND.
CC
BOOST (Pin 8): High Side Bootstrapped Supply. An ex-
ternal capacitor should be tied between this pin and TS
(Pin 2). Normally, a bootstrap diode is connected between
GND (Pin 4): Chip Ground.
IN (Pin 5): Input Signal. Input referenced to an internal
V
V
(Pin 7) and this pin. Voltage swing at this pin is from
CC
CC
supply powered by V
(Pin 6) and referenced to GND
LOGIC
– V to V + V – V , where V is the forward volt-
D
IN
CC
D
D
(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.
age drop of the bootstrap diode.
Exposed Pad (Pin 9): Ground. Must be electrically con-
nected to GND (Pin 4) and soldered to PCB ground for
optimal thermal performance.
V
(Pin 6): Logic Supply. This pin powers the input
LOGIC
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 V (Pin 7) to simplify PCB routing.
CC
BLOCK DIAGRAM
V
CC
UNDERVOLTAGE
LOCKOUT
7
BOOST
8
TG
V
LEVEL
SHIFTER
LOGIC
UNDERVOLTAGE
LOCKOUT
1
6
TS
2
INTERNAL
SUPPLY
SHOOT-
THROUGH
PROTECTION
7k
V
CC
THREE-STATE
BG
INPUT
IN
3
5
BUFFER
7k
GND
GND
4
9
4442 BD
4442fa
6
LTC4442/LTC4442-1
TIMING DIAGRAM
V
IL(TG)
IN
V
IL(BG)
90%
10%
TG
BG
4442 TD
90%
10%
t
t
r(TG)
pLH(TG)
r(BG)
t
pLH(BG)
t
t
t
f(BG)
pHL(BG)
f(TG)
t
pHL(TG)
t
OPERATION
Overview
TG HIGH
TG LOW
V
IH(TG)
TG HIGH
TG LOW
The LTC4442 receives a ground-referenced, low voltage
digitalinputsignaltodrivetwoN-channelpowerMOSFETs
in a synchronous buck power supply configuration. The
V
V
IL(TG)
IN
gateofthelowsideMOSFETisdriveneithertoV orGND,
CC
BG LOW
BG HIGH
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).
V
IL(BG)
BG LOW
BG HIGH
IH(BG)
4442 F01
Input Stage
Figure 1. Three-State Input Operation
TheLTC4442employsauniquethree-stateinputstagewith
Thethresholdsarepositionedtoallowforaregioninwhich
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.
transition thresholds that are proportional to the V
LOGIC
supply. The V
supply can be tied to the controller
IC’s power supply so that the input thresholds will match
LOGIC
thoseofthecontroller’soutputsignal.Alternatively,V
LOGIC
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 ac-
complished 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 buf-
fer output will remain in a high impedance state until the
controllerconfirmsthatitssupplyisnotinanundervoltage
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.
can be tied to V to simplify routing. An internal voltage
CC
regulator in the LTC4442 limits the input threshold values
for V
supply voltages greater than 5V.
LOGIC
Therelationshipbetweenthetransitionthresholdsandthe
three input states of the LTC4442 is illustrated in Figure 1.
WhenthevoltageonINisgreaterthanthethresholdV
,
IH(TG)
TG is pulled up to BOOST, turning the high side MOSFET
on. This MOSFET will stay on until IN falls below V
.
IL(TG)
, BG is pulled up
Similarly, when IN is less than V
IH(BG)
to V , turning the low side (synchronous) MOSFET on.
BG will stay high until IN increases above the threshold
CC
V
.
IL(BG)
4442fa
7
LTC4442/LTC4442-1
OPERATION
The hysteresis between the corresponding V and V
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.
V
IN
IH
IL
UP TO 38V
8
LTC4442
BOOST
C
GD
Q1
HIGH SIDE
POWER
TG
TS
1
2
7
MOSFET
N1
C
GS
LOAD
Undervoltage Lockout
INDUCTOR
V
CC
TheLTC4442containsundervoltagelockoutdetectorsthat
monitor both the V and V
supplies. When V falls
falls below 2.65V, the output pins
CC
LOGIC
LOGIC
CC
Q2
N2
C
GD
below 3.04V or V
LOW SIDE
POWER
BG
3
4
BG and TG are pulled to GND and TS, respectively. This
turns off both of the external MOSFETs. When V and
MOSFET
Q3
C
GS
CC
GND
4442 F02
V
have adequate supply voltage for the LTC4442 to
LOGIC
operate reliably, normal operation will resume.
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 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
eliminating cross-conduction current from flowing from
SincethepowerMOSFETgenerallyaccountsforthemajor-
ity 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.
the V supply through the MOSFETs to ground during a
IN
switch transition.
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
outputsisthepreventionofcross-conductioncurrent. For
example, when BG turns the low-side power MOSFET off
and TG turns the high-side power MOSFET on, the volt-
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 V (~0.7V) of their positive rails (V and BOOST,
age on the TS pin will rise to V very rapidly. This high
IN
frequency positive voltage transient will couple through
BE
CC
respectively).BothBGandTGhaveN-channelMOSFETpull-
down devices (N1 and N2) which pull BG and TG down to
theirnegativerails,GNDandTS.AnadditionalNPNbipolar
junction transistor (Q3) is present on BG to increase its
pull-downdrivecurrentcapacity.Thelargevoltageswingof
the BG and TG output pins is important in driving external
the C capacitance of the low side power MOSFET to
GD
the BG pin. If the BG pin is not held down sufficiently, the
voltage on the BG pin will rise above the threshold volt-
age 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
power MOSFETs, whose R
is inversely proportional
GS
DS(ON)
to its gate overdrive voltage (V – V ).
fromV toground,therebyintroducingsubstantialpower
TH
IN
loss. A similar effect occurs on TG due to the C and C
GS
GD
capacitances of the high side MOSFET.
4442fa
8
LTC4442/LTC4442-1
OPERATION
TG results in a rapid 8ns fall time with a 3nF load. These
powerful pull-down devices minimize the power loss as-
sociatedwithMOSFETturn-offtimeandcross-conduction
current.
The LTC4442’s powerful parallel combination of the
N-channelMOSFET(N2)andNPN(Q3)ontheBGpull-down
generates a phenomenal 5ns fall time on BG while driving
a 3nF load. Similarly, the 1Ω pull-down MOSFET (N1) on
APPLICATIONS INFORMATION
Power Dissipation
The gate charge losses are primarily due to the large AC
currentsrequiredtochargeanddischargethecapacitance
of the external MOSFETs during switching. For identical
To ensure proper operation and long-term reliability, the
LTC4442 must not operate beyond its maximum tem-
perature rating. Package junction temperature can be
calculated by:
pure capacitive loads C
on TG and BG at switching
LOAD
frequency fin, the load losses would be:
2
2
P
= (C
)(f )[(V
– TS) + (V ) ]
CLOAD
LOAD IN
BOOST CC
T = T + (P )(θ )
J
A
D
JA
In a typical synchronous buck configuration, V
– TS
BOOST
where:
is equal to V – V , where V is the forward voltage
CC
D
D
T = Junction temperature
drop across the diode between V and BOOST. If this
J
CC
T = Ambient temperature
drop is small relative to V , the load losses can be
A
CC
P = Power dissipation
approximated as:
D
JA
θ
= Junction-to-ambient thermal resistance
2
P
≈ 2(C )(f )(V )
LOAD IN CC
CLOAD
Power dissipation consists of standby, switching and
capacitive load power losses:
Unlike a pure capacitive load, a power MOSFET’s gate
capacitance seen by the driver output varies with its V
GS
P = P + P + P
voltagelevelduringswitching.AMOSFET’scapacitiveload
D
DC
AC
QG
power dissipation can be calculated using its gate charge,
where:
Q . The Q value corresponding to the MOSFET’s V
GS
G
G
P
AC
P
= Quiescent power loss
DC
value (V in this case) can be readily obtained from the
CC
P
= Internal switching loss at input frequency f
IN
manufacturer’s Q vs V curves. For identical MOSFETs
G
GS
= Loss due turning on and off the external MOSFET
QG
on TG and BG:
with gate charge Q at frequency f
G
IN
P
≈ 2(V )(Q )(f )
QG
CC
G
IN
The LTC4442 consumes very little quiescent current. The
DC power loss at V = 5V and V = V − TS = 7V
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.
LOGIC
CC
BOOST
is only (730ꢀA)(5V) + (625ꢀA)(7V) = 8mW.
Ataparticularswitchingfrequency,theinternalpowerloss
increases due to both AC currents required to charge and
discharge internal nodal capacitances and cross-conduc-
tion currents in the internal logic gates. The sum of the
quiescent current and internal switching current with no
loadareshownintheTypicalPerformanceCharacteristics
plot of Switching Supply Current vs Input Frequency.
Bypassing and Grounding
TheLTC4442requiresproperbypassingontheV
,V
LOGIC CC
and V
– TS supplies due to its high speed switching
BOOST
(nanoseconds)andlargeACcurrents(Amperes).Careless
component placement and PCB trace routing may cause
excessive ringing and undershoot/overshoot.
4442fa
9
LTC4442/LTC4442-1
APPLICATIONS INFORMATION
To obtain the optimum performance from the LTC4442:
A. Mount the bypass capacitors as close as possible
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.
between the V
and GND pins, the V and GND
LOGIC
CC
pins, and the BOOST and TS pins. The leads should
be shortened as much as possible to reduce lead
inductance.
