TI UCC25600DRG4

UCC25600
www.ti.com ............................................................................................................................................. SLUS846A – SEPTEMBER 2008 – REVISED MARCH 2009
8-Pin High-Performance Resonant Mode Controller
FEATURES
1
•
•
•
•
•
•
•
•
•
•
•
•
Variable Switching Frequency Control
Programmable Minimum Switching Frequency
With 4% Accuracy (3% accuracy at
temperature range: -20°C to 105°C)
Programmable Maximum Switching Frequency
Programmable Dead Time for Best Efficiency
Programmable Soft-Start Time
Easy ON/OFF Control
Over-Current Protection
Over-Temperature Protection
Bias Voltage UVLO and OVP
Integrated Gate Driver With 0.4-A Source and
0.8-A Sink Capability
Operating Temperature Range: –40°C to 125°C
SOIC 8-Pin Package
APPLICATIONS
•
•
•
•
•
100-W to 1-kW Power Supplies
LCD, Plasma and DLP TVs
Adaptors, Computing and ATX Power Supplies
Home Audio Systems
Electronic Lighting Ballasts
DESCRIPTION
The UCC25600 high performance resonant mode
controller is designed for dc-to-dc applications
utilizing resonant topologies, especially the LLC half
bridge resonant converter. This highly integrated
controller implements frequency modulation control
and complete system functions in only an 8-pin
package. Switching to the UCC25600 will greatly
simplify the system design, layout and improve time
to market, all at a price point lower than competitive
16-pin device offerings.
The internal oscillator supports the switching
frequencies from 30 kHz to 350 kHz. This high
accuracy oscillator realizes the minimum switching
frequency limiting with 4% tolerance, allowing the
designer to avoid "over design" of the power stage
and, thus, further reducing overall system cost. The
programmable dead time enables zero-voltage
switching with minimum magnetizing current. This will
maximize system efficiency across a variety of
applications. The programmable soft-start timer
maximizes design flexibility demanded by the varied
requirements of end equipments utilizing a half bridge
topology. By incorporating 0.4-A source and 0.8-A
sink driving capability, a low cost, reliable gate driver
transformer is a real option.
The UCC25600 delivers complete system protection
functions including over current, UVLO, bias supply
OVP and over temperature protection.
TYPICAL APPLICATION DIAGRAM
*
*
*
Vs
8
5
7
6
GD1
OC
GD2
RT
UCC25600
VCC
DT
GND
SS
3
2
1
4
1
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.
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 © 2008–2009, Texas Instruments Incorporated
UCC25600
SLUS846A – SEPTEMBER 2008 – REVISED MARCH 2009 ............................................................................................................................................. www.ti.com
ORDERING INFORMATION
PART NUMBER
PACKAGE
OPERATING TEMPERATURE
UCC25600D
8-Pin SOIC
-40°C to 125°C
ABSOLUTE MAXIMUM RATINGS (1) (2) (3) (4)
over operating free-air temperature range (unless otherwise noted)
PARAMETER
LIMIT
UNIT
Supply voltage, VCC
22
Voltage, GD1, GD2
Gate drive current – continuous, GD1, GD2
+/- 25
Current, RT
-5
Current, DT
-0.7
Operating junction temperature, TJ
−40 to 125
Storage temperature, TSTG
−65 to 150
Lead temperature (10 seconds)
(1)
(2)
(3)
(4)
V
-0.5 to VCC + 0.5
mA
°C
260
These are stress limits. Stress beyond these limits may cause permanent damage to the device. Functional operation of the device at
these or any conditions beyond those indicated under RECOMMENDED OPERATING CONDITIONS is not implied. Exposure to
absolute maximum rated conditions for extended periods of time may affect device reliability.
All voltages are with respect to GND.
All currents are positive into the terminal, negative out of the terminal.
In normal use, terminals GD1 and GD2 are connected to an external gate driver and are internally limited in output current.
