TPS65105: Using Vo2 and Vo3 without Vo1

Dice-K

Mastermind 6500 points

Part Number: TPS65105

Hi support team,

I want to use only Vo2 and Vo3 of TPS65105.
Can I use Vo2 and Vo3 without Vo1?

If possible, is it okay if the red frame parts of the reference circuit shown below are not mounted?

TPS65105_only_vo2_vo3_2.pdf

As a result of not mounting, the pins in the blue frame become floating.
Please let me know the correct pin treatment.
VCOMIN: GND connection.
BASE: VIN connection.
FB4: VIN connection.
ENR: GND connection.
VCOM: Floating.
SW, FB1, SUP: Please let me know the treatment.

In my opinion, it is impossible because Vo1 is input to the SUP pin and used as an energy source for Vo2 and Vo3.

・ Use Vo1, Vo2, Vo3
・ Do not use VCOM or Vo4
I think it is possible to use it.
In that case, are the following pin treatment correct?
VCOMIN: GND connection.
VCOM: Floating.
ENR: GND connection.
BASE: VIN connection.
FB4: VIN connection.

Regards,
Dice-K

over 2 years ago

+1 Liaqat Khan over 2 years ago

TI__Mastermind 18550 points

Hello Dice-K,

VO2 and VO3 can not be used without VO1 for the TPS65105 because VO1 is the input supply for VO2/VO3 output rails. So you have to generate VO1 to be able to use VO2/3.

Kind Regards,

Liaqat

0 Dice-K over 2 years ago in reply to Liaqat Khan

Mastermind 6500 points

Hi Liaqat,
Thank you for your reply.

Then I will use it as follows.
・ Use Vo1, Vo2, Vo3
・ Do not use VCOM or Vo4

I attach a file.

TPS65105_only_vo123.pdf

VCOMIN: GND connection.
VCOM: OPEN.
ENR: GND connection.
BASE: VIN connection.
FB4: VIN connection.

As a result, the parts in the red frame do not be mounted.

Please let me know if there are any problem.

Best regards,
Dice-K

+1 Liaqat Khan over 2 years ago in reply to Dice-K

TI__Mastermind 18550 points

Hello,

Instead of BASE. FB4 connected directly to VIN, I would suggest to use a 10K pull up resistor to connect to Vin. The rest is fine.

Kind Regards,

Liaqat

0 Dice-K over 2 years ago in reply to Liaqat Khan

Mastermind 6500 points

Hi Liaqat,
Thank you for your reply.

We do not connect BASE and FB4 directly to VIN, but insert a 10kΩ pull-up resistor.

Best regards,
Dice-K

+1 Liaqat Khan over 2 years ago in reply to Dice-K

TI__Mastermind 18550 points

Hi Dice-K,

It is all good then.

Kind Regards,

Liaqat

0 Dice-K over 2 years ago in reply to Liaqat Khan

Mastermind 6500 points

Hi Liaqat,
Thank you for your reply.

Should we place each pull-up resistor on each pin?

Best regards,
Dice-K

+1 Liaqat Khan over 2 years ago in reply to Dice-K

TI__Mastermind 18550 points

Yes, separate resistor in each pin.

Kind Regards,

Liaqat

0 Dice-K over 1 year ago in reply to Liaqat Khan

Mastermind 6500 points

Hi Liaqat,
Excuse me often.

Is the reason for adding pull-up resistors to BASE and FB4 to reduce the influence of VIN noise?

Best regards,
Dice-K

0 Liaqat Khan over 1 year ago in reply to Dice-K

TI__Mastermind 18550 points

Hello,

In general, I suggest to not leave pins floating for various reasons including noise, latch-up etc.

Kind Regards,

Liaqat

0 Dice-K over 1 year ago in reply to Liaqat Khan

Mastermind 6500 points

Hi Liaqat,
Thank you for your reply.

I want to know why we insert a pull-up resistor, not why we don't float the pin.

I think as follows.
・The purpose of the pull-up resistor is to reduce the influence of VIN noise.
・If the position of the pull-up resistor is far from the pin, the wiring between the resistor and the pin may suck in external noise and take it into this IC.
So place a pull-up resistor near the pin.

Best regards,
Dice-K

+1 Liaqat Khan over 1 year ago in reply to Dice-K

TI__Mastermind 18550 points

Hello,

I suggested to put pull up resistor instead of direct connection to Vin to avoid any chance of high current flowing into the pins during power up/down of the device, I am not too concerned about placement of resistor or coupling noise into Vin.

Kind Regards,

Liaqat

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TPS65105: Using Vo2 and Vo3 without Vo1