Negative input negative output with buck converter

A M

Prodigy 20 points

Other Parts Discussed in Thread: LM2991, LM5001

Hello,

I have a requirement as below,

Input : -15V

Output : -5V / 500mA

Eff: >90%

Request to advice ti parts to realise this solution with proven circuit and application note.

Rgds.

over 3 years ago

0 Peter James Miller over 3 years ago

TI__Guru 52945 points

A M,

TI does not offer a dedicated Negative Input / Negative output (Quadrant 3) BUCK Converter.

We do offer a Quadrant 3 LDO that you can consider - the LM2991 and you can use WeBench to provide you with a reference design.

Alternately, you can use a PWM controller or BOOST converter, with a level shift circuit, to operate an inverted BUCK from the negative rail.

The Parallel Universe of Negative Input Voltages.pdf

0 A M over 3 years ago in reply to Peter James Miller

Prodigy 20 points

Hi Peter,

Please help me to understand, how to use LM5001 or Eq buck controller for negative input to negative output buck converter.

Kindly share the complete circuit in incorporated with level shift circuit.

Regards,

0 A M over 3 years ago in reply to A M

Prodigy 20 points

Request to go through below link

e2e.ti.com/.../negative-input-negative-output-with-buck-converter

0 Peter James Miller over 3 years ago in reply to A M

TI__Guru 52945 points

A M

I can not respond through that thread, as that thread is locked.

I have reached out to the TI posters from that thread to get updated links to the documents referenced in that post for you.

Did you read through the article that I provided?

0 Peter James Miller over 3 years ago in reply to A M

TI__Guru 52945 points

A M

Here is the link to the LM5001 schematic that Youhao Xi linked in that other thread

http://e2e.ti.com/cfs-file.ashx/__key/communityserver-discussions-components-files/196/1108.LM5001-_2D00_15Vin-_2D00_5VOUT.pdf

0 A M over 3 years ago in reply to Peter James Miller

Prodigy 20 points

Hello Peter,

Thanks for schematic of LM5001 as a negative -15V input to negative -5V/500mA output buck converter.

Advised schematic will meet our requirements.

Request to advise the value /rating of components used in circuit as below

1) PNP Transistors part number

2) Value of components used in EN, RT, VCC , COMP pins of LM5001

3) Value Input and output capacitor ( if any recommendation )

4) Value & Rating of Inductor and freewheel Diode ( if any recommendation )

Nonetheless I can calculate the value of input and output capacitor and Inductor as a consider buck converter.

Regards,

0 Peter James Miller over 3 years ago in reply to A M

TI__Guru 52945 points

A M

The EN resistor divider should be selected based on your desired input voltage to enable conversion. That will depend on your design and system requirements.

RT, L and COUT will depend on your design requirements balancing Efficiency and size. You can use TI's WeBench design tool to help you select switching frequency and calculate RT, C, L, and Compensation by generating a 12V to 5V design with a conventional positive to positive design.

For the PNP transistor, I would recommend a 20V rated low-current transistor (10-20mA). If you are using the two transistor option for compensation, I would recommend selecting a co-packaged 2-transistor pair for better matching.

https://www.ti.com/design-resources/design-tools-simulation/webench-power-designer.html

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Negative input negative output with buck converter