LINER LTC4443IDD-TRPBF High speed synchronous n-channel mosfet driver Datasheet

LTC4443/LTC4443-1
High Speed Synchronous
N-Channel MOSFET Drivers
FEATURES
DESCRIPTION
n
The LTC®4443 is a high frequency gate driver with integrated
bootstrap Schottky diode designed to drive two N-channel
MOSFETs in a synchronous buck DC/DC converter topology.
The powerful driver capability reduces switching losses
in MOSFETs with high gate capacitance.
n
n
n
n
n
n
n
n
n
n
n
Integrated Schottky Diode
Wide VCC Range: 6V to 9.5V
38V Maximum Input Supply Voltage
Adaptive Shoot-Through Protection
2.4A Peak Pull-Up Current
5A Peak Pull-Down Current
8ns TG Fall Time Driving 3000pF Load
12ns TG Rise Time Driving 3000pF Load
Separate Supply to Match PWM Controller
Drives Dual N-Channel MOSFETs
Undervoltage Lockout
Low Profile (0.75mm) 3mm × 3mm DFN Package
APPLICATIONS
n
n
Distributed Power Architectures
High Density Power Modules
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
The LTC4443 features a separate supply for the input logic
to match the signal swing of the controller IC. If the input
signal is not being driven, the LTC4443 activates a shutdown
mode that turns off both external MOSFETs. The input
logic signal is internally level-shifted to the bootstrapped
supply, which may function at up to 42V above ground.
The Schottky diode required for the bootstrapped supply
is integrated to simplify layout and reduce parts count.
The LTC4443 contains undervoltage lockout circuits on
both the driver and logic supplies that turn off the external
MOSFETs when an undervoltage condition is present.
The LTC4443 and LTC4443-1 have different undervoltage
lockout thresholds to accommodate a wide variety of applications. An adaptive shoot-through protection feature is
also built-in to prevent power loss resulting from MOSFET
cross-conduction current.
The LTC4443/LTC4443-1 are available in a tiny 3mm ×
3mm DFN package.
TYPICAL APPLICATION
Synchronous Buck Converter Driver
LTC4443 Driving 3000pF Capacitive Loads
VIN
32V
INPUT (IN)
5V/DIV
BOOST
VCC
6V
TG
VLOGIC
VCC LTC4443 TS
PWM
IN
VOUT
BG
GND
4443 TA01a
BOTTOM
GATE (BG)
5V/DIV
TOP GATE
(TG-TS)
5V/DIV
10ns/DIV
4443 TA01b
4443fa
1
LTC4443/LTC4443-1
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
Supply Voltage
VLOGIC .................................................... –0.3V to 10V
VCC......................................................... –0.3V to 10V
BOOST – TS ........................................... –0.3V to 10V
BOOST Voltage .......................................... –0.3V to 42V
BOOST – VCC ............................................................38V
TS Voltage..................................................... –5V to 38V
TS + VCC....................................................................42V
IN Voltage .................................................. –0.3V to 10V
Driver Output TG (with Respect to TS)....... –0.3V to 10V
Driver Output BG........................................ –0.3V to 10V
Operating Temperature Range (Note 2).... –40°C to 85°C
