LM2776: the same function as "Figure 29. TPS60400 as Doubler" using LM2776

Hirotaka Matsumoto

Part Number: LM2776
Other Parts Discussed in Thread: TPS60400

Hi all

Would you mind if we ask LM2776?

Using LM2776, is it possible to realize the same function as "Figure 29. TPS60400 as Doubler"?
If you have reply, could you let us know?

Kind regards,

Hirotaka Matsumoto

over 8 years ago

0 Juha Karttunen over 8 years ago

TI__Intellectual 1120 points

Hirotaka-san,

Yes, I think it is possible in principle. However, my concern is that as LM2776 is operating in PFM mode when output current is small, there is possibiltity that it is not switching fast enough if load is only in the positive 2x rail and not in inverted rail. I will test how the circuit works in the lab and get back to you with results.

Regards,

Juha

0 Hirotaka Matsumoto over 8 years ago in reply to Juha Karttunen

Guru 27585 points

Juha san

Thank you very much for your reply!

I will test how the circuit works in the lab and get back to you with results.
->OK, we are waiting for your test results.

Kind regards,

Hirotaka Matsumoto

0 Hirotaka Matsumoto over 8 years ago in reply to Juha Karttunen

Guru 27585 points

Juha san

Thank you for your support about LM2776.
Is it possible to get your reply(test result) next week?

Kind regards,

Hirotaka Matsumoto

0 Juha Karttunen over 8 years ago in reply to Hirotaka Matsumoto

TI__Intellectual 1120 points

Hirotaka-san,

I will try to get results by the next week.

Regards,

Juha

0 Hirotaka Matsumoto over 8 years ago in reply to Juha Karttunen

Guru 27585 points

Jusa san,

Than you for your cooperation.

Kind regards,

Hirotaka Matsumoto

0 Juha Karttunen over 8 years ago in reply to Hirotaka Matsumoto

TI__Intellectual 1120 points

Hirotaka-san,

I tested the circuit and it seems to work in practice. However there are limitations. There should be some kind of load in both outputs (+10V and -5V). I observed two different cases which could be problems:

1) If there is no load at -5V output, charge pump is in PFM mode and does not switch often enough to keep +10V up. Typical output current threshold for PFM->PWM mode transition is 40-50mA, so ideally there should be at least 50mA output current in -5V output.

2) If there is no load at +10V output and at same time there is heavy load in -5V output, I observed up to +16V in +10V output. Even small load (1mA) fixes this.

In my opinion charge pumps without PFM mode feature are more suitable for this kind of application.

Regards,
Juha

0 Hirotaka Matsumoto over 8 years ago in reply to Juha Karttunen

Guru 27585 points

Juha san

Thank you very much for your update!
We would like to confirm a few points.
Please refer to the attachment file.
20170214_LM2776.pdf

Could you give us the reply?

Kind regards,

Hirotaka Matsumoto

0 Juha Karttunen over 8 years ago in reply to Hirotaka Matsumoto

TI__Intellectual 1120 points

Hirotaka-san,

I used 1uF capacitors.

Regards,

Juha

Power management

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LM2776: the same function as "Figure 29. TPS60400 as Doubler" using LM2776