ELECTROSTATIC DISCHARGE (ESD) PROTECTION
PARAMETER
RATING
Human Body Model (HBM)
UNIT
2,000
Charged Device Model (CDM)
V
500
DISSIPATION RATINGS
PACKAGE
THERMAL IMPEDANCE,
JUNCTION-TO-AMBIENT
8-Pin SOIC
(1)
(2)
150°C/watt
TA = 25°C POWER RATING
(1) (2)
667 mW
TA = 85°C POWER RATING
(1)
267 mW
(1)
Thermal resistance is a strong function of board construction and layout. Air flow will reduce thermal resistance. This number is only a
general guide.
Thermal resistance calculated with a low-K methodology.
RECOMMENDED OPERATING CONDITIONS
over operating free-air temperature range (unless otherwise noted)
PARAMETER
MINIMUM
VCC input voltage from a low-impedance source
MAXIMUM
UNIT
11.5
18.0
RT resistance
1
8.666
DT resistance
3.3
39
SS capacitor
0.01
1
2
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V
kΩ
µF
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ELECTRICAL CHARACTERISTICS
over operating free-air temperature range, −40°C < TA < 125°C, TJ = TA, VCC = 12 V, GND = 0 V, RRT = 4.7 kΩ, RDT = 16.9
kΩ, CVCC = 1 µF, (unless otherwise noted)
SYMBOL
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNITS
Bias Supply (VCC)
1
1.5
2.5
5
7.5
100
400
Measured at VCC rising
9.9
10.5
11.1
UVLO turn-off threshold
Measured at VCC falling
8.9
9.5
10.1
UVLO hysteresis
Measured at VCC
0.7 1
OVP turn-off threshold
Measured at VCC rising
18
20
22
OVP turn-on threshold
Measured at VCC falling
16
18
20
OVP hysteresis
Measured at VCC
1.5
2
2.5
Dead time
RDT = 16.9 kΩ
390
420
450
FSW(min)
Minimum switching frequency at
GD1, GD2
-40°C to 125°C
40.04
41.70
43.36
-20°C to 105°C
40.45
41.70
42.95
KICO
Switching frequency gain/I (RT)
RRT = 4.7 kΩ, IRT = 0 to 1 mA
60
80
100
Hz/µA
50
ns
VUVLO
VOVP
VCC current, disabled
SS = 0 V
VCC current, enabled
SS = 5 V, CGD1 = CGD2 = 1 nF
VCC current, UVLO
VCC = 9 V
UVLO turn-on threshold
1.3
mA
µA
V
Dead Time (DT)
TDT
ns
Oscillator
GD1, GD2 on time mismatching
FSW_BM
FSW(start)
-50
Switching frequency starting burst
mode
SS = 5 V
300
350
400
Switching frequency to come out of
burst mode
SS = 5 V
280
330
380
-40°C to 125°C
122
142.5
162
-20°C to 105°C
125
142.5
160
Switching frequency at soft start
kHz
kHz
External Disable/Soft Start
ISS
Enable threshold
Measure at SS rising
1.1
1.2
1.3
Disable threshold
Measured at SS falling
0.85
1
1.1
Disable hysteresis
Measured at SS
0.15
Disable prop. delay
Measured between SS (falling) and
GD2 (falling)
250
500
750
Source current on ISS pin
VSS = 0.5 V
-225
-175
-125
Source current on ISS pin
VSS = 1.35 V
-5.5
-5
-4.5
0.35
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V
ns
µA
3
UCC25600
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ELECTRICAL CHARACTERISTICS (continued)
over operating free-air temperature range, −40°C < TA < 125°C, TJ = TA, VCC = 12 V, GND = 0 V, RRT = 4.7 kΩ, RDT = 16.9
kΩ, CVCC = 1 µF, (unless otherwise noted)
SYMBOL
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNITS
Peak Current Limit
VOC1(off)
Level 1 over current threshold – VOC
rising
0.9
1
1.1
VOC2(off)
Level 2 over current latch threshold
– VOC rising
1.8
2.0
2.2
VOC1(on)
Level 1 over current threshold – VOC
falling
0.5
0.6
0.7
Td_OC
Propagation delay
60
200
500
ns
IOC
OC bias current
VOC = 0.8 V
200
nA
