参数资料
型号: TLV5580IPWRG4
厂商: TEXAS INSTRUMENTS INC
元件分类: ADC
英文描述: 1-CH 8-BIT PROPRIETARY METHOD ADC, PARALLEL ACCESS, PDSO28
封装: GREEN, PLASTIC, TSSOP-28
文件页数: 7/36页
文件大小: 478K
代理商: TLV5580IPWRG4
TLV5580
8BIT, 80 MSPS LOW POWER A/D CONVERTER
SLAS205B DECEMBER 1998 REVISED OCTOBER 2003
www.ti.com
15
PRINCIPLE OF OPERATION
DC COUPLED INPUT
_
+
AVDD
VIN
REFTI
REFTO
REFBI
REFBO
AIN
TLV5580
_
+
VREF
VIN
REFTI
REFTO
REFBI
REFBO
AIN
TLV5580
RIN
R1
RIN
R2
(a)
(b)
Figure 13. DC-Coupled Input Circuit
For dc-coupled systems an op amp can level-shift a ground-referenced input signal. A circuit as shown in
Figure 13(a) is acceptable. Alternatively, the user might want a bipolar shift together with the bottom reference
voltage as seen in Figure 13(b). In this case the AIN voltage is given by:
AIN
+ 2
R
2 ÷
R
1 )
R
2
V
REF
–V
IN
AC COUPLED INPUT
VIN
AIN
TLV5580
R1
R2
VBIAS
+
C1
C2
Figure 14. AC-Coupled Input Circuit
For many applications, especially in single supply operation, ac coupling offers a convenient way for biasing
the analog input signal at the proper signal range. Figure 14 shows a typical configuration. To maintain the
outlined specifications, the component values need to be carefully selected. The most important issue is the
positioning of the 3 dB high-pass corner point f3 dB, which is a function of R2 and the parallel combination of
C1 and C2, called Ceq. This is given by the following equation:
f
–3 dB +
1
÷ 2π xR
2
xCeq
where Ceq is the parallel combination of C1 and C2.
Since C1 is typically a large electrolytic or tantalum capacitor, the impedance becomes inductive at higher
frequencies. Adding a small ceramic or polystyrene capacitor, C2 of approximately 0.01
F, which is not
inductive within the frequency range of interest, maintains low impedance. If the minimum expected input signal
frequency is 20 kHz, and R2 equals 1 k
and R1 equals 50 , the parallel capacitance of C1 and C2 must be
a minimum of 8 nF to avoid attenuating signals close to 20 kHz.
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