LTC4447EDD-PBF [Linear]
High Speed Synchronous N-Channel MOSFET Driver; 高速同步N沟道MOSFET驱动器
| 型号： | LTC4447EDD-PBF |
| 厂家： | 
Linear |
| 描述： | High Speed Synchronous N-Channel MOSFET Driver |
| 文件： | 总12页 (文件大小：181K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC4447
High Speed Synchronous
N-Channel MOSFET Driver
FEATURES
DESCRIPTION
TheLTC®4447isahighfrequencygatedriverwithintegrat-
ed bootstrap Schottky diode that is designed to drive two
N-Channel MOSFETs in a synchronous DC/DC converter.
Thepowerfulrail-to-raildrivercapabilityreducesswitching
losses in MOSFETs with high gate capacitance.
■
Integrated Schottky Diode
■
4V to 6.5V V Operating Voltage
CC
■
38V Maximum Input Supply Voltage
■
Adaptive Shoot-Through Protection
■
Rail-to-Rail Output Drivers
■
3.2A Peak Pull-Up Current
TheLTC4447featuresaseparatesupplyfortheinputlogic
to match the signal swing of the controller IC. If the input
signal is not being driven, the LTC4447 activates a shut-
downmodethatturnsoffbothexternalMOSFETs.Theinput
logic signal is internally level-shifted to the bootstrapped
supply, which functions at up to 42V above ground. The
Schottky diode required for the bootstrapped supply is
integrated to simplify layout and reduce parts count.
■
4.5A Peak Pull-Down Current
■
8ns TG Risetime Driving 3000pF Load
■
7ns TG Falltime Driving 3000pF Load
■
Separate Supply to Match PWM Controller
■
Drives Dual N-Channel MOSFETs
Undervoltage Lockout
■
■
Low Profile (0.75mm) 3mm × 3mm DFN Package
The LTC4447 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
■
Distributed Power Architectures
High Density Power Modules
■
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All
other trademarks are the property of their respective owners.
The LTC4447 is available in the 3mm × 3mm DFN
package.
TYPICAL APPLICATION
Synchronous Buck Converter Driver
LTC4447 Driving 3000pF Capacitive Loads
V
CC
4V TO 6.5V
INPUT (IN)
5V/DIV
V
CC
V
IN
BOOST
TO 38V
V
LOGIC
TOP GATE
(TG - TS)
5V/DIV
LTC4447
GND
TG
TS
BG
V
OUT
BOTTOM GATE
(BG) 5V/DIV
PWM
IN
4447 TA01a
4447 TA01b
10ns/DIV
4447f
1
LTC4447
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
Supply Voltage
TOP VIEW
V
...................................................... –0.3V to 7V
LOGIC
NC
NC
1
2
3
4
5
6
12 BOOST
11 BOOST
10 BOOST
V ........................................................... –0.3V to 7V
CC
TG
BOOST – TS............................................. –0.3V to 7V
13
TS
9
8
7
V
V
CC
BOOST Voltage .......................................... –0.3V to 42V
BG
LOGIC
BOOST – V ............................................................38V
GND
IN
CC
TS + V ....................................................................42V
CC
DDMA PACKAGE
12-LEAD (3mm 3mm) PLASTIC DFN
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 Temperature Range (Note 2).... –40°C to 85°C
Junction Temperature (Note 3) ............................. 125°C
Storage Temperature Range................... –65°C to 150°C
θ
= 43°C/W, θ = 3°C/W
JA
JC
EXPOSED PAD (PIN 13) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC4447EDD#PBF
LTC4447IDD#PBF
TAPE AND REEL
PART MARKING*
LDHD
PACKAGE DESCRIPTION
12-Lead (3mm × 3mm) Plastic DFN
12-Lead (3mm × 3mm) Plastic DFN
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 85°C
LTC4447EDD#TRPBF
LTC4447IDD#TRPBF
LDHD
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 ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = VLOGIC = 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
●
●
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
600
800
μA
VCC
●
●
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
V
Schottky Diode Forward Voltage
I = 10mA
D
0.38
0.48
V
V
D
D
I = 100mA
4447f
2
LTC4447
ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = VLOGIC = 5V, VTS = GND = 0V, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
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
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
●
●
V
V
≥ 5V, IN Falling
= 3.3V, IN Falling
2.75
1.8
3.25
2.09
3.75
2.5
V
V
LOGIC
LOGIC
●
●
V
V
≥ 5V, IN Falling
= 3.3V, IN Falling
0.8
0.8
1.25
1.1
1.6
1.4
V
V
LOGIC
LOGIC
●
●
V
V
≥ 5V, IN Rising
= 3.3V, IN Rising
1.05
0.9
1.5
1.21
1.85
1.5
V
V
LOGIC
LOGIC
I
Maximum Current Into or Out of IN in
Shutdown Mode
V
V
≥ 5V, IN Floating
= 3.3V, IN Floating
150
75
300
150
μA
μA
LOGIC
LOGIC
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)
●
●
I
I
2
3.2
2.4
1.5
A
Low Side Gate Driver Output (BG)
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
100
100
3.2
4.5
mV
mV
A
OH(BG)
OL(BG)
PU(BG)
PD(BG)
BG
BG
OH(BG)
CC
BG
V
●
●
I
I
2
3
A
Switching Time
t
t
t
t
t
t
t
t
BG Low to TG High Propagation Delay
IN Low toTG 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 LTC4447I is guaranteed to meet specifications from –40°C
to 85°C. The LTC4447E is guaranteed to meet specifications from 0°C
to 85°C with specifications over the –40°C to 85°C temperature range
assured by design, characterization and correlation with statistical
process controls.
