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LDC1614: Non synchronous operation

Harald Hartl
Prodigy 20 points
Part Number: LDC1614


Dear Sirs,

Driving 3 LDCs with one common external 40 MHz clock and configuring them for consecutive sampling all 4 channels on each device leads to a non synchronous operation.

Following Ti´s Application Note SNOA949 the timing should be:

ts = 16*SETTLECOUNT/f_REF

tc = (16*RCOUNT+4)/f_REF

tsd = 692ns + 5/f_REF

Since I wake up all devices at the same time, using the same settings for SETTLECOUNT and RCOUNT, and the timing depends only on f_REF (which is common for all LDCs)

i do not understand why the LDCs do show different timing. Devices start sampling in a synchronous matter but due to different timing they drift against each other as time goes by.

Please let me know what is wrong in my thoughts.

Best regards,

Hary

  • 0
    TI__Genius 13650 points
    Hello Hary,
    even if SETTLECOUNT and RCOUNT are clocked by the external (shared) clock, the LDC1614 has an internal oscillator which controls the digital core of the device. This time can be slightly different from device to device and cause differences in the channel switching delay. The difference in the channel switch delay is the reason why conversion timing drifts apart between the devices in your setup.