TPS54561: TPS54561 with -5V inverted output

Roy T

Part Number: TPS54561
Other Parts Discussed in Thread: LM61480

Referencing:

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1226147/lm61480-q1--5v-inverting-output-possible

Current PCB uses TPS54561 for +5V and -5V supplies. Load is a LED where Anode = +5V, Cathode = -5V. Iout = 2.8A from each supply

In this configuration an external diode is used to bypass the TPS54561 N-FET (Async DCDC mode?) without this diode the supplies do not start.

Is this due to the over-current limit on the TPS54561 or another feature? I notice the LM61480 specifically mentions Reverse current limit, whereas the TPS54561 datasheet does not appear to.

Regards,

Roy

over 1 year ago

0 Henry Kou over 1 year ago

TI__Expert 3766 points

Hi Roy,

I need some further information on the schematic. Can you send this as well?

Regards,

Henry

0 Roy T over 1 year ago in reply to Henry Kou

Prodigy 75 points

Schematic for positive and negative. Standard wiring except for addition of D1 and D2

0 Henry Kou over 1 year ago in reply to Roy T

TI__Expert 3766 points

Great, thanks. I will take a look and update you on my findings.

Regards,

Henry

0 Henry Kou over 1 year ago

TI__Expert 3766 points

Hi Roy,

After taking a look at the schematics, I don't see anything particularly wrong with the connections as per the diagram below. If your inquiry is about the diode, the converter needs an external catch diode since the converter only has an integrated HS FET as you said. Therefore, to properly produce the SW waveform, a LS external diode is needed to generate a voltage output.

Regards,

Henry

0 Roy T over 1 year ago

Prodigy 75 points

Hi Henry,

Thank you. I missed that this was not a sync DC-DC. On the TPS54561 at the SW pin output there is an internal Diode and MOSFET to ground. Can you help me understand what this is doing? I thought (incorrectly obviously) this was part of the current path.

0 Roy T over 1 year ago

Prodigy 75 points

Hi Henry,

+1 Henry Kou over 1 year ago in reply to Roy T

TI__Expert 3766 points

Hi Roy,

That circuitry is part enables the part to function at high duty cycles and is called the "Wimp FET".

Regards,

Henry

Power management

Power management forum

TPS54561: TPS54561 with -5V inverted output