Order
Now
Product
Folder
Support &
Community
Tools &
Software
Technical
Documents
UCC24624
SLUSD48B – JULY 2018 – REVISED NOVEMBER 2018
UCC24624 Dual-Channel Synchronous Rectifier Controller for LLC Resonant Converters
1 Features
3 Description
•
•
The UCC24624 high-performance synchronous
rectifier (SR) controller is dedicated for LLC resonant
converters to replace the lossy diode output rectifiers
with SR MOSFETs and improve the overall system
efficiency.
1
•
•
•
•
•
•
•
•
230-V VD Pins Rating
23-ns Turn-Off Delay to Support LLC Operating
Above Resonant Frequency and Up to 625-kHz
Switching Frequency
Proportional Gate Drive to Extend the SR
Conduction Time
Adjustable Turn-Off Threshold for Minimum Body
Diode Conduction
Automatic Standby Mode Detection With 180 µA
of Low Standby Current
Wide 4.25-V to 26-V VDD Operation Range With
Internal Clamp
Adaptive Turn-on Delay for Better DCM Ring
Rejection
Two-Channel Interlock to Prevent Shoot-Through
Integrated 1.5-A Source and 4-A Sink Capability
Gate Driver for N-Channel MOSFETs
8-Pin SOIC Package
2 Applications
•
•
•
•
•
•
Desktop PC, AIO PC, ATX and Server Power
AC-DC Adaptors
LCD, LED, and OLED TVs
Industrial AC/DC and Isolated DC/DC Power
Power Tool Chargers, LED Lighting Power
Create a Custom Design Using the UCC24624
With WEBENCH® Power Designer
The UCC24624 SR controller uses drain-to-source
voltage sensing method to achieve on and off control
of the SR MOSFET. Proportional gate drive is
implemented to extend the SR conduction time,
minimize the body diode conduction time. To
compensate for the offset voltage caused by the SR
MOSFET parasitic inductance, the UCC24624
implements an adjustable positive turn-off threshold
to accommodate different SR MOSFET packages.
UCC24624 has a built-in 475-ns on-time blanking and
a fixed 650-ns off-time blanking to avoid SR false
turn-on and turn-off. UCC24624 also integrates a twochannel interlock function that prevents the two SRs
from being on at the same time. With 230-V voltagesensing pins and 28-V ABS maximum VDD rating, it
can be directly used in converters with output voltage
up to 24.75 V. The internal clamp allows the
controller to support 36-V output voltage easily by
adding an external current limiting resistor on VDD.
Device Information(1)
PART NUMBER
UCC24624
PACKAGE
BODY SIZE (NOM)
SOIC (8)
4.90 mm × 3.91 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
space
space
space
Typical Application Schematic
Q1
Lr
Vout
Vin
Cr
Q2
UCC24624
S1
VG1
VG2
PGND
VDD
REG
VD2
VD1
VSS
S2
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
UCC24624
SLUSD48B – JULY 2018 – REVISED NOVEMBER 2018
www.ti.com
Table of Contents
1
2
3
4
5
6
7
8
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Description, Continued .........................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
3
4
5
7.1
7.2
7.3
7.4
7.5
7.6
7.7
5
5
5
5
6
7
8
Absolute Maximum Ratings ......................................
ESD Ratings..............................................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Electrical Characteristics...........................................
Timing Requirements ................................................
Typical Characteristics ..............................................
Detailed Description ............................................ 10
8.1 Overview ................................................................. 10
8.2 Functional Block Diagram ....................................... 11
8.3 Feature Description................................................. 12
8.4 Device Functional Modes........................................ 20
9
Application and Implementation ........................ 21
9.1 Application Information............................................ 21
9.2 Typical Application ................................................. 21
10 Power Supply Recommendations ..................... 25
11 Layout................................................................... 26
11.1 Layout Guidelines ................................................. 26
11.2 Layout Example .................................................... 26
12 Device and Documentation Support ................. 28
12.1
12.2
12.3
12.4
12.5
12.6
Device Support ....................................................
Receiving Notification of Documentation Updates
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
28
28
28
28
28
28
13 Mechanical, Packaging, and Orderable
Information ........................................................... 29
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision A (September 2018) to Revision B
•
2
Page
First release of production-data data sheet ........................................................................................................................... 1
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
Product Folder Links: UCC24624
UCC24624
www.ti.com
SLUSD48B – JULY 2018 – REVISED NOVEMBER 2018
5 Description, Continued
With the built-in standby mode detection based on average switching frequency, UCC24624 enters the standby
mode automatically without using external components. The low standby mode current of 180 µA supports
meeting modern no-load power consumption requirements such as CoC, and DoE regulations. UCC24624 can
be used with the UCC25630x LLC and UCC28056 PFC controllers to achieve high efficiency while maintaining
excellent light load and no-load performances. Other PFC controllers, such as UCC28064A, UCC28180, and
UCC28070 can be used to achieve higher power levels. 1.5-A peak source and 4-A peak sink driving capability
allows UCC24624 to support LLC converters up to 1 kW.
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
Product Folder Links: UCC24624
3
UCC24624
SLUSD48B – JULY 2018 – REVISED NOVEMBER 2018
www.ti.com
6 Pin Configuration and Functions
D Package
8-Pin SOIC
Top View
VG1 1
8 VG2
PGND 2
7 VDD
REG 3
6 VD2
VD1 4
5 VSS
Pin Functions
PIN
NO.
1
NAME
VG1
I/O
DESCRIPTION
O
VG1 is the controlled MOSFET gate drive for channel 1. Connect VG1 to the gate of the channel 1
SR MOSFET through a small series resistor using short PCB traces to achieve optimal switching
performance. The VG1 output can achieve 1.5-A peak source current, and 4-A peak sink current
when connected to a large N-channel power MOSFET.
2
PGND
-
PGND is the power return pin of the UCC24624. The IC bias current and high peak current from the
gate drivers return to this pin. Short PCB traces and the ceramic bypass capacitor are required to
minimize the high slew rate current impacts to the IC operation. The PGND should be connected
directly to the SR MOSFET source pins.
3
REG
O
REG is the internal linear regulator output and the device's internal bias pin. An internal linear
regulator from VDD to REG generates a well-regulated 11-V voltage. TI recommends putting a 2.2-μF
bypass capacitor from REG pin to PGND pin.
4
VD1
I
VD1 is the channel 1 SR MOSFET drain voltage sensing input. Connect this pin to channel 1 SR
MOSFET drain pin. The layout should avoid the VD1 pin trace sharing the power path to minimize the
impacts of parasitic inductance.
5
VSS
I
VSS is used to sense the voltage drop across the SR MOSFETs. Since both channels are sharing
the same VSS pin to sense the MOSFET voltage, special attention is required. The layout should
avoid the VSS pin trace sharing the power path to minimize the impacts of parasitic inductor. See
Layout Example for more details. A resistor can be added between VSS pin and SR MOSFET source
pins to adjust the SR turn-off threshold if it is needed.
6
VD2
I
VD2 is the channel 2 SR MOSFET drain voltage sensing input. Connect this pin to channel 2 SR
MOSFET drain pin. The layout must avoid the VD2 pin trace sharing the power path to minimize the
impacts of parasitic inductance.
7
VDD
I
VDD is the internal linear regulator input. Connect this pin to the output voltage when the output
voltage is less than 24.75 V. When the output voltage is higher than 24.75 V, add a series resistor
between LLC output voltage and the VDD pin to limit the internal clamping circuit current.