GD1, GD2 output voltage high
IGD1, IGD2 = −20 mA
GD1, GD2 on resistance high
IGD1, IGD2 = −20 mA
GD1, GD2 output voltage low
IGD1, IGD2 = 20 mA
GD1, GD2 on resistance low
IGD1, IGD2 = 20 mA
Rise time GDx
1 V to 9 V, CLOAD = 1 nF
Fall time GDx
9 V to 1 V, CLOAD = 1 nF
12
25
GD1, GD2 output voltage during
UVLO
VCC = 6 V, IGD1, IGD2 = 1.2 mA
-200
V
Gate Drive
9
11
V
12
30
Ω
0.08
0.2
V
4
10
Ω
18
35
0.5
1.75
ns
V
Thermal Shutdown
4
Thermal shutdown threshold
160
Thermal shutdown recovery
threshold
140
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°C
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DEVICE INFORMATION
8-Pin SOIC, Top View
DT
1
8
GD1
RT
2
7
VCC
OC
3
6
GND
SS
4
5
GD2
TERMINAL FUNCTIONS
TERMINAL
NAME
DT
NO.
1
DESCRIPTION
I/O
I
This pin sets the dead time of high-side and low-side switch driving signals. Connect
a resistor to ground. With internal 2.25-V voltage reference, the current flowing
through the resistor sets the dead time. To prevent shoot through when this pin is
accidentally short to ground, the minimum dead time is set to 120 ns. Any dead time
setting less than 120 ns will automatically have 120-ns dead time.
RT
2
I
The current flowing out of this pin sets the frequency of the gate driver signals.
Connect the opto-coupler collector to this pin to control the switching frequency for
regulation purpose. Parallel a resistor to ground to set the minimum current flowing
out of the pin and set the minimum switching frequency. To set the maximum
switching frequency limiting, simply series a resistor with the opto-coupler transistor.
This resistor sets the maximum current flowing out of the pin and limits the maximum
switching frequency.
OC
3
I
Over-current protection pin. When the voltage on this pin is above 1 V, gate driver
signals are actively pulled low. After the voltage falls below 0.6 V, the gate driver
signal recovers with soft start. When OC pin voltage is above 2 V, the device is
latched off. Bringing VCC below UVLO level resets the overcurrent latch off.
SS
4
I
Soft-start pin. This pin sets the soft-start time of the system. Connect a capacitor to
ground. Pulling this pin below 1 V will disable the device to allow easy ON/OFF
control. The soft-start function is enabled after all fault conditions, including bias
supply OV, UVLO, over-current protection and over-temperature protection.
GD1
8
O
GD2
5
O
High-side and low-side switch gate driver. Connect gate driver transformer primary
side to these two pins to drive the half bridge.
GND
6
-
Ground.
VCC
7
-
Bias Supply. Connect this pin to a power supply less than 20 V. Parallel a 1-µF
capacitor to ground to filter out noise.
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Block Diagram
2.25V
T
J
160oC/140oC
DT
+
TSD
Thermal
ShutDown
1
OV
+
10.5V
9.5V
Dead time
generator
RDT
20V
18V
UVLO
+
7 VCC
2.5V
Feed
back
RT
2
Ic
8 GD1
OSC
Vss
UVLO
OV
Q
OC
TSD
SET
VCC
D
5 GD2
FAULT
Q
CLR
5uA
6 GND
GD_Stop
6V
170uA
OC
OC
SS
3
+
1V
Vss
4
OC_latch
Css
+
+
2V
1.2V/1V
FAULT
S
R
6
SET
CLR
Q
Q
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TYPICAL CHARACTERISTICS
At VCC = 12 V, RRT = 4.7 kΩ, RDT = 16.9 kΩ, VSS = 5 V, VOC = 0 V; all voltages are with respect to GND, TJ = TA
= 25°C, unless otherwise noted.
