LTC4449EDCB#TRMPBF [Linear]
LTC4449 - High Speed Synchronous N-Channel MOSFET Driver; Package: DFN; Pins: 8; Temperature Range: -40°C to 85°C;
| 型号： | LTC4449EDCB#TRMPBF |
| 厂家： | 
Linear |
| 描述： | LTC4449 - High Speed Synchronous N-Channel MOSFET Driver; Package: DFN; Pins: 8; Temperature Range: -40°C to 85°C 驱动器 |
| 文件： | 总12页 (文件大小：164K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC4449
High Speed Synchronous
N-Channel MOSFET Driver
FEATURES
DESCRIPTION
The LTC®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.
n
4V to 6.5V V Operating Voltage
CC
n
38V Maximum Input Supply Voltage
n
Adaptive Shoot-Through Protection
n
Rail-to-Rail Output Drivers
n
3.2A Peak Pull-Up Current
n
4.5A Peak Pull-Down Current
The LTC4449 features a separate supply for the input logic
to match the signal swing of the controller IC. If the input
signalisnotbeingdriven,theLTC4449activatesashutdown
modethatturnsoffbothexternalMOSFETs.Theinputlogic
signalisinternallylevel-shiftedtothebootstrappedsupply,
which functions at up to 42V above ground.
n
8ns TG Risetime Driving 3000pF Load
n
7ns TG Falltime Driving 3000pF Load
n
Separate Supply to Match PWM Controller
n
Drives Dual N-Channel MOSFETs
Undervoltage Lockout
n
n
Low Profile (0.75mm) 2mm × 3mm DFN Package
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 cross-
conduction current.
APPLICATIONS
n
Distributed Power Architectures
High Density Power Modules
n
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
The LTC4449 is available in the 2mm × 3mm DFN
package.
TYPICAL APPLICATION
Synchronous Buck Converter Driver
LTC4449 Driving 3000pF Capacitive Loads
V
CC
4V TO 6.5V
V
CC
INPUT (IN)
5V/DIV
V
IN
BOOST
TO 38V
V
LOGIC
LTC4449
GND
TOP GATE
(TG - TS)
5V/DIV
TG
TS
BG
V
OUT
PWM
IN
BOTTOM GATE
(BG) 5V/DIV
4449 TA01a
4449 TA01b
10ns/DIV
4449f
1
LTC4449
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
Supply Voltage
TOP VIEW
V
...................................................... –0.3V to 7V
LOGIC
8
7
6
5
TG
TS
1
2
3
4
BOOST
V ........................................................... –0.3V to 7V
CC
V
V
CC
9
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
BG
LOGIC
GND
IN
DCB PACKAGE
8-LEAD (2mm s 3mm) PLASTIC DFN
θ
JA
= 64°C/W, θ = 10.6°C/W
JC
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
(Notes 2, 3)............................................–40°C to 125°C
Storage Temperature Range...................–65°C to 150°C
ORDER INFORMATION
LEAD FREE FINISH
LTC4449EDCB#PBF
LTC4449IDCB#PBF
TAPE AND REEL
PART MARKING*
LFKC
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC4449EDCB#TRPBF
LTC4449IDCB#TRPBF
–40°C to 85°C
–40°C to 125°C
8-Lead (2mm × 3mm) Plastic DFN
8-Lead (2mm × 3mm) Plastic DFN
LFKC
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 The l denotes the specifications which apply over the full operating junction
temperature range, otherwise specifications are at TA = 25°C. VCC = VLOGIC = VBOOST = 5V, VTS = GND = 0V, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Logic Supply (V
)
LOGIC
V
Operating Range
3
6.5
V
LOGIC
I
DC Supply Current
IN = Floating
730
900
μA
VLOGIC
l
l
UVLO
Undervoltage Lockout Threshold
V
V
Rising
Falling
2.5
2.4
2.75
2.65
100
3
2.9
V
V
mV
LOGIC
LOGIC
Hysteresis
Gate Driver Supply (V
)
CC
V
Operating Range
4
6.5
V
CC
I
DC Supply Current
IN = Floating
300
400
μA
VCC
l
l
UVLO
