DM8148 EVB VTT pull up capacitor

daniel sun

Dear Sir

Please check VTT terminal side In DM8148 EVB DDR address line
, why we need to tie these extra 0.1uf to VDDQ_1.5V between VTT rail ?

over 13 years ago

0 Steve Clynes over 13 years ago

TI__Mastermind 43875 points

These capacitors are there to ensure that transitions on the address lines do not cause noise on the VTT voltage.

BR,

Steve

0 David Liang over 12 years ago in reply to Steve Clynes

Prodigy 10 points

Dear Sir:

Why not connect these capacitors to GND for noise issue?Thanks.

David

0 Biser Gatchev-XID over 12 years ago in reply to David Liang

TI__Guru**** 393215 points

Hi David,

please check this thread for explanation: https://e2e.ti.com/support/dsp/davinci_digital_media_processors/int-dm814x/f/720/t/203543.aspx?Redirected=true

0 Steve Clynes over 12 years ago in reply to Biser Gatchev-XID

TI__Mastermind 43875 points

For AC signals it does not matter whether the capacitor is connected to GND or VCC since, for AC signals, VCC and GND provide the same impedance.

It does not really have anything to do with sourcing the voltage hence needing VCC, it is really about impedance. The resistors source the charge but the capacitors store it.

BR,

Steve

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DM8148 EVB VTT pull up capacitor