LM2776: Regarding <10mV ripple negative supplies for precision signal conditioning.

Part Number: LM2776
Other Parts Discussed in Thread: TPS7A30, TPS63700, TPS60402,

Hello TI support,

We are amplifying 2mV signal with precision signal conditioning circuit having gain of around=500. We need negtive supplies for the opamps. I came across LM2776 but simulation results of LM2776 show ripple of ~100mV at 20KHz with load of 5mA at -5V. Now 5mA is expected load of negative supplies in our board. 100mV will degrade the output due to PSRR, so is there a better way with TI to generate inverted supplies with ~10mV ripple & ~5mA load current? We have +5V available in our board.

Regards,

26 days ago

0 Febin 24 days ago

TI__Mastermind 27270 points

Hello JK,

With LM2776, it could be challenging...

Have you also looked at our LDO portfolio?

Thanks,

Febin

0 JK 24 days ago in reply to Febin

Prodigy 60 points

Hello Febin,

Yes, I have looked over TI LDOs. So what is your recommendation over here?

Regards,

0 Daniel Esparza 23 days ago in reply to JK

TI__Expert 6505 points

Hello JK,

You can include the TPS7A30 regulator with a 10nF noise reduction capacitor at the output to improve the PSRR.

Best regards,

Daniel Esparza

0 JK 22 days ago in reply to Daniel Esparza

Prodigy 60 points

Hello Daniel,

Thanks for suggesting TPS7A30. Besides TPS7A30, can TPS63700 be solution for having ripple near 10mV at 5mA to 10mA load current? Please advise.

Regards,

0 Daniel Esparza 22 days ago in reply to JK

TI__Expert 6505 points

Hello JK,

The TPS60402 might be a better option since the switching frequency is 50KHz, which is well within the bandwidth of the LDO. At 50KHz, the LDO's PSRR is about 50dB if a 10nF CNRSS and a 10uF output capacitors are installed. The output ripple of the TPS60402 is specified at 20mvp-p, and with the PSRR of the LDO, the expected ripple, attenuated by about 50dB, should be < 1mvp-p.

Best regards,

Daniel

0 JK 21 days ago in reply to Daniel Esparza

Prodigy 60 points

Hello Daniel,

Actually, I was just thinking to use stand alone (without LDO) TPS63700 having lesser ripple as per attached graph. I thought may be TPS63700 give near 10mVp-p at 5V input with 5mA load. Your thoughts..

Regards,

0 Daniel Esparza 21 days ago in reply to JK

TI__Expert 6505 points

Hello JK,

The ripple appears to be close to 10mv at 20mA as shown in the datasheet, so it might be a possible option for your application. Another device you may want to consider is the LM27762:

Best regards,

Daniel Esparza

0 JK 20 days ago in reply to Daniel Esparza

Prodigy 60 points

Hello Daniel,

Thanks for suggesting LM27762. Will consider LM27762/ TPS63700. Appreciate your support.

Regards,

0 Daniel Esparza 15 days ago in reply to JK

TI__Expert 6505 points

Hello JK,

You are welcome.

Best regards,

Daniel Esparza

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LM2776: Regarding <10mV ripple negative supplies for precision signal conditioning.