TPS1685EVM: Vout = 0 when during system start-up with load on

Hi Jexy,

Is eload used in cc mode. 

Regards 

Kunal Goel

I used it in CC mode and tried CR mode as well. Results are similar. 

Hi Jexy,

Device has startup current limit around 0.5A. So for two devices on EVM it will be 1A. Now load is 4A>1A , so device will enter current limit and might be hitting thermal shutdown due to high power stress at startup. 

Please try gradually increasing load. We can try with maybe 0.5 or 1A load first and see if VOUT is coming.

Regards

Kunal Goel

I'll be in the lab Monday to try. In the meantime, is there anyway we can slow down the current ramp? Based on the test report by Dell, we would need to have the load already on when we turn on Vin or EN. 

Hi Jexy,

One thing is load turn on threshold. Actual load will not be like eload which will draw current at 0V. It will have some turn on threshold. Similarly in eload we can keep load turn on threshold .

Regards

Kunal Goel

Kunal,

Just to be clear, are you suggesting to slow down the turn on threshold on the eload? I can try to see if this is possible. What rate would you recommend?

Kunal,

I ran 3 more test case, 2 below that still fails: 0.54A (passing), 1A and 4A with the open dVdT pin (fastest V/ns) and slowest SR on the load (0.001A/us).

0.54A

1A

4A

Thanks Jexy. I meant not the slew rate but there is a load turn on threshold option . It means for eg if you set it at 30V that means load will draw current when voltage across load crosses 30V. 

Actual load will have some threshold like this.

Kunal,

Is there anyway I can still perform the test of Vin on, EN off, load already on. Then turn on EN and not run into issues? I need to collect this data for customer 

Hi Jexy,

I think it will be a challenge.  We can try with different dvdt caps maybe.

What would you recommend to use? 

I've tried with the 47nF, which gives us 1V/ms. I also tried with the pin open, which i thought would have the fastest slew rate.

Is there a way to increase the V/ms? 

Hi Jexy,

Pin open will give fastest slew rate.  We can try with caps like 2.2nf, 4.7nf but starting into high load will be a challenge. 

Regards 

Kunal Goel