Undervoltage Lockout Threshold
V
V
Rising
Falling
2.75
2.60
3.20
3.04
160
3.65
3.50
V
V
mV
CC
CC
Hysteresis
I
DC Supply Current
IN = Floating
300
400
μA
BOOST
4449f
2
LTC4449
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating junction
temperature range, otherwise specifications are at TA = 25°C. VCC = VLOGIC = VBOOST = 5V, VTS = GND = 0V, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Input Signal (IN)
l
l
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
3.5
2.2
4
V
V
IH(TG)
IL(TG)
IH(BG)
IL(BG)
IN(SD)
LOGIC
LOGIC
= 3.3V, IN Rising
1.9
2.6
l
l
V
LOGIC
V
LOGIC
≥ 5V, IN Falling
= 3.3V, IN Falling
2.75
1.8
3.25
2.09
3.75
2.5
V
V
l
l
V
LOGIC
V
LOGIC
≥ 5V, IN Falling
= 3.3V, IN Falling
0.8
0.8
1.25
1.1
1.6
1.4
V
V
l
l
V
LOGIC
V
LOGIC
≥ 5V, IN Rising
= 3.3V, IN Rising
1.05
0.9
1.5
1.21
1.85
1.5
V
V
I
Maximum Current Into or Out of IN in
Shutdown Mode
V
LOGIC
V
LOGIC
≥ 5V, IN Floating
= 3.3V, IN Floating
150
75
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
= –100mA, V
= V
– V
TG
140
80
mV
mV
A
OH(TG)
OL(TG)
PU(TG)
PD(TG)
TG
OH(TG)
BOOST
= 100mA, V
= V – V
TG TS
TG
OL(TG)
l
l
I
I
2
3.2
2.4
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
= –100mA, V
= 100mA
= V – V
BG
100
100
3.2
mV
mV
A
OH(BG)
OL(BG)
PU(BG)
PD(BG)
BG
OH(BG)
CC
BG
l
l
I
I
2
3
4.5
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 Risetime
14
13
13
11
8
ns
ns
ns
ns
ns
ns
ns
ns
PLH(TG)
PHL(TG)
PLH(BG)
PHL(BG)
r(TG)
10% to 90%, C = 3nF
L
TG Output Falltime
10% to 90%, C = 3nF
7
f(TG)
L
BG Output Risetime
10% to 90%, C = 3nF
7
r(BG)
L
BG Output Falltime
10% to 90%, C = 3nF
4
f(BG)
L
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
–40°C to 125°C operating junction temperature range. The LTC4449E is
guaranteed to meet specifications from 0°C to 85°C with specifications
over the –40°C to 85°C operating junction temperature range assured by
design, characterization and correlation with statistical process controls.
The junction temperature T is calculated from the ambient temperature T
J A
and power dissipation P according to the following formula:
D
T = T + (PD • 64°C/W)
J
A
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.
4449f
3
LTC4449
TYPICAL PERFORMANCE CHARACTERISTICS
Input Thresholds
vs VLOGIC Supply Voltage
Input Thresholds for VLOGIC = 3.3V
vs Temperature
Input Thresholds for VLOGIC ≥ 5V
vs Temperature
5
4
3
2
1
0
4.0
3.5
3.0
2.5
2.0
3.0
2.5
2.0
1.5
1.0
0.5
V
≥ 5V
V
= 3.3V
LOGIC
V
LOGIC
IH(TG)
V
V
V
V
IH(TG)
IL(TG)
IH(TG)
IL(TG)
V
IL(TG)
V
IL(BG)
1.5
1.0
0.5
0
V
IL(BG)
V
IL(BG)
V
IH(BG)
V
V
IH(BG)
IH(BG)
–40
–10
20
50
80
110
3.0 3.5 4.0 4.5 5.0
5.5 6.0 6.5
–40
–10
20
50
80
110
TEMPERATURE (°C)
V
SUPPLY (V)
TEMPERATURE (°C)
LOGIC
4449 G03
4449 G01
4449 G02
BG or TG Input Threshold Hysteresis
vs VLOGIC Supply Voltage
BG or TG Input Threshold Hysteresis
vs Temperature
Quiescent Supply Current
vs Supply Voltage
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
IN FLOATING
TS = GND
I
VLOGIC
V
= 5V
LOGIC
I
I
BOOST
V
= 3.3V
LOGIC
20
VCC
–40
–10
50
80
110
3.0 3.5 4.0 4.5 5.0
5.5 6.0 6.5
3.0
4.0 4.5 5.0 5.5 6.0 6.5 7.0
SUPPLY VOLTAGE (V)
3.5
V
SUPPLY (V)
TEMPERATURE (°C)
LOGIC
4449 G05
4449 G04
4449 G06
VLOGIC Undervoltage Lockout
Thresholds vs Temperature
VCC Undervoltage Lockout
Thresholds vs Temperature
Undervoltage Lockout Threshold
Hysteresis vs Temperature
2.9
2.8
2.7
2.6
2.5
