TI UCC27200D

UCC27200, UCC27201
www.ti.com
SLUS746 – DECEMBER 2006
120-V Boot, 3-A Peak, High Frequency, High-Side/Low-Side Driver
FEATURES
CONTENTS
•
•
Device Ratings
2
Electrical Characteristics
4
Device Information
11
Application Information
14
Additional References
22
•
•
•
•
•
•
•
•
•
Specified from -40 °C to 140 °C
Drives Two N-Channel MOSFETs in
High-Side/Low-Side Configuration
Maximum Boot Voltage 120 V
Maximum VDD Voltage 20 V
On-Chip 0.65-V VF, 0.6-Ω RD Bootstrap Diode
Greater than 1 MHz of Operation
20-ns Propagation Delay Times
3-A Sink, 3-A Source Output Currents
8-ns Rise/7-ns Fall Time with 1000-pF Load
1-ns Delay Matching
Under Voltage Lockout for High-Side and
Low-Side Driver
DESCRIPTION
The UCC27200/1 family of high frequency
N-Channel MOSFET drivers include a 120-V
bootstrap diode and high-side/low-side driver with
independent inputs for maximum control flexibility.
This allows for N-Channel MOSFET control in
half-bridge, full-bridge, two-switch forward and active
clamp forward converters. The low-side and the
high-side gate drivers are independently controlled
and matched to 1-ns between the turn-on and
turn-off of each other.
APPLICATIONS
•
•
•
•
•
•
•
Power Supplies for Telecom, Datacom, and
Merchant Markets
Half-Bridge Applications and Full-Bridge
Converters
Isolated Bus Architecture
Two-Switch Forward Converters
Active-Clamp Forward Converters
High Voltage Synchronous-Buck Converters
Class-D Audio Amplifiers
Simplified Application Diagram
+12V
+100V
SECONDARY
SIDE
CIRCUIT
V DD
HB
DRIVE
HI
LI
CONTROL
HI
PWM
CONTROLLER
HO
HS
DRIVE
LO
LO
UCC27200/1
VSS
ISOLATION
AND
FEEDBACK
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas
Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
PowerPad is a trademark of Texas Instruments.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2006, Texas Instruments Incorporated
UCC27200, UCC27201
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SLUS746 – DECEMBER 2006
DESCRIPTION (CONT.)
An on-chip bootstrap diode eliminates the external discrete diodes. Under-voltage lockout is provided for both
the high-side and the low-side drivers forcing the outputs low if the drive voltage is below the specified threshold.
Two versions of the UCC27200 are offered. The UCC27200 has high noise immune CMOS input thresholds
while the UCC27201 has TTL compatible thresholds.
Both devices are offered in 8-pin SOIC (D), PowerPad™ SOIC-8 (DDA) and SON-8 (DRM) packages.
ORDERING INFORMATION
PACKAGED DEVICES (1)
TEMPERATURE RANGE
TA = TJ
INPUT COMPATIBILITY
SOIC-8 (D) (2)
PowerPad™ SOIC-8
(DDA) (2)
SON-8 (DRM) (3)
CMOS
UCC27200D
UCC27200DDA
UCC27200DRMT
TTL
UCC27201D
UCC27201DDA
UCC27201DRMT
-40°C to +140°C
(1)
(2)
(3)
These products are packaged in Lead (Pb)-Free and green lead finish of PdNiAu which is compatible with MSL level 1 at 255-260°C
peak reflow temperature to be compatible with either lead free or Sn/Pb soldering operations.
D (SOIC-8) and DDA (Power Pad™ SOIC-8) packages are available taped and reeled. Add R suffix to device type (e.g. UCC27200DR)
to order quantities of 2,500 devices per reel.
DRM (SON-8) package comes either in a small reel of 250 pieces as part number UCC27200DRMT, or larger reels of 3000 pieces as
part number UCC27200 DRMR.