8
VG2
O
VG2 is the controlled MOSFET gate drive for channel 2. Connect VG2 to the gate of the channel 2
MOSFET through a small series resistor using short PCB traces to achieve optimal switching
performance. The VG2 output can achieve 1.5-A peak source current and 4-A peak sink current
when connected to a large N-channel power MOSFET.
4
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
Product Folder Links: UCC24624
UCC24624
www.ti.com
SLUSD48B – JULY 2018 – REVISED NOVEMBER 2018
7 Specifications
7.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted) (1)
Input voltage
(1)
MIN
MAX
VDD (2)
–0.3
28
V
VD1, VD2
–0.7
230
V
–2
230
V
–0.3
VREG+0.7
V
13.5
V
±4
A
VD1, VD2 for IVD1, IVD2 ≤ –10 mA and less than 300 ns
Output voltage
VG1, VG2
REG
UNIT
Output current,
peak
VG1 or VG2
TJ
Junction temperature
–40
125
°C
Tstg
Storage temperature
–65
150
°C
(1)
(2)
(3)
(3)
pulsed, tPULSE ≤ 4 ms, duty cycle ≤ 1%
Stresses beyond those listed under Absolute Maximum Rating may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Condition. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
VDD is internally clamped at 27.5 V typical with 15 mA of sink current capability.
In normal use, VG1 or VG2 is connected to the gate of a power MOSFET through a small resistor. When used this way, VG1 or
VG2current is limited by the UCC24624 and no absolute maximum output current considerations are required. The series resistor shall
beselected to minimize overshoot and ringing due to series inductance of the VG1 or VG2 output and power-MOSFET gate-drive
loop.Continuous VG1 or VG2 current is subject to the maximum operating junction temperature limitation.
7.2 ESD Ratings
Human body model (HBM), per
ANSI/ESDA/JEDEC JS-001 (1)
V(ESD)
(1)
(2)
Electrostatic discharge
Charged device model (CDM), per
JEDEC specificationJESD22C101 (2)
VALUE
UNIT
All pins except pins 4 and 6
±2000
V
Pins 4 and 6
±1000
V
All pins
±500
V
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.
7.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)
MIN
VVDD
Supply voltage
CVDD
VDD bypass capacitor
CREG
REG pin bypass capacitor
NOM
4.25
Switching frequency
TJ
Junction temperature
UNIT
26
V
0.1
µF
2.2
VVD1, VVD2 Voltage on sensing pins
fSW
MAX
µF
–0.5
-40
200
V
625
kHz
125
°C
7.4 Thermal Information
DEVICE
THERMAL METRIC (1)
D (SOIC)
UNIT
8 PINS
RθJA
Junction-to-ambient thermal resistance
108.4
°C/W
RθJC(top)
Junction-to-case (top) thermal resistance
43.5
°C/W
RθJB
Junction-to-board thermal resistance
53.6
°C/W
ΨJT
Junction-to-top characterization parameter
4.9
°C/W
(1)
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report.
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
Product Folder Links: UCC24624
5
UCC24624
SLUSD48B – JULY 2018 – REVISED NOVEMBER 2018
www.ti.com
Thermal Information (continued)
DEVICE
THERMAL METRIC (1)
D (SOIC)
UNIT
8 PINS
ΨJB
Junction-to-board characterization parameter
52.8
°C/W
RθJC(bot)
Junction-to-case (bottom) thermal resistance
N/A
°C/W
7.5 Electrical Characteristics
At VVDD = 12 VDC, CVG1 = CVG2 = 0 pF, CREG = 2.2 µF VVD1 = VVD2 = 0 V, –40°C ≤ TJ = TA ≤ +125°C, all voltages are with
respect to PGND, and currents are positive into and negative out of the specified terminal, unless otherwise noted. Typical
values are at TJ = +25°C.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
5
150
275
µA
0.77
1.1
1.5
mA
BIAS SUPPLY
IVDDSTART
IVDDRUN
VDD current, REG under voltage
VDD current, run
IVDDSTBY
VDD current, standby mode
VDDCLAMP
VDD clamp voltage
VVDD = 4 V, VVD1 = VVD2 = 0 V
VVDD = 12 V
VVDD = 5 V
0.7
1
1.5
mA
VVDD = 12 V, 25℃
110
180
200
µA
VVDD = 5 V, 25℃
IVDD = 15 mA
100
180
200
µA
24.75
27.5
29.5
V
UNDER VOLTAGE LOCKOUT (UVLO)
VREGON
REG turn-on threshold
4.1
4.5
4.8
V
VREGOFF
REG turn-off threshold
3.63
4
4.25
V
VREGHYST
REG UVLO hysteresis
VREGHYST = VREGON – VREGOFF
0.450
0.500
0.555
V
MOSFET VOLTAGE SENSING
VTHVGON
SR turn-on threshold
VVD1, or VVD2 falling
–435
–265
–160
mV
VTHVGOFF
SR turn-off threshold
VVD1, or VVD2 rising
2
10.5
18
mV
IVS_OFFSET
VSS pin offset current for turn-off
threshold adjustment
260
330
400
µA
VTHPGD_LO
Low-level regulation threshold
–80
–35
0
mV
VTHPGD_HI
High-level regulation threshold
–165
–100
–40
mV
VTHARM
SR turn-on re-arming threshold
IVDBIAS
Bias current on VD1 or VD2
VVD1 = VVD2 = -150 mV
1.4
1.5
1.7
V
–10
0
0.5
µA
3.5
6.5
11.25
Ω
Ω
GATE DRIVER
RVG_PU
VG pull-up resistance
RVG_PD
VG pull-down resistance
VGHI
VG high clamp level
VGUV
VG output low voltage, VDD low bias VVDD = 4 V, IVG = 25 mA
VGLO
VG output low voltage
IVGSOURCE
VG maximum source current (1)
IVGSINK
VG maximum sink current (1)
IVG = 0 mA
VVDD
=
12 V, IVG = 100 mA
0.2
0.9
1.5
9.95
10.9
11.68
1
20
100
mV
5
100
175
mV
0.9
1.5
2.4
A
2.6
4
6.7
A
9.9
11
11.9
9
25
75
mV
V
REG SUPPLY
VREG
REG pin regulation level
VVDD = 15 V, ILOAD_REG = 0 mA
VREGLG
Load regulation on REG
VVDD = 15 V, ILOAD_REG = 0 mA to 30 mA
VREGDO
REG drop out on passthrough mode
VVDD = 5 V, ILOAD_REG = 0 mA to 10 mA
0.1
0.28
0.5
V
IREGSC
REG short circuit current
VVDD = 12 V, VREG = 0 V
4.5
9.5
13
mA
IREGLIM
REG current limit
VVDD = 12 V, VREG = 8 V
41
60
95
mA
(1)
6
V
Ensured by design. Not production tested.
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
Product Folder Links: UCC24624
UCC24624
www.ti.com
SLUSD48B – JULY 2018 – REVISED NOVEMBER 2018
7.6 Timing Requirements
At VVDD = 12 VDC, CVG1 = CVG2 = 0 pF, CREG = 2.2 µF, VVD1 = VVD2 = 0 V, –40°C ≤ TJ = TA ≤ +125°C, all voltages are with
respect to PGND, and currents are positive into and negative out of the specified terminal, unless otherwise noted. Typical
values are at TJ = +25°C.
