TLV61048: Problem under 45mA load (on 13V)

Dear,

It is now an avg of 13V (added 1uF from cathode to gnd) but our display is still flickering. Will measure ripple voltage tommorow and update this case.

Looks to be unstable.

Greetings

Thomas Van Aken

Hi Thomas:

Where did you measure the Vout? 

I wonder the converter enters into power save mode with such load. Please catch the waveform at Vin, Vout, SW to check it.

Dear

It is super busy here, will try to send you this tonight.

Dear

Vin gets dirty from the chip. But see Vin, Vout, Vsw!

VOUT:

VSW:

Vin:

Greetings

Thomas Van Aken

Hi Thomas:

May you use a resistance for loading to help debug? I'm not sure if it's caused by load transient.

According to the waveform of Vin and Vsw, it seems the Vin drops obviously. May you check the valley value of Vin? The UVLO of TLV61048 is 2.4V. 

Vin drops to 2.4V (but this is caused by the boost conv.), will now do a cont. load test instead of the oled.

Dear,

Problem stays with cont. load of 20mA. See attachment! (other scope since we have alot of other set-ups).

Dear

Any idea what happens? Since we need to fix this asap ...

Hi Thomas:

Sorry, it seems the reply is missing.

What's your power supply? I wonder why it drops so much? Do you have current probe to catch the current waveform of inductance?

Additionally, please also remove the load to check if it can startup without load. 

Another thing is, the time Vin drop is when Vout rising high enough. It doesn't look like caused by inrush current during startup. 

It can start up with no load.

Yes we have ac current probes.

Greetings

Thomas Van Aken

Hi Thomas:

If it can startup without load, it means the issues is not caused by the inrush current during the startup.

I suspect if the input power supply can handle such load. It has an obviously drop. 

Dear

Just tried with a lab psu as input (same problem) so it is really the boost IC I think ... 

It should be able to handle the 10uH right? I've ordered a 3.3uH one to test.

Greetings

Thomas Van Aken

Hi Thomas:

Did you measure the waveform when you use a PSU? Does the Vin drop as before? 

Yes, like crazy, with a 40mA load I am now getting the output rather ok, but the boost really does something bad with the VIN of the lab PSU, tried different ones, all the same problem:

Greetings

Thomas Van Aken4

From 72mA loads it starts getting stable, but our loads are 0-60mA, we even burned a screen by connecting this IC ... 

Ps.: here I changed to 1MHz, will go back to 600k now.

Greetings

Thomas Van Aken

600kHz same behaviour, but gets more stable after a lower current (45mA+-), still this can blow our 3V3 IC when we don't draw any currents or super low ones.

Same problem with 3.3uH ... is there something we need to do, to keep a clean 3V3 with this IC? It is really putting alot of dirt on the input.

Dear 

We really need a solution ... Can you at least recommend a part for following set-up (this is already 2nd time):

- 3V3 in

- 13V out (that can handle 100mA peak, normal maximum should be around 60mA, normal running current 20mA).

Greetings

Thomas Van Aken

Hi Thomas:

There are two main issue actually. 

The first is the original issue you post. The input power or the connection is too weak to supply the load, and Vin drops.

The second is the device can work well, but cause the Vin unstable. 

For the second one, it's caused by the power save mode of the device during the light load. The device will switch several pulse and then stop to reduce the power loss. I'll recommend you enlarge the input capacitance or choose a force PWM part(but the efficiency during light load is much lower)

Any part number?