DEVICE RATINGS
ABSOLUTE MAXIMUM RATINGS
Over operating free-air temperature, unless noted, all voltages are with respect to VSS (1)
PARAMETER
Supply voltage range,
(2)
VALUE
VDD
-0.3 to 20
Input voltages on LI and HI, VLI, VHI
Output voltage on LO, VLO
Output voltage on HO, VHO
Voltage on HS, VHS
-0.3 to 20
DC
-0.3 to VDD + 0.3,
Repetitive pulse <100 ns
-2 to VDD + 0.3
DC
VHS – 0.3 to VHB + 0.3
Repetitive pulse <100 ns
VHS - 2 to VHB + 0.3, (VHB - VHS <20)
DC
Repetitive pulse <100 ns
-5 to 120
Voltage on HB, VHB
-0.3 to 120
Voltage On HB-HS
-0.3 to 20
Operating virtual junction temperature range, TJ
-40 to +150
Storage temperature, TSTG
-65 to +150
Power dissipation at TA = 25°C (D package)
(3)
Power dissipation at TA = 25°C (DRM package)
(2)
(3)
°C
+300
1.3
Power dissipation at TA = 25°C (DDA package) (3)
(1)
V
-1 to 120
Lead temperature (soldering, 10 sec.)
2
UNIT
2.7
(3)
W
3.3
Stresses beyond those listed under “absolute maximum ratings” may cause permanent damage to the device. These are stress ratings
only, and functional operation of the device at these or any other conditions beyond those indicated under “recommended operating
conditions” is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
All voltages are with respect to Vss. Currents are positive into, negative out of the specified terminal.
This data was taken using the JEDEC proposed high-K test PCB. See THERMAL CHARACTERISTICS section for details.
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RECOMMENDED OPERATING CONDITIONS
over operating free-air temperature range (unless otherwise noted)
PARAMETER
MIN
NOM
VHS
Voltage on HS
-1
105
Voltage on HS, (repetitive pulse <100 ns)
-5
110
VHS + 8,
VDD –1
VHS + 17,
115
-40
+140
Voltage on HB
12
UNIT
Supply voltage range
VHB
8
MAX
VDD
Voltage slew rate on HS
TJ
17
50
Operating junction temperature range
V
V / ns
°C
ELECTROSTATIC DISCHARGE (ESD) PROTECTION
METHOD
MIN
Human body model
2000
CDM
1000
UNIT
V
THERMAL CHARACTERISTICS
over operating free-air temperature range, maximum power dissipation at ambient temperature: PDISS = (150-TA) / θJA,
(unless otherwise noted)
(1)
(2)
PACKAGE
θJA (°C/W)(Junction to
Ambient)
θJC (°C/W)( Junction to Case)
θJP (°C/W) ( Junction to
PowerPad™)
D
95
71
NA
DDA (1)
46
71
4.8
DRM (2)
38
56
4.1
Test board conditions:
• 3in x 3in, four4 layers, thickness: 0.062 in.
• 2-oz copper traces located on the top and bottom of the PCB.
• 2-oz copper ground planes on the internal 2 layers.
• Six thermal vias in the PowerPad™ area under the device package.
Test board conditions:
• 3in x 3in, 4 layers, thickness: 0.062 in.
• 2-oz copper traces located on the top and bottom of the PCB.
• 2-oz copper ground planes on the internal 2 layers.
• Four thermal vias in the PowerPad™ area under the device package.
