TPS25830-Q1: Current limit

Sorry to update, when load up to 3.48A,the BUS voltage fall down to about 1V rather than 0V.

Is it normal?

Hello Ailing,

I see that the customer is using the Buck Average current limit configuration and an RC circuit is in parallel with R_limit to be compliant to the MFi OCP. 

If R_limit is 11.8kΩ, R_para must also be 11.8kΩ. The schematic shows R_para is two resistors in series that add to 16.4kΩ. Our "How to Pass MFi OCP" Application Report also advises adding a 330uF cap to the CSP pin. See Table 5.

When the load exceeds the current limit threshold, VBUS will begin to drop, so VBUS decreasing to ~1V is expected behavior.

Is VBUS being measured with a multimeter? Is there an oscilloscope shot of when VBUS decreases to ~1V?

BR,

Seong

Hello Kim,

R_para and R_limt are both 11.8k,and 66uF cap was added  to the CSP pin.

Seong Kim said:

When the load exceeds the current limit threshold, VBUS will begin to drop, so VBUS decreasing to ~1V is expected behavior.

If it's the expected behavior ,I want to double confirm two questions :

1.Why it's 1V rather than 0V , where is the 1V comes from ?

2.Whether the fault pin should active ? We measured that the pin24 is still high when overcurrent occured.

Seong Kim said:

Is VBUS being measured with a multimeter? Is there an oscilloscope shot of when VBUS decreases to ~1V?

We measured with a multimeter .

Hello Kim，

I want to be sure whether it's current limiting by buck average current in our design?

Hi Ailing,

Are you using an external mosfet to limit the current?

BR,

Seong

Hello Kim,

No external mosfet, only  R_limit to limit the current.

Hello Kim,

so it's normal   no fault indication when overcurrent occurred?