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ADS8370

REFM

REFIN

REFOUT

AGND

0.1 mF

1 mF

ADS8370

REFM

REFIN

REFOUT

AGND

0.1 mF

1 mF

REF3240

22 mF

50 W

AGND

ADS8370

AGND

+VA

_

+

53 W

53 W

40 pF

40 pF

+IN

−IN

AGND

ANALOG INPUT

ADS8370

SLAS450 – JUNE 2005

PRINCIPLES OF OPERATION (continued)

Figure 48. ADS8370 Using Internal Reference

The REFIN pin is also internally buffered. This eliminates the need to put a high bandwidth buffer on the board

to drive the ADC reference and saves system area and power. When an external reference is used, the

reference must be of low noise, which may be achieved by the addition of bypass capacitors from the REFIN pin

to the REFM pin. See Figure 49 for operation of the ADS8370 with an external reference. REFM must be

connected to the analog ground plane.

Figure 49. ADS8370 Using External Reference

Figure 50. Simplified Analog Input

When the converter enters hold mode, the voltage difference between the +IN and –IN inputs is captured on the

internal capacitor array. The +IN input has a range of –0.2 V to (+VREF + 0.2 V), whereas the –IN input has a

range of –0.2 V to +0.2 V. The input span [+IN – (–IN)] is limited from 0 V to VREF.

The input current on the analog inputs depends upon throughput and the frequency content of the analog input

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