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ELECTRICAL CHARACTERISTICS
over operating free-air temperature range, VDD = VHB = 12 V, VHS = VSS = 0 V, No load on LO or HO, TA = TJ = -40°C to
+140°C, (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
Supply Currents
IDD
VDD quiescent current
VLI = VHI = 0
0.4
0.8
UCC27200
f = 500 kHz, CLOAD = 0
2.5
4
UCC27201
IDDO
VDD operating current
f = 500 kHz, CLOAD = 0
3.8
5.5
IHB
Boot voltage quiescent current
VLI = VHI = 0 V
0.4
0.8
IHBO
Boot voltage operating current
f = 500 kHz, CLOAD = 0
2.5
4
IHBS
HB to VSS quiescent current
VHS = VHB = 110 V
0.0005
1
IHBSO
HB to VSS operating current
f = 500 kHz, CLOAD = 0
0.1
mA
uA
mA
Input
VHIT
Input rising threshold
VLIT
Input falling threshold
5.8
VIHYS
Input voltage hysteresis
0.4
VHIT
Input voltage threshold
1.7
VLIT
Input voltage threshold
VIHYS
Input voltage Hysteresis
RIN
Input pulldown resistance
UCC27200
UCC27201
3
0.8
8
5.4
V
2.5
1.6
100
mV
100
200
350
6.2
7.1
7.8
kΩ
Undervoltage Protection (UVLO)
VDD rising threshold
VDD threshold hysteresis
0.5
VHB rising threshold
5.8
VHB threshold hysteresis
6.7
7.2
V
0.4
Bootstrap Diode
VF
Low-current forward voltage
I VDD - HB = 100 µA
0.65
0.85
VFI
High-current forward voltage
I VDD - HB = 100 mA
0.85
1.1
RD
Dynamic resistance, ∆VF/∆I
I VDD - HB = 100 mA and 80
mA
0.6
1.0
ILO = 100 mA
0.18
0.4
TJ = -40 to 125°C
ILO = -100 mA, VLOH = VDD VLO
0.25
0.4
TJ = -40 to 140°C
ILO = -100 mA, VLOH = VDD VLO
0.25
0.42
V
Ω
LO Gate Driver
VLOL
VLOH
Low level output voltage
High level output voltage
Peak pull-up current
VLO = 0 V
3
Peak pull-down current
VLO = 12 V
3
V
A
HO Gate Driver
4
VHOL
Low level output voltage
VHOH
High level output voltage
IHO = 100 mA
0.18
0.4
TJ = -40 to 125°C
IHO = -100 mA, VHOH = VHBVHO
0.25
0.4
TJ = -40 to 140°C
IHO = -100 mA, VHOH = VHBVHO
0.25
0.42
Peak pull-up current
VHO = 0 V
3
Peak pull-down current
VHO = 12 V
3
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A
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SLUS746 – DECEMBER 2006
ELECTRICAL CHARACTERISTICS (continued)
over operating free-air temperature range, VDD = VHB = 12 V, VHS = VSS = 0 V, No load on LO or HO, TA = TJ = -40°C to
+140°C, (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
Propagation Delays
TDLFF
VLI falling to VLO falling
TDHFF
VHI falling to VHO falling
TDLRR
VLI rising to VLO rising
TDHRR
VHI rising to VHO rising
TJ = -40 to 125°C
CLOAD = 0
20
45
TJ = -40 to 140°C
CLOAD = 0
20
50
TJ = -40 to 125°C
CLOAD = 0
20
45
TJ = -40 to 140°C
CLOAD = 0
20
50
TJ = -40 to 125°C
CLOAD = 0
20
45
TJ = -40 to 140°C
CLOAD = 0
20
50
TJ = -40 to 125°C
CLOAD = 0
20
45
TJ = -40 to 140°C
CLOAD = 0
20
50
ns
Delay Matching
TMON
LI ON, HI OFF
1
7
TMOFF
LI OFF, HI ON
1
7
ns
Output Rise and Fall Time
tR
LO, HO
CLOAD = 1000 pF
8
tF
LO, HO
CLOAD = 1000 pF
7
tR
LO, HO (3 V to 9 V)
CLOAD = 0.1 µF
0.35
0.6
tF
LO, HO (3 V to 9 V)
CLOAD = 0.1 µF
0.3
0.6
IF = 20 mA, IREV = 0.5 A (1) (2)
20
ns
us
Miscellaneous
Minimum input pulse width that changes the output
Bootstrap diode turn-off time
(1)
(2)
50
ns
Typical values for TA = 25°C
IF: Forward current applied to bootstrap diode, IREV: Reverse current applied to bootstrap diode.
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TYPICAL CHARACTERISTICS
UCC27200 IDD OPERATING CURRENT
vs
FREQUENCY
UCC27201 IDD OPERATING CURRENT
vs
FREQUENCY
10.0
10.0
VDD = 12 V
No Load on Outputs
VDD = 12 V
No Load on Outputs
150oC
IDDO - Operating Current - mA
IDDO - Operating Current - mA
25oC
150oC
125oC
1.0
25oC
o
-40 C
0.1
125oC
1.0
-40oC
0.1
100
10
1000
100
10
Frequency - kHz
Figure 1.
