TPS2559: current regulator,

Hi, Yang,

TPS2559 is a current limited power switch, there's build in soft start which cause output current rising slowing. This soft start can't be disable and can't be adjusted.

You can use current limit function to use TPS2559 as a current source. For example, you set the current limit point at 1.6A. If your load is over 1.6A, TSP2559 will limited the current at 1.6A.

Feel free to ask any questions.

Regards,
Bob

Hi Bob,

My circuit is below. It  follows TI's TOF design. Limit current setting is 2A. I place a adjustable resister RL as a VCSEL.  U27's trigger is 10KHz duty 50%.

I want the current on  RL to be 2A, 10K, 50%.

When RL> 1.5ohm, the output wave is 10K square;

When RL<1.5ohm, the output wave on RL is nothing but a little periodicity like soft-start's head.

Can you help me with this problem?

Hi, Yang,

Understood your case.

Can you please attach the waveform of RL>1.5ohm and RL<1.5ohm.

Regards,
Bob

Hi, Yang,

Since I don't get your further question, I will close this thread. Feel free to ask further if any questions.

Regards,
Bob

Bob,

Sorry to be late. This picture is captured when RL is 1.5ohm. 

Hi, Yang,

I did a test, and below is waveform. Vin=3V and load is 1ohm. Part is enabled, then I apply the 1 ohm load on it. Dark blue is Vout, light blue is voltage on load, green is output current. 

From my test, the current rise time is ~ 10us and voltage rise time is even faster.  Your clock is 10K and duty is 50%, so the turn on time for each cycle is 50us. Thus this time should be enough for current rise and voltage.

I noticed that there's a small inductor(L7), what's this inductor used for? The voltage your measured is behind the inductor, correct? Is there any possibility that the inductor influence the voltage?

Regards,

Bob

Hi Bob,

I short the inductor ,Iout seems no change. I noticed Iout rised as yours at the first time while dropped and acted as my picture upper.

The circuit could just work under 1KHz .I'm confused about this.

Hi, Yang,

We simulated it and the result shows no this problem at 10Khz. I will test on bench and send you result then.

Regards,
Bob

Hi, Yang,

Sorry for late reply.

Below is my bench test waveform, Vout is output of TPS2559, VD is drain of Mosfet(I used CSD16403), Iout is output current. My bench is TPS2559EVM+1ohm Power resistor + CSD16403. The TPS2559 setting is same as yours, Vin below is 5V, waveform is similar when Vin is 3V.

Have you solved your problem? Is below waveform what your expect?

Regards,

Bob