T is calculated from the ambient temperature T and power dissipation
J A
P
according to the following formula:
D
T = T + (PD • 43°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.
4447f
3
LTC4447
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
4447 G03
4447 G01
4447 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
VCC
V
= 3.3V
LOGIC
20
–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
4447 G05
4447 G04
4447 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)
4447 G08
4447 G09a
4447 G09b
4447f
4
LTC4447
TYPICAL PERFORMANCE CHARACTERISTICS
Schottky Diode Forward Voltage
vs Diode Current
Schottky Diode Forward Voltage
vs Temperature
Supply Current vs Input
Frequency
6
5
4
0.6
0.5
0.6
0.5
NO LOAD
LOGIC
TS = GND
V
= V = 5V
CC
I
= 100mA
D
0.4
0.3
0.4
0.3
0.2
0.1
I
I
D
= 10mA
VCC
3
2
1
0
I
= 1mA
D
0.2
0.1
0
I
VLOGIC
600k
0
200k
400k
1M
0
800k
–40
–10
20
50
80
110
0
50
100
150
200
FREQUENCY (Hz)
DIODE CURRENT (mA)
TEMPERATURE (°C)
4447 G12
4447 G11
4447 G10
Switching Supply Current vs Load
Capacitance
Rise and Fall Time vs VCC Supply
Voltage
Rise and Fall Time vs Load
Capacitance
100
10
1
100
10
1
15
V
= V = 5V
V
= 5V
CC
C
= 3.3nF
LOGIC
CC
LOAD
TS = GND
TS = GND
TS = GND
t
r(TG)
I
CC
f
IN
= 500kHz
10
5
t
I
f(TG)
CC
t
f(TG)
t
r(TG)
f
IN
= 100kHz
t
r(BG)
t
I
r(BG)
LOGIC
f
IN
= 500kHz
t
f(BG)
t
f(BG)
0.1
0
30
1
3
LOAD CAPACITANCE (nF)
10
30
3.5
5.0
SUPPLY VOLTAGE (V)
5.5
6.0
6.5
1
3
10
4.0
4.5
LOAD CAPACITANCE (nF)
V
CC
4447 G13
4447 G15
4447 G14
Propagation Delay vs VLOGIC
Supply Voltage
Propagation Delay vs
VCC Supply Voltage
Propagation Delay vs
Temperature
25
20
15
25
20
15
10
5
20
15
10
5
NO LOAD
NO LOAD
NO LOAD
LOGIC
TS = GND
V
= 5V
V
= V
= 5V
V
= 5V
CC
CC
LOGIC
t
pHL(TG)
TS = GND
TS = GND
t
pLH(TG)
t
t
pLH(TG)
pLH(BG)
t
t
pLH(TG)
t
t
pLH(BG)
t
pHL(TG)
pLH(BG)
t
pHL(TG)
t
pHL(BG)
t
pHL(BG)
10
5
pHL(BG)
0
–40
–10
20
50
80
110
5.5
SUPPLY VOLTAGE (V)
6.5
3.0 3.5 4.0 4.5
5.0
6.0
5.5
SUPPLY VOLTAGE (V)
6.5
4.0
4.5
5.0
6.0
TEMPERATURE (°C)
V
V
LOGIC
CC
4447 G18
4447 G16
4447 G17
4447f
5
LTC4447
PIN FUNCTIONS
NC (Pins 1, 2): No Connection Required.
of the controller that is driving IN (Pin 7) to match input
thresholds or to V (Pin 9) to simplify PCB routing.