Junction Temperature (Note 3) ............................. 125°C
Storage Temperature Range................... –65°C to 150°C
TOP VIEW
NC
NC
TG
TS
BG
GND
12 BOOST
11 BOOST
10 BOOST
9 VCC
8 VLOGIC
7 IN
1
2
3
13
4
5
6
DDMA PACKAGE
12-LEAD (3mm s 3mm) PLASTIC DFN
θJA = 43°C/W, θJC = 3°C/W
EXPOSED PAD (PIN 13) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC4443EDD#PBF
LTC4443EDD#TRPBF
LCXH
12-Lead (3mm × 3mm) Plastic DFN
–40°C to 85°C
LTC4443IDD#PBF
LTC4443IDD#TRPBF
LCXH
12-Lead (3mm × 3mm) Plastic DFN
–40°C to 85°C
LTC4443EDD-1#PBF
LTC4443EDD-1#TRPBF
LCYN
12-Lead (3mm × 3mm) Plastic DFN
–40°C to 85°C
LTC4443IDD-1#PBF
LTC4443IDD-1#TRPBF
LCYN
12-Lead (3mm × 3mm) Plastic DFN
–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 l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 7V, VTS = GND = 0V, VLOGIC = 5V, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Logic Supply (VLOGIC)
VLOGIC
Operating Range
3
IVLOGIC
DC Supply Current
IN = Floating
UVLO
Undervoltage Lockout Threshold
VLOGIC Rising
VLOGIC Falling
Hysteresis
l
l
2.5
2.4
9.5
V
730
850
μA
2.75
2.65
100
3.0
2.9
V
V
mV
9.5
V
600
800
μA
Gate Driver Supply (VCC)
VCC
Operating Range
6
IVCC
DC Supply Current
IN = Floating
UVLO
Undervoltage Lockout Threshold
VCC Rising (LTC4443)
VCC Falling (LTC4443)
Hysteresis (LTC4443)
l
l
2.75
2.60
3.20
3.04
160
3.65
3.50
V
V
mV
VCC Rising (LTC4443-1)
VCC Falling (LTC4443-1)
Hysteresis (LTC4443-1)
l
l
5.6
4.7
6.2
5.3
850
6.7
5.8
V
V
mV
4443fa
2
LTC4443/LTC4443-1
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 7V, VTS = GND = 0V, VLOGIC = 5V, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
VD
Schottky Diode Forward Voltage
ID = 10mA
ID = 100mA
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 Theshold
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
TYP
MAX
0.38
0.48
UNITS
V
V
Input Signal (IN)
l
l
3.0
1.9
3.5
2.2
4.0
2.6
3.25
2.09
l
l
0.8
0.8
200
100
1.25
1.10
V
V
V
V
1.6
1.4
V
V
1.50
1.21
V
V
300
150
μA
μA
0.7
V
High Side Gate Driver Output (TG)
VOH(TG)
TG High Output Voltage
ITG = –10mA, VOH(TG) = VBOOST – VTG
ITG = 100mA, VOL(TG) = VTG – VTS
VOL(TG)
TG Low Output Voltage
100
mV
IPU(TG)
TG Peak Pull-Up Current
l
1.5
2.4
A
IPD(TG)
TG Peak Pull-Down Current
l
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
l
1.4
2.4
A
IPD(BG)
BG Peak Pull-Down Current
l
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
tf(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 LTC4443I/LTC4443I-1 are guaranteed to meet specifications
from –40°C to 85°C. The LTC4443E/LTC4443E-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 • 43°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.
4443fa
3
LTC4443/LTC4443-1
TYPICAL PERFORMANCE CHARACTERISTICS
Input Thresholds for VLOGIC = 3.3V
vs Temperature
3.0
5
VIL(TG)
3
2
VIL(BG)
VIH(BG)
1
0
3
4
7
6
5
8
VLOGIC SUPPLY (V)
5
VLOGIC = 3.3V
2.5
VIH(TG)
2.0
VIL(TG)
1.5
VIL(BG)
1.0
VIH(BG)
0
–40
10
–10
20
50
80
TEMPERATURE (°C)
BG OR TG INPUT THRESHOLD HYSTERSIS (V)
BG OR TG INPUT THRESHOLD HYSTERESIS (V)
0.3
0.2
0.1
0
3
4
6
5
7
8
VLOGIC SUPPLY (V)
9
2
VIL(BG)
VIH(BG)
0
–40
110
10
