UCC28C44: protection

[FAE] Andrew Wang

Part Number: UCC28C44

Hi Team,

Customer wants to know some more detail how this device can protect from overload, I put my understanding, please help correct, thx.

1) What is the triggering condition of overload protection?

[Andrew] An external series resistor (RCS) senses OC and converts it to voltage at CS pin. The CS input is compared with an internal error amplifier output voltage. When overload peak current is detected, internal PWM generator will stay at zero duty until overload condition is removed.

2) When overload is triggered, beside PWM off, what else device would do? In any sequence?

[Andrew] I think customer is trying to understand if key word 'overload protection' mentioned in the datasheet equal to 'PWM off' ?

3) Right after current-limit is triggered, will current output continue to increase for a while? If so, how do we determine and limit actual max output current?

[Andrew] I think customer tried to understand how to set a absolute current limit (and by which pin) if output current can continue increasing for a while even current-limit is triggered, output short to ground for example.

Thanks!

Andrew

over 3 years ago

0 Hong Huang over 3 years ago

TI__Guru 73035 points

Hi,

The current limit mechanism should be referred to the function block diagram on page 12 of the datasheet. When CS reaches about 1V, the pulse of OUT pin is terminated. Each switching cycle there is still the pulse showing on OUT pin, the pulse width depends on how fast CS pin reaches about 1V plus the propagation delay from CS to OUT (about 70ns at worst case). There are no other actions. Again, please use the block diagram on page 12 to help your understanding.

0 [FAE] Andrew Wang over 3 years ago in reply to Hong Huang

TI__Genius 10685 points

Hi Hong,

Thanks for feedback, yes I did read page 12 before posting this question.

Could you double check my Q3 please? Thanks!

Andrew

+1 Hong Huang over 3 years ago in reply to [FAE] Andrew Wang

TI__Guru 73035 points

Hi,

After CS reaches the current limit, before OUT pin starts to turn off, there is a propagation delay up to 70ns inside IC. OUT pin has falling time which depending on the external MOSFET gate charge. Before OUT reaches MOSFET off threshold, the current cannot be off. But internal IC, after CS reaches the limit threshold, the 70ns needs to consider and during which the OUT pin keeps on.

0 [FAE] Andrew Wang over 3 years ago in reply to Hong Huang

TI__Genius 10685 points

Got it, thanks for the info!!

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UCC28C44: protection