PARAMETER
TEST CONDITIONS
MIN
NOM
MAX
UNIT
GATE DRIVER
tdVGON
SR turn-on propagation delay, for
both channels
VVD1, VVD2 moves from 4.7 V to -0.5 V in
5 ns
110
155
225
ns
tdVGOFF
SR turn-off propagation delay, for
both channels
VVD1, VVD2 moves from -0.5 V to 4.7 V in
5 ns
5.5
23
40
ns
trVG
VVG1, VVG2 rise time
10% to 90%, VVDD = 12 V, CVG = 6.8 nF
13
23
40
ns
tfVG
VVG1, VVG2 fall time
90% to 10%, VVDD = 12 V, CVG = 6.8 nF
19
35
ns
325
475
625
ns
BLANKING TIME
tONMIN
On-time blanking
tMGPU
Minimum gate pullup time
180
275
370
ns
tOFFMIN
Off-time blanking
440
650
855
ns
tSTBY_DET
Standby mode detection-time
5.5
7.5
10
ms
fSLEEP
Average frequency entering standby
mode
6.55
9
12.2
kHz
fWAKE
Average frequency coming out of
standby mode
11.5
15.6
21
kHz
IVG1, IVG2 = 1.5 A
STANDBY
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
Product Folder Links: UCC24624
7
UCC24624
SLUSD48B – JULY 2018 – REVISED NOVEMBER 2018
www.ti.com
7.7 Typical Characteristics
1.5
1.4
VDD Current RUN (IVDD RUN) (mA)
4.5
4.45
4.4
UVLO Thresholds (V)
4.35
4.3
4.25
4.2
UVLO ON
UVLO OFF
4.15
4.1
4.05
4
3.95
3.9
-40
-20
0
20
40
60
80
100
Junction Temperature (oC)
120
1.3
1.2
1.1
1
0.9
0.8
0.7
5-V VDD
12-V VDD
0.6
0.5
-40
140
-20
0
20
40
60
80
100
Junction Temperature (oC)
D001
CVG1 = CVG2 = 0 pF
Figure 1. UVLO Thresholds vs Temperature
SR Turn-off Threshold VTHVGOFF (mV)
SR Turn-on Threshold VTHVGON (mV)
0
-100
-150
-200
-250
-300
-350
-400
-450
-20
0
20
40
60
80
100
Junction Temperature ( oC)
120
140
11.6
11.4
11.2
11
10.8
10.6
10.4
10.2
10
9.8
9.6
9.4
9.2
9
8.8
8.6
-40
12-V VDD
5-V VDD
-20
0
20
40
60
80
100
Junction Temperature (oC)
120
140
D004
Figure 4. SR Turn-off Threshold Voltages vs Temperature
11
-20
-22
-24
-26
-28
-30
-32
-34
-36
-38
-40
-42
-44
-46
-48
-50
-40
REG Pin Regulation Level VREG (V)
Proportional Gate Drive Threshold VTHPGD_LO (mV)
D002
VVD1= VVD2 = 1 V
D003
Figure 3. SR Turn-on Threshold Voltage vs Temperature
10.95
10.9
10.85
10.8
10.75
10.7
10.65
10.6
-20
0
20
40
60
80
100
Junction Temperature ( oC)
120
140
D005
ILOAD_REG = 0 mA
ILOAD_REG = 30 mA
10.55
10.5
-40
Figure 5. Proportional Gate Drive Threshold vs Temperature
8
140
Figure 2. Bias Supply Current vs Temperature (No
Switching)
-50
-500
-40
120
-20
0
20
40
60
80
100
Junction Temperature ( oC)
120
140
D006
Figure 6. REG Pin Voltage vs Temperature at Different
Loading Conditions
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
Product Folder Links: UCC24624
UCC24624
www.ti.com
SLUSD48B – JULY 2018 – REVISED NOVEMBER 2018
675
0.3
Blanking Time tONMIN and tOFFMIN (ns)
REG Drop-out in Pass-through Mode VREGDO (V)
Typical Characteristics (continued)
0.28
0.26
0.24
0.22
0.2
0.18
0.16
0.14
-40
-20
0
20
40
60
80
100
Junction Temperature ( oC)
120
650
625
600
575
550
On-time Blanking
Off-time Blanking
525
500
475
450
-40
140
-20
0
20
40
60
80
100
Junction Temperature (oC)
120
140
D008
D007
ILOAD_REG = 10 mA
Figure 8. Blanking Time vs Temperature
Figure 7. REG Dropout in Pass-through Mode vs
Temperature
Turn-off Propagation Delay tdVGOFF (ns)
Turn-on Propagation Delay tdVGON (ns)
195
190
185
180
175
170
165
160
155
150
145
140
135
-40
-20
0
20
40
60
80
100
Junction Temperature (oC)
120
140
0
20
40
60
80
100
Junction Temperature ( oC)
120
140
D010
Figure 10. SR Turn-off Propagation Delay vs Temperature
205
337.5
VSS Pin Offset Current IVS_OFFSET (PA)
VDD Standby Mode Current IVDDSTBY (PA)
-20
D009
Figure 9. SR Turn-on Delay Time vs Temperature
200
195
190
185
180
175
12-V VDD
5-V VDD
170
165
-40
26
25.6
25.2
24.8
24.4
24
23.6
23.2
22.8
22.4
22
21.6
21.2
20.8
20.4
20
-40
-20
0
20
40
60
80
100
Junction Temperature (oC)
120
140
335
332.5
330
327.5
325
322.5
320
317.5
315
312.5
-40
D011
Figure 11. Standby Current vs Temperature
-20
0
20
40
60
80
100
Junction Temperature ( oC)
120
140
D012
Figure 12. VSS Pin Offset Current vs Temperature
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
Product Folder Links: UCC24624
9
UCC24624
SLUSD48B – JULY 2018 – REVISED NOVEMBER 2018
www.ti.com
8 Detailed Description
8.1 Overview
The UCC24624 is a high performance synchronous rectifier (SR) controller for LLC resonant converter
applications. It integrates two channels of SR control into a single 8-pin SOIC package, minimizes the external
components, and simplifies PCB layout. The UCC24624 synchronous rectifier controller uses drain-to-source
voltage (VDS) sensing to determine the SR MOSFET conduction interval. The SR MOSFET is turned on when its
VDS falls below –265-mV turn-on threshold, and is turned off when VDS rises above the turn-off threshold (the
turn-off threshold is user programmable at 10.5 mV or greater). The SR conduction voltage drop is continuously
monitored and regulated to minimize the conduction loss and body diode conduction time. The extremely fast
turn-off comparator and driving circuit allows the fast turn off of SR MOSFETs, even when the LLC converter
operates above its resonant frequency. Fixed 475-ns minimum on-time blanking allows the controller to support
the SR operating at up to 625-kHz switching frequency. The 650-ns minimum off-time blanking makes the IC
more robust against the noise caused by the parasitic ringing. The two channels have interlock logic to prevent
shoot-through between the two SR MOSFETs. To minimize standby power, automatic standby mode disables
the gate pulses when the average switching frequency of the converter becomes lower than 9 kHz. When the
load increases such that the average switching frequency on channel 1 rises above 15.6 kHz, the controller
resumes normal SR operation. In standby mode, two channels are turned off and the gate-drive outputs are
actively held low. Other functionality are disabled during standby mode to minimize the IC current consumption.
The wide VDD range and gate driver clamp make the controller applicable for different output voltage
applications. With an internal voltage clamp on the VDD pin, the UCC24624 can be directly powered by an
output voltage higher than 24.75 V with a series resistor between VDD and the LLC converter output.