BIAS SUPPLY CURRENT
vs
BIAS SUPPLY VOLTAGE
SWITCHING FREQUENCY
vs
RT CURRENT
350
Fsw - Switching Frequency - kHz
Ivcc - Bias Supply Current - mA
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
300
250
200
150
100
-40 °C
OC Open
0.2
25 °C
50
0.1
125 °C
0
0
6
7
8
9
10
11
12
13
14
0
1
2
Vvcc - Bias Supply Voltage - V
3
4
5
IRT - RT Current - mA
Figure 1.
Figure 2.
DEAD TIME
vs
DT CURRENT
DEAD TIME
vs
DT RESISTOR
1000
1000
- 40 °C
900
900
25 °C
800
125 °C
DT - Dead Time -
DT - Dead Time -
800
700
600
500
400
700
600
500
400
300
300
200
200
100
100
0
0
0
100
200
300
400
500
600
700
-40 °C
25 °C
125 °C
0
5
10
15
20
25
30
35
40
45
RDT - DT Resistor - kOhm
IDT - DT Current - uA
Figure 3.
Figure 4.
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TYPICAL CHARACTERISTICS (continued)
GATE DRIVE FALLING; VCC=15V
10
0.8
1.4
14
0.7
1.2
12
0.6
10
Gate Drive Voltage 0.5
1
8
0.8
6
0.6
4
0.4
2
0
-2
0
100
200
300
400
500
Gate Drive Source
Current
8
6
0.3
4
0.2
0.2
2
0.1
0
0
0
-0.2
600
-2
0
200
400
600
-0.1
1000
800
Time - ns
Time - ns
Figure 5.
Figure 6.
OC PROPAGATION DELAY
vs
TEMPERATURE
UVLO THRESHOLD
vs
TEMPERATURE
300
12
UVLO On Threshold - VCC Rising
UVLO Off Threshold -VCC Falling
UVLO Threshold -
250
Propagation Delay - ns
0.4
Gate Drive Current - A
Gate Drive Voltage - V
12
16
Gate Drive Voltage - V
Gate Drive
Voltage
Gate Drive Sink
Current
14
1.6
Gate Drive Current - A
16
GATE DRIVE RISING; VCC=15V
200
150
11
10
100
9
50
0
8
-60 -40 -20
0
20
40
60
80 100 120 140
-60 -40 -20
Tj - Junction Temperature - °C
Figure 7.
8
0
20
40
60
80
100 120 140
Tj - Junction Temperature - °C
Figure 8.
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TYPICAL CHARACTERISTICS (continued)
VCC OVER VOLTAGE THRESHOLD
vs
TEMPERATURE
OVER CURRENT THRESHOLD
vs
TEMPERATURE
2.5
OVP Off Threshold - VCC Rising
21
Voc Over Current Threshold - V
VCC Over Voltage Threshold - V
22
OVP On Threshold -VCC Falling
20
19
18
2
OC Off Threshold - Voc Rising
OC On Threshold - Voc Falling
1.5
OC Latch Threshold - Voc Rising
1
0.5
17
16
0
-60 -40 -20
0
20
40
60
80
100 120 140
-60 -40 -20
Tj - Junction Temperature - °C
0
20
40
60
80 100 120 140
Tj - Junction Temperature - °C
Figure 9.
Figure 10.
ON TIME MISMATCH
vs
SWITCHING FREQUENCY
On Time Mismatch - ns
100
80
60
40
20
0
0
50
100
150
200
250
300
350
Switching Frequency - kHz
Figure 11.
