LM5069: OUT PIN#9 sinking current?

David Dobler

Part Number: LM5069

Hi,

we are using the LM5069 mainly as inrush current controller when we power up a Load. VIN is at 48V the max current is approx 450mA. Our Design is more or less the same as the typical application diagram on page 1 from the LM5069 datasheet. The Load can be physically attached respectively removed from from the LM5069 over a dedicated connector. To shutdown the load we remotly switch off the LM5069 by pulling the UVLO pin to GND. To check if a Load is connected while the UVLO Pin is pulled to GND but VIN is at 48V we put a probe Voltage approx 5V to the Load and check it with an ADC. In this setup we see that the OUT Pin of the LM5069 draws around 6mA. Please explain us we the OUT Pin is drawing around 6mA, since we did not found any hint in the device datasheet.

Attached you will find the relevant page of our schematic.

So VIN is at 48V. UVLO is pulled to GND over a FET and a probe voltage

thanks and kind regards,

DavidLM5069_DETAIL_TI.pdf

over 5 years ago

0 Rakesh over 5 years ago

TI__Guru** 105361 points

Hi David,

Welcome to E2E!

There is an internal Vds measurement circuit which draws current if OUT pin has potential. You would need to place a blocking FET like Q2 in figure-1 (in http://www.ti.com/lit/an/snva683/snva683.pdf) to overcome this.

BR, Rakesh

0 David Dobler over 5 years ago in reply to Rakesh

Prodigy 50 points

Hi Rakesh,

thanks for your support. Would it it general be possible to connect the OUT Pin#9 to the SENSE Pin#1 just to do not meassure the Vds of the FET and hence do not use the power-limit function of the LM5069.

kind regards,

David

0 David Dobler over 5 years ago in reply to David Dobler

Prodigy 50 points

although if I look at the functional block diagram on page 11 of the device datasheet I would say that the VDS measurment circuit has a high impedance so 6mA in this case is quit a huge current.

0 Rakesh over 5 years ago in reply to David Dobler

TI__Guru** 105361 points

Hi David,

When the device is disabled the GATE is pulled down by 2mA sink current, this get path from the OUT as shown below. Also, there can be other paths with active voltage source on output. Unfortunately, we don't have much data for this case as we have not evaluated considering it as non common use case.

BR, Rakesh

Power management

Power management forum

LM5069: OUT PIN#9 sinking current?