Are MAX3232 capacitors polarized?

Gracufl Penguin

Other Parts Discussed in Thread: MAX3232

I have been using regular ceramic 0.1uF capacitors for the MAX3232 and have had no issues till now (I am having an issue that the RS232 when connected is increasing the noise on the 3.3v rail).

I see in the datasheet that the capacitors are polarized. Should I be using tantalums for these and not regular ceramics?

Also, in order to counter the noise, should I try and increase the value a little bit instead of 0.1uF?

Thanks

over 13 years ago

0 Igor Sherer over 13 years ago

Guru 31280 points

Hi,

According to the datasheet regular ceramic capacitors are acceptable (MAX3232 page 7, Notes -> B).

What about V+ Capacitor, is it connected to VCC or ground?

One more thing, what is the supply voltage in your case?

0 Gracufl Penguin over 13 years ago in reply to Igor Sherer

Intellectual 300 points

The supply voltage is 3.3v and the V+ is connected to Vcc

0 Igor Sherer over 13 years ago in reply to Gracufl Penguin

Guru 31280 points

Ok, can you try to connect the V+ capacitor to ground: GND -----| |----- V+

Does this reduce the noise?

0 Gracufl Penguin over 13 years ago in reply to Igor Sherer

Intellectual 300 points

I don't know, my board is made and I have to see if I can cut the track to do so.

What is the logic of connecting it to ground and not Vcc and why may it improve things?

0 Ron Michallick over 13 years ago

TI__Guru**** 165346 points

Gracufl,

The MAX3232 can use any type of capacitor in the charge pump. The noise could reduced by increasing the ESR of C1. It is the charging or discharging of C1 that causes noise on VCC. The return lead connection of the V+ capacitor changes which phase of the internal clock that cause the noise. Increasing the bypass capacitance may help noise also.

Regards,
Ron Michallick

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Are MAX3232 capacitors polarized?