3.3
3.2
3.1
3.0
2.9
250
200
150
100
50
V
UVLO
UVLO
CC
RISING THRESHOLD
FALLING THRESHOLD
RISING THRESHOLD
FALLING THRESHOLD
V
LOGIC
0
–40
–10
20
50
80
110
–40
–10
20
50
80
110
–40
–10
20
50
80
110
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
4449 G08
4449 G09a
4449 G09b
4449f
4
LTC4449
TYPICAL PERFORMANCE CHARACTERISTICS
Supply Current
vs Input Frequency
Switching Supply Current
vs Load Capacitance
Rise and Fall Time
vs VCC (Boost) Supply Voltage
100
10
1
15
6
5
4
V
= V = 5V
CC
NO LOAD
LOGIC
TS = GND
C
= 3.3nF
LOGIC
LOAD
TS = GND
V
= V = 5V
TS = GND
CC
I
CC
= 500kHz
f
IN
10
5
t
I
CC
f(TG)
t
I
r(TG)
VCC
f
= 100kHz
IN
3
2
1
0
t
I
r(BG)
LOGIC
f
= 500kHz
IN
t
f(BG)
I
VLOGIC
600k
0.1
0
200k
400k
1M
5.5
(BOOST) SUPPLY VOLTAGE (V)
6.5
0
800k
1
3
10
30
3.5
5.0
6.0
4.0
V
CC
4.5
LOAD CAPACITANCE (nF)
FREQUENCY (Hz)
4449 G13
4449 G12
4449 G14
Rise and Fall Time
vs Load Capacitance
Propagation Delay
Propagation Delay
vs VLOGIC Supply Voltage
vs VCC (Boost) Supply Voltage
100
10
1
25
20
15
20
15
10
5
V
= 5V
CC
NO LOAD
NO LOAD
TS = GND
V
= BOOST = 5V
V
= 5V
CC
LOGIC
t
r(TG)
TS = GND
TS = GND
t
pLH(TG)
t
t
pLH(BG)
pLH(TG)
t
f(TG)
t
t
pLH(BG)
pHL(BG)
t
r(BG)
t
pHL(TG)
t
pHL(TG)
t
pHL(BG)
t
f(BG)
10
5
1
3
10
30
5.5
SUPPLY VOLTAGE (V)
6.5
5.0
5.5
6.0
6.5
3.0 3.5 4.0 4.5
5.0
6.0
4.0
4.5
LOAD CAPACITANCE (nF)
V
V
(BOOST) SUPPLY VOLTAGE (V)
CC
LOGIC
4449 G15
4449 G16
4449 G17
Propagation Delay
vs Temperature
25
20
15
10
5
NO LOAD
V
= V
= 5V
CC
LOGIC
t
pHL(TG)
TS = GND
t
pLH(TG)
t
pLH(BG)
t
pHL(BG)
0
–40
–10
20
50
80
110
TEMPERATURE (°C)
4449 G18
4449f
5
LTC4449
PIN FUNCTIONS
TG (Pin 1): High Side Gate Driver Output (Top Gate). This
pin swings between TS and BOOST.
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 7) to match input
TS (Pin 2): High Side MOSFET Source Connection (Top
Source).
thresholds or to V (Pin 9) to simplify PCB routing.
CC
V
(Pin 7): Output Driver Supply. This pin powers the low
CC
BG (Pin 3): Low Side Gate Driver Output (Bottom Gate).
This pin swings between V and GND.
side gate driver output directly and the high side gate driver
outputthroughanexternalSchottkydiodeconnectedbetween
this pin and BOOST. A low ESR ceramic bypass capacitor
should be tied between this pin and GND (Pin 6).
CC
GND (Pin 4, Exposed Pad Pin 9): Chip Ground. The
exposed pad must be soldered to PCB ground for optimal
electrical and thermal performance.
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
IN (Pin 5): Input Signal. Input referenced to an internal
supply baised off of V
(Pin 8) and GND (Pin 6). If
LOGIC
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.
between V (Pin 9) and this pin. Voltage swing at this
CC
pin is from V – V to V + V – V , where V is the
CC
D
IN
CC
D
D
forward voltage drop of the Schottky diode.
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
4449 BD
4449f
6
LTC4449
TIMING DIAGRAM
V
IL(TG)
IN
V
V
IL(BG)
IL(BG)
90%
10%
TG
BG
t
t
r(TG)
f(TG)
90%
10%
4449 TD
t
t
r(BG)
pLH(BG)
pLH(TG)
t
t
f(BG)
t
t
pHL(TG)
pHL(BG)
OPERATION
Overview
TG HIGH
TG LOW
V
IH(TG)
TG HIGH
The LTC4449 receives a ground-referenced, low voltage
digitalinputsignaltodrivetwoN-channelpowerMOSFETs
in a synchronous power supply configuration. The gate
V
V
IL(TG)
TG LOW
IN
of the low side MOSFET is driven either to V or GND,
CC
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).
BG LOW
BG HIGH
V
IL(BG)
BG LOW
BG HIGH
IH(BG)
4449 F01
Input Stage
Figure 1. Three-State Input Operation
TheLTC4449employsauniquethree-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
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
bufferoutputwillremaininahighimpedancestateuntilthe
controllerconfirmsthatitssupplyisnotinanundervoltage
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.
can be tied to V to simplify routing. An internal voltage
CC
regulator in the LTC4449 limits the input threshold values
for V
supply voltages greater than 5V.
LOGIC
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 V
, TG is pulled up to BOOST, turning the
IH(TG)
high side MOSFET on. This MOSFET will stay on until IN
falls below V
. Similarly, when IN is less than V
,
IL(TG)
IH(BG)
BG is pulled up to V , turning the low side (synchronous)
CC
MOSFET on. BG will stay high until IN increases above
the threshold V
.
IL(BG)
4449f
7
LTC4449
OPERATION
The hysteresis between the corresponding V and V
V
IN
IH
IL
LTC4449
BOOST
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.
C
GD
Q1
P1
N1
HIGH SIDE
POWER
MOSFET
TG
TS
C
GS
LOAD
INDUCTOR
Undervoltage Lockout
V
CC
TheLTC4449containsundervoltagelockoutdetectorsthat
monitor both the V and V
supplies. When V falls
C
Q2
Q3
P2
N2
GD
CC
LOGIC
LOGIC
CC
LOW SIDE
POWER
MOSFET
BG
below 3.04V or V
falls below 2.65V, the output pins
BG and TG are pulled to GND and TS, respectively. This
C
GS
turns off both of the external MOSFETs. When V and
GND
CC
V
have adequate supply voltage for the LTC4449 to
4449 F02
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 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
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 pull-
up 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.
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
outputs is the prevention of cross-conduction current. For
example,whenBGturnsthelowsidepowerMOSFEToffand
TG turns the high side power MOSFET on, the voltage on
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
the TS pin will rise to V very rapidly. This high frequency
positive voltage transient will couple through the C
IN
GD
BG and TG outputs to their positive rails (V and BOOST,
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
CC
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
current to flow through the MOSFETs from V to ground,
IN
therebyintroducingsubstantialpowerloss.Asimilareffect
R
is inversely proportional to its gate overdrive
occurs on TG due to the C and C capacitances of the
DS(ON)
voltage (V – V ).
GS
GD
high side MOSFET.
GS
TH
4449f
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 0.8Ω 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
load are shown in the Typical Performance Characteristics
plot of Switching Supply Current vs Input Frequency.
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:
The gate charge losses are primarily due to the large AC
currentsrequiredtochargeanddischargethecapacitance
of the external MOSFETs during switching. For identical
pure capacitive loads C
on TG and BG at switching
LOAD
T = T + (P )(θ )
J
A
D
JA
frequency fin, the load losses would be:
where:
2
2
P
= (C
)(f )[(V
) + (V ) ]
CLOAD
LOAD IN
BOOST – TS
CC
T = junction temperature
J
In a typical synchronous buck configuration, V
BOOST – TS
T = ambient temperature
A
is equal to V – V , where V is the forward voltage drop
CC
D
D
P = power dissipation
D
JA
of the external Schottky diode between V and BOOST.
CC
θ
= junction-to-ambient thermal resistance
If this drop is small relative to V , the load losses can
CC
Power dissipation consists of standby, switching and
capacitive load power losses:
be approximated as:
2
P
≈ 2(C )(f )(V )
LOAD IN CC
CLOAD
P = P + P + P
D
DC
AC
QG
Unlike a pure capacitive load, a power MOSFET’s gate
capacitance seen by the driver output varies with its V
where:
GS
voltagelevelduringswitching.AMOSFET’scapacitiveload
P
AC
P
= quiescent power loss
= internal switching loss at input frequency f
= loss due turning on and off the external
DC
power dissipation can be calculated using its gate charge,
P
IN
Q . The Q value corresponding to the MOSFET’s V
GS
G
G
QG
value (V in this case) can be readily obtained from the
CC
MOSFET with gate charge Q at frequency f
G
IN
manufacturer’s Q vs V curves. For identical MOSFETs
G
GS
The LTC4449 consumes very little quiescent current. The
DC power loss at V = 5V and V = 5V is only (730ꢀA
on TG and BG:
LOGIC
CC
P
≈ 2(V )(Q )(f )
QG
CC
G
IN
+ 600μA)(5V) = 6.65mW.
