參數資料
型號: MAX117MJI
廠商: MAXIM INTEGRATED PRODUCTS INC
元件分類: ADC
英文描述: +3V, 400ksps, 4/8-Channel, 8-Bit ADCs with 1UA Power-Down
中文描述: 8-CH 8-BIT FLASH METHOD ADC, PARALLEL ACCESS, CDIP28
封裝: 0.600 INCH, CERDIP-28
文件頁數: 9/12頁
文件大小: 106K
代理商: MAX117MJI
that contain the conversion result (D0–D7).
INT
also
goes low after the falling edge of
RD
and is reset on the
rising edge of
RD
or
CS
. The total conversion time is
therefore: t
WR
+ t
RD
+ t
ACC1
= 1800ns.
Pipelined Operation
Besides the two standard write-read-mode options,
“pipelined” operation can be achieved by connecting
WR
and
RD
together (Figure 6). With
CS
low, driving
WR
and
RD
low initiates a conversion and concurrently
reads the result of the previous conversion.
_____________Analog Considerations
Referenc e
Figures 7a, 7b, and 7c show typical reference connec-
tions. The voltages at REF+ and REF- set the ADC’s
analog input range (Figure 10). The voltage at REF-
defines the input that produces an output code of all
zeros, and the voltage at REF+ defines the input that
produces an output code of all ones.
The internal resistance from REF+ to REF- can be as
low as 1k
, and current will flow through it even when
the MAX113/MAX117 are shut down. Figure 7d shows
how an N-channel MOSFET can be connected to REF-
to break this current path during power-down. The FET
should have an on-resistance of less than 2
with a 3V
gate drive. When REF- is switched, as in Figure 7d, a
new conversion can be initiated after waiting a time
equal to the power-up delay (t
UP
) plus the N-channel
FET’s turn-on time.
Although REF+ is frequently connected to V
DD
, the cir-
cuit of Figure 7d uses a low-current, low-dropout, 2.5V
voltage reference: the MAX872. Since the MAX872
cannot continuously furnish enough current for the ref-
erence resistance, this circuit is intended for applica-
tions where the MAX113/MAX117 are normally in stand-
by and are turned on in order to make measurements
at intervals greater than 100μs. C1 (the capacitor con-
nected to REF+) is slowly charged by the MAX872 dur-
ing the standby period, and furnishes the reference
current during the short measurement period.
The 4.7μF value of C1 ensures a voltage drop of less
than 1/2LSB when performing four to eight successive
conversions. Larger capacitors reduce the error still fur-
ther. Use ceramic or tantalum capacitors for C1.
M
+3V, 400ksps, 4/8-Channel,
8-Bit ADCs with 1μA Power-Down
_______________________________________________________________________________________
9
t
ACQ
t
INTL
RD, WR
INT
NEW DATA (N)
t
WR
t
ACQ
t
AH
t
CSH
t
IHWR
t
CSS
t
ID
OLD DATA (N - 1)
D0–D7
ADDRESS
VALID (N)
ADDRESS
VALID (N + 1)
A0–A2
CS
Figure 6. Pipelined Mode Timing (
WR
=
RD
) (Mode = 1)
REF-
MAX113
MAX117
V
DD
REF+
IN_
V
IN+
V
IN-
GND
+3V
0.1
μ
F
4.7
μ
F
Figure 7a. Power Supply as Reference
+3V
0.1μF
4
REF-
MAX113
MAX117
REF+
IN_
8
1
3
7
0.1μF
4.7μF
2
6
GND
V
DD
+2.5V
34.8k
3.01k
LM10
V
IN+
V
IN-
REF-
MAX113
MAX117
REF+
0.1μF
0.1μF
* CURRENT PATH MUST STILL
EXIST FROM V
IN-
TOGND
R*
IN_
V
IN-
V
DD
V
IN+
GND
+3V
+2.5V
0.1μF
4.7μF
Figure 7b. External Reference, 2.5V Full Scale
Figure 7c. Input Not Referenced to GND
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