Texas Instruments UCC28740EVM-525 User manual

User Guide
SLUUAL8 – July 2013
Using the UCC28740EVM-525 10 W Constant-
Voltage, Constant-Current Charger Adaptor
Module
User’s Guide
Literature Number: SLUUAL8
July, 2013

SLUUAL8
Using the UCC28740EVM-525 10 W Constant-Voltage, Constant-Current Charger Adapter Module
PSS- High Performance Isolated
Contents
1Introduction.....................................................................................................................................4
2Description......................................................................................................................................4
2.1Typical Applications .................................................................................................................. 4
2.2Features.................................................................................................................................... 5
3Electrical Performance Specifications .........................................................................................6
4Schematic........................................................................................................................................7
5Test Setup .......................................................................................................................................8
5.1Test Equipment......................................................................................................................... 8
5.2Recommended Test Setup .......................................................................................................9
5.3List of Test Points ................................................................................................................... 10
5.4Applying Power to the EVM ....................................................................................................11
5.5No-Load Power Consumption................................................................................................. 11
5.6Line/Load Regulation and Efficiency Measurement Procedure .............................................. 11
5.7Output Voltage Ripple............................................................................................................. 12
5.8Equipment Shutdown.............................................................................................................. 12
6Performance Data and Typical Characteristic Curves..............................................................13
6.1Efficiency................................................................................................................................. 13
6.2Load Regulation...................................................................................................................... 14
6.3Line Regulation ....................................................................................................................... 15
6.4No-Load Power Consumption................................................................................................. 15
6.5Output Voltage vs Output Current........................................................................................... 16
6.6Control Law............................................................................................................................. 17
6.7Bode Plot ................................................................................................................................ 18
6.8Transient Response................................................................................................................ 19
6.9Output Ripple .......................................................................................................................... 20
6.10Turn On Waveform ................................................................................................................. 21
6.11Switching Waveform ............................................................................................................... 22
6.12EMI Dithering Waveform......................................................................................................... 23
7EVM Assembly Drawing and PCB layout ...................................................................................23
8Bill of Materials .............................................................................................................................28
Figures
Figure 1.UCC28740EVM-525 Schematic .........................................................................................7
Figure 2.UCC28740EVM-525 Recommended Test Set Up For No-Load Operation ....................9
Figure 3.UCC28740EVM-525 Recommended Test Set Up With Load ........................................10
Figure 4.UCC28740EVM-525 Average Efficiency.........................................................................13
Figure 5.UCC28740EVM-525 Load Regulation.............................................................................14
Figure 6.UCC28740EVM-525 Line Regulation ..............................................................................15
Figure 7.UCC28740EVM-525 No-Load Power Consumption.......................................................15
Figure 8.UCC28740EVM-525 Output Voltage as a Function of Load Current ...........................16
Figure 9.UCC28740EVM-525 Control Law Showing Switching Frequency as a Function of
Load Current ....................................................................................................................17
Figure 10.UCC28740EVM-525 Loop Response Gain and Phase ..................................................18

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Figure 11.UCC28740EVM-525 Load Transient ...............................................................................19
Figure 12.Output Ripple ...................................................................................................................20
Figure 13.Output voltage Turn On Waveform ................................................................................21
Figure 14.Switching Waveform........................................................................................................22
Figure 15.EMI Dithering Waveform .................................................................................................23
Figure 16.UCC28740EVM-525 Top Layer Assembly Drawing (Top view)....................................24
Figure 17.UCC28740EVM-525 Bottom Layer Assembly Drawing (Bottom view)........................25
Figure 18.UCC28740EVM-525 Top Copper (Top View)..................................................................26
Figure 19.UCC28740EVM-525 Bottom Copper (Bottom View)......................................................27
Tables
Table 1.UCC28740EVM-525 EVM-001 Electrical Performance Specifications...........................6
Table 2.Test Point Functional Description..................................................................................10
Table 3.The EVM components list according to the schematic shown in Figure 1................28

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1 Introduction
The UCC28740EVM-525 evaluation module is a 10 Watt off-line discontinuous mode (DCM) flyback
converter that provides constant-voltage (CV) and constant-current (CC) output regulation by using
an optical coupler for tight voltage regulation and improved the transient response to large load
steps and primary side control for accurate constant current regulation. The target application for this
converter design is USB adapters for consumer electronics. The UCC28740 uses frequency
modulation, peak primary current modulation, valley switching and valley skipping in its control
algorithm in order to maximize efficiency over the entire operating range.
2 Description
This evaluation module uses the UCC28740 Constant-Voltage, Constant-Current Flyback Controller
Using Opto-Coupled Feed-Back in a 10 W converter to provide 2 A of constant charge current. The
input accepts a voltge range of 85 VAC to 265 VAC. The output is designed for 5 V when in
constant voltage mode and will deliver 2.1 A of constant charge down to an output voltage of less
than 2 V. Depending upon the operating conditions, the control law algorithm will modulate the
switching frequency or the peak primary current to satisfy the power transfer requirements. As the
load is increased from zero, the converter will transition through a frequency modulation mode
where the peak primary current is held constant at one-quarter of its full-load peak value as the
switching frequency increases from a minimum value to maintain energy transfer up to 32 kHz.
When the load is increased to the level at which the switching frequency reaches 32 kHz, the
controller will keep the switching frequency fixed and modulate the peak primary current, increasing
it from one-quarter its peak value up to its maximum full load peak current value; this area of
operation is refered to as the amplitude modulation range. Further increase in load demand will
transition the controller into another frequency modulation mode where the peak primary current is
constant at its maximum designed value and the switching frequency is increased as needed, up to
the controller’s maximum 100 kHz switching frequency. Opto-coupled feed-back maintains a tightly
regulated output with fast dynamic response to load transients. The controller will further enhance
its efficient operation with valley switching. The UCC28740 also uses dithering of the gate drive
helps to ease EMI compliance.
This user’s guide provides the schematic, component list, assembly drawing, art work, and test set
up necessary to evaluate the UCC28740 in a typical off-line converter application.
2.1 Typical Applications
The UCC28740 is suited for use in isolated off-line systems requiring high efficiency and fault
protection features including:
USB-Compliant Adapters and Chargers for Consumer Electronics such as smart phones, tablet
computers, and cameras
Stand-by Supply for TV and Desktop
White Goods

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2.2 Features
The UCC28740EVM-525 features include:
AC Input Range 85 VAC to 265 VAC
DC Output of 5 V, 2.1 A
No-Load Power Consumption less than 20 mW
Opto-Coupled Feedback for Constant Voltage Regulation and Fast Dynamic Response
Primary Side Control for Tight Constant Current Performance
± 3% Output Volage Regulation
± 5% Output Current Regulation
Average Efficiency > 80%
Output Over Current and Short Circuit Protection
Output Over Voltage Protection
Input Brown-Out Protection
Auto Re-Start on Fault
Quasi-Resonant Valley Switching
Frequency Dither
Internal 700V Start-Up Switch to Start up the Supply Directly From the Bulk Rail
Caution
High voltage levels are present on the evaluation module whenever it is energized. Proper precautions
must be taken when working with the EVM. The large bulk capacitors, C3 and C4, and the output
capacitors, C8 and C10, must be completely discharged before the EVM can be handled. Serious injury
can occur if proper safety precautions are not followed.

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3 Electrical Performance Specifications
Table 1. UCC28740EVM-525 EVM-001 Electrical Performance Specifications
PARAMETER TEST CONDITIONS MIN NOM MAX UNITS
Input Characteristics
Voltage range, VIN 85 115/230 265 VRMS
Maximum input current VIN = VINmin, IOUT = IOUTmax 0.265 ARMS
Line frequency 47 60/50 63 Hz
No-load power
consumption VINmin≤VIN≤VINmax,IOUT=0A 20 mW
Output Characteristics
Output voltage, VOUT VINmin≤VIN≤VINmax,0A≤IOUT≤IOUTmax4.85 5 5.15 V
Output load current, CV
mode, IOUTmax VINmin≤VIN≤VINmax 1.995 2.1 2.205 A
Output voltage regulation
Line Regulation:
VINmin≤VIN≤VINmax,IOUT=IOUTmax 0.1 %
Load Regulation: 0A ≤IOUT≤IOUTmax 0.1 %
Output voltage ripple VINmin≤VIN≤VINmax,0A≤IOUT≤IOUTmax150 mVpp
Output over current, IOCC VINmin≤VIN≤VINmax 2.5 A
Minimum output voltage,
CC mode VINmin≤VIN≤VINmax,IOUT=IOCC1.78 2 V
Brown-out protection IOUT=IOUTmax68 VRMS
Transient response
undershoot IOUT=IOUTmaxto0Aloadtransient4.3 V
Transient response time IOUT=IOUTmaxto0Aloadtransient20 ms
Systems Characteristics
Switching frequency, fSW 1.2 71 kHz
Average efficiency 25%,50%,75%,100%loadaverageat
nominalinputvoltages81 %
Operating temperature 25 ºC

