THS1040 Datasheet, PDF (19/32 Pages) Texas Instruments – 3-V, 10-BIT , 40-MSPS CMOS ANALOG TO DIGITAL CONVERTER

THS1040
SLAS290C − OCTOBER 2001 − REVISED OCTOBER 2004
PRINCIPLES OF OPERATION
onboard reference generator configuration
The internal bandgap reference A1 can provide a supply-voltage-independent and temperature-independent
voltage on pin VREF.
External connections to REFSENSE control A1’s output to the VREF pin as shown in Table 1.
Table 1. Effect of REFSENSE Connection on VREF Value
REFSENSE CONNECTION
VREF pin
AGND
External divider junction
AVDD
A1 OUTPUT TO VREF
0.5 V
1V
(1 + Ra/Rb)/2 V
Open circuit
SEE:
Figure 25
Figure 26
Figure 27
Figure 28
REFSENSE = AV_DD powers the internal bandgap reference A1 down, saving power when A1 is not required.
If MODE is connected to AV_DD or AV_DD/2, then the voltage at VREF determines the ADC reference voltages:
REFT
+
AVDD
2
)
VREF
2
(9)
REFB +
AVDD
2
*
VREF
2
(10)
REFT–REFB + VREF
(11)
VBG
+
_
ADC
References
Buffer A2
MODE =
AVDD
2
or AVDD
+
VREF = 0.5 V
_
REFSENSE
0.1 µF 1 µF
AGND
Figure 25. 0.5-V VREF Using the Internal Bandgap Reference A1
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