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1clock cycle

ADC Input

Clock

SYNC

: -1 ns<

< tCLK/2

tCLK/2

-1ns

tCLK/2

0ns

ADS5294

SLAS776B – NOVEMBER 2011 – REVISED JULY 2012

www.ti.com

SYNCHRONIZATION PULSE

ADDR.

D15

D14

D13

D12

D11

D10

(HEX)

TP_HARD_SYNC

EN_SYNC

The SYNC pin can be used to synchronize the data output from channels within the same chip or from channels

across chips when decimation filters are used with reduced output data rate.

When the decimation filters are used (for example, the decimate by two filter is enabled), then, effectively, the

device outputs one digital code for every two analog input samples. If the SYNC function is not enabled, then the

filters are not synchronized (even within a chip) – this means that one channel may be sending out codes

corresponding to input samples N, N+1 and so on, while another may be sending out code corresponding to

N+1, N+2 and so on.

To achieve synchronization, the SYNC pulse must arrive at all the ADS529x chips at the same time instant (as

shown in the timing diagram of Figure 54

The ADS5294 generates an internal synchronization signal which is used to reset the internal clock dividers used

by the decimation filter.

Using the SYNC signal in this way ensures that all channels will output digital codes corresponding to the same

set of input samples.

SYNC Timings:

Synchronizing the filters using the SYNC pin is enabled by default. No register bits are required to be

written. Even EN_SYNC bit is not required.It is important for register bit TP_HARD_SYNC to be 0 for

this mode to work. As shown by Figure 54, the SYNC rising edge can be positioned anywhere within the

window. The width of the SYNC must be at least one clock cycle.

Figure 54. Synchronization Pulse Timing

Note that the SYNC DOES NOT synchronize the sampling instants of the ADC across chips. All channels within

a single chip sample their analog inputs simultaneously. To ensure that channels across two chips will sample

their analog inputs simultaneously, the input clock needs to be routed to both chips with identical length. This

ensuring that the input clocks arrive at both the chips at the same time. This needs to be taken care of in the

board design and routing. The SYNC pin cannot be used to synchronize the sampling instants.

In addition to the above, the SYNC can also be used to synchronize the RAMP test patterns across channels. In

order to synchronize the test patterns, TP_HARD_SYNC must be set as 1. Setting TP_HARD_SYNC =1 actually

disables the sync of the filters.

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