Figure 2.
BOOT VOLTAGE OPERATING CURRENT
vs
FREQUENCY
HB TO VSS OPERATING CURRENT
vs
FREQUENCY
10.0
1.0
HB = 12 V
No Load on Outputs
IHBSO - Operating Current - mA
HB = 12 V
No Load on Outputs
IHBO - Operating Current - mA
1000
Frequency - kHz
150oC
125oC
1.0
25oC
-40oC
0.1
150oC
0.01
25oC
125oC
0.1
-40oC
0.001
10
100
1000
10
Frequency - kHz
Figure 3.
6
100
Frequency - kHz
Figure 4.
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TYPICAL CHARACTERISTICS (continued)
UCC27200 INPUT THRESHOLD
vs
SUPPLY VOLTAGE
UCC27201 INPUT THRESHOLD
vs
SUPPLY VOLTAGE
2.0
T = 25oC
T = 25oC
HI, LI - Input Threshold Voltage - V
HI, LI - Input Threshold Voltage/VDD Voltage - %
50
Rising
48
46
Falling
44
42
1.8
Rising
Falling
1.6
1.4
1.2
1.0
40
8
10
12
14
16
18
8
20
10
VDD - Supply Voltage - V
18
16
Figure 5.
Figure 6.
UCC27200 INPUT THRESHOLD
vs
TEMPERATURE
UCC27201 INPUT THRESHOLD
vs
TEMPERATURE
50
20
2.0
VDD = 12 V
VDD = 12 V
HI, LI - Input Threshold Voltage - V
HI, LI - Input Threshold Voltage/VDD Voltage - %
14
12
VDD - Supply Voltage - V
48
Rising
46
Falling
44
42
40
1.8
Rising
1.6
Falling
1.4
1.2
1.0
-50
-25
0
25
50
75
100
125
150
-50
TA - Temperature - oC
-25
0
25
50
75
TA - Temperature -
Figure 7.
100
125
150
oC
Figure 8.
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TYPICAL CHARACTERISTICS (continued)
LO AND HO HIGH LEVEL OUTPUT VOLTAGE
vs
TEMPERATURE
LO AND HO LOW LEVEL OUTPUT VOLTAGE
vs
TEMPERATURE
0.45
0.45
VDD = VHB = 16 V
ILO = IHO = -100 mA
0.35
VDD = VHB = 12 V
0.30
VDD = VHB = 8 V
0.25
0.20
0.15
0.10
ILO = IHO = 100 mA
0.40
VOL - LO/HO Output Voltage - V
VOH - LO/HO Output Voltage - V
0.40
VDD = VHB = 20 V
0.35
VDD = VHB = 16 V
0.30
VDD = VHB = 12 V
0.25
VDD = VHB = 8 V
0.20
0.15
0.10
0.05
0.05
VDD = VHB = 20 V
0.0
0.0
-50
-25
0
25
50
75
100
125
-50
150
-25
0
25
50
75
100
125
150
TA - Temperature - oC
TA - Temperature - oC
Figure 9.
Figure 10.
UNDERVOLTAGE LOCKOUT THRESHOLD
vs
TEMPERATURE
UNDERVOLTAGE LOCKOUT THRESHOLD HYSTERESIS
vs
TEMPERATURE
7.8
0.8
7.6
0.7
7.4
Hysteresis - V
Threshold - V
0.6
VDD Rising Threshold
7.2
7.0
6.8
6.6
VDD UVLO Hysteresis
0.5
0.4
0.3
HB UVLO Hysteresis
HB Rising Threshold
6.4
0.2
6.2
0.1
6.0
5.8
0
-50
-25
0
25
50
75
100
125
150
-50
TA - Temperature - oC
0
25
50
75
TA - Temperature - oC
Figure 11.
8
-25
Figure 12.
