ADS4149: ADS4149 VCM is unstable after power on

means that VCM would only used offset for INP and INM series 100 Ohm,AVDD is 1.8V

Best Regards,

Charlie

Charlie,

Is there some other load on the net that is connected to VCM? What voltage is DRVDD? Can you send your schematic?

If you have the VCM connected to both INP and INM using series 100 Ohm resistors, if you remove these resistors, what voltage do you get for VCM coming out of ADC? 

Regards,

Jim

Hi Jim,

Thank your reply! schematic as picture.

By the way,I remove series ressiters R1 and R2,ready to do it.

Besr Regards,

Charlie

Charlie,

After looking at your schematic it appears you are connecting an external 0.95VA power net to the VCM pin on the ADC. Is this correct? If so, this needs to be removed as the VCM is an output.

If this is only a net name with no connection to a power rail, what voltage is this reading with R22, R23, C32 and C141 removed?

Regards,

Jim

Hi Jim,

0.95VA is only net name

Best Regards,

Charlie

Charlie,

What voltage is this net with R22, R23, C32 and C141 removed?

Regards,

Jim

Hi Jim,

After removed R22,R23,C32,C141,VCM still unstable.(0.26~0.67V)

I have one question that VCM work whether or not it need write register command,usually,VCM should output alter power on

I found that addr=03H/Data=03H,VCM is 1.1V,voltage stabilization,I don't know why.VCM need be controlled?How to generate VCM

Figure 70. Register Address 03h  HI PERF MODE 1
Bits 7-2 Always write 0
Bits 1-0 HI PERF MODE 1: High performance mode 1
00 = Default performance after reset
01 = Do not use
10 = Do not use
11 = For best performance across sampling clock and input signal frequencies, set the HIGH PERF
MODE 1 bits

Best Regards,

Charlie