24-Bit, 4-Channel, Simultaneous-Sampling,

Cascadable, Sigma-Delta ADC

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27

Applications Information

Multiple Device Synchronization

Synchronizing Multiple Devices

Using a Shared XIN Clock Source

To synchronize multiple devices sharing a single XIN

clock source, transition the SYNC input that is shared

by all devices high to low. When an external sync

source is not available, connect DRDYOUT of one

MAX11040 to the SYNC input of all devices in the

chain. The MAX11040 ignores any SYNC transitions

applied during the power-on reset.

Synchronizing Multiple Devices

Using Independent XIN Clock Sources

If it is undesirable to connect the XIN clock sources

together, due to EMI or other reasons, use DRDYIN,

DRDYOUT, and SYNC to align the conversion timing as

shown in Figure 17. This minimizes the effects of drift

between the clock sources by resynchronizing after

each conversion when DRDYOUT transitions low. In

this configuration, the maximum correction caused by a

SYNC edge is one XIN clock cycle.

The resulting sampling rate is determined by the sampling

frequency of the device with the slowest clock source,

plus the delay through the DRDYIN to DRDYOUT chain

between this slowest device and the end of the chain.

Synchronizing Multiple Devices

to an Independent Clock Source

To periodically synchronize multiple devices to an inde-

pendent timing source, connect the timing source to

the SYNC inputs of the devices. If minimal jitter is

important in the application, program the MAX11040’s

to a frequency slightly slower than the external frequen-

cy, such that SYNC falling edges only occur a short

time after the DRDYOUT signals.

MAX11040

SYNC

CS

SCLK

DIN

CASCIN

DRDYIN

DRDYOUT

FAULT

OVRFLW

DOUT

XIN

DEVICE n+1

DEVICE 0

DEVICE n

MAX11040

SYNC

CS

SCLK

DIN

CASCIN

DRDYIN

CASCOUT

FAULT

OVRFLW

DOUT

XIN

XOUT CLKOUT

MAX11040

SYNC

CS

SCLK

DIN

CASCIN

DRDYIN

CASCOUT

DRDYOUT

FAULT

OVRFLW

DOUT

XIN

XOUT

XOUT

DRDYOUT

DSP OR

MICROCONTROLLER

CASCADE UP TO 8 DEVICES

Figure 17. One Crystal per MAX11040 and All SYNC Inputs Driven by DRDYOUT of the Last Device in the Chain