LM5050-1-Q1: Gate Source voltage

ilgin sarican

Part Number: LM5050-1-Q1
Other Parts Discussed in Thread: LM5050-1

Hi,

In my circuit there is a buck converter and then oring circuit that is connected to output of buck converter.

I have Choroma DC electronic load, resistive and capacitive(20mF)

While the buck converter is not operating but input voltage(24v) is present, I measured gate source voltage of Q1 and Q2.

The electronic load is not yet turned on, but the capacitor (20 mf) is still connected to the output.

Until the output capacitor voltage reaches approximately 400 mV, gate source behaves like pictures below,

CH4(green): gate-source, CH2: Vout

After output voltage reaches 400mV, gate-source voltage is constanly 14V.

Has anyone experienced this situation before?

What could be the problem with this circuit?

Thanks,

over 1 year ago

0 Praveen GD over 1 year ago

TI__Guru 57737 points

Hi Sarican,

Do you see the same behavior of LM5050-1 Gate voltage when the electronic load is disconnected ?

0 ilgin sarican over 1 year ago in reply to Praveen GD

Prodigy 215 points

Hello, I dont' see the same behavior, I measured constant 14V at gate-source.

0 Praveen GD over 1 year ago in reply to ilgin sarican

TI__Guru 57737 points

Please share waveform capture with the IN, OUT, GATE and VS signals in both conditions - startup with and without electronic load connected. Probably the issue could be resolved if you set the electronic load to be ON after the Vout has reached a voltage > say, 3V.

0 ilgin sarican over 1 year ago in reply to Praveen GD

Prodigy 215 points

Hello, the first picture, without electronic load connection

CH1: VS, CH2: IN, CH3:OUT, CH4: GATE

The second picture with electronic load connection:

CH1: VS, CH2: IN, CH3:OUT, CH4: GATE

I use electronic load but in real system, the load will be connected to output directly , maybe load can be a battery.

I wonder why until output capacitor(20mf) charges 400mV, gate signal behaves like that?

0 Praveen GD over 1 year ago in reply to ilgin sarican

TI__Guru 57737 points

Hi Sarican,

Thanks for sharing the waveforms. From the waveforms it looks like the VS= 12V and VIN = 0.8V.

Please note that the valid operating range of the device is only VIN: 1 V to 75 V. Do you see the same behavior when the VIN>=1V ?

0 ilgin sarican over 1 year ago in reply to Praveen GD

Prodigy 215 points

Hello,

When VIN=24V, I don't see the same behavior.

What should be the gate voltage when VIN<1V and VS=12V?

I measure 14V if load is not connected.If load is connected, the gate voltage is like second picture.

The valid operating range of the device is VIN: 1 V to 75 V, but I wonder why capacitor charges 0.8V when VIN<1V ?

Is it about leakage because VIN is floating?

0 ilgin sarican over 1 year ago in reply to Praveen GD

Prodigy 215 points

Hello again,

I soldered 1K ohm parallel to C7, and measured 0V at GATE pin.

+1 Praveen GD over 1 year ago in reply to ilgin sarican

TI__Guru 57737 points

Hi Sarican,

The device may or may not perform as expected when VIN<1V. For VIN<1V, the device performance is not guaranteed.

In the waveform shared below, the Vin (CH-2) is trying to ramp up to 0.8V but looks like it is not able to ramp up beyond 0.4V. Am I reading the waveform correct ?

0 ilgin sarican over 1 year ago in reply to Praveen GD

Prodigy 215 points

Yes, you are reading correct, as you said the device is not working as expected, because VIN<1V.

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LM5050-1-Q1: Gate Source voltage