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APPLICATION INFORMATION
Principal of Operation
The soft-switching capability, high efficiency and long holdup time make the LLC resonant converter attractive for
many applications, such as digital TV, ac/dc adapters and computer power supplies. Figure 12 shows the
schematic of the LLC resonant converter.
Cr
Lr
n:1:1
Lm
Figure 12. LLC Resonant Converter
The LLC resonant converter is based on the Series Resonant Converter (SRC). By utilizing the transformer
magnetizing inductor, zero-voltage switching can be achieved over a wide range of input voltage and load. As a
result of multiple resonances, zero-voltage switching can be maintained even when the switching frequency is
higher or lower than resonant frequency. This simplifies the converter design to avoid the zero-current switching
region, which can lead to system damage. The converter achieves the best efficiency when operated close to its
resonant frequency at a nominal input voltage. As the switching frequency is lowered the voltage gain is
significantly increased. This allows the converter to maintain regulation when the input voltage falls low. These
features make the converter ideally suited to operate from the output of a high-voltage boost PFC pre-regulator,
allowing it to hold up through brief periods of ac line-voltage dropout.
Due to the nature of resonant converter, all the voltages and currents on the resonant components are
approximately sinusoidal. The gain characteristic of LLC resonant converter is analyzed based on the First
Harmonic Approximation (FHA), which means all the voltages and currents are treated as sinusoidal shape with
the frequency same as switching frequency.
According to the operation principle of the converter, the LLC resonant converter can be draw as the equivalent
circuit as shown in Figure 13.
Cr
Vge
Lr
Lm
Re
Voe
Figure 13. LLC Resonant Converter Equivalent Circuit
10
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In this equivalent circuit, the Vge and Voe are the fundamental harmonics of the voltage generated by the half
bridge and the voltage on the transformer primary side, respectively. These voltages can be calculated through
Fourier analysis. The load resistor Re is the equivalent resistor of the load, and it can be calculated as:
Re =
8 2
n R
p2
(1)
Based on this equivalent circuit, the converter gain at different switching frequencies can be calculated as:
jw Lm Re
Vo
jw Lm + Re
=
jw Lm Re
1
VDC / 2
+
+ jw Lr
jw Lm + Re jwCr
(2)
In this equation VDC/2 is the equivalent input voltage due to the half bridge structure.
Table 1. Circuit Definition Calculations
NORMALIZED GAIN
M=
Vo
VDC / 2
RESONANT
FREQUENCY
f0 =
1
2p Lr Cr
NORMALIZED
FREQUENCY
QUALITY FACTOR
Qe =
Lr / Cr
Re
fn =
f
f0
INDUCTOR RATIO
Ln =
Lm
Lr
Following the definitions in Table 1, the converter gain at different switching frequencies can be written as:
M=
Ln f n 2
Ln f n 2 + ( f n - 1)( f n + 1 + jf n LnQe )
(3)
Because of the FHA, this gain equation is an approximation. When the switching frequency moves away from the
resonant frequency, the error becomes larger. However, this equation can be used as the design tool. The final
results need to be verified by the time based simulation or hardware test.
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From Equation 3, when switching frequency is equal to resonant frequency, fn = 1 and converter voltage gain is
equal to 1. Converter gain at different loads and inductor ratio conditions are shown in Figure 14 through
Figure 17.
M
vs
ƒn
M
vs
ƒn
2
2
Ln = 1
Ln = 5
Qe = 0.1
Qe = 0.2
Qe = 0.5
Qe = 1
Qe = 2
Qe = 5
1.5
Qe = 0.1
Qe = 0.2
Qe = 0.5
Qe = 1
Qe = 2
Qe = 5
1.5
M
M
1
1
0.5
0.5
0
0.1
0.5
1
1.5
0
0.1
2
0.5
1
fn
1.5
2
fn
Figure 14.
Figure 15.
