AD7380 datasheet(20/31 Pages) AD

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AD7389-4

Data Sheet

Rev. 0 | Page 20 of 31

INTERNAL REFERENCE

The AD7389-uses a low noise, low drift (10 ppm/°C) 2.5 V

buffered internal reference during conversion. The internal

2.5 V reference of the AD7389-4 allows excellent performance

with typically 90.5 dB of SNR. When using the internal 2.5 V

reference for an external circuit, the internal 2.5 V reference can

be accessed via the REFOUT pin. It is recommended to add a

buffer, such as the ADA4807-2, when using the 2.5 V internal

reference as a source for a common-mode voltage (VCM).

Connecting a 1 µF capacitor to the REFOUT pin is

recommended.

SOFTWARE RESET

The AD7389-4 has two reset modes: a soft reset and a hard

reset. A reset is initiated by writing to the reset bits in the

Configuration 2 register.

A soft reset maintains the contents of the configurable registers

but refreshes the interface and the ADC blocks. Any internal

state machines are reinitialized, and the oversampling block

and FIFO are flushed. The alert indication register is cleared.

The reference and LDO regulator remain powered.

tRESET

SDI

SOFTWARE RESET

Figure 33. Software Reset Operation

A hard reset, in addition to the blocks reset by a soft reset,

resets all user registers to the default status, resets the reference

buffer, and resets the internal oscillator block.

DIAGNOSTIC SELF TEST

The AD7389-4 runs a diagnostic self test after a POR or after a

software hard reset to ensure the correct configuration is

loaded into the device.

The result of the self test is displayed in the SETUP_F bit in the

alert indication register. If the SETUP_F bit is set to Logic 1, the

diagnostic self test has failed. If the test fails, perform a software

hard reset to reset the AD7389-4 registers to the default status.

SHUTDOWN

NORMAL

SDI

tSTARTUP

SHUTDOWN MODE

NORMAL MODE

ACCURATE CONVERSION

Figure 34. Shutdown Mode Operation

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