IN FLOATING
0.9 BOOST > VCC
0.8
0.30
VLOGIC = 5V
0.25
0.20
VLOGIC = 3.3V
0.15
0.10
0.7
IVLOGIC
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
VCC Undervoltage Lockout
Thresholds vs Temperature
7.0
2.9
VCC UVLO THRESHOLD (V)
VLOGIC UVLO THRESHOLD (V)
DIODE FORWARD VOLTAGE (V)
6.5
0.10
10
9
4443 G06
3.0
0.60
0.20
7
6
5
8
SUPPLY VOLTAGE (V)
4
4443 G05
VLOGIC Undervoltage Lockout
Thresholds vs Temperature
0.30
110
1.0
0.35
Schottky Diode Forward Voltage
vs Diode Current
0.40
20
80
50
TEMPERATURE (°C)
Quiescent Supply Current vs
Supply Voltage
0.40
4443 G04
0.50
–10
4443 G03
BG or TG Input Threshold Hysteresis
vs Temperature
BG or TG Input Threshold Hysteresis
vs VLOGIC Supply Voltage
0.4
VIL(TG)
3
4443 G02
4443 G01
0.5
VIH(TG)
1
0.5
9
VLOGIC ≥ 5V
4
SUPPLY CURRENT (mA)
INPUT THRESHOLD (V)
INPUT THRESHOLD (V)
VIH(TG)
4
Input Thresholds for VLOGIC ≥ 5V
vs Temperature
INPUT THRESHOLD (V)
Input Thresholds vs VLOGIC Supply
Voltage
RISING THRESHOLD
2.8
FALLING THRESHOLD
2.7
2.6
6.0
LTC4443-1 RISING THRESHOLD
LTC4443-1 FALLING THRESHOLD
5.5
5.0
4.5
4.0
3.5
3.0
LTC4443 RISING THRESHOLD
LTC4443 FALLING THRESHOLD
2.5
0
0
50
100
150
DIODE CURRENT (mA)
200
4443 G07
2.5
–40
–10
20
80
50
TEMPERATURE (°C)
110
4443 G08
2.0
–40
–10
20
80
50
TEMPERATURE (°C)
110
4443 G09
4443fa
4
LTC4443/LTC4443-1
TYPICAL PERFORMANCE CHARACTERISTICS
Undervoltage Lockout Threshold
Hysteresis vs Temperature
Switching Supply Current
vs Input Frequency
100
7
800
700
600
500
400
300
LTC4443
VCC UVLO
200
100
0
–40
IVCC
3
2
0
20
80
50
TEMPERATURE (°C)
110
200k
400k
600k
tPLH(TG)
20
tPLH(BG)
tPHL(TG)
tPHL(BG)
8
9
7
6
VLOGIC SUPPLY VOLTAGE (V)
5
40
tPHL(TG)
15
tPHL(BG)
10
10
5
4443 G13
tPLH(TG)
25
tPLH(BG)
20
8
7
9
6
VCC SUPPLY VOLTAGE (V)
0
–40
10
6
5
4
3
–10
20
50
80
TEMPERATURE (°C)
4443 G14
110
4443 G15
Rise and Fall Time vs
Load Capacitance
VCC = 7V
TS = GND
CLOAD = 3.3nF
TS = GND
tr(BG)
tr(TG)
15
RISE/FALL TIME (ns)
RISE/FALL TIME (ns)
–100mA
tPHL(TG)
10
100
20
–10mA
tPHL(BG)
15
Rise and Fall Time vs
VCC Supply Voltage
9
–1mA
30
5
4
TS = GND
30
NO LOAD
VLOGIC = 5V
VCC = 7V
TS = GND
35
tPLH(BG)
20
Output High Voltage vs
VCC Supply Voltage
7
1
10
3
LOAD CAPACITANCE (nF)
Propagation Delay vs
Temperature
tPLH(TG)
25
0
0
8
0.3
4443 G12
5
5
BG OR TG HIGH OUTPUT VOLTAGE (V)
0.1
NO LOAD
VLOGIC = 5V
TS = GND
30
15
10
ILOGIC
fIN = 500kHz
1M
800k
35
PROPAGATION DELAY (ns)
PROPAGATION DELAY (ns)
25
4
1
Propagation Delay vs
VCC Supply Voltage
30
3
ICC
fIN = 100kHz
4443 G11
NO LOAD
VCC = 7V
TS = GND
10
10
FREQUENCY (Hz)
Propagation Delay vs
VLOGIC Supply Voltage
35
ICC
fIN = 500kHz
0
0
4443 G10
40
VLOGIC = 5V
VCC = 7V
TS = GND
IVLOGIC
1
VLOGIC UVLO
–10
4
PROPAGATION DELAY (ns)
900
NO LOAD
= 5V
V
6 VLOGIC
CC = 7V
TS = GND
5
SUPPLY CURRENT (mA)
LTC4443-1
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
6
VCC SUPPLY VOLTAGE (V)
9
10
4443 G16
4
5
8
9
6
7
VCC SUPPLY VOLTAGE (V)
10
4443 G17
1
10
3
LOAD CAPACITANCE (nF)
30
4443 G18
4443fa
5
LTC4443/LTC4443-1
PIN FUNCTIONS
TG (Pin 3): High Side Gate Driver Output (Top Gate). This
pin swings between TS and BOOST.
