THS1031CPWR datasheet(16/41 Pages) TI

16 / 41 page

THS1031

3-V TO 5.5-V, 10-BIT, 30 MSPS

CMOS ANALOG-TO-DIGITAL CONVERTER

SLAS242E – NOVEMBER 1999 – REVISED MARCH 2002

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

full external reference mode (mode = AGND)

Sample

and

Hold

–1/2

ADC

Core

PGA

REFTF

REFBF

AIN+

REFTS

REFBS

Internal

Reference

Buffer

Figure 12. ADC Reference Generation, MODE = AGND

When MODE is connected to AGND, the internal reference buffer is powered down, its inputs and outputs

disconnected, and REFTS and REFBS internally connected to REFTF and REFBF respectively. These nodes

are connected by the user to external sources to provide the ADC reference voltages. The internal connections

are designed for use in kelvin connection mode (Figure 14). When using external reference mode as shown

in Figure 13, REFTS must be shorted to REFTF and REFBS must be shorted to REFBF externally. The mean

of REFTF and REFBF must be equal to AVDD/2 (see Figure 13).

AIN

REFTS

REFBS

REFTF

REFBF

REFSENSE

MODE

AVDD

+FS

–FS

+ [(FS+) – (FS–)]

0.1

µF

0.1

µF

0.1

µF

AVDD

DC SOURCE =

GAIN

– [(FS+) – (FS–)]

AVDD

DC SOURCE =

GAIN

Figure 13. Full External Reference Mode

It is also possible to use REFTS and REFBS as sense lines to drive the REFTF and REFBF lines (Kelvin mode)

to overcome any voltage drops within the system (see Figure 14).

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