10
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
Product Folder Links: UCC24624
UCC24624
www.ti.com
SLUSD48B – JULY 2018 – REVISED NOVEMBER 2018
8.2 Functional Block Diagram
VDD
REG
START
11-V Linear
Regulator
REG
UVLO
POWER & FAULT
MANAGEMENT
STBY
27.5V
VD1
Turn-on
comparator, CH1
±
-265mV
PROPORTIONAL
GATE DRIVE
CONTROL
GATE
DRIVER
VG1
+
SR2 ON
START
ARM1
Minimum
OFF time
ARM1
Q
SR1 ON
R
Turn-off
comparator, CH1
+
VTHOFF
S
Q
(-35mV)
Prop-DRV
threshold
PGND
±
Minimum
ON time
SR1 ON
FREQUENCY
DETECTION
STBY
REG
+
1.5V
±
VD2
±
-265mV
ARM1
PROPORTIONAL
GATE DRIVE
CONTROL
Turn-on
comparator, CH2
GATE
DRIVER
VG2
+
SR1 ON
START
ARM2
Minimum
OFF time
+
VTHOFF
ARM2
S
Q
SR2 ON
Turn-off
comparator, CH2
R
Q
(-35mV)
Prop-DRV
threshold
VTHOFF
10.5 mV
±
VSS
Minimum
ON time
330 µA
+
1.5V
±
ARM2
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
Product Folder Links: UCC24624
11
UCC24624
SLUSD48B – JULY 2018 – REVISED NOVEMBER 2018
www.ti.com
8.3 Feature Description
8.3.1 Power Management
The UCC24624 synchronous-rectifier (SR) controller is powered from the REG pin through an internal linear
regulator between the VDD pin and the REG pin. This configuration allows for optimal design of the gate driver
stage to achieve fast driving speed, low driving loss and high noise immunity.
A typical application diagram of UCC24624 is shown in Figure 13. In most cases, the UCC24624 can be directly
powered from the LLC resonant converter output. Both SR MOSFETs are located in the secondary side current
return paths for easier voltage sensing, IC biasing, and gate driving.
Q1
Lr
Vout
Vin
Cr
Q2
UCC24624
S1
1
VG1
VG2
8
2
PGND
VDD
7
3
REG
VD2
6
VSS
5
4
VD1
S2
Figure 13. UCC24624 Application Diagram in LLC Resonant Converter
During start-up, the output voltage rises from 0 V. With the rise of the output voltage, the internal linear regulator
operates in a pass-through mode, and the REG pin voltage rises together with the output voltage. The UVLO
function of UCC24624 monitors the voltage on REG pin instead of VDD pin. Before the REG pin voltage
increases above the UVLO on threshold (VREGON), UCC24624 consumes the minimum current of IVDDSTART.
Once the REG pin voltage rises above the UVLO on threshold, the device starts to consume the full operating
current, including IVDDRUN and the gate driving currents, and controls the on and off of the SR MOSFETs.
When VDD voltage is above approximately 11 V, the internal linear regulator operates in the regulator mode. The
REG pin voltage is now well regulated to 11 V. This allows the optimal driving voltage for the SR MOSFET
without increasing the gate driver loss for typical power MOSFETs. The internal regulator is rated at 30 mA of
load regulation capability for higher switching frequency operation, or driving high SR MOSFET gate
capacitances. It is required to have sufficient bypass capacitance on the REG pin to ensure stable operation of
the linear regulator. A 2.2-μF X5R or better ceramic bypass capacitor is recommended.
When VDD voltage falls below 11 V, the internal linear regulator operates in the pass-through mode again.
Depending on the load current, the regulator has a voltage drop of approximately 0.2 V. The UCC24624
continues to operate during this mode until the REG pin voltage drops below the UVLO turn-off level (VREGOFF).
A basic timing diagram of the VDD and the REG pin voltages can be found in Figure 14.
12
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
Product Folder Links: UCC24624
UCC24624
www.ti.com
SLUSD48B – JULY 2018 – REVISED NOVEMBER 2018
Feature Description (continued)
VVDD
VREG
VREG
VVDD
VON
VOFF
t
SR Control Enable (internal signal)
t
Figure 14. Timing diagram for VDD and REG
The UCC24624 VDD may be connected directly to the converter output when the output voltage is less than
VDDCLAMP minimum value of 24.75 V. However, for the applications where the output voltage is higher than that
level, including special conditions such as over voltage transients, the UCC24624 can still work with some simple
modification. To allow UCC24624 to operate with higher output voltages, UCC24624 is equipped with an internal
voltage clamp, at 27.5 V typical clamping voltage. Add a series resistor between the LLC converter output
voltage and the UCC24624 VDD pin, as shown in Figure 15. This way the voltage on VDD is limited by the
internal clamp. The clamp current must be kept less than 15 mA. For example, at 36-V output, use a resistor
larger than 750 Ω. Because the gate drive voltage is only 11 V, this added resistor still allows enough voltage on
the gate drive to maintain the reliable operation of the SRs. Furthermore, the current consumption of the SR
controller is mainly caused by the SR MOSFET gate charge. The added resistor won't increase the power
consumption if the clamping circuit is not activated. Instead, it relocates some loss from the UCC24624 to the
resistor and improves the thermal handling of the UCC24624.
Q1
Lr
Vout
Vin
Cr
Q2
UCC24624
S1
VG1
VG2
PGND
VDD
REG
VD2
VD1
VSS
S2
Figure 15. UCC24624 Configuration for an Output Voltage Higher Than 24.75 V
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
Product Folder Links: UCC24624
13
UCC24624
SLUSD48B – JULY 2018 – REVISED NOVEMBER 2018
www.ti.com
Feature Description (continued)
8.3.2 Synchronous Rectifier Control
The UCC24624 SR controller determines the conduction time of the SR-MOSFET by comparing the drain-tosource voltage of the MOSFET against a turn-on threshold and a turn-off threshold. The gate driver output is
driven high when the VDS of the MOSFET becomes more negative than VTHVGON and is driven low when VDS
becomes more positive than VTHVGOFF as illustrated in Figure 16.
VDS
ISD
VTHVGOFF
t
VTHREG
VTHVGON
VGATE
90%
10%
tr_VG
t
tdVGON
Figure 16. SR Operation Principle
Note that before SR MOSFET turns on, there is a small delay caused by the internal comparator delay and the
gate driver delay. During the delay time, the SR MOSFET body diode is conducting. For LLC resonant
converters, this delay is essential for appropriate operation. Due to the large junction capacitors of the SR
MOSFETs, the SR often sees a leading-edge current spike early in the conduction period, follow by the real
conduction current. Normally, a prolonged minimum on time can override this spike to make the circuit operate
normally. However, this causes large negative current that transfer the energy from the output to the input and
reduces the overall converter efficiency. In UCC24624, 155-ns turn-on delay is added, to help ignore the leading
edge spike.
When the SR MOSFET body diode is conducting, VD pin becomes negative relative to the VSS pin by the body
diode drop. The VD and VSS pins must be connected directly to the SR MOSFET pins to avoid any overlapping
of sensing paths to the power path and minimize the negative voltage and ringing caused by parasitic
inductance. Low package inductance MOSFETs, such as in SON package, are preferred to minimize this effect
as well.
