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ADM1278 Severe Overcurrent & Regulation

Question asked by henry-tang on Jun 17, 2016

Dear Sir / Madam,

 

I'm wondering whether can you share more operation details about Severe Overcurrent?

According to definition on datasheet, "ADM1278 can detect an overcurrent event at approximately

125% to 225% of the normal current limit (ISET) and can respond to and control the current within 1 μs. "

 

And I source 180A current at output load, the normal current limit value is 73A (default setting for ADM1278 EVB).

I adjust threshold through evaluation GUI, but I find that the MOSFET is turned off when condition as below:

When Severe overcurrent Threshold 125% : MOSFET turned off when 26A (Should be 91A)

When Severe overcurrent Threshold 150% : MOSFET turned off when 36A (Should be 109A)

Does ADM1278 have other mechanism to determine it belongs to Severe overcurrent even beside current value?

 

 

And I ask the question about pull down current mode in other discussion.

ytu mentioned that "The regulation pull-down is activated when Vcb is reached the FET is regulating at current limit".

According to page.28 in datasheet, "When the voltage across the sense resistor reaches the circuit breaker trip voltage, Vcb , the 60 µA TIMER pull-up current is activated, and the gate begins to regulate the current at the current limit."

 

The voltage across the sense resistor should mean Vsensecl but Vcb is equal to Vsensecl minus Vcbos.

So which means Vsensecl should be always bigger than Vcb? (is that what we mean reach Vcb?)

Sorry, I don't really understand the meaning in this regulation mode, is any condition necessary to enter regulation mode?

 

Any suggestion or opinion is highly appreciated!

 

Henry

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