This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

UCC28911: The precision of Low voltage, current-limiting protection.

Part Number: UCC28911
Other Parts Discussed in Thread: LM8364

Dears:

Customer will evaluate UCC28911 and have some issue as below:

A. The precision of low voltage protection.

b. The precision of current-limiting protection.

c. The precision of constant-current source.

d. What is the function of LM8364? Can UCC28911 realize the function?

 

Btw, the customer's project requirement as follows:

Is there any other PN to promote except for UCC28911? 

1. anti shock isolation mode

2. the output power is about 10W.

3. no optocoupler primary feedback PSR

4. Integrated MOS tube (more than 700V)

5. Integrated high voltage constant current source to start

6. it is best to support CV (constant voltage) and CC (constant current) mode.

7. low power consumption, high light load efficiency

8. under-voltage protection

9. over current protection / overload protection

10. best equipped with PFC

11. over temperature protection

12. output overvoltage protection

13. short circuit protection

14. two output cross load, good voltage regulation performance.

15. it's best to have Green mode.

  • Hello Lian,

    Thank you for your interest in UCC28911 and other TI products. Based on items 2-9 on your customer’s list of requirements, the UCC28911 is the only TI device that is suitable for this application.

    Regarding the issues listed:

    A. The precision of low voltage protection:
    The UCC28911 does not have specific protection for output low-voltage, so I assume this question refers to input Brown-out protection. It is accomplished by sensing the current out of the VS pin when the internal MOSFET switch is on. Per the datasheet, when VS current (Ivsl) decreases below -75uA (Ivsl(stop) tolerance range 60uA ~ 100uA = -20%, +33%), the UCC28911 will shut down and begin UVLO restart cycles until VS current rises above -215uA (Ivsl(run) tolerance range 175uA ~ 260uA = -19%, +21%). The VS current itself depends on the tolerance of the VS resistor-divider network, the transformer Np/Na turns-ratio, and the instantaneous voltage across the bulk capacitor.

    B. The precision of current-limiting protection:
    This is the same as constant-current (CC) regulation of the output current. For a single output, the CC-regulation accuracy is +/-5%. If your customer’s application has 2 outputs (based on requirement item #14), then CC-regulation is dependent on the split of the total loading between the two outputs. The combined load accuracy is still +/-5%, but if one output load is fixed and the other output is overloaded, the accuracy of the overloaded output will appear to be worse than +/-5% because of the magnitude of the overload variation with respect to that output’s nominal current rating.

    C. The precision of constant-current source:
    I assume this refers to item #5 on the requirements list. The datasheet specification table shows 3 different start-up current levels (Ich1, Ich2, ICh3), depending on the voltage at VDD during the start-up. The typical values are not precise and may vary considerably, but the minimum and maximum values of each level are guaranteed over the full range of operating temperature (-40C to +125C).

    D. What is the function of LM8364:
    In the schematic diagram of the PMP30002 reference design that you provided, the LM8364 serves as a comparator to detect input over-voltage and shuts down the UCC28911 if the input voltage exceeds 285Vac. The LM8364 is a micro-power comparator with a built-in 2.5-V reference and an open-drain output. The UCC28911 does not have an input OV protection feature. Even though it is part of the reference design, for most world-wide applications with 85Vac ~ 264Vac input range, this input OVP is not necessary and such protection is not on your customer’s requirements list.

    Regarding the requirements list,
    1. Safety isolation is determined by the transformer design and pcb layout, not by the controller.
    2. through 9. The UCC28911 supports these requirements.
    10. For a 10-W application, PFC is not required.
    11. Internal over-temperature protection is provided within the UCC28911, but not external OTP.
    13. Short-circuit protection is provided when VDD falls below the UVLO threshold during CC operation.
    14. The UCC28911 provides primary-side regulation, so the cross-regulation performance of 2 flyback outputs depends on the converter design techniques. These references can help maximize that performance:
    training.ti.com/.../Multi-Output_Flyback_Cross_Reg_3-Sept-17_complete.pptx
    training.ti.com/multiple-output-flybacks-how-improve-cross-regulation
    15. The UCC28911 can achieve very low stand-by power due to its low minimum switching frequency of 420 Hz (typical).

    If this answers your questions, please click the “Resolved” button.

    Regards,
    Ulrich