MAX3243E Vcc ripple issue

user6397248

When measuring the VCC ripple (pin26) of TI_MAX3243EIRHBR, it was found that there was a lot of noise interference, resulting in a large pk-pk value
After bead ripple noise should be reduced, but the result is larger, is it the IC itself?

over 5 years ago

0 Miguel Robertson over 5 years ago

TI__Guru 62920 points

Hello,

The VCC rail is used to power the device's charge pump, which generates the V+/V- rails by transferring charge between different capacitors. Because the circuit frequently charges and discharges capacitances, it can draw sudden current spikes from VCC. This can lead to ripple on the rail due to its non-zero source impedance (e.g., due to regulator output impedance and trace routing parasitics). Adding higher-impedance series elements like beads would worsen the ripple seen by the IC (but may improve the ripple as measured on the other side of the bead). You can read more about the charge pump operation and how different capacitor value influence the ripple in this blog:

https://e2e.ti.com/blogs_/b/analogwire/archive/2018/06/28/how-the-rs-232-transceiver-s-regulated-charge-pump-circuitry-works

Regards,
Max

0 user6397248 over 5 years ago in reply to Miguel Robertson

Prodigy 40 points

Hi Max

Has method can be eliminated or reduced Ripple noise ?

0 Hao L over 5 years ago in reply to user6397248

TI__Mastermind 25705 points

Hi,

You could consider 1) reducing the sourcing impedance of the Vcc; 2) increasing the decoupling capacitor value. Sometimes deploying two cap, one large and one small, could help. In the layout, please make sure the supply and ground routing have good width. Also please place the decoupling cap, C1~C4 to the IC as closely as possible.

Regards,

Hao

0 user6397248 over 5 years ago in reply to Hao L

Prodigy 40 points

Hi Hao and Max

Remove bead(B280), ripple noise is improved.

Thank you for the information

0 user6397248 over 5 years ago in reply to user6397248

Prodigy 40 points

Hi Hao and Max

Why adding higher-impedance series elements like beads would worsen the ripple seen by the IC ?

Thanks

0 Hao L over 5 years ago in reply to user6397248

TI__Mastermind 25705 points

Thanks for your update. I think the inductance of the beads makes the transient current more smooth but makes the transient voltage more sharp. You can compare the charge pump waveform between the two setup.

Regards,

Hao

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MAX3243E Vcc ripple issue