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4 Schematic
Figure 1. UCC28740EVM-525 Schematic
VDD
1
VS
2
FB
3
GND
4CS 5
DRV 6
HV 8
U1
UCC28740D
~
+
~
-
D2 HD06-T 6.8 µF
C3
6.8 µF
C4
D6
SBR10U45SP5-13
1 µH
L2
PGND
PGND
1.87 R10
D4 US1M-E3/61T
49.9
R12
270 µF
C8
270 µF
C10
1 µF
C14
2.2 µF
C1
277 VAC, 2 A
F1 RST 2
1 2
J1
LINE
NEUTRAL
INPUT: 100 VRMS - 265 VRMS, 0.3 A PEAK, 47 Hz TO 63 Hz
1.00k R16
196k R7
SGND
1 2
4 3
U2 LTV-817A
1 2 3 4
56
J2
C12
2700pF
C13
R18
D7 BAS16-7-F
PGND
SGND
1
FLa
5
FLb3
2
PRI BIAS
OUT
4
560 µH
T1
0.047 µF
C5
100 pF
C6
1
1
1
U3 TL431AIDBZ
42.2k R19
TP4
TP2
49.9
R21
TP3
TP1
DANGER HIGH VOLTAGE
+VOUT
NC NC
-VOUT
OUTPUT: 5V, 2.1A MAX
24.3
R1
1.27k
R9
JMP1
27.4k R3
BAS21
D1
105k R2
22.0k
R4
1.50k R15
JMP2
10 ohm
t°
RT1
0 R5
220 µH
L1
R13 R14
SGND
1
1 µF C7
0 R8
0
R17
1Do Not Populate
1.87
R11
1 µF
C11
C9
2.2 µF
C2
D3 SMBJ120A-13-F
D5
SBR10U45SP5-13
JMP3
1 µF
C15
TP5 TP6
Q1 STU7NM60N
1 1
42.2k R20
0
R6

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5 Test Setup
Figure 2 shows the equipment set up when measuring the input power consumption during no-load
operation. Note the addition of the 10 Ωshunt resistor in Figure 2. During the no-load test, the
power analyzer should be set for long averging mode in order the include several cycles of operation
and an appropriate current scale factor for using the external shunt must be used. Figure 3 shows
the recommended test equipment set up to evaluate the UCC28740EVM-525 with a load.
Warning
High voltages that may cause injury exist on this evaluation module (EVM). Please ensure
all safety procedures are followed when working on this EVM. Never leave a powered EVM
unattended.
5.1 Test Equipment
AC Voltage Source: The input source shall be an isolated variable AC source capable of supplying
between 85 VAC and 265 VAC at no less than 20 W and connected as shown in Figures 2 and 3. For
accurate efficiency calculations, a power meter should be inserted between the neutral line of the
AC source and the Neutral terminal of the EVM. For highest accuracy, connect the voltage
terminals of the power meter directly across the Line and Neutral terminals of the EVM.
Output Load: A programmable electronic load capable of sinking 0 A to 3 A shall be used. For
constant current mode testing of the EVM, the electronic load should be set to constant resistance
mode.
Power Meter: A power analyzer shall be capable of measuring low input current, typically less than
10mA, and a long averaging mode, if low power standby mode input power measurements are to be
taken. An example of such an analyzer is the Voltech PM100 Single Phase Power Analyzer. An
external 10 Ωshunt, with a current scale factor of 10 A/V, was used at a high sample rate over an
extended period of time in order to display the averaged results (refer to Figure 2).
Multimeters: For highest accuracy, VOUT can be monitored by connecting a DC voltmeter, DMM V1,
directly across the +VOUT and –VOUT terminals as shown in Figure 2 and Figure 3. A DC current
meter, DMM A1, should be placed in series with the electronic load for accurate output current
measurements.
Oscilloscope: A digital or analog oscilloscope with 500 MHz scope probes is recommended.
Fan: Forced air cooling is not required.
Recommended Wire Gauge: a minimum of AWG 18 wire is recommended. The wire connections
between the AC source and the EVM, and the wire connections between the EVM and the load
should be less than two feet long.

