Bypass Capacitors

Mohith Manoj

Other Parts Discussed in Thread: ADS1298, ADS1298ECGFE-PDK

The datasheet (MAY2011) version of bypass capacitor practice for ADS1298 suggests a combination of 1uF and 0.1uF capacitors be used to bypass each supply.

From the PDK schematic, it appears that each supply pin needs to be bypassed. However I am not able to confirm the same from the layout drawing of PDK.

Q: Is it required that each supply pin be decoupled separately? Or, can decoupling can be done in groups? say for example for TQFP-64 package

GROUP1+: pins 19(AVDD), 21(AVDD) & 22(AVDD)

GROUP1-: pins 20(AVSS) & 23(AVSS)

GROUP2+: pins 59(AVDD), 56(AVDD) & 54(AVDD1)

GROUP2-: pins 58(AVSS), 57(AVSS) & 53(AVSS1)

Note: I am using bipolar supply configuration.

over 14 years ago

0 Tom Hendrick over 14 years ago

TI__Guru**** 181641 points

Hi Horizon,

If it would be helpful to you, we can post the Gerber files for the ADS1298ECGFE-PDK - this would give you a clearer picture of how we did the layout. Grouping 'pin pairs' would be fine assuming you have a relatively clean power source - we've bumped up some capacitor values in the past and have had good success using that approach. For instance, group pin and use one 10uF bulk cap and individual 0.1uF caps. The ADS1298 was characterized with the capacitor arrangement noted in the data sheet, so I do not have any specific detail for you on what performance/specification hits you might take if you deviate from the suggested bypass arrangements.