Besides the simple comparator, UCC24624 also includes a proportional gate drive feature. For many SR
controllers, the SR MOSFET is turned on with the full driving voltage. In this way, the conduction loss can be
minimized. However, this method has a few major drawbacks. Because the turn-off threshold is a fixed value,
often to prevent negative current, the SR is turned off before the current reaches zero. This causes some SR
MOSFET body diode conduction time and increases the conduction loss. Another issue is associated with the
LLC converter operating above the resonant frequency. When the converter operates above the resonant
frequency, the SR current slope (di/dt) at turn-off could be as high as 150 A/μs. This high current slope could
cause negative current if the SR controller has long turn-off propagation delays. Furthermore, the time to
discharge the SR MOSFET gate voltage from its full driving voltage to its threshold level introduces another
delay. This further increases the negative current.
14
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
Product Folder Links: UCC24624
UCC24624
www.ti.com
SLUSD48B – JULY 2018 – REVISED NOVEMBER 2018
Feature Description (continued)
Instead of always keeping the SR MOSFET on with the full gate-drive voltage, UCC24624 reduces its gate-drive
voltage when the voltage drop across the SR MOSFET drain to source becomes more than –35 mV (less
negative, closer to zero when current approaching zero). During this time, UCC24624 reduces its gate drive
voltage from 11 V to close to the SR MOSFET's threshold voltage, and tries to regulate the SR MOSFET VDS
voltage to –35 mV (VTHPGD_LO). This brings two major benefits to the application: a) Preventing the SR premature
turn off, which causes extra loss associated with body diode conduction b) Shorter turn-off delay since the SR
MOSFET gate voltage is already reduced close to the MOSFET threshold voltage level and the SR MOSFET can
be turned off with virtually no delay.
The SR MOSFET is only driven high with its full driving capability of 1.5 A during the gate driver minimum pull-up
time tMGPU. After that, the SR MOSFET gate is kept high by a weak current source of approximately 200 µA.
Keep the resistor between the SR MOSFET gate and source larger than 100 kΩ to ensure the full driving voltage
and a minimized conduction loss.
Due to the sinusoidal current shape in the secondary side SR MOSFETs in an LLC resonant converter, the
proportional gate drive could start to reduce the SR gate voltage even at the current rising edge. This increases
the conduction loss and reduces the converter efficiency. In UCC24624, the proportional gate drive is disabled
during the first half of the SR conduction time, based on the previous cycle's SR conduction time. Therefore, the
gate drive voltage is only reduced during the SR current falling edge and this helps to maintain the low
conduction loss. The gate drive voltage is forced to reduce if the SR voltage drop does not reach the proportional
gate-drive threshold VTHPGD_LO within the 90% of the previous cycle on time. And the proportional gate drive now
tries to regulate the VDS to –100 mV (VTHPGD_HI). This further ensures the fast turn-off speed for high di/dt
conditions.
To prevent the SR MOSFET premature turn off caused by the large package inductance, an offset resistor can
be added between the VSS pin and the SR MOSFET source pins to further increase the turn off threshold. See
below section for the details of choosing the resistor value.
8.3.3 Turn-off Threshold Adjustment
When SR MOSFETs are implemented in LLC converters, they are often turned off too early, which creates long
body diode conduction times. This results in more power loss, lower efficiency, and higher thermal stress.
The SR MOSFET early turn off is caused by the parasitic inductance in the SR voltage sensing path. As
illustrated in Figure 17, the VDS voltage sensed by the synchronous rectifier controller (VSENSE) is the
combination of the MOSFET on-state resistor voltage drop VSR, together with the voltage drops on parasitic
inductors LD and LS. A better layout approach can minimize these parasitic inductors. However, the minimum
value it can achieve is the package inductance of the SR MOSFET. With different packages, this parasitic
inductance could vary from 2 to 10 nH.
VSENSE
-
VSR
+
LD
LS
SR
ISR
Figure 17. SR Controller Sensed Voltage
The overall sensed voltage can be represented by Equation 1.
85'05' = F d+54 × 4&5KJ + :.& + .5 ; ×
@+54
h
@P
(1)
Because of the sinusoidal current shape and high output current, the current slope (di/dt) creates a significant
voltage drop across the package inductance. This causes the SR controller to detect a smaller voltage drop and
turn off the SR MOSFET early.
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
Product Folder Links: UCC24624
15
UCC24624
SLUSD48B – JULY 2018 – REVISED NOVEMBER 2018
www.ti.com
Feature Description (continued)
To overcome this issue, UCC24624 implements several techniques.
First, the proportional gate drive feature is implemented. As discussed earlier, the proportional gate drive reduces
the SR MOSFET gate drive voltage when the SR current is small, and increases its voltage drop. This increased
voltage drop could overwhelm the offset voltage introduced by the package inductance. Thus the SR MOSFET
conduction time is extended.
Second, the turn-off threshold is set at 10.5 mV, instead of typically being set as a negative threshold. Because
of the high di/dt and unavoidable SR package inductance, positive voltage is always expected at zero SR
current. The positive turn-off threshold allows the SR MOSFET to continue conduction toward the end of the
intended conduction period without the concern of causing negative SR current because of anticipating the
positive offset voltage on the package inductances.
Last, UCC24624 also allows the user to further increase the turn-off threshold to accommodate higher parasitic
inductance MOSFET packages, such as TO-220 packages. As illustrated in Figure 18, UCC24624 has an
internal current source that flows out of the VSS pin. By connecting a resistor from the VSS pin to the SR
MOSFET source, the voltage drop across the external resistor increases the turn-off threshold. This increased
turn-off threshold makes it more suitable for TO-220 packages. Less than 70-mV offset is recommended. When
using the low inductance MOSFET packages, such as SON5x6, the external resistor is not needed because the
proportional gate drive alone can take care of the offset caused by the smaller package inductance.
NOTE
To ensure normal system operation, VSS pin must never be kept open.
VD1,
VD2
Turn-off
comparator
+
±
VTHOFF
SR
10.5 mV
Roffset
330 µA
VSS
UCC24624
Figure 18. Adjustable Turn-off Threshold
The internal current source is at 330 µA and the external offset resistor value is recommended to be less than
212 Ω. The offset resistor Roffset can be calculated by using Equation 2 with the desired turn-off threshold VTHOFF.
4KBBOAP =
86*1(( F 10.5I8
330ä#
(2)
This added offset voltage only changes the SR turn-off threshold, while the proportional gate drive threshold
remains the same.
8.3.4 Noise Immunity
To ensure reliable SR operation and to avoid false turn-on and turn-off, features such as blanking time, adaptive
turn-on delay, and interlock logic are implemented. As illustrated in Figure 19, the SR control is blanked by the
on-time blanking, off-time blanking and two-channel interlock logic.
16
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
Product Folder Links: UCC24624
UCC24624
www.ti.com
SLUSD48B – JULY 2018 – REVISED NOVEMBER 2018
Feature Description (continued)
VVD2
VTHARM
VVD2
ISD2
VVD2
VVD2
VTHVGOFF
t
VTHREG
VTHVGON
VVD1
VVD1
VTHARM
VTHARM
ISD1
ISD1
VTHVGOFF
VTHVGOFF
VTHREG
VTHREG
VTHVGON
t
VTHVGON
S1 Gate
S2 Gate
S1 Gate
t
S1 on-time
blanking
S2 on-time
blanking
S1 on-time
blanking
t
S1 off-time
blanking
S1 off-time
blanking
S2 off-time
blanking
t
S2 gate prohibited
by interlock
S1 gate prohibited
by interlock
S2 gate prohibited
by interlock
t
Figure 19. Blanking Time and Interlock Logic in UCC24624
8.3.4.1 On-Time Blanking
Right after the SR MOSFET turn on, the SR is driven fully on. For the LLC resonant converter, the SR current
rises from zero. It is desired to keep the SR on during this situation and allow the current to rise to a high enough
level to maintain the full conduction time. In UCC24624, after the SR is turned on, a minimum on time blanking of
475 ns is implemented. During the on-time blanking time, the SR keeps conducting regardless of its drain to
source voltage. This on-time blanking limits the maximum switching frequency of the LLC converter to 625 kHz.
8.3.4.2 Off-Time Blanking
When the converter operates in burst mode, during the off period of the secondary side synchronous rectifiers,
there is large parasitic ringing (DCM ring) caused by the transformer magnetizing inductance and the switch
node capacitance. During the first few ringing cycles of the off period, there is a good chance that the SR
MOSFET drain voltage will resonate below the SR controller turn-on threshold. The SR MOSFET could be falsely
turned on at these instances, which could introduce extra power loss and EMI noise.
In UCC24624, a fixed 650-ns off-time blanking period is implemented. After the SR is turned off, and after its
drain voltage rises above 1.5 V, the SR won't turn on again for at least the off-time blanking time, regardless of
its drain to source voltage. Additional adaptive turn-on delay is also implemented to further enhance the noise
immunity capability during burst mode operation.
8.3.4.3 Two-Channel Interlock
In LLC converters, the two SR MOSFETs are directly connected with the transformer secondary side. If for any
reason, both SRs turn on at the same time, the transformer secondary side is shorted. This could cause large
current and destructive component failures.
To prevent this shoot-through current of the two SR MOSFETs, UCC24624 include a two-channel interlock
mechanism. The turn-on of one SR MOSFET, prevents the turn-on of the other SR MOSFET, as illustrated in
Figure 19.
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
Product Folder Links: UCC24624
17
UCC24624
SLUSD48B – JULY 2018 – REVISED NOVEMBER 2018
www.ti.com
Feature Description (continued)
8.3.4.4 SR Turn-on Re-arm
After been turned off in each switching cycle, the VG1 and VG2 outputs may only turn on again when the
controller has been armed for the new switching cycle. The controller is armed for each successive SR cycle only
at off-time blanking TOFFMIN expiring after the VD pin voltage rises 1.5 V above the VSS pin.
8.3.4.5 Adaptive Turn-on Delay
To further enhance noise immunity of the SR controller, UCC24624 implements an adaptive turn-on delay.
During most operating conditions, 155-ns of turn-on delay is applied to both channel's turn-on stage. However, at
a lighter load, or during burst off period, this turn-on delay is increased to further enhance the noise immunity and
allow the controller to reject the leading edge current spike and DCM ring. In these conditions, the turn-on delay
is increased to 275 ns. The turn-on delay increasing can be observed in below conditions.
•
•
Burst mode operation. During LLC normal operation, two SR MOSFETs are turned on and off alternatively, in
a complementary fashion. However, during burst operation, after one SR MOSFET turns off, the other SR
MOSFET stays off. This gives the indication of the LLC converter entering the burst-mode operation. In
UCC24624, after one channel SR is turned off, its turn-on delay for the next turn-on is increased to 275 ns,
for improved DCM ring rejection capability. If the other channel SR is turned on after this channel SR turning
off, the LLC is still in normal operating mode. The turn-on delay is reset to the 155-ns value. Otherwise,
UCC24624 detects the LLC entering burst-mode operation and the SR turn-on delay stays at 275 ns to help
reject the DCM ring. This adaptive turn-on delay allows long turn-on delay during burst mode operation, with
shorter delay during normal operation to minimize the conduction loss.
Short SR conduction time. At light load, the SR current could start with a short leading edge spike of positive
current, followed by the negative current, and then the full positive current, as shown in Figure 20. This is
caused by the SR parasitic capacitance and the LLC resonant behavior. When the negative current appears,
the SR is turned off with minimum on time (on-time blanking). This is the indication that the leading edge
current spike causes abnormal operation. Once the short SR conduction time is detected, the IC sets the
turn-on delay to 275 ns. This long turn-on delay can further help to reject the leading edge current spike. It
also helps to provide better DCM ring rejection during burst mode operation, since the burst mode operation
only happens at light load. This increased turn-on delay time is reset when the SR voltage drop is more than
40 mV (VDS more negative than -40 mV) at the middle of its conduction time for 8 consecutive cycles.
SR
current
0
SR
gate
0
Ton_min
Figure 20. SR current with leading edge spike
To avoid the DCM ring turn on and SR leading edge current spike, an extra resistor can be added between the
SR MOSFET drain and UCC24624 VD pins, as shown in Figure 21. The extra resistor helps to further improve
the noise immunity. Furthermore, this resistor also limits the negative current flowing into the VD pins, during SR
body diode conduction time. A resistor value around 1 kΩ is recommended if this resistor is needed.
18
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
Product Folder Links: UCC24624
UCC24624
www.ti.com
SLUSD48B – JULY 2018 – REVISED NOVEMBER 2018
Feature Description (continued)
UCC24624
1k
VG1
VG2
PGND
VDD
REG
VD2
VD1
VSS
1k
Figure 21. UCC24624 configuration with VD resistors
8.3.5 Gate Voltage Clamping
With the wide VDD voltage range capability, UCC24624 clamps the gate driver voltage to a maximum level of 11
V to allow fast driving speed, low driving loss, and compatibility with different MOSFETs. The 11-V level is
chosen to minimize the conduction loss for non-logic level MOSFETs. The gate-driver voltage clamp is achieved
through the regulated REG pin voltage. When the VDD voltage is above 11 V, the linear regulator regulates the
REG pin voltage to 11 V, which is also the power supply of the gate driver stage. This way, the MOSFET gate is
well clamped at 11 V, regardless of how high the VDD voltage is. When the VDD voltage is getting close to or
below the programmed REG pin regulation voltage, UCC24624 can no longer regulate the REG pin voltage.
Instead, it enters a pass-through mode where the REG pin voltage follows the VDD pin voltage minus a smaller
linear regulator dropout voltage. During this time, the gate driver voltage is lower than its programmed value but
still provides the SR driving capability. The UCC24624 is disabled once the REG pin voltage drops below its
UVLO OFF level VREGOFF.
8.3.6 Standby Mode
With stringent efficiency standards such as Department of Energy (DoE) level VI and Code of Conduct (CoC)
version 5 tier 2, external power supplies are expected to maintain a very low standby power at no load
conditions. It is essential for the SR controller to enter the low power standby mode to help reduce the no load
power consumption.
During standby mode, the power converter loss allocation is quite different compared with heavy load. At heavier
load, both conduction loss and switching loss are quite high. However, at light load, the conduction loss becomes
insignificant and switching loss dominates the total loss. To help improve the standby power, modern power
supply controllers often enter burst mode to save the switching loss. Furthermore, in each burst switching cycle,
the energy delivered is maximized to minimize the number of switching cycles needed and further reduces the
switching loss.
Traditionally, the SR controller monitors the SR conduction time to distinguish the normal operation mode or the
standby mode. Because of the burst mode operation, the converter is equivalently operating at a much higher
power level with long SR conduction time. This criterion is no longer suitable for the modern power supply
controller designed for delivering minimum standby power.
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
Product Folder Links: UCC24624
19
UCC24624
SLUSD48B – JULY 2018 – REVISED NOVEMBER 2018
www.ti.com
Feature Description (continued)
Instead, in UCC24624, a frequency based standby mode detection is used. UCC24624 continuously monitors the
average switching frequency of SR channel 1. Once the average switching frequency of channel 1 SR MOSFET
drops below 9 kHz for 7.5 ms, the UCC24624 enters the standby mode, stops SR MOSFETs switching, and
reduces its current consumption to IVDDSTBY. During standby mode, the SR switching cycle is continuously
monitored through the body diode conduction. Once the average switching frequency is more than 15.6 kHz
within 7.5 ms, the SR MOSFET operation is enabled again. UCC24624 ignores the first SR switching cycle after
coming out of standby mode to make sure the SR isn't turned on in the middle of the switching cycle.