TS (Pin 4): High Side MOSFET Source Connection (Top
Source).
BG (Pin 5): Low Side Gate Driver Output (Bottom Gate).
This pin swings between VCC and GND.
GND (Pin 6): Chip Ground.
IN (Pin 7): Input Signal. Input referenced to an internal
supply powered by VLOGIC (Pin 8) and referenced to GND
(Pin 6). If this pin is floating, an internal resistive divider
triggers a shutdown mode in which both BG (Pin 5) and
TG (Pin 3) are pulled low. Trace capacitance on this pin
should be minimized to keep the shutdown time low.
VLOGIC (Pin 8): Logic Supply. This pin powers the input
buffer and logic. Connect this pin to the power supply
of the controller that is driving IN (Pin 7) to match input
thresholds or to VCC (Pin 9) to simplify PCB routing.
VCC (Pin 9): Output Driver Supply. This pin powers the
low side gate driver output directly and the high side gate
driver output through an internal Schottky diode connected between this pin and BOOST. A low ESR ceramic
bypass capacitor should be tied between this pin and
GND (Pin 6).
BOOST (Pins 10, 11, 12): High Side Bootstrapped Supply.
An external capacitor should be tied between these pins
and TS (Pin 4). An internal Schottky diode is connected
between VCC (Pin 9) and these pins. Voltage swing at these
pins is from VCC – VD to VIN + VCC – VD, where VD is the
forward voltage drop of the bootstrap diode.
Exposed Pad (Pin 13): Ground. The Exposed Pad must be
soldered to PCB ground for optimal electrical and thermal
performance.
BLOCK DIAGRAM
9
BOOST
VCC
UNDERVOLTAGE
LOCKOUT
BOOST
BOOST
8
VLOGIC
UNDERVOLTAGE
LOCKOUT
TG
LEVEL
SHIFTER
TS
INTERNAL
SUPPLY
10
3
4
VCC
THREE-STATE
INPUT
BUFFER
IN
11
SHOOTTHROUGH
PROTECTION
7k
7
12
BG
5
7k
6
GND
13 GND
4443 BD
4443fa
6
LTC4443/LTC4443-1
TIMING DIAGRAM
IN
TG
BG
VIL(TG)
VIL(BG)
90%
10%
90%
4443 TD
10%
tr(TG)
tpLH(TG)
tr(BG)
tpLH(BG)
tf(BG)
tpHL(BG)
tf(TG)
tpHL(TG)
OPERATION
Overview
The LTC4443 receives a ground-referenced, low voltage
digital input signal to drive two N-channel power MOSFETs
in a synchronous buck power supply configuration. The
gate of the low side MOSFET is driven either to VCC or GND,
depending on the state of the input. Similarly, the gate of
the high side MOSFET is driven to either BOOST or TS by
a supply bootstrapped off of the switch node (TS).