CC
TG (Pin 3): High Side Gate Driver Output (Top Gate). This
pin swings between TS and BOOST.
V
(Pin 9): Output Driver Supply. This pin powers the
CC
low side gate driver output directly and the high side gate
driver output through an internal Schottky diode con-
nected between this pin and BOOST. A low ESR ceramic
bypass capacitor should be tied between this pin and
GND (Pin 6).
TS (Pin 4): High Side MOSFET Source Connection (Top
Source).
BG (Pin 5): Low Side Gate Driver Output (Bottom Gate).
This pin swings between V and GND.
CC
GND (Pin 6): Chip Ground.
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
IN (Pin 7): Input Signal. Input referenced to an internal
supply baised off of V
(Pin 8) and GND (Pin 6). If
LOGIC
betweenV (Pin 9)andthesepins.Voltageswingatthese
CC
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.
pins 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.
Exposed Pad (Pin 13): Ground. The exposed pad must be
soldered to PCB ground for optimal electrical and thermal
performance.
V
(Pin 8): Logic Supply. This pin powers the input
LOGIC
buffer and logic. Connect this pin to the power supply
BLOCK DIAGRAM
V
12
CC
UNDERVOLTAGE
LOCKOUT
9
11
BOOST
10
TG
V
LEVEL
SHIFTER
LOGIC
UNDERVOLTAGE
LOCKOUT
3
8
TS
4
INTERNAL
SUPPLY
SHOOT-
THROUGH
PROTECTION
7k
V
CC
THREE-STATE
INPUT
BUFFER
BG
IN
5
7
7k
GND
GND
6
13
4447 BD
4447f
6
LTC4447
TIMING DIAGRAM
V
IL(TG)
IN
V
V
IL(BG)
IL(BG)
90%
10%
TG
BG
t
t
r(TG)
f(TG)
90%
10%
4447 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 LTC4447 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)
4447 F01
Input Stage
Figure 1. Three-State Input Operation
TheLTC4447employsauniquethree-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 LTC4447 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 LTC4447 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 LTC4447 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)
4447f
7
LTC4447
OPERATION
The hysteresis between the corresponding V and V
V
IN
IH
IL
LTC4447
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
TheLTC4447containsundervoltagelockoutdetectorsthat
monitor both the V and V
supplies. When V falls
C
Q2
Q3
P2
N2
GD
CC
LOGIC
LOGIC
CC
LOW SIDE
POWER
BG
below 3.04V or V
falls below 2.65V, the output pins
MOSFET
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
4447 F02
V
have adequate supply voltage for the LTC4447 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 LTC4447
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
SincethepowerMOSFETsgenerallyaccountforthemajor-
ity 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 LTC4447’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, 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 LTC4447’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
age on the TS pin will rise to V very rapidly. This high
IN
frequencypositivevoltagetransientwillcouplethroughthe
the BG and TG outputs to their positive rails (V and
C
GD
capacitance of the low side power MOSFET to the BG
CC
BOOST, respectively). Both BG and TG have N-channel
MOSFET pull-down devices (N1 and N2) which pull BG
and TG down to their negative rails, GND and TS. An ad-
ditional 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
pin. If the BG pin is not held down sufficiently, the voltage
on the BG pin will rise above the threshold voltage of the
lowsidepowerMOSFET,momentarilyturningitbackon.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 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)
GS GD
voltage (V – V ).
high side MOSFET.
GS
TH
4447f
8
LTC4447
OPERATION
The LTC4447’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
loadareshownintheTypicalPerformanceCharacteristics
plot of Switching Supply Current vs Input Frequency.
To ensure proper operation and long-term reliability,
the LTC4447 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
LOAD IN
) + (V ) ]
CLOAD
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 internal 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
= quiescent power loss
= internal switching loss at input frequency f
= loss due turning on and off the external
DC
P
QG
power dissipation can be calculated using its gate charge,
IN
Q . The Q value corresponding to the MOSFET’s V
GS
G
G
P
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 LTC4447 consumes very little quiescent current. The
on TG and BG:
DC power loss at V
= 5V and V = 5V is only (730ꢀA
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 LTC4447 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
4447f
9
LTC4447
APPLICATIONS INFORMATION
Bypassing and Grounding
5A peak currents and any significant ground drop will
degrade signal integrity.