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125
150
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SLUS746 – DECEMBER 2006
TYPICAL CHARACTERISTICS (continued)
UCC27200 PROPAGATION DELAYS
vs
TEMPERATURE
UCC27201 PROPAGATION DELAYS
vs
TEMPERATURE
36
36
VDD = VHD = 12 V
34
32
30
TDHRR
28
26
24
22
20
Propagation Delay - ns
32
Propagation Delay - ns
VDD = VHB = 12 V
34
TDHFF
TDLFF
18
30
28
26
24
22
TDLFF
TDLRR
20
18
16
TDHFF
16
TDLRR
14
TDHRR
14
-50
-25
0
50
75
25
100
TA - Temperature - oC
125
150
-50
-25
0
25
50
75
100
125
150
TA - Temperature - oC
Figure 13.
Figure 14.
UCC27200 PROPAGATION DELAY
vs
SUPPLY VOLTAGE
UCC27201 PROPAGATION DELAY
vs
SUPPLY VOLTAGE
26
26
T = 25oC
T = 25oC
24
Propagation Delay - ns
Propagation Delay - ns
24
22
LI Falling
20
LI Rising
HI Falling
LI Falling
22
LI Rising
20
HI Rising
HI Rising
18
HI Falling
16
18
8
10
12
14
18
16
20
8
VDD = VHB - Supply Voltage - V
Figure 15.
10
12
14
16
18
20
VDD = VHB - Supply Voltage - V
Figure 16.
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TYPICAL CHARACTERISTICS (continued)
DELAY MATCHING
vs
TEMPERATURE
OUTPUT CURRENT
vs
OUTPUT VOLTAGE
3.5
7
VDD = VHB = 12 V
VDD = VHB = 12 V
3.0
Delay Matching - ns
5
4
UCC27200TMOFF
3
UCC27201TMOFF
UCC27201TMON
UCC27200TMON
2
ILO, IHO - Output Current - A
6
2.5
Pull-Down Current
Pull-Up Current
2.0
1.5
1.0
0.5
1
0
0
0
-50
-25
0
25
50
75
100
125
2
4
150
8
6
10
12
VLO, VHO - Output Voltage - V
TA - Temperature - oC
Figure 17.
Figure 18.
DIODE CURRENT
vs
DIODE VOLTAGE
QUIESCENT CURRENT
vs
SUPPLY VOLTAGE
700
100.0
Inputs Low
T = 25oC
600
IDD, IHB - Supply Current - mA
Diode Current - mA
10.0
1.0
0.1
500
IHB
400
300
IDD
200
0.01
100
0
0.001
0.5
0.6
0.7
0.8
0.9
0
Figure 19.
10
4
8
12
VDD, VHB - Supply Voltage - V
Diode Voltage - V
Figure 20.
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DEVICE INFORMATION
SOIC-8(D)
TOP VIEW
VDD
1
Power Pad TM SOIC-8(DDA)
TOP VIEW
8
8 LO
VDD 1
LO
Exposed
Thermal
Die Pad
HB
2
7
VSS
HB
2
HO
3
6
LI
HO
3
6 LI
HS
4
5
HI
HS
4
5 HI
7
VSS
SON-8 (DRM)
TOP VIEW
8 LO
VDD 1
HB 2
Exposed
Thermal
Die Pad*
7
VSS
HO 3
6
LI
4
5
HI
HS
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TERMINAL FUNCTIONS
TERMINAL
NAME
VDD
NO.
1
I/O
DESCRIPTION
I
Positive supply to the lower gate driver. De-couple this pin to VSS (GND). Typical
decoupling capacitor range is 0.22 µF to 1.0 µF.
HB
2
I
High-side bootstrap supply. The bootstrap diode is on-chip but the external bootstrap
capacitor is required. Connect positive side of the bootstrap capacitor to this pin. Typical
range of HB bypass capacitor is 0.022 µF to 0.1 µF, the value is dependant on the gate
charge of the high-side MOSFET however.
HO
3
O
High-side output. Connect to the gate of the high-side power MOSFET.
HS
4
I
High-side source connection. Connect to source of high-side power MOSFET. Connect
negative side of bootstrap capacitor to this pin.
HI
5
I
High-side input.
LI
6
I
Low-side input.
