THS1030_13 Datasheet, PDF (26/39 Pages) Texas Instruments – 3-V TO 5.5-V, 10-BIT, 30MSPS CMOS ANALOG-TO-DIGITAL CONVERTER

THS1030
3ĆV TO 5.5ĆV, 10ĆBIT, 30 MSPS
CMOS ANALOGĆTOĆDIGITAL CONVERTER
SLAS243E − NOVEMBER 1999 − REVISED DECEMBER 2003
PRINCIPLES OF OPERATION
details (continued)
The ac input resistance R_AIN is then
R_AIN = dIin / dVin
= 1 / (dVin / dIin)
= 1 / (C_S x f_clk)
driving the VREF pin (differential mode)
Figure 30 shows the equivalent load on the VREF pin when driving the internal reference buffer via this pin
(MODE = AV_DD/2 and REFSENSE = AV_DD ).
AVDD
VREF
RIN
14 kΩ
AGND
REFSENSE = AVDD,
Mode = AVDD
2
+
_
AVDD + VREF
4
Figure 30. Equivalent Circuit of VREF
The current flowing into I_IN is given by
ǒ₃
IIN +
Ǔ _{VREF * AVDD}
ǒ_{4 RIN}Ǔ
(11)
Note that the actual I_IN may differ from this value by up to ±50% due to device-to-device processing variations
and allowing for operating temperature variations.
The user should ensure that VREF is driven from a low noise, low drift source, well-decoupled to analog ground
and capable of driving I_IN.
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