LV2862: Application of LV2862 at low load current

Shirin Fartash Toloue

Part Number: LV2862
Other Parts Discussed in Thread: LMR36506

Hello,

We are using 2 of the LV2862 with a similar design as in datasheet.

One of them converts 48V to 24V and the other one converts the 24V to 5V. The maximum load current connected to a conductivity sensor is 20mA. The issue with the current switching regulator is that it is always in the ECO mode and the sawtooth signal creates a noise in the output which is not desirable. Is there anyway that we could use the same switching regulator and get rid of the ECO mode. ( I added some resistors in the output to increase the load current and could get out of the ECO mode but that is not desired and we do not want to waste the current that way). If not what would be your suggestion for our specific application which works at low currents?

Best Regards,

Shirin Toloue

over 1 year ago

0 Frank De Stasi over 1 year ago

TI__Guru 72035 points

Hello

The light load mode of this device can not be disabled.

As you mentioned, a heavier load will bring the device to full frequency.

You may also want to try an output filter.

However, we have many newer devices that are programmed to remain in constant frequency PWM

mode at all loads. You might want to look at one of the LMR36506 family; the "F" versions.

Thanks

0 Shirin Fartash Toloue over 1 year ago in reply to Frank De Stasi

Prodigy 10 points

The other issue is that we observe that there is so much voltage due to the LV2862 entering/exiting ECO mode. Even when the regulator goes into ECO mode, it shouldn't cause the output voltage to drop below the tolerance that is specified for the regulator in its datasheet. In our case when observing the output voltage (5V) on oscilloscope when LV2862 is in ECO mode, the peak-peak voltage of the sawtooth signal is about 400mV while in the datasheet (page15, fig 8-10 for Vout=5V the peak-peak sawtooth signal is not more than 40mv. Can you help us with that explain why this happens in our case? Is that because the example in the datasheet is no load? thanks

0 Frank De Stasi over 1 year ago in reply to Shirin Fartash Toloue

TI__Guru 72035 points

Hello

Can you show us the 'scope shots of the output voltage you mention.

What is the load step ?

Thanks

0 Shirin Fartash Toloue over 1 year ago in reply to Frank De Stasi

Prodigy 10 points

Load is 20 mA

Load is 20mA

0 Frank De Stasi over 1 year ago in reply to Shirin Fartash Toloue

TI__Guru 72035 points

Hello

Can you provide us with your schematic.

Thanks

0 Shirin Fartash Toloue over 1 year ago in reply to Frank De Stasi

Prodigy 10 points

Here is the schematic for power regulation

0 Richard Fu22 over 1 year ago in reply to Shirin Fartash Toloue

TI__Mastermind 31015 points

Hi Shirin,

I'll be helping you with your issues. Let me take a look at the schematic and this case and I'll get back to you by next week.

Thanks,

Richard

0 Shirin Fartash Toloue over 1 year ago in reply to Richard Fu22

Prodigy 10 points

Hello Richard,

Any update on this issue?

0 Richard Fu22 over 1 year ago in reply to Shirin Fartash Toloue

TI__Mastermind 31015 points

Hi Shirin,

I've been a bit swamped, but I'm still looking into this issue. Appreciate your the patience.

Richard

0 Richard Fu22 over 1 year ago

TI__Mastermind 31015 points

Hi Shirin,

Schematic-wise, there doesn't seem to be anything too strange. From how I see it, there are two sitautions.

1) More difficult, but if LV2862 is required, you may try increasing your inductor value and output cap. Even at 20mA, it looks like the part is still in eco-mode. At no load, you may want to check the BOOT-SW voltage to make sure capacitor still has enough charge to turn on the high-side FET.

2) Easier solution: As Frank has said, the easier solution is to utilize a part that has FPWM which allows continuous conduction mode at no-load.

Thanks,

Richard

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LV2862: Application of LV2862 at low load current