THS1031
3-V TO 5.5-V, 10-BIT, 30 MSPS
CMOS ANALOG-TO-DIGITAL CONVERTER
SLAS242E – NOVEMBER 1999 – REVISED MARCH 2002
20
POST OFFICE BOX 655303
•
DALLAS, TEXAS 75265
PRINCIPLES OF OPERATION
onboard reference generator configuration
The onboard reference generator (ORG) can supply a supply-voltage-independent and temperature-
independent voltage on pin VREF.
External connections to REFSENSE control the ORG’s output to the VREF pin as shown in Table 2.
Table 2. Effect of REFSENSE Connection on VREF Value
REFSENSE CONNECTION
ORG OUTPUT TO VREF
REFER TO:
VREF pin
1 V
Figure 20
AGND
2 V
Figure 21
External divider junction
(1 + RA/RB)
Figure 22
AVDD
Open circuit
Figure 23
REFSENSE = AV
DD
powers the ORG down, saving power when the ORG function is not required.
If MODE = AV
DD
/2, the voltage on VREF determines the ADC reference voltages:
REFTF
+
AV
DD
2
)
VREF
2
REFBF
+
AV
DD
2
*
VREF
2
REFTF
*
REFBF
+
VREF
_
+
_
+
VBG
Internal
Reference
Buffer
Mode =
REFSENSE
0.1
µ
F
1
µ
F
Tantalum
AGND
VREF = 1 V
AVDD
2
Figure 20. 1-V VREF Using ORG
(7)