VIH(TG)
TG HIGH
TG LOW
TG HIGH
TG LOW
VIL(TG)
IN
VIL(BG)
BG LOW
BG HIGH
BG LOW
BG HIGH
VIH(BG)
4443 F01
Input Stage
The LTC4443 employs a unique three-state input stage with
transition thresholds that are proportional to the VLOGIC
supply. The VLOGIC supply can be tied to the controller
IC’s power supply so that the input thresholds will match
those of the controller’s output signal. Alternatively, VLOGIC
can be tied to VCC to simplify routing. An internal voltage
regulator in the LTC4443 limits the input threshold values
for VLOGIC supply voltages greater than 5V.
The relationship between the transition thresholds and the
three input states of the LTC4443 is illustrated in Figure 1.
When the voltage on IN is greater than the threshold VIH(TG),
TG is pulled up to BOOST, turning the high side MOSFET
on. This MOSFET will stay on until IN falls below VIL(TG).
Similarly, when IN is less than VIH(BG), BG is pulled up
to VCC, turning the low side (synchronous) MOSFET on.
BG will stay high until IN increases above the threshold
VIL(BG).
Figure 1. Three-State Input Operation
The thresholds are positioned to allow for a region in which
both BG and TG are low. An internal resistive divider will
pull IN into this region if the signal driving the IN pin goes
into a high impedance state.
One application of this three-state input is to keep both of
the power MOSFETs off while an undervoltage condition
exists on the controller IC power supply. This can be accomplished by driving the IN pin with a logic buffer that
has an enable pin. With the enable pin of the buffer tied
to the power good pin of the controller IC, the logic buffer output will remain in a high impedance state until the
controller confirms that its supply is not in an undervoltage
state. The three-state input of the LTC4443 will therefore
pull IN into the region where TG and BG are low until the
controller has enough voltage to operate predictably.
4443fa
7
LTC4443/LTC4443-1
OPERATION
The hysteresis between the corresponding VIH and VIL
voltage levels eliminates false triggering due to noise
during switch transitions; however, care should be taken
to keep noise from coupling into the IN pin, particularly
in high frequency, high voltage applications.
VIN
LTC4443
BOOST
CGD
Q1
TG
N1
CGS
HIGH SIDE
POWER
MOSFET
TS
Undervoltage Lockout
The LTC4443 contains undervoltage lockout detectors that
monitor both the VCC and VLOGIC supplies. When VCC falls
below 3.04V or VLOGIC falls below 2.65V, the output pins
BG and TG are pulled to GND and TS, respectively. This
turns off both of the external MOSFETs. When VCC and
VLOGIC have adequate supply voltage for the LTC4443 to
operate reliably, normal operation will resume.
LOAD
INDUCTOR
VCC
Q2
CGD
BG
Q3
N2
CGS
LOW SIDE
POWER
MOSFET
GND
4443 F02
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 LTC4443
does not allow the bottom MOSFET to turn on until the
gate-source voltage on the top MOSFET is sufficiently
low, and vice-versa. This feature improves efficiency by
eliminating cross-conduction current from flowing from
the VIN supply through the MOSFETs to ground during a
switch transition.
Since the power MOSFET generally accounts for the majority of power loss in a converter, it is important to quickly
turn it on and off, thereby minimizing the transition time
and power loss. The LTC4443’s peak pull-up current of
2.4A for both BG and TG (Q1 and Q2) produces a rapid
turn-on transition for the MOSFETs. This high current is
capable of driving a 3nF load with a 12ns rise time.
Output Stage
A simplified version of the LTC4443’s output stage is
shown in Figure 2. The pull-up device on both the BG and
TG outputs is an NPN bipolar junction transistor (Q1 and
Q2). The BG and TG outputs are pulled up to within an
NPN VBE (~0.7V) of their positive rails (VCC and BOOST,
respectively). Both BG and TG have N-channel MOSFET pulldown devices (N1 and N2) which pull BG and TG down to
their negative rails, GND and TS. An additional NPN bipolar
junction transistor (Q3) is present on BG to increase its
pull-down drive current capacity. The large voltage swing of
the BG and TG output pins is important in driving external
power MOSFETs, whose RDS(ON) is inversely proportional
to its gate overdrive voltage (VGS – VTH).
