THS1031
3-V TO 5.5-V, 10-BIT, 30 MSPS
CMOS ANALOG-TO-DIGITAL CONVERTER
SLAS242E – NOVEMBER 1999 – REVISED MARCH 2002
16
POST OFFICE BOX 655303
•
DALLAS, TEXAS 75265
PRINCIPLES OF OPERATION
full external reference mode (mode = AGND)
Sample
and
Hold
1
–1/2
–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 AV
DD
/2 (see Figure 13).
AIN
REFTS
REFBS
REFTF
REFBF
REFSENSE
MODE
AVDD
+FS
–FS
+ [(FS+) – (FS–)]
×
0.1
µ
F
10
µ
F
0.1
µ
F
0.1
µ
F
AVDD
2
AVDD
2
DC SOURCE =
GAIN
2
– [(FS+) – (FS–)]
×
AVDD
2
DC SOURCE =
GAIN
2
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).