8.4 Device Functional Modes
8.4.1 UVLO Mode
UCC24624 uses the REG pin voltage to detect UVLO instead of the VDD pin voltage. When the REG voltage
has not yet reached the VREGON threshold, or has fallen below the UVLO threshold VREGOFF, the device
operates in the low-power UVLO mode. In this mode, most internal functions are disabled and VDD current is
IVDDSTART. If the REG pin is above 2 V, there is an active pull down from VG1 and VG2 to PGND to prevent the
SR from falsely turning on due to noise. When the REG pin voltage is less than 2 V, there is a weak pull down
from VG1 and VG2 to PGND and this also prevents noise from turning on SR MOSFETs. The device exits UVLO
mode when REG increases above the VREGON threshold.
8.4.2 Standby Mode
Standby mode is a low-power operating mode to help achieve low standby power for the entire power supply.
UCC24624 detects the average operation frequency of channel 1 SR MOSFET and enters or exits the standby
mode operation automatically. VDD current reduces to IVDDSTBY level. During standby mode, the majority of the
SR control functions are disabled, except the switching frequency monitoring and the active pull down on the
gate drivers.
8.4.3 Run Mode
Run mode is the normal operating mode of the controller, when not in UVLO mode, or standby mode. In this
mode, VDD current is higher because all internal control and timing functions are operating and the VG1 and
VG2 outputs are driving the MOSFETs for synchronous rectification. VDD current is the sum of IVDDRUN plus the
average current necessary to drive the load on the VG1 and VG2 outputs. The VG1 and VG2 voltages are
automatically adjusted based on the SR MOSFET drain-to-source voltages.
20
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
Product Folder Links: UCC24624
UCC24624
www.ti.com
SLUSD48B – JULY 2018 – REVISED NOVEMBER 2018
9 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
9.1 Application Information
UCC24624 is a high performance synchronous rectifier controller used to replace output diode rectifiers in an
LLC converter with synchronous rectifier (SR) MOSFETs. The SR-MOSFETs can achieve very low conduction
loss compared to that of diode rectifiers, significantly improving the efficiency and thermal performance of the
converter.
9.2 Typical Application
The UCC24624EVM-015 was used to replace rectifier diodes in a 120-W LLC converter using the UCC256302
LLC controller. The power converter had an input voltage (VIN) range of 340 V to 410 V with a typical input of 390
V, with a regulated 12-V output. More details about this power stage can be found in UCC256301 LLC
Evaluation Module. More information regarding designing PFC and LLC stages can be found on these training
topics (LLC Design Principles and Optimization for Transient Response, A new way to PFC and an even better
way to LLC, and PFC for not dummies).
The schematic of the UCC24624EVM-15 is shown in Figure 22.
Figure 22. Schematic of UCC24624EVM-15
The top and bottom view of UCC24624EVM-015 are shown in Figure 35 and Figure 36.
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
Product Folder Links: UCC24624
21
UCC24624
SLUSD48B – JULY 2018 – REVISED NOVEMBER 2018
www.ti.com
Typical Application (continued)
9.2.1 Design Requirements
The overall system requirements are summarized in Table 1.
Table 1. UCC24624EVM-015 LLC Power Stage Specifications
PARAMETER
TEST CONDITION
MIN
TYP
MAX
UNITS
340
390
410
VDC
INPUT CHARACTERISTICS
DC voltage range
OUTPUT CHARACTERISTICS
Output Voltage
No load to full load = 10 A
Output Current
340-V to 41-V VDC
12
VDC
10
A
160
kHz
SYSTEM CHARACTERISTICS
Switching frequency
Peak efficiency
53
390 VDC, load = 10 A
96.5%
9.2.2 Detailed Design Procedure
9.2.2.1 MOSFET Selection
In this UCC256302-based LLC resonant converter, the transformer secondary side is a center-tap structure. The
SR MOSFET voltage stress, without considering the ringing voltages, must be twice of the output voltage. Given
the 12-V output, this determines the SR steady state voltage stress of 24 V. However, due to the switching
noises at MOSFET turn off, there is always extra voltage stress. To ensure enough design margin, 60-V rating
MOSFETs were selected.
The selection of the MOSFET on-state resistance is the trade-off among performance at full load, light load, as
well as cost. The lower on-state resistance gives lower conduction loss at heavy load while increases the
switching loss at lighter load. It is also higher cost. Generally, the on-state resistance must be selected so that
the 35-mV proportional gate drive threshold doesn't get activated until last 25% of the overall conduction time.
The SR MOSFET on-state resistance can be selected as Equation 3. A 2.5-mΩ MOSFET was selected as the
synchronous rectifier.
4&5KJ =
2¾2 × 35I8
= 3.15I3
è × +KQP _I=T
(3)
9.2.2.2 Snubber Design
It may be required to adjust snubbing components C3, C4, R2 and R5 to dampen noise.
To adjust these components requires knowing the LLC transformers secondary leakage inductance (Lslk) and
measuring the secondary resonant ring frequency (fr) in circuit at minimal load of 10% or less. TI also
recommends that the SR is not engaged while doing this and capacitors C3 and C4 are removed from the
evaluation module. ConnectTP6 to ground to disable the gate driver.
The secondary winding capacitance (Cs) then needs to be calculated based on Equation 4. Note that for a
transformer with a secondary winding leakage inductance of 3.8 µH and a ring frequency of 2 MHz, the parasitic
capacitance would be 1.7 nF.
%O =
1
1
=
= 1.7J(
2
(2 × è × BN ) × .OHG (2 × è × 2/*V)2 × 3.8ä*
(4)
Based on the calculated Cs, Lslk and fr the snubber resistors R2 and R5 can be set to critically dampen the
ringing on the secondary, which requires setting the Q of the circuit equal to 1.
42 = 45 =
22
1 .OHG 1 3.8ä*
¨
= ¨
N 47 3
3 %O
1 1.7J(
Submit Documentation Feedback
(5)
Copyright © 2018, Texas Instruments Incorporated
Product Folder Links: UCC24624
UCC24624
www.ti.com
SLUSD48B – JULY 2018 – REVISED NOVEMBER 2018
Capacitors C3 and C5 are used to limit the time the snubber resistor is applied to the aux winding during the
switching cycle. It is recommended to set the snubber capacitor C3 with Equation 6 based on the LLC converters
minimum switching frequency (fSW). For an LLC converter with a minimum switching at 85 kHz in the example
would require a C3 and C4 would be roughly 497 pF.
%3 = %4 =
0.01
0.01
=
N 497L(
5 × BOS × 43 5 × 85G*V × 47.3×
(6)
Note that the calculations for R2, R5, C3, and C4 are just starting points and must be adjusted based on
individual preference, performance and efficiency requirements.
9.2.3 Application Curves
The typical operation waveforms, as well as the efficiency performance are summarized in following sections.