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5.2 Recommended Test Setup
Figure 2. UCC28740EVM-525 Recommended Test Set Up For No-Load Operation

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Figure 3. UCC28740EVM-525 Recommended Test Set Up With Load
5.3 List of Test Points
Table 2. Test Point Functional Description
TEST POINT NAME DESCRIPTION
TP1 PGND Primary side power ground
TP2 +LOOP Loop injection point, EVM output
TP3 -LOOP Loop injection point

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TEST POINT NAME DESCRIPTION
TP4 SGND Secondary side ground
TP5 +VOUT Positive output terminal of the EVM to the load
TP6 -VOUT Return connection of the EVM output to the load
5.4 Applying Power to the EVM
1. Set up the EVM as shown in Figure 2 if testing at no-load, or Figure 3 if testing with a load.
2. If testing with a load, set the electronic load to constant resistance mode.
3. Set the AC source voltage between 85 VAC and 265 VAC.
4. Monitor the output voltage on DMM V1.
5. Monitor the output current on DMM A1.
5.5 No-Load Power Consumption
1. Use the test set up shown in Figure 2.
a. Set the power analyzer to external shunt mode.
b. Set the appropriate current scale factor for using an external shunt on the power analyzer.
A 10 Ωshunt scales to 10,000 mV/A for the PM100 Voltech.
c. Set the power analyzer for long averaging time to include several cycles of operation. The
PM100 Voltech used for this test data was set to a long averaging time of 30 for accurate
power consumption measurement.
2. Apply power to the EVM per section 5.4.
3. Monitor the input power on the power analyzer while varying thinput voltage.
4. Make sure the EVM is off and the bulk capacitors and output capacitors are completely
discharged before handling the EVM.
5.6 Line/Load Regulation and Efficiency Measurement Procedure
1. For load regulation, use the test set up shown in Figure 3.
a. Be sure to remove the exteranal 10 Ωshunt from the power analyzer and set the analyzer
to normal mode (not long averaging).
b. Set the AC source to a constant voltage between 85 VAC and 265 VAC.
c. Vary the load so that the output current varies from 0 A up to 2.1 A, as measured on DMM
A1.
d. Observe that the output voltage on DMM V1remains within 3% of the 5 V constant voltage
regulation value.

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e. Observe that if the constant resistance level of the electronic load is decreased lower than
the full load value, the EVM will maintain constant current regulation within 5% of the
programed value until the output voltge drops below 2 V. The EVM will automatically
restart once the constant resistance load is increased.
2. For line regulation, use the test set up shown in Figure 3
a. Set the constant resistance load to sink the full load current, approximately 2.38 Ω.
b. Vary the AC source from 85 VAC to 265 VAC
c. Observe that the output voltage on DMM V1stays within 3% of the 5 V constant voltage
regulation value.
5.7 Output Voltage Ripple
1. Expose the ground barrel of the scope probe and place the tip of the probe on TP5, +VOUT,
and rest the exposed ground barrel of the probe on TP6, -VOUT, for output voltage ripple
measurements.
5.8 Equipment Shutdown
1. To quickly discharge the output capacitors, make sure there is a load greater than 0 A on the
EVM.
2. Turn off the AC source.

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6 Performance Data and Typical Characteristic Curves
Figure 4 through 11 present typical performance curves for UCC28740EVM-525.
6.1 Efficiency
Figure 4. UCC28740EVM-525 Average Efficiency
The average efficiency at 115 VAC, 60 Hz nominal input and 230 VAC, 50 Hz nominal input exceeds
the 0.80 design goal. Further increases in efficiency could be achieved with a transformer made
with a custom core and designed to operate at lower switching frequency over the entire operating
range.
85
115 230 265
0.750
0.755
0.760
0.765
0.770
0.775
0.780
0.785
0.790
0.795
0.800
0.805
0.810
0.815
0.820
85 115 145 175 205 235 265
EFFICIENCY
INPUTVOLTAGE(V
AC
)
AVERAGEEFFICIENCY

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6.2 Load Regulation
Figure 5. UCC28740EVM-525 Load Regulation
Figure 5 shows the actual measured load regulation exceeded the 3% design goal.
85 115 230 265
‐0.5
‐0.4
‐0.3
‐0.2
‐0.1
0
0.1
0.2
0.3
0.4
0.5
85 135 185 235
OUTPUTVOLTAGEREGULATION(%)
INPUTVOLTAGE(V
AC
)
LOADREGULATION

