1.0

5.0

4.0

3.0

2.0

0

Output Current (A)

4.75 V

5.25 V

+/-5%

3.0 V

2.7 V

Board-End

Cable-End

21

UCC28704

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SLUSCA8A – FEBRUARY 2016 – REVISED FEBRUARY 2016

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Copyright © 2016, Texas Instruments Incorporated

Feature Description (continued)

7.3.8 Constant Current Under-Voltage Protection

The constant current output under voltage shutdown (CCUV) feature is to provide protection for USB connectors

from over-heat or burn-out due to soft-short circuit fault. A partial or soft-short can happen due to the presence of

foreign objects at the terminals of the USB upstream facing port, UFP, for example, smartphones with USB

Micro-B or USB Type-C connectors. When this happens along with the converter operates in CC mode with

condition resulting in a potential USB burn-out condition which is named as soft-short fault to distinguish from a

hard-short circuit fault. Traditional over-current protection and short-circuit protection cannot tell a soft-short fault.

The UCC28704 provides protection when soft-short circuit fault occurs with the corresponding converter V-I

characteristics as shown in Figure 21.

As shown in Figure 22, the CCUV feature of UCC28704 detects the operation of the converter under this

condition when the controller is operating in CC mode and when the output voltage drops out of regulation,

continuously for 120 ms, then it initiates a CCUV fault and sets the CCUV latch. Once the CCUV latch is set, the

controller goes through 3 cycles of VDD-UVLO without any PWM operation and clears the latch on the 4th VDD

UVLO power-up. If the CCUV condition still exists, then the controller enters into CCUV fault after 120 ms and

repeats the UVLO cycles. This 120-ms time delay allows converter normal start up without triggering the CCUV

protection. The flyback design should allow output voltage rise above CCUV protection level under normal

operating conditions within 120ms or the CCUV fault may be triggered.

Figure 21. Typical Target Output V-I Curves