M
vs
ƒn
M
vs
ƒn
2
2
Qe = 0.1
Qe = 0.2
Qe = 0.5
Qe = 1
Qe = 2
Qe = 5
Ln = 10
1.5
Ln = 20
1.5
Qe = 0.1
Qe = 0.2
Qe = 0.5
Qe = 1
Qe = 2
Qe = 5
M
M
1
1
0.5
0.5
0
0.1
0.5
1
1.5
2
0
0.1
fn
0.5
1
1.5
2
fn
Figure 16.
Figure 17.
Based on its theory of operation the LLC resonant converter is controlled through Pulse Frequency Modulation
(PFM). The output voltage is regulated by adjusting the switching frequency according to the input and output
conditions. Optimal efficiency is achieved at the nominal input voltage by setting the switching frequency close to
the resonant frequency. When the input voltage droops low the switching frequency is decreased to boost the
gain and maintain regulation.
The UCC25600 resonant half-bridge controller uses variable switching frequency control to adjust the resonant
tank impedance and regulate output voltage. This 8-pin package device integrates the critical functions for
optimizing the system performance while greatly simplifying the design and layout.
12
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Adjustable Dead Time
Resonant half-bridge converter relies on the resonant tank current at MOSFETs turn-off to achieve soft switching
and reduce switching loss. Higher turn-off current provides more energy to discharge the junction capacitor, while
it generates more turn-off loss. Smaller turn-off current reduces turn-off loss, but it requires longer time to
discharge MOSFETs junction capacitors and achieve soft switching. By choosing an appropriate dead time,
turn-off current is minimized while still maintaining zero-voltage switching, and best system performance is
realized.
In UCC25600, dead time can be adjusted through a single resistor from DT pin to ground. With internal 2.25-V
voltage reference, the current flow through the resistor sets the dead time.
td = 20ns + Rdt ´ 24ns / k W
(4)
To prevent shoot through when DT pin accidentally connects to ground, a minimum 120-ns dead time is inserted
into the two gate driver outputs. Any dead-time setting less than 120-ns, will be limited to 120-ns.
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Oscillator
With variable switching frequency control, UCC25600 relies on the internal oscillator to vary the switching
frequency. The oscillator is controlled by the current flowing out of RT pin. Except during soft start, the
relationship between the gate signal frequency and the current flowing out of RT pin can be represented as:
fS =
1
1
» I RT ´ 83Hz / m A
2 6ns ´1A + 150ns
I RT
(5)
Since the switching frequency is proportional to the current, by limiting the maximum and minimum current
flowing out of RT pin, the minimum and maximum switching frequency of the converter could be easily limited.
As shown in Figure 18, putting a resistor from RT pin to ground limits the minimum current and putting a resistor
in series with the opto-coupler limits the maximum current.
UCC25600
Maximum
frequency limiting
RT
R1
Minimum
frequency limiting
R2
Figure 18. Maximum and Minimum Frequency Setting for UCC25600
The frequency limiting resistor can be calculated based on following equations.
I f max =
I f min =
6ns
1
- 150ns
2 f max
(6)
6ns
1
- 150ns
2 f min
(7)
æ 1
1 ö
I f max = 2.5V ç +
÷
è R1 R2 ø
I f min =
14
(8)
2.5V
R2
(9)
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UCC25600
www.ti.com ............................................................................................................................................. SLUS846A – SEPTEMBER 2008 – REVISED MARCH 2009
Soft Start
During start up and fault recovery conditions, soft start is always implemented to prevent excessive resonant tank
current and ensure Zero-Voltage Switching (ZVS). During soft start, the switching frequency is increased. The
soft-start time can be programmed by placing a capacitor from SS pin to ground.
The soft-start pin also serves as an ON/OFF control pin of the device. By actively pulling the SS pin below 1 V,
the device is disabled. When the pull down is removed, SS pin voltage is increased because of internal charging
current. Once SS pin becomes above 1.2 V, the device starts to generated gate-driver signal and enters
soft-start mode. The time sequence of soft start is shown in Figure 19.
4V
1.2V
Vss
Gate driver
t ss _ delay
t ss
Figure 19. Soft-Start Sequence
To prevent a long delay between the ON command and apperance of a gate driver signal, the SS pin current is
set as two different levels. When SS pin voltage is below 1.2 V, its output current is 175 µA. This high current
could charge the soft-start pin capacitor to 1.2 V in a short period of time, and reduces the time delay. This time
delay can be calculated using following equation:
tSS _ delay =
1.2V
CSS
175m A
(10)
The switching frequency during soft start is determined by both the current flowing out of the RT pin and the
voltage on SS pin. The switching frequency can be calculated based on the following equation:
fS =
1
2
1
6ns ´1A
I RT
V
æ
ö
+ ç1.81mA - SS ÷
2 .2 k W ø
è
+ 150ns
(11)
After SS pin voltage reaches 4 V, soft-start period is finished and switching frequency becomes the same as
demanded by the RT pin current. The time used to charge SS pin from 1.2 V to 4 V is defined as soft-start time
and can be calculated as:
tSS =
2.8V
CSS
5m A
(12)
To ensure reliable operation, the gate drivers restart with GD2 turning high. This prevents uncertainty during
system start up.
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15
UCC25600
SLUS846A – SEPTEMBER 2008 – REVISED MARCH 2009 ............................................................................................................................................. www.ti.com
Burst-Mode Operation
During light load condition, the resonant converter tends to increase its switching frequency and maintain the
output voltage regulation. However, due to ringing caused by transformer parasitic capacitor and the
rectification-diode-junction capacitors, the energy could be directly transferred to the load through these
capacitors. When this power becomes more than the load requires, output voltage become higher than the
regulation level. In this case, further increasing the switching frequency will not help the situation because energy
transfer to the load is not through the power stage itself.
To prevent output over voltage during this condition, the UCC25600 includes the burst-mode operation function.
When the control loop demands switching frequency higher than 350 kHz, the gate driver is disabled and the
power stage stops switching. When the output voltage drops, the control loop begins to demand switching
frequency less than 330 kHz, the gate driver recovers and the power stage begins to deliver power again. This
allows output voltage to be regulated.
This burst mode can be easily disabled by limiting the maximum switching frequency to less than 350 kHz. In this
way, the control loop will never demand a switching frequency higher than 350kHz and burst mode operation will
not occur.
16
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UCC25600
www.ti.com ............................................................................................................................................. SLUS846A – SEPTEMBER 2008 – REVISED MARCH 2009
Over-Current Protection
To prevent power stage failure under excessive load current condition, the UCC25600 includes an over-current
protection function. With a dedicated OC pin, the power stage is shut down when OC pin voltage is above 1 V.
Once the OC pin voltage becomes lower than 0.6 V, the gate driver recovers with soft start. To enhance system
safety, the UCC25600 latches up the whole system when OC pin becomes above 2 V. Bring VCC below UVLO
level to reset the device.
The current can be indirectly sensed through the voltage across resonant capacitor by using the sensing network
shown in Figure 20.
Lr
From half bridge
TR
Lm
Rs
D2
To OC
Cp
Rp
Cs
D1
Cr
Figure 20. Current Sensing for LLC Resonant Converter
The general concept of this sensing method is that, ac voltage across the resonant capacitor is proportional to
load current.
According to the FHA model, peak voltage of the ac component on the resonant capacitor can be calculated as:
VCr _ pk =
jf L Q + 1
4
nVo n n2 e
p
f n Ln
(13)
Therefore, the resonant capacitor voltage reaches its maximum value at the minimum switching frequency and
maximum load. According to this equation, the current sensing network components can be calculated. Due to
the nature of FHA, the final circuit parameters need to be verified through actual hardware test.
Calculated Current Sensing Network Components
NAME
FUNCTION
DESIGN EQUATION
2
Transfer ac voltage across resonant
capacitor into current source
Rs =
CS
Blocking dc voltage on resonant capacitor
Cs =
RP
Load resistor of the current source
Rp =
CP
Filter capacitor
Cp =
RS
VCr _ pk (max )
2 PRs (max)
10
Rs f min
Rs
p
VCr _ pk (max )
10
R p f min
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UCC25600
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Gate Driver
Half-bridge resonant converter is controlled by the nearly 50% duty cycle variable frequency square wave
voltage. This allows the half bridge to be easily driven by the gate-driver transformer. Compared with a
half-bridge driver device, a gate-driver transformer provides a simple and reliable solution, which:
• Eliminate the need for gate driver power supply
• Enable simplified layout
• Preventing shoot through due to the transformer coupling
• No latch up
The UCC25600 integrates two-gate drivers with 0.4-A source and 0.8-A sink capability to directly drive the gate
driver transformer.
For LLC resonant converter, it is critical for the gate-driver signal to be precisely symmetrical. Otherwise, the
resonant tank operation will be asymmetrical. The load current distribution will be unbalanced for the output
rectifiers, which in turn requires over design of the power stages and thermal management.
In UCC25600, the gate-driver outputs are precisely trimmed to have less than 50 ns mismatch. Although the
gate-driver signal is quite symmetrical, it is still recommended to insert the dc blocking capacitor in the
gate-driver transformer primary side to prevent transformer saturation during fast transients.
VCC
Connect a regulated bias supply to VCC pin. When VCC becomes above 10.5 V the device is enabled and after
all fault conditions are cleared the gate driver starts with soft start. When VCC drops below 9.5 V, the device
enters UVLO protection mode and both gate drivers are actively pulled low. When VCC rises above 20 V the
device enters VCC over-voltage protection mode and the device is disabled with both gate drivers actively pulled
low. VCC over-voltage protection will recover with soft start when VCC voltage returns below 18 V.
Over-Temperature Protection
UCC25600 continuously senses its junction temperature. When its junction temperature rises above 160°C the
device will enter over-temperature protection mode with both gate drivers actively pulled low. When junction
temperature drops below 140°C, gate driver restarts with soft start.
18
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PACKAGE OPTION ADDENDUM
www.ti.com
23-Jun-2009
PACKAGING INFORMATION
Orderable Device
Status (1)
Package
Type
Package
Drawing
Pins Package Eco Plan (2)
Qty
UCC25600D
ACTIVE
SOIC
D
8
UCC25600DR
ACTIVE
SOIC
D
UCC25600DRG4
ACTIVE
SOIC
D
75
Lead/Ball Finish
MSL Peak Temp (3)
Green (RoHS &
no Sb/Br)
CU NIPDAU
Level-1-260C-UNLIM
8
2500 Green (RoHS &
no Sb/Br)
CU NIPDAU
Level-1-260C-UNLIM
8
2500 Green (RoHS &
no Sb/Br)
CU NIPDAU
Level-1-260C-UNLIM
(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)
Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check
http://www.ti.com/productcontent for the latest availability information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements
for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered
at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and
package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS
compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame
retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material)
(3)
MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder
temperature.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is
provided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the
accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and continues to take
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incoming materials and chemicals. TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited
information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI
to Customer on an annual basis.
Addendum-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
6-Mar-2009
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
UCC25600DR
Package Package Pins
Type Drawing
SOIC
D
8
SPQ
Reel
Reel
Diameter Width
(mm) W1 (mm)
2500
330.0
12.4
Pack Materials-Page 1
A0 (mm)
B0 (mm)
K0 (mm)
P1
(mm)
6.4
5.2
2.1
8.0
W
Pin1
(mm) Quadrant
12.0
Q1
PACKAGE MATERIALS INFORMATION
www.ti.com
6-Mar-2009
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
UCC25600DR
SOIC
D
8
2500
340.5
338.1
20.6
Pack Materials-Page 2
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