TPS2042: OVER CURRENT OUTPUT

Hi Poster,

Thanks for your reaching out.

And please let me learn about your question firstly. You mean that you want to use this dual power switch to have a total current limit with 1A? Actually we have one single channel power switch with 1A current limit.

Could you please help capture the waveform with your test, hope it can includes VIN/EN/VOUT/Current channels?

Best regards

Shuai 

Hi,

no, my question is why the OC1 or OC2 output of TPS2042 doesn't goes low when the load current from one channel of usb is more than 1A.

TPS2042 have 2 switch, one used for bus power of first usb port, and the second used for bus power of second usb port. The 2 open drain output OC1 and OC2 are "ored" together, using only 1 pullup resistor. 

The input to tps2042 is a +5V from a stepdown converter, and this 5V is stable.

the load to usb port is simulated by a resistor.

Hi Giovanni Copler，

Based on my internal confirmation, there are two concerns with the schematic of TPS2042:

One is that the 100nF capacitors should place as close as the OUT1/2 than the 100uF capacitor.

The second concern is about the OC1 and OC2 open drain connection, these two OC alert are seperated.

Best regards

Shuai

Hi Giovanni Copler,

As datasheet showed, the typical current limit for each channel is 0.9A, the MAX current limit is 1.1A which means when the current exceed 1.1A, the OC pin should goes low.

Could you please share what load are you using when you try to trigger the 1.4A current? And also could you please have the test after you seperate the two OC pin into two channels?

Best regards

Shuai

Hi,

yes, with a current above 1.1A i will expect oc output goes low, but it doens't!!!

My load is a 3.5 ohm resistor placed between +Vbus and gnd of usb port, so current is about 5V/3.5 ohm = 1.4A.

I try so separate the two OC1 and OC2 output, but the risult is the same.

Only if a place a resistor of about 1.8 ohm (current 5/1.8 = 2.7 A) the oc output goes low, and the current in the resistor is limited to 1A, and after some seconds decrease until 0.5 A because the chip temperature rise .

Hi,

I will check this behavior and also the operated spec with TPS2042. 

I will come back to you when I have the conclusion.

Regards

Shuai

Hi,

After my research about the current limit, actually for TPS2042B, it has two current limit related parameters one is Ioc, the other is Ios.

Under the current limit with Peaking algorithm showed like figure 9-5. When the current reaches to the Ioc, then the device will trigger overcurrent and then limit the current to Ios.

From the datasheet electrical characteristics, the overcurrent trip threshold of TPS2042B is about 1.55A. Thus I think it's matched with your test results that the OC pin didn't goes low even you put a 1.4A load. Could you please try with the Ioc current limit threshold?

By the way, the EVM is on the way to my lab, and I will also test about this point when I get the EVM.

Best regards

Shuai

Hi,

I test with the TPS2042BEVM and below is the waveform with OUT, OC and OUT current. I use the electrical load for sink current and I think below test results is matched with the current limit profiles as the current limit with peaking descripted. 

When the current reaches the IOC (Overcurrent trip threshold) then the OC alert pin will go low. I increase the current gradually and OC goes low when the current reaches 1.6A. Also when I try to sink 1.8A current from the beginning, then the current limit waveform is like below, the current limit will be firstly trigger by IOC and then limit the current to IOS (short-circuit output current). 

Best regards

Shuai

Hi,

but why in my circuits, i can draw 1.4 A current without having the OC output to goes low ?

in effect, there are two different state:

#1: i turn on my board, after some second the microcontroller enable the TPS2041. Then i connect my resistor to the Vbus of usb. The resistor is 2.7 ohm. The current in the resistor is about 1.48A. The OC output don't change, it's HIGH

#2: i connect the resistor load before turnig on the board. In this scenario, the current is limited to about 1 A and the OC output goes LOW.

Why this difference ?

Hi Sir,

Your test results are expected.

As datasheet descripted, there are three overcurrent conditions and I think your test scenario 2 is matched with below first overloads conditions

Best regards

Shuai