Texas Instruments | UCC28056 Selection | Application notes | Texas Instruments UCC28056 Selection Application notes

Texas Instruments UCC28056 Selection Application notes
UCC28056X Selection Guide
Sonal Singh
The UCC28056A, UCC28056B, and UCC28056C are
PFC controllers that work in a dual-mode configuration
where it operates in transition mode at heavier load
conditions and transitions to discontinuous conduction
mode at lighter load conditions. When used with the
LLC controller, these 6-pin devices, thanks to its high
efficiency at light-load conditions, eliminate the need
for an auxiliary flyback converter while achieving less
than 80 mW no-load input power at 230 Vac. This
application note addresses the new variants of the
UCC28056 device family and showcases the changes
implemented on each variant and highlights the
advantages that they serve.
Burst Mode Threshold
The UCC28056 transitions to burst mode operation
when the load is below 10% of its maximum output
power. As the output load decreases, the controller
starts to operate in discontinuous conduction mode
and its switching frequency is decreased up to 18 kHz
at high line conditions.
Feature Differentiation
Table 1 showcases the differences among the various
versions of the UCC28056 devices.
Table 1. Feature Variation of the UCC28056X
Family
FEATURE
UCC28056
UCC28056A
UCC28056B
UCC28056C
ZCD
Improvement
No
Yes
Yes
Yes
Burst Mode
Threshold
10%
15%
15%
10%
OVP1
Threshold
10%
8%
10%
10%
OVP2
Threshold
Yes
No
Yes
Yes
ZCD Improvement
Integration of the zero current detection (ZCD) and the
current sense (CS) pins helps reduce the pin count
and produce a smaller package. This makes this pin
sensitive to the layout of the PCB. The noise can be
injected in the ZCD/CS pin either from the downstream
DC/DC converter (flyback/LLC) or the parasitic
capacitance of the layout. A traditional approach is to
introduce an auxiliary winding and sense the ZCD
event by monitoring this smaller current and moving
the traces away from the high switching nodes of the
primary FET. The disadvantage of using this approach
is increased cost and component count since a custom
PFC inductor and external components are required.
Figure 1. Modified Minimum Burst Mode Fall
Threshold
The UCC28056A and UCC28056B implement a higher
burst threshold which prevents the frequency from
dropping into the audible noise band. The UCC28056A
and UCC28056B enter the burst mode operation at
15% of the maximum output load which maintains the
minimum frequency of the controller at 22 kHz and
prevents any intrusion into the audible range. The red
line in Figure 1 indicates the increased burst mode
threshold.
Table 2. Burst Mode Threshold Variation
FEATURE
UCC28056
UCC28056A
UCC28056B
UCC28056C
Burst Mode
Threshold
10%
15%
15%
10%
VBSTFall
0.5 V
0.75 V
0.75 V
0.5 V
VBSTRise
0.625 V
0.875 V
0.875 V
0.625 V
The UCC28056A, UCC28056B, and UCC28056C
address this issue and make the controller more
robust and immune to layout, thus more tolerant and
less sensitive to downstream noise.
SLUA974 – June 2019
Submit Documentation Feedback
UCC28056X Selection Guide Sonal Singh
Copyright © 2019, Texas Instruments Incorporated
1
www.ti.com
Over Voltage Protection OVP1
The OVP1 protection is triggered when there is
excessive voltage on the output capacitors. This is
achieved by monitoring the voltage on the VOSNS pin
through a resistive divider. When the VOSNS pin rises
above the VOVP1Rise threshold, the controller stops
switching to prevent the further increase of output
voltage. The output voltage that trips the OVP1 fault
can be calculated with Equation 1:
where
•
•
VOSOvp1Rise is the VOSNS over voltage threshold,
rising threshold
Ros1/2/3 are the resistor values of the VOSNS
resistor divider from the UCC28056EVM
Reducing the OVP1 threshold can decrease this
overshoot, provide additional margin, and prevent any
component damage related to it. A lower OVP1
threshold allows for lower voltage-rated output
components/capacitors, reducing system cost.
Table 3. OVP1 Threshold Variation
FEATURE
UCC28056
UCC28056A
UCC28056B
UCC28056C
OVP1
Threshold
10%
8%
10%
10%
VOSOvp1Rise
2.75 V
2.7 V
2.75 V
2.75 V
VOSOvp1Fall
2.675 V
2.625 V
2.675 V
2.675 V
Over Voltage Protection OVP2
(1)
(2)
This is a second level of output voltage protection,
which is independent to the OVP1 sensing. The OVP2
protection is triggered when the controller senses the
excessive voltage stress across the boost MOSFET.
The controller monitors the voltage at the ZCD/CS pin
during the discharge period (TDCH). The OVP2 trigger
is considered as a long fault and the controller stops
switching for 1 sec. You can estimate the output
voltage at which the OVP2 triggers using Equation 3:
where
•
•
VOVP2Th is the second-level output overvoltage fault
threshold typ 1.125 V
KZC is the attenuation factor considered as 401 per
the UCC28056 EVM design
(3)
(4)
Figure 2. Reference for Output Voltage Sense
Circuit
2
Once the Vout is greater than the VoutOVP2 voltage,
the controller enters the fault condition and the one
second restart. The resistor divider placed on the
ZCD/CS pin is used to sense output voltage during
inductance demagnetization time and is also used to
sense converter-rectified input voltage. Based on the
voltage on the ZCD/CS pin, the IC decides whether or
not to switch depending on if the voltage is higher or
lower than the internal Brown-in threshold. In some
cases, if the customer wants to select the quiet low
Brown-in threshold, it is not possible to set Brown-in
and OVP2 at the desired level since they depend on
the same resistor divider. The UCC28056A has the
OVP2 fault disabled for applications where this fault is
undesirable.
UCC28056X Selection Guide Sonal Singh
SLUA974 – June 2019
Submit Documentation Feedback
Copyright © 2019, Texas Instruments Incorporated
IMPORTANT NOTICE AND DISCLAIMER
TI PROVIDES TECHNICAL AND RELIABILITY DATA (INCLUDING DATASHEETS), DESIGN RESOURCES (INCLUDING REFERENCE
DESIGNS), APPLICATION OR OTHER DESIGN ADVICE, WEB TOOLS, SAFETY INFORMATION, AND OTHER RESOURCES “AS IS”
AND WITH ALL FAULTS, AND DISCLAIMS ALL WARRANTIES, EXPRESS AND IMPLIED, INCLUDING WITHOUT LIMITATION ANY
IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT OF THIRD
PARTY INTELLECTUAL PROPERTY RIGHTS.
These resources are intended for skilled developers designing with TI products. You are solely responsible for (1) selecting the appropriate
TI products for your application, (2) designing, validating and testing your application, and (3) ensuring your application meets applicable
standards, and any other safety, security, or other requirements. These resources are subject to change without notice. TI grants you
permission to use these resources only for development of an application that uses the TI products described in the resource. Other
reproduction and display of these resources is prohibited. No license is granted to any other TI intellectual property right or to any third
party intellectual property right. TI disclaims responsibility for, and you will fully indemnify TI and its representatives against, any claims,
damages, costs, losses, and liabilities arising out of your use of these resources.
TI’s products are provided subject to TI’s Terms of Sale (www.ti.com/legal/termsofsale.html) or other applicable terms available either on
ti.com or provided in conjunction with such TI products. TI’s provision of these resources does not expand or otherwise alter TI’s applicable
warranties or warranty disclaimers for TI products.
Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265
Copyright © 2019, Texas Instruments Incorporated
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertising