參數(shù)資料
型號: MAX158BEWI+T
廠商: Maxim Integrated Products
文件頁數(shù): 12/12頁
文件大?。?/td> 0K
描述: IC ADC 8BIT 8CH W/MUX&REF 28SOIC
產(chǎn)品培訓模塊: Lead (SnPb) Finish for COTS
Obsolescence Mitigation Program
標準包裝: 1,000
位數(shù): 8
采樣率(每秒): 400k
數(shù)據(jù)接口: 并聯(lián)
轉換器數(shù)目: 3
功率耗散(最大): 75mW
電壓電源: 單電源
工作溫度: -40°C ~ 85°C
安裝類型: 表面貼裝
封裝/外殼: 28-SOIC(0.295",7.50mm 寬)
供應商設備封裝: 28-SOIC W
包裝: 帶卷 (TR)
輸入數(shù)目和類型: 8 個單端,單極
Input Current
The converters’ analog inputs behave somewhat differ-
ently from conventional ADCs. The sampled data com-
parators take varying amounts of current from the input,
depending on the cycle they are in. The equivalent cir-
cuit of the converter is shown in Figure 9a. When the
conversion starts, AIN(n) is connected to the MS and
LS comparators. Thus, AIN(n) is connected to thirty-one
1pF capacitors.
To acquire the input signal in approximately 1s, the input
capacitors must charge to the input voltage through the
on-resistance of the multiplexer (about 600
) and the
comparator’s analog switches (2k
to 5k per compara-
tor). In addition, about 12pF of stray capacitance must be
charged. The input can be modeled as an equivalent RC
network shown in Figure 9b. As RS (source impedance)
increases, the capacitors take longer to charge.
Since the length of the input acquisition time is internal-
ly set, large source resistances (greater than 100
) will
cause settling errors. The output impedance of an op-
amp is its open-loop output impedance divided by the
loop gain at the frequency of interest. It is important
that the amplifier driving the converter input have suffi-
cient loop gain at approximately 1MHz to maintain low
output impedance.
Input Filtering
The transients in the analog input caused by the sam-
pled data comparators do not degrade the converter’s
performance, since the ADC does not “l(fā)ook” at the
input when these transients occur. The comparator’s
outputs track the input during the first 1s of the con-
version, and are then latched. Therefore, at least 1s
will be provided to charge the ADC’s input capaci-
tance. It is not necessary to filter these transients with
an external capacitor on the AIN terminals.
Sinusoidal Inputs
The MAX154/MAX158 can measure input signals with
slew rates as high as 157mV/s to the rated specifications.
This means that the analog input frequency can be as
high as 10kHz without the aid of an external track/hold.
The maximum sampling rate is limited by the conversion
time (typical tCRD = 2s) plus the time required between
conversions (tp = 500ns). It is calculated as:
fMAX =
1
=
1
= 400kHz
tCRD + tp
(2.0 + 0.5) s
fMAX permits a maximum sampling rate of 50kHz per
channel when using the MAX158 and 100kHz per
channel when using the MAX154. These rates are well
above the Nyquist requirement of 20kHz sampling rate
for a 10kHz input bandwidth.
MAX154/MAX158
CMOS High-Speed 8-Bit ADCs with
Multiplexer and Reference
_______________________________________________________________________________________
9
MAX154
MAX158
VIN
GND
VDD
REFOUT
VREF+
AINx(+)
AINx(-)
+5V
0.1
F47F
0.01
F
VREF-
MAX154
MAX158
VIN
GND
VDD
VREF+
AINx(+)
AINx(-)
+5V
0.1
F
47
F
VREF-
MAX154
MAX158
VIN
GND
* Current path must
still exist from
VIN(-) to Ground
VDD
VREF+
AINx(+)
AINx(-)
*
+5V
2.5V
0.1
F
47
F
VREF-
Figure 8a. Internal Reference
Figure 8b. Power Supply as Reference
Figure 8c. Inputs Not Referenced to GND
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