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.
4443fa
8
LTC4443/LTC4443-1
OPERATION
The LTC4443’s powerful parallel combination of the
N-channel MOSFET (N2) and NPN (Q3) on the BG pull-down
generates a phenomenal 5ns fall time on BG while driving
a 3nF load. Similarly, the 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.
APPLICATIONS INFORMATION
Power Dissipation
To ensure proper operation and long-term reliability, the
LTC4443 must not operate beyond its maximum temperature rating. Package junction temperature can be
calculated by:
TJ = TA + (PD)(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 LTC4443 consumes very little quiescent current. The
DC power loss at VLOGIC = 5V and VCC = VBOOST − TS =
7V is only (730μA)(5V) + (600μA)(7V) = 7.85mW.
At a particular switching frequency, the internal power loss
increases due to both AC currents required to charge and
discharge internal nodal capacitances and cross-conduction currents in the internal logic gates. The sum of the
quiescent current and internal switching current with no
load are shown in the Typical Performance Characteristics
plot of Switching Supply Current vs Input Frequency.
The gate charge losses are primarily due to the large AC
currents required to charge and discharge the capacitance
of the external MOSFETs during switching. For identical
pure capacitive loads CLOAD on TG and BG at switching
frequency fin, the load losses would be:
PCLOAD = (CLOAD)(fIN)[(VBOOST – TS)2 + (VCC)2]
In a typical synchronous buck configuration, VBOOST – TS
is equal to VCC – VD, where VD is the forward voltage drop
of the internal Schottky diode between VCC and BOOST. If
this drop is small relative to VCC, the load losses can be
approximated as:
PCLOAD ≈ 2(CLOAD)(fIN)(VCC)2
Unlike a pure capacitive load, a power MOSFET’s gate
capacitance seen by the driver output varies with its VGS
voltage level during switching. A MOSFET’s capacitive load
power dissipation can be calculated using its gate charge,
QG. The QG value corresponding to the MOSFET’s VGS
value (VCC in this case) can be readily obtained from the
manufacturer’s QG vs VGS curves. For identical MOSFETs
on TG and BG:
PQG ≈ 2(VCC)(QG)(fIN)
To avoid damaging junction temperatures due to power
dissipation, the LTC4443 includes a temperature monitor
that will pull BG and TG low if the junction temperature
exceeds 160°C. Normal operation will resume when the
junction temperature cools to less than 135°C.
4443fa
9
LTC4443/LTC4443-1
APPLICATIONS INFORMATION
Bypassing and Grounding
The LTC4443 requires proper bypassing on the VLOGIC, VCC
and VBOOST – TS supplies due to its high speed switching
(nanoseconds) and large AC currents (Amperes). Careless
component placement and PCB trace routing may cause
excessive ringing and undershoot/overshoot.
To obtain the optimum performance from the LTC4443:
A. Mount the bypass capacitors as close as possible
between the VLOGIC and GND pins, the VCC and GND
pins, and the BOOST and TS pins. The leads should
be shortened as much as possible to reduce lead
inductance.
B. Use a low inductance, low impedance ground plane
to reduce any ground drop and stray capacitance.
Remember that the LTC4443 switches greater than
5A peak currents and any significant ground drop will
degrade signal integrity.
C. Plan the power/ground routing carefully. Know where
the large load switching current is coming from and
going to. Maintain separate ground return paths for
the input pin and the output power stage.
D. Keep the copper trace between the driver output pin
and the load short and wide.
E. Be sure to solder the Exposed Pad on the back side of
the LTC4443 packages to the board. Correctly soldered
to a double-sided copper board, the LTC4443 has a
thermal resistance of approximately 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.