TheLTC4447requiresproperbypassingontheV
,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) and large AC currents (amperes). Careless
component placement and PCB trace routing may cause
excessive ringing and under/overshoot.
To obtain the optimum performance from the LTC4447:
• 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 LTC4447 packages to the board. Correctly soldered
to a double-sided copper board, the LTC4447 has a
thermal resistance of approximately 43°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 LTC4447 switches greater than
TYPICAL APPLICATION
LTC7510/LTC4447 12V to 1.5V/30A Digital Step-Down DC/DC Converter with PMBus Serial Interface
12V
5V
R1
C5
0.22μF
SDATA
V
12SEN
PMBus
V
SCLK
CC
INTERFACE
V
D33
SMB_AL_N
V
C2
BOOST
D25
LTC7510
R2
M1
RJK0305
×2
+
L1
0.3μH
POWER
MANAGEMENT
INTERFACE
V
V
TG
PWRGD
OUTEN
LOGIC
C4
C1
R
C3
LTC4447
V
OUT
GND
TS
CC
C6
R3
+
M2
RJK0301
×2
330μF
×6
PWM
IN
BG
GND
1μF
SYNC_IN
MULTIPHASE
INTERFACE
D1
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
4447 TA02
OUT/ISH
SADDR
RTN
I-SHARE
I
SH_GND
V
SET
FSET
RESET_N
V
TRIM
I
MAXSET
4447f
10
LTC4447
PACKAGE DESCRIPTION
DDMA Package
12-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1743 Rev A)
0.70 0.05
1.19 0.05
0.93 0.05
2.25 REF
0.57 0.05
2.38 0.05
1.35 0.05
3.50 0.05
2.10 0.05
0.81 0.05
PACKAGE
OUTLINE
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
R = 0.115
0.11 0.05
TYP
7
3.00 0.10
12
0.40 0.10
0.81 0.10
2.38 0.10
1.35 0.10
0.63 0.05
3.00 0.10
PIN 1 NOTCH
R = 0.20 OR
0.25 × 45°
CHAMFER
PIN 1
TOP MARK
(SEE NOTE 6)
R = 0.05
TYP
6
1
0.23 0.05
0.45 BSC
0.75 0.05
0.00 – 0.05
0.200 REF
2.25 REF
(DD12MA) DFN 0507 REV A
BOTTOM VIEW—EXPOSED PAD
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
4447f
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However,noresponsibilityisassumedforitsuse.LinearTechnologyCorporationmakesnorepresenta-
t ion t h a t t he in ter c onne c t ion o f i t s cir cui t s a s de s cr ib e d her ein w ill no t in fr inge on ex is t ing p a ten t r igh t s.
11
LTC4447
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC1154
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 Drivers
Synchronous Rectifier Driver for Forward Converters
Internal Charge Pump 4.5V to 18V Supply Range
Internal Charge Pump 4.5V to 18V Supply Range
LTC1155
LT®1161
8V to 48V Supply Range, t = 200μs, t
= 28μs
OFF
ON
LTC1163
1.8V to 6V Supply Range, t = 95μs, t
= 45μs
OFF
ON
LTC1693 Family
LTC3900
1.5A Peak Output Current, 4.5V ≤ V ≤ 13.2V
IN
Pulse Drive Transformer Synchronous Input
Gate Drive Transformer Synchronous Input
LTC3901
Secondary Side Synchronous Driver for Push-Pull and
Full-Bridge Converters
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
LTC4442/LTC4442-1 High Speed Synchronous N-Channel MOSFET Driver
LTC4443/LTC4443-1 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
5A Peak Output Current, Internal Schottky Diode, 38V Maximum
Input Supply Voltage, 6V ≤ V ≤ 9.5V, 3mm × 3mm DFN-12
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
LTC7510
Digital DC/DC Controller with PMBus Interface
Digital Controller, PMBus Serial Interface, 150kHz to 2MHz
Switching Frequency
4447f
LT 0608 • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
12
●
●
© LINEAR TECHNOLOGY CORPORATION 2008
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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