D. Keep the copper traces between the driver output pins
and the load short and wide.
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.
E. Be sure to solder the Exposed Pad on the back side of
the LTC4442 packages to the board. Correctly soldered
2
to a 2500mm 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.
TYPICAL APPLICATION
LTC7510/LTC4442-1 12V to 1.5V/30A Digital Step-Down DC/DC Converter with PMBus Serial Interface
7V V
DRIVE
12V
5V
R1
R2
D2
C5
SDATA
V
12SEN
CMDSH3
0.22μF
PMBus
V
SCLK
CC
INTERFACE
V
SMB_AL_N
D33
V
C2
BOOST
D25
LTC7510
M1
RJK0305
×2
+
POWER
MANAGEMENT
INTERFACE
V
V
TG
PWRGD
OUTEN
LOGIC
CC
L1
C4
C1
C3
LTC4442-1
0.3μH
GND
TS
V
OUT
M2
C6
R3
PWM
IN
BG
+
RJK0301
×2
330μF
×6
GND
1μF
SYNC_IN
MULTIPHASE
INTERFACE
D1
R
SYNC_OUT
CM
TEMPSEN
LOAD
I
SENN
FAULT1
FAULT2
R
FAULT
OUTPUTS
SENSE
I
SENP
SENP
SENN
V
V
1k
1k
1k
1k
1k
I
4442 TA02
OUT/ISH
SADDR
RTN
I-SHARE
I
SH_GND
V
SET
FSET
RESET_N
V
TRIM
I
MAXSET
4442fa
10
LTC4442/LTC4442-1
PACKAGE DESCRIPTION
MS8E Package
8-Lead Plastic MSOP, Exposed Die Pad
(Reference LTC DWG # 05-08-1662 Rev D)
BOTTOM VIEW OF
EXPOSED PAD OPTION
2.06 ± 0.102
(.081 ± .004)
1
1.83 ± 0.102
(.072 ± .004)
0.889 ± 0.127
(.035 ± .005)
2.794 ± 0.102
(.110 ± .004)
5.23
(.206)
MIN
3.20 – 3.45
(.126 – .136)
2.083 ± 0.102
(.082 ± .004)
8
3.00 ± 0.102
(.118 ± .004)
(NOTE 3)
0.52
(.0205)
REF
0.65
(.0256)
BSC
0.42 ± 0.038
(.0165 ± .0015)
TYP
8
7 6
5
RECOMMENDED SOLDER PAD LAYOUT
3.00 ± 0.102
(.118 ± .004)
(NOTE 4)
4.90 ± 0.152
(.193 ± .006)
DETAIL “A”
0.254
(.010)
0° – 6° TYP
GAUGE PLANE
1
2
3
4
0.53 ± 0.152
(.021 ± .006)
1.10
(.043)
MAX
0.86
(.034)
REF
DETAIL “A”
0.18
(.007)
SEATING
PLANE
0.22 – 0.38
(.009 – .015)
TYP
0.1016 ± 0.0508
(.004 ± .002)
0.65
(.0256)
BSC
MSOP (MS8E) 0307 REV D
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
4442fa
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 representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
11
LTC4442/LTC4442-1
RELATED PARTS
PART NUMBER
LTC1154
LTC1155
LT®1161
DESCRIPTION
COMMENTS
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
High Speed Single/Dual N-Channel MOSFET Driver
Synchronous Rectifier Driver for Forward Converter
Internal Charge Pump, 4.5V to 18V Supply Range
Internal Charge Pump, 4.5V to 18V Supply Range
8V to 48V Supply Range, t = 200μs, t = 28μs
ON
OFF
LTC1163
LTC1693
LTC3900
LTC3901
1.8V to 6V Supply Range, t = 95μs, t = 45μs
ON OFF
CMOS Compatible Input, V Range: 4.5V to 13.2V
CC
Pulse Transformer Synchronization Input
Gate Drive Transformer Synchronous Input
Secondary Side Synchronous Driver for Push-Pull and
Full-Bridge Converter
LTC4440
LTC4441
LTC7510
High Speed, High Voltage, High Side Gate Driver
6A MOSFET Driver
Wide Operating V Range: Up to 80V DC, 100V Transient
IN
Adjustable Gate Drive from 5V to 8V, 5V ≤ V ≤ 28V
IN
Digital DC/DC Controller with PMBus Interface
Digital Controller, PMBus Serial Interface, 150kHz to 2MHz
Switching Frequency
4442fa
LT 0108 REV A • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
12
●
●
© LINEAR TECHNOLOGY CORPORATION 2007
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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