VSS
7
O
Negative supply terminal for the device which is generally grounded.
LO
8
O
Low-side output. Connect to the gate of the low-side power MOSFET.
-
Utilized on the DDA and DRM packages only. Electrically referenced to VSS (GND).
Connect to a large thermal mass trace or GND plane to dramatically improve thermal
performance. The PowerPad™ must be connected to VSS (GND) with a trace on the PCB
when using the DRM package (cannot be left floating).
PowerPAD™
12
PAD
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FUNCTIONAL BLOCK DIAGRAM
2
HB
3
HO
4
HS
8
LO
7
VSS
UVLO
LEVEL
SHIFT
HI
5
VDD
1
UVLO
LI
6
Figure 21.
TIMING DIAGRAMS
LI
Input
(HI, LI)
HI
TDLRR, TDHRR
LO
Output
(HO, LO)
TDLFF, TDHFF
HO
TMON
TMOFF
Figure 22.
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APPLICATION INFORMATION
Functional Description
The UCC27200 and UCC27201 are high-side/low-side drivers. The high-side and low-side each have
independent inputs which allow maximum flexibility of input control signals in the application. The boot diode for
the high-side driver bias supply is internal to the UCC27200 and UCC27201. The UCC27200 is the CMOS
compatible input version and the UCC27201 is the TTL or logic compatible version. The high-side driver is
referenced to the switch node (HS) which is typically the source pin of the high side MOSFET and drain pin of
the low-side MOSFET. The low-side driver is referenced to VSS which is typically ground. The functions
contained are the input stages, UVLO protection, level shift, boot diode, and output driver stages.
NOTE:
The term “UCC2720x” applies to both the UCC27200 and UCC27201.
Input Stages
The input stages provide the interface to the PWM output signals. The input impedance of the UCC27200 is 200
kΩ nominal and input capacitance is approximately 2 pF. The 200 kΩ is a pull-down resistance to Vss (ground).
The CMOS compatible input of the UCC27200 provides a rising threshold of 48% of VDD and falling threshold of
45% of VDD. The inputs of the UCC27200 are intended to be driven from 0 to VDD levels.
The input stages of the UCC27201 incorporate an open drain configuration to provide the lower input thresholds.
The input impedance is 200 kΩ nominal and input capacitance is approximately 4 pF. The 200 kΩ is a pull-down
resistance to VSS (ground). The logic level compatible input provides a rising threshold of 1.7 V and a falling
threshold of 1.6 V.
UVLO (Under Voltage Lockout)
The bias supplies for the high-side and low-side drivers have UVLO protection. VDD as well as
differential voltages are monitored. The VDD UVLO disables both drivers when VDD is below
threshold. The rising VDD threshold is 7.1 V with 0.5-V hysteresis. The VHB UVLO disables only
driver when the VHB to VHS differential voltage is below the specified threshold. The VHB
threshold is 6.7 V with 0.4-V hysteresis.
VHB to VHS
the specified
the high-side
UVLO rising
Level Shift
The level shift circuit is the interface from the high-side input to the high-side driver stage which is referenced to
the switch node (HS). The level shift allows control of the HO output referenced to the HS pin and provides
excellent delay matching with the low-side driver.
Boot Diode
The boot diode necessary to generate the high-side bias is included in the UCC2720x family of drivers. The
diode anode is connected to VDD and cathode connected to VHB. With the VHB capacitor connected to HB and
the HS pins, the VHB capacitor charge is refreshed every switching cycle when HS transitions to ground. The
boot diode provides fast recovery times, low diode resistance, and voltage rating margin to allow for efficient and
reliable operation.
Output Stages
The output stages are the interface to the power MOSFETs in the power train. High slew rate, low resistance
and high peak current capability of both output drivers allow for efficient switching of the power MOSFETs. The
low-side output stage is referenced from VDD to VSS and the high-side is referenced from VHB to VHS.
14
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APPLICATION INFORMATION (continued)
Design Tips
Switching the MOSFETs
Achieving optimum drive performance at high frequency efficiently requires special attention to layout and
minimizing parasitic inductances. Care must be taken at the driver die and package level as well as the PCB
layout to reduce parasitic inductances as much as possible. Figure 23 shows the main parasitic inductance
elements and current flow paths during the turn ON and OFF of the MOSFET by charging and discharging its
CGS capacitance.
