TPS61041: Suitable DC/DC Boost for powering OP amps in audio application?

Hi Martin,

What's the max current needed for the OPA? I'd like to check whether the Iout is big enough to cover your application.

Martin Likavec said:

2. Is constant switching frequency (PWM mode) better than PFM mode for audio application?

PWM mode is more recommended to make both the positive and negative output stable.

Martin Likavec said:

I found only mentioned TPS61041 but it works in PFM mode and I am scared if this is good for audio (op amp). Looking for advice if I can use it and some switching noise depending on the frequency change will not be transmitted and hear in audio.

Again I need the total Iout to check the work frequency. We also have device such as TPS61377, which can work in FPWM mode. 

Martin Likavec said:

My last question - is it good to connect OP amp directly to this type of symmetric power rail? Boost + charge pump circuit? (picture for reference)

It depends on the OPA you used. When the Iout is confirmed, the Vout ripple can be estimated, then you may check whether it is acceptable based on the OPA PSRR.

Regards

Lei

Hi Lei,

Thank you for respond.

So, I must rather find the PWM mode Boost controller.

Iout will be about 20mA max. Or maybe lower? What do you think? According to my schematic below.

Thanks for recommendation TPS61377 but it is quite overkill. So much not necessary pins. Some another similar to TPS61041?

For now, I have in schematic placed this OP amp - OPA2990 WSON 2x2. And also this one looks good OPA1678, but package is bigger.  But you can recommend me another. UPDATE: I will use OPA1678. I made space on PCB.

This my my audio application. There are connected signals from XLR connector. 

Thanks
Regards,
Martin

Hi Lei,

Regarding to Boost converters..

I found these two: TPS61170 or LM2735XSD. I will rather use TPS61170 because it is smaller. Could you help me to choose right inductor value for application with OPA?

Hi Martin,

For TPS61170 in your +/- 12V application, a 10μH inductor will be a good choice.

Martin Likavec said:

Iout will be about 20mA max. Or maybe lower? What do you think? According to my schematic below.

The +/- 12V output are used for the power of OPA, right? From the schematic I think the Iout should be small.

Martin Likavec said:

Thanks for recommendation TPS61377 but it is quite overkill. So much not necessary pins. Some another similar to TPS61041?

As my calculation, when 10μH inductor is used for TPS61170, it works in PWM mode when the total Iout (from both +/- 12V) is greater than 50mA. So, if the total Iout is 20mA, TPS61170 should still work in PFM mode.

There is a more recommended device for your application, the new pre-released device TLV61047, which is in SOT23 package with 2.9mm x 1.6mm. Although the size is bigger than TPS61170, the advantage  of TLV61047 is that it works in quasi-constant fixed frequency (~1.6MHz) even in DCM mode when the load is light, for example, Vin = 5V, Vout =12V, Iout = 5mA.

The datasheet should be available on website just these days. 

Regards

Lei

Hi Lei, 

Thanks for suggested boost controller, but SOT-23 is so big for my pcb. Need some DFN package.

What do you think about to use 100uH inductor with TPS61170. Than I will be still in CCM.

Regards,
Martin

Hi Martin,

100μH is too large, there should be instability issues.

Will the TPS61372 with WCSP package be available for your application? The size is smaller than TPS61170 and it had FPWM mode.

Regards

Lei

Thanks, I will try.

Hi Martin,

Thank you. Just let me know if you see any concerns.

Regards

Lei