TYPICAL APPLICATION
LTC7510/LTC4443-1 12V to 1.5V/30A Digital Step-Down DC/DC Converter with PMBus Serial Interface
7V DRIVE
12V
5V
R1
SDATA
PMBus
INTERFACE
SCLK
VD33
SMB_AL_N
LTC7510
POWER
MANAGEMENT
INTERFACE
C5
0.22μF
V12SEN
VCC
VD25
C2
OUTEN
BOOST
R2
+
PWRGD
C4
C1 C3
GND
PWM
MULTIPHASE
INTERFACE
TG
VLOGIC
LTC4443-1
VCC
TS
IN
1μF
SYNC_IN
RCM
SYNC_OUT
BG
GND
M1
RJK0305
s2
M2
RJK0301
s2
L1
0.3μH
R3
C6
VOUT
+
330μF
s6
D1
TEMPSEN
LOAD
FAULT
OUTPUTS
FAULT1
FAULT2
ISENN
RSENSE
ISENP
VSENP
VSENN
I-SHARE
IOUT/ISH
ISH_GND
1k
SADDR
1k
VSET
RTN
4443 TA02
1k
FSET
1k
RESET_N
VTRIM
1k
IMAXSET
4443fa
10
LTC4443/LTC4443-1
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
0.81 ±0.05
2.10 ±0.05
1.07 ±0.05
PACKAGE
OUTLINE
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
TYP
7
3.00 ±0.10
0.11 ± 0.05
12
0.40 ± 0.10
2.38 ±0.10
3.00 ±0.10
0.81 ± 0.10
PIN 1
TOP MARK
(SEE NOTE 6)
0.200 REF
0.75 ±0.05
R = 0.05
TYP
0.63 ± 0.05
1.35 ± 0.10
6
PIN 1 NOTCH
R = 0.20 OR
0.25 × 45°
CHAMFER
1
0.23 ± 0.05
0.45 BSC
2.25 REF
(DD12MA) DFN 0507 REV A
BOTTOM VIEW—EXPOSED PAD
0.00 – 0.05
NOTE:
1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD AND TIE BARS SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE
TOP AND BOTTOM OF PACKAGE
4443fa
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
11
LTC4443/LTC4443-1
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT 1161
Quad Protected High Side MOSFET Driver
8V to 48V Supply Range, tON = 200μs, tOFF = 28μs
LTC1693 Family
High Speed Single/Dual N-Channel MOSFET Drivers
1.5A Peak Output Current, 4.5V ≤ VIN ≤ 13.2V
LTC4440
High Speed, High Voltage High Side Gate Driver
High Side Source Up to 100V, 8V ≤ VCC ≤ 15V
®
LTC4440-5
High Speed, High Voltage High Side Gate Driver
High Side Source Up to 80V, 4V ≤ VCC ≤ 15V
LTC4441
6A MOSFET Driver
6A Peak Output Current, Adjustable Gate Drive from 5V to 8V,
5V ≤ VIN ≤ 25V
LTC4442/LTC4442-1
High Speed Synchronous N-Channel MOSFET Driver
5A Peak Output Current, Three-State Input, 38V Maximum Input
Supply Voltage, 6V ≤ VCC ≤ 9.5V, MS8E Package
LTC4444
High Voltage Synchronous N-Channel MOSFET Driver
High Side Source Up to 100V, 3A Peak Output Current,
7.2V ≤ VCC ≤ 13.5V
LTC4445/LTC4445-1
Dual High Speed Synchronous N-Channel MOSFET Driver
Two Independent Drivers, Internal Schottky Diodes,
38V Maximum Input Supply Voltage, 6V ≤ VCC ≤ 9.5V,
LTC4447
High Speed Synchronous N-Channel MOSFET Driver
4.5A Peak Output Current, Rail-to-Rail Drivers, 38V Maximum
Input Supply Voltage, 4V ≤ VCC ≤ 6.5V
LTC7510
Digital DC/DC Controller with PMBus Interface
Digital Controller, PMBus Serial Interface, 150kHz to 2MHz
Switching Frequency
4443fa
12 Linear Technology Corporation
LT 0608 REV A • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2008
Similar pages