L bond wire
L pin
L trace
1
VDD
I SOURCE
Rsource
Driver
Output
Stage
Cvdd
L pin L trace
L bond wire
Rg
8
LO
I sink
Rsink
L pin L trace
L bond wire
7
Cgs
L trace
Vss
Figure 23. MOSFET Drive Paths and Circuit Parasitics
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APPLICATION INFORMATION (continued)
The ISOURCE current charges the CGS gate capacitor and the ISINK current discharges it. The rise and fall time of
the voltage across the gate to source defines how quickly the MOSFET can be switched. Based on actual
measurements, the analytical curves in Figure 24 and Figure 25 indicate the output voltage and current of the
drivers during the discharge of the load capacitor. Figure 24 shows voltage and current as a function of time.
Figure 25 indicates the relationship of voltage and current during fast switching. These figures demonstrate the
actual switching process and limitations due to parasitic inductances.
12
11
12
11
10
10
9
8
9
6
8
5
7
4
3
LO Voltage, V
LO Falling, V or A
7
2
1
0
1
2
5
4
3
2
3
4
5
6
1
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
0
1
t, ns
2
Voltage
3
Current
2
1
0
1
2
3
4
5
LO Current, A
Figure 24. Turn-Off Voltage and Current vs Time
16
Figure 25. Turn-Off Voltage and Current Switching
Diagram
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APPLICATION INFORMATION (continued)
Turning off the MOSFET needs to be achieved as fast as possible to minimize switching losses. For this reason
the UCC2720x drivers are designed for high peak currents and low output resistance. The sink capability is
specified as 0.18 V at 100-mA dc current implying 1.8-Ω RDS(on). With 12-V drive voltage, no parasitic inductance
and a linear resistance, one would expect initial sink current amplitude of 6.7 A for both high-side and low-side
drivers. Assuming a pure R-C discharge circuit of the gate capacitor, one would expect the voltage and current
waveforms to be exponential. Due to the parasitic inductances and non-linear resistance of the driver
MOSFET’S, the actual waveforms have some ringing and the peak-sink current of the drivers is approximately
3.3 A as shown in Figure 18. The overall parasitic inductance of the drive circuit is estimated at 4 nH. The
internal parasitic inductance of the SOIC-8 package is estimated to be 2 nH including bond wires and leads. The
SON-8 package reduces the internal parasitic inductances by more than 50%.
Actual measured waveforms are shown in Figure 26 and Figure 27. As shown, the typical rise time of 8 ns and
fall time of 7 ns is conservatively rated.
Figure 26. VLO and VHO Rise Time, 1-nF Load, 5 ns/Div
Figure 27. VLO and VHO Fall Time, 1-nF Load, 5-ns/Div
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APPLICATION INFORMATION (continued)
Dynamic Switching of the MOSFETs
The true behavior of MOSFETS presents a dynamic capacitive load primarily at the gate to source threshold
voltage. Using the turn off case as the example, when the gate to source threshold voltage is reached the drain
voltage starts rising, the drain to gate parasitic capacitance couples charge into the gate resulting in the turn off
plateau. The relatively low threshold voltages of many MOSFETS and the increased charge that has to be
removed (Miller charge) makes good driver performance necessary for efficient switching. An open loop half
bridge power converter was utilized to evaluate performance in actual applications. The schematic of the
half-bridge converter is shown in Figure 30. The turn off waveforms of the UCC27200 driving two MOSFETs in
parallel is shown in Figure 28 and Figure 29.
Figure 28. VLO Fall Time in Half-Bridge Converter
18
Figure 29. VHO Fall Time in Half-Bridge Converter
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+
+
+
APPLICATION INFORMATION (continued)
Figure 30. Open Loop Half-Bridge Converter
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APPLICATION INFORMATION (continued)
Delay Matching and Narrow Pulse Widths
The total delays encountered in the PWM, driver and power stage need to be considered for a number of
reasons, primarily delay in current limit response. Also to be considered are differences in delays between the
drivers which can lead to various concerns depending on the topology. The sync-buck topology switching
requires careful selection of dead-time between the high- and low-side switches to avoid 1) cross conduction
and 2) excessive body diode conduction. Bridge topologies can be affected by a resulting volt-sec imbalance on
the transformer if there is imbalance in the high and low side pulse widths in a steady state condition.
