TPS60403: Is Cfly need for Doubler?

Hirotsugu Kobayashi

Mastermind 9540 points

Part Number: TPS60403

Hi, team.

When using tps60403 in Doubler, is Cfly necessary?

When there is no Cfly, it moves by 50kHz not 250kHz.

Best Regards,

over 7 years ago

0 Chris Glaser over 7 years ago

TI__Guru**** 150830 points

Hi Kobayashi-san,

Do you refer to Figure 29 or Figure 30 in the D/S? Or do you want to design something else?

0 Hirotsugu Kobayashi over 7 years ago in reply to Chris Glaser

Mastermind 9540 points

Hi Chris,
Only Doubler is needed, so I think Cfly is unnecessary.
But If Cfly is removed, I'd like to know the reason that switching frequency will be 50kHz.

Best Regards,

0 Chris Glaser over 7 years ago in reply to Hirotsugu Kobayashi

TI__Guru**** 150830 points

It's not clear what you mean by doubler. Are you trying to create a 2x positive output voltage or negative? Can you share your schematic?

0 Hirotsugu Kobayashi over 7 years ago in reply to Chris Glaser

Mastermind 9540 points

Hi, Chris

My question is to create 2x positive output.

The schematic is similar as Fig.29, but I dont't need negative output.

So I remove Cfly, Fsw is changed to 50kHz.

When there is no Cfly, please tell me the reason that a frequency changes.

Best Regards,

0 Chris Glaser over 7 years ago in reply to Hirotsugu Kobayashi

TI__Guru**** 150830 points

Thank you for explaining.

Can you post waveforms of with and without Cfly?

Is OUT and C1- completely floating in your circuit? If so, does grounding OUT change the frequency?

0 Hirotsugu Kobayashi over 7 years ago in reply to Chris Glaser

Mastermind 9540 points

Hi, CHris.

Waveform of with and without Cfy is attaced.

with Cfly : 250kHz

without Cfly : 56kHz

OUT and C1- is floating.

Is it necessary to connect a OUT to ground?

Best Regards,

0 Chris Glaser over 7 years ago in reply to Hirotsugu Kobayashi

TI__Guru**** 150830 points

We can confirm similar results here. The reason is that a negative voltage (on OUT) is required for some of the IC's logic. You can see in the block diagram that the negative voltage is an input to several blocks which ultimately control the oscillator.

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TPS60403: Is Cfly need for Doubler?