• CH1 = VG1(TP4), CH3 = Q1 drain (TP2), CH2 = VG2(TP5), CH4 = Q1 drain (TP3)
Figure 23. VIN = 340 V, IOUT = 0 A, No Gate Drive Under
Light Load (VG1, VG2)
Figure 24. VIN = 340 V, IOUT = 0.3 A, LLC is Operating In
Burst Mode
Figure 25. VIN = 340 V, IOUT = 10 A Full Load
Figure 26. VIN = 390 V, IOUT = 0 A, No Gate Drive Under
Light Load (VG1, VG2)
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
Product Folder Links: UCC24624
23
UCC24624
SLUSD48B – JULY 2018 – REVISED NOVEMBER 2018
www.ti.com
Figure 27. VIN = 390 V, IOUT = 0.3 A, LLC is Operating In
Burst Mode
Figure 28. VIN = 390 V, IOUT = 10 A Full Load
Figure 29. VIN = 410 V, IOUT = 0 A, No Gate Drive Under
Light Load (VG1, VG2)
Figure 30. VIN = 410 V, IOUT = 0.3 A, LLC is Operating In
Burst Mode
0.97
0.96
Efficiency
0.95
0.94
0.93
0.92
0.91
0
Figure 31. VIN = 410 V, IOUT = 10 A Full Load
24
1
2
3
4
5
6
Load Current (A)
7
8
9
10
D007
Figure 32. VIN = 390 V, Power Converter System Efficiency
Using SR FETs
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
Product Folder Links: UCC24624
UCC24624
www.ti.com
SLUSD48B – JULY 2018 – REVISED NOVEMBER 2018
10 Power Supply Recommendations
UCC24624 internal circuits are powered from REG pin only. There is an internal linear regulator between VDD
pin and REG pin to provide a well-regulated REG pin voltage when VDD voltage is above 11 V. This allows the
device to have better bypassing and better gate driver performance.
It is important to keep the sufficient bypass cap on REG pin. A minimum of 1-μF bypass capacitor is required.
When the gate charge current is higher than 5 mA, it is required to have at least 2.2-μF bypass capacitor on
REG pin.
VDD pin is the main power source of the device. Keep the voltage on VDD pin between 4.25 V and 26 V for
normal operation. Referring to for the tolerances on the REG pin UVLO ON and OFF levels.
For the applications where LLC output voltage is higher than 24.75 V, an external resistor between LLC output
voltage and UCC24624 can be used to allow internal clamp circuit keeping the VDD voltage below its
recommended maximum voltage rating, as shown in Figure 15. The series resistor can be calculated as in
Equation 7. In Equation 7, VOUT(max) is the maximum output voltage of LLC converter, including its transient
conditions, VCLAMP(min) is the minimum clamping voltage considering tolerance, and ILIM is the maximum current
allowed by the clamping circuit of 15 mA.
4.+/ =
8176 :max; F 8%.#/2 (min)
15I#
(7)
After the resistor is inserted, calculate the minimum voltage on VDD to ensure sufficient voltage on VDD for the
SR driving. The voltage on VDD based on RLIM can be calculated as Equation 8. The VDD voltage under this
condition must be higher than desired minimum SR driving voltage. In this equation, VOUT is the nominal output
voltage, RLIM is the current limiting resistor value. Qg is the SR gate charge for each SR MOSFET and fSW is the
maximum switching frequency of LLC converter.
88&& (min) = 8176 F 4.+/ × (2 × 3C × B59 + +8&&470 )
(8)
If the output voltage is higher than 36 V, or no suitable current limit resistor RLIM can be selected, the auxiliary
winding can be used to power up the UCC24624. The circuit diagram of powering UCC24624 using auxiliary
winding is shown in Figure 33. Other option would be to use a linear regulator to create bias power from the
output voltage directly. But this is a less efficient solution.
Q1
Lr
Vout
Vin
Cr
Q2
UCC24624
S1
VG1
VG2
PGND
VDD
REG
VD2
VD1
VSS
S2
Figure 33. Powering UCC24624 Using Auxiliary Winding
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
Product Folder Links: UCC24624
25
UCC24624
SLUSD48B – JULY 2018 – REVISED NOVEMBER 2018
www.ti.com
11 Layout
11.1 Layout Guidelines
The printed circuit board (PCB) requires careful layout to minimize current loop areas and track lengths,
especially when using single-sided PCBs.
• Place a ceramic MLCC bypass capacitor as close as possible to REG and GND.
• Avoid connecting VD1 or VD2 and VSS sense points at locations where stray inductance is added to the SR
MOSFET package inductance, as this tends to turn off the SR prematurely.
• Run a trace from the VD1 or VD2 pin directly to the MOSFET drain pad to avoid sensing voltage across the
stray inductance in the SR drain current path.
• Run a trace from the VSS pin directly to the MOSFET source pad to avoid sensing voltage across the stray
inductance in the SR source current path. Because this trace shares both the gate driver path and the
MOSFET voltage sensing path, TI recommends making this trace as short as possible.
• Run parallel traces from VG1 or VG2 and PGND to the SR MOSFET. Include a series gate resistance to
dampen ringing if it is needed.
11.2 Layout Example
To LLC Transformer
SR2
SR1
RG1
CREG
RG2
1
8
2
7
3
6
Bottom Layer
4
5
Via
UCC24624
Top Layer
CVDD
Figure 34. UCC24624 Layout Example
26
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
Product Folder Links: UCC24624
UCC24624
www.ti.com
SLUSD48B – JULY 2018 – REVISED NOVEMBER 2018
Layout Example (continued)
Figure 35. UCC24624EVM-015 (Top View)
Figure 36. UCC24624EVM-015 (Bottom View)
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
Product Folder Links: UCC24624
27
UCC24624
SLUSD48B – JULY 2018 – REVISED NOVEMBER 2018
www.ti.com
12 Device and Documentation Support
12.1 Device Support
12.1.1 Development Support
12.1.1.1 Custom Design With WEBENCH® Tools
Click here to create a custom design using the UCC24624 device with the WEBENCH® Power Designer.
1. Start by entering the input voltage (VIN), output voltage (VOUT), and output current (IOUT) requirements.
2. Optimize the design for key parameters such as efficiency, footprint, and cost using the optimizer dial.
3. Compare the generated design with other possible solutions from Texas Instruments.
The WEBENCH Power Designer provides a customized schematic along with a list of materials with real-time
pricing and component availability.
In most cases, these actions are available:
• Run electrical simulations to see important waveforms and circuit performance
• Run thermal simulations to understand board thermal performance
• Export customized schematic and layout into popular CAD formats
• Print PDF reports for the design, and share the design with colleagues
Get more information about WEBENCH tools at www.ti.com/WEBENCH.
12.2 Receiving Notification of Documentation Updates
To receive notification of documentation updates, navigate to the device product folder on ti.com. In the upper
right corner, click on Alert me to register and receive a weekly digest of any product information that has
changed. For change details, review the revision history included in any revised document.
12.3 Community Resources
The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective
contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of
Use.
TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration
among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help
solve problems with fellow engineers.
Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and
contact information for technical support.
12.4 Trademarks
E2E is a trademark of Texas Instruments.
WEBENCH is a registered trademark of Texas Instruments.
12.5 Electrostatic Discharge Caution
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more
susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
12.6 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
28
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
Product Folder Links: UCC24624
UCC24624
www.ti.com
SLUSD48B – JULY 2018 – REVISED NOVEMBER 2018
13 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
Product Folder Links: UCC24624
29
PACKAGE OPTION ADDENDUM
www.ti.com
10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
UCC24624DR
ACTIVE
SOIC
D
8
2500
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 125
U24624
UCC24624DT
ACTIVE
SOIC
D
8
250
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 125
U24624
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
工商网监
湘ICP备2023018690号