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6.3 Line Regulation
Figure 6. UCC28740EVM-525 Line Regulation
Figure 6 shows the actual measured line regulation exceeded the 3% design goal.
6.4 No-Load Power Consumption
Figure 7. UCC28740EVM-525 No-Load Power Consumption
‐0.5
‐0.4
‐0.3
‐0.2
‐0.1
0
0.1
0.2
0.3
0.4
0.5
0 102030405060708090100
OUTPUTVOLTAGEREGULATION(%)
PERCENTOFFULLLOAD(%)
LINEREGULATION
0
2
4
6
8
10
12
14
16
18
20
85 115 145 175 205 235 265
INPUTPOWER(mW)
INPUTVOLTAGE(V
AC
)
NO‐LOADPOWERCONSUMPTION

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No load power consumption measured less than 20 mW over the entire line input range.
6.5 Output Voltage vs Output Current
Figure 8. UCC28740EVM-525 Output Voltage as a Function of Load Current
In Figure 8, the converter is in constant-voltage operating mode from 0 A load up to approximately
2.2 A. Once reaching this output over-current threshold, the converter transitions into constant-
current mode where the load current remains constant until the output voltge falls below 2 V, at
which point the converter shuts down. If the load demand is decreased to the constant current
operating region, the converter will automatically re-start.
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
00.511.522.5
OUTPUTVOLTAGE(V)
LOADCURRENT(A)
OUTPUTVOLTAGEASAFUNCTIONOFLINE
ANDLOAD
85VAC,60Hz 115VAC,60Hz 230VAC,50Hz 265VAC,50Hz

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6.6 Control Law
Figure 9. UCC28740EVM-525 Control Law Showing Switching Frequency as a Function of Load
Current
As the load increases, the UCC28740 will transition from a frequency modulation mode at light load,
where the peak primary current is fixed at ¼ of its maximum programmed value, into a 32 kHz fixed
frequency, peak current amplitude modulation mode. Further increase in load will force a transition
into another frequency modulation mode where the peak primary side current is fixed at its peak
programmed value and the frequency will increase from 32 kHz up to the maimum frequency
required for energy transfer. The maximum designed switching frequency for this module is 71 kHz.
For ease in measuring the switching frequency, the data was taken with a DC input voltage. This
reduced the frequency dithering to only the controller’s EMI dithering scheme and limited the valley
skipping that would have been a result of the line frequency modulating the AC input.
0
10
20
30
40
50
60
70
80
90
100
0 0.3 0.6 0.9 1.2 1.5 1.8 2.1
SWITCHINGFREQUENCY(kHz)
LOADCURRENT(A)
CONTROLLAWinCVMODE
120VDC 163VDC 325VDC 375VDC

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6.7 Bode Plot
Figure 10. UCC28740EVM-525 Loop Response Gain and Phase
The gain, phase plot was measured with an AP Instruments Inc. Model 200 analog network
analyzer. The loop result was obtained by inserting a 200mV AC signal across TP2 and TP3. The
crossover frequency, with a 115 VAC, 60 Hz input and load current of 2 A, measured 1.38 kHz with a
phase margin of 71 degrees.
‐180
‐90
0
90
180
‐60
‐30
0
30
60
10 100 1000 10000
PHASE(degrees)
GAIN(dB)
FREQUENCY(Hz)
GAIN(dB) PHASE(degrees)

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6.8 Transient Response
Figure 11. UCC28740EVM-525 Load Transient
The transient response shown in Figure 11 was taken with a 115 VAC, 60 Hz input voltage and a
load transition from 0 A to full load. Channel 1 is the load current on a scale of 1 A per division,
channel 4 is the otutput voltage on a scale of 1 V per division. The cursor shows the minimum
acceptable voltage limit, 4.30 V, under transient conditions. Also note that the output waveform was
taken with the probe on TP5 with the ground referenced to TP4 but not using the tip and barrel
technique accounting for the high frequency noise seen on the waveform.

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6.9 Output Ripple
Figure 12. Output Ripple
Figure 12 shows the output voltage ripple, measured using tip and barrel across TP5 and TP6 on
the EVM. The measurement was taken at full load with an input voltage of 85 VAC, 60 Hz and the
waveform is AC coupled. The cursor shows the maximum peak to peak limit permitted for the
design.