Narrow pulse width performance is an important consideration when transient and short circuit conditions are
encountered. Although there may be relatively long steady state PWM output-driver-MOSFET signals, very
narrow pulses may be encountered in 1) soft start, 2) large load transients, and 3) short circuit conditions.
The UCC2720x driver family offers excellent performance regarding high and low-side driver delay matching and
narrow pulse width performance. The delay matching waveforms are shown in Figure 31 and Figure 32. The
UCC2720x driver narrow pulse performance is shown in Figure 33 and Figure 34.
20
Figure 31. VLO and VHO Rising Edge Delay Matching
Figure 32. VLO and VHO Falling Edge Delay Matching
Figure 33. 20-ns Input Pulse Delay Matching
Figure 34. 10-ns Input Pulse Delay Matching
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APPLICATION INFORMATION (continued)
Boot Diode Performance
The UCC2720x family of drivers incorporates the bootstrap diode necessary to generate the high side bias
internally. The characteristics of this diode are important to achieve efficient, reliable operation. The dc
characteristics to consider are VF and dynamic resistance. A low VF and high dynamic resistance results in a
high forward voltage during charging of the bootstrap capacitor. The UCC2720x has a boot diode rated at 0.65-V
VF and dynamic resistance of 0.6 Ω for reliable charge transfer to the bootstrap capacitor. The dynamic
characteristics to consider are diode recovery time and stored charge. Diode recovery times that are specified
with no conditions can be misleading. Diode recovery times at no forward current (IF) can be noticeably less than
with forward current applied. The UCC2720x boot diode recovery is specified at 20ns at IF = 20 mA, IREV = 0.5
A. At 0 mA IF the reverse recovery time is 15 ns.
Another less obvious consideration is how the stored charge of the diode is affected by applied voltage. On
every switching transition when the HS node transitions from low to high, charge is removed from the boot
capacitor to charge the capacitance of the reverse biased diode. This is a portion of the driver power losses and
reduces the voltage on the HB capacitor. At higher applied voltages, the stored charge of the UCC2720x PN
diode is often less than a comparable Schottky diode.
Layout Recommendations
To
•
•
•
•
•
•
•
•
improve the switching characteristics and efficiency of a design, the following layout rules should be followed.
Locate the driver as close as possible to the MOSFETs.
Locate the VDD and VHB (bootstrap) capacitors as close as possible to the driver.
Pay close attention to the GND trace. Use the thermal pad of the DDA and DRM package as GND by
connecting it to the VSS pin (GND). NOTE: On the DRM package the PowerPAD™ MUST be connected to
VSS on the PCB as this connection is not internal in the driver package. The GND trace from the driver goes
directly to the source of the MOSFET but should not be in the high current path of the MOSFET(S) drain or
source current.
Use similar rules for the HS node as for GND for the high side driver.
Use wide traces for LO and HO closely following the associated GND or HS traces. 60 mil to 100 mil width is
preferable where possible.
Use as least two or more vias if the driver outputs or SW node needs to be routed from one layer to another.
For GND the number of vias needs to be a consideration of the thermal pad requirements as well as parasitic
inductance.
Avoid LI and HI (driver input) going close to the HS node or any other high dV/dT traces that can induce
significant noise into the relatively high impedance leads.
Keep in mind that a poor layout can cause a significant drop in efficiency versus a good PCB layout and can
even lead to decreased reliability of the whole system.
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APPLICATION INFORMATION (continued)
Figure 35. Example Component Placement
Additional References
These references and links to additional information may be found at www.ti.com.
1. Additional layout guidelines for PCB land patterns may be found in Application Brief SLUA271
2. Additional thermal performance guidelines may be found in Application Reports SLMA002A and SLMA004
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