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 160°C. Normal operation will resume when the
junction temperature cools to less than 135°C.
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
4449f
9
LTC4449
APPLICATIONS INFORMATION
Bypassing and Grounding
5A peak currents and any significant ground drop will
degrade signal integrity.
TheLTC4449requiresproperbypassingontheV
,V
LOGIC CC
and V
supplies due to its high speed switching
• 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.
BOOST – TS
(nanoseconds)andlargeACcurrents(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
• Keep the copper trace between the driver output pin
and the load short and wide.
between the V
and GND pins, the V and GND
• 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 64°C/W. Failure
to make good thermal contact between the exposed
back side and the copper board will result in thermal
resistances far greater.
LOGIC
CC
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
4449f
10
LTC4449
TYPICAL APPLICATION
R U N 1
W P M 1
W P M 2
P G O O D 2
P H S M D
C L K O U T
C L K I N
P G O O D 1
G A V
I
V I N S N S
T R A C K / S S 1
F R E Q
T R A C K / S S 2
C C
V
4449f
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However,noresponsibilityisassumedforitsuse.LinearTechnologyCorporationmakesnorepresentation
that the interconnection of its circuits as described herein will not infringe on existing patent rights.
11
LTC4449
PACKAGE DESCRIPTION
DCB Package
8-Lead Plastic DFN (2mm × 3mm)
(Reference LTC DWG # 05-08-1718 Rev A)
R = 0.115
2.00 p0.10
(2 SIDES)
0.40 p 0.10
TYP
R = 0.05
TYP
5
8
0.70 p0.05
1.35 p0.10
1.35 p0.05
1.65 p 0.05
3.50 p0.05
2.10 p0.05
1.65 p 0.10
3.00 p0.10
(2 SIDES)
PIN 1 NOTCH
R = 0.20 OR 0.25
s 45o CHAMFER
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
PACKAGE
OUTLINE
(DCB8) DFN 0106 REV A
4
1
0.23 p 0.05
0.25 p 0.05
0.45 BSC
0.45 BSC
0.75 p0.05
0.200 REF
1.35 REF
1.35 REF
BOTTOM VIEW—EXPOSED PAD
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
0.00 – 0.05
NOTE:
1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE
2. DRAWING NOT TO SCALE
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
3. ALL DIMENSIONS ARE IN MILLIMETERS
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE
TOP AND BOTTOM OF PACKAGE
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC4442/LTC4442-1 High Speed Synchronous N-Channel MOSFET Driver
5A Peak Output Current, Three-State Input, 38V Maximum Input
Supply Voltage, 6V ≤ V ≤ 9.5V, MS8E Package
CC
LTC4444/LTC4444-5 High Voltage/High Speed Synchronous N-Channel MOSFET
Driver
3A Peak Output Current, 100V Maximum Input Supply Voltage,
4.5V ≤ V ≤ 13.5V, with Adaptive Shoot Through Protection
CC
LTC4446
High Voltage High Side/Low Side N-Channel MOSFET Driver
3A Output Current, 100V Input Supply Voltage, 7.2V ≤ V ≤ 13.5V,
CC
without Adaptive Shoot Through Protection
LTC1693-1/-2/-3/-5 High Speed Single/Dual N-Channel MOSFET Drivers
1.5A Peak Output Current, 4.5V ≤ V ≤ 13.2V
IN
LTC4440
LTC4440-5
LTC4441
High Speed, High Voltage High Side Gate Driver
High Speed, High Voltage High Side Gate Driver
6A MOSFET Driver
High Side Source Up to 100V, 8V ≤ V ≤ 15V
CC
High Side Source Up to 80V, 4V ≤ V ≤ 15V
CC
6A Peak Output Current, Adjustable Gate Drive from 5V to 8V,
5V ≤ V ≤ 25V
IN
LTC3900
LTC3901
Synchronous Rectifier Driver for Forward Converters
Pulse Drive Transformer Synchronous Input
Gate Drive Transformer Synchronous Input
Secondary Side Synchronous Driver for Push-Pull and
Full-Bridge Converters
LTC1154
LTC1155
LT®1161
LTC1163
LTC3860
High Side Micropower MOSFET Driver
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
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
ON
OFF
1.8V to 6V Supply Range, t = 95μs, t = 45μs
ON
OFF
Optimized for High Current Outputs, 3V ≤ V ≤ 20V
IN
4449f
LT 0110 • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
12
●
●
© LINEAR TECHNOLOGY CORPORATION 2010
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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