HI-7159A 데이터 시트보기 (PDF) - Intersil
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HI-7159A Datasheet PDF : 14 Pages
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HI-7159A
It may also be possible to directly program the host’s serial
hardware for operation at nonstandard baud rates, allowing
HI-7159A operation at any arbitrary frequency. For example:
50Hz AC rejection requires a 2MHz clock. At this frequency
the “9600” baud rate becomes 7812.5 baud. The host’s
UART must be programmed with the proper divider to
operate at this baud rate. The data clock (see Figure 2) is
defined as 16 times the baud rate, so the data clock of this
configuration would be 125kHz. The data clock can also be
determined by dividing the oscillator (clock) frequency by the
correct divider from Table 12.
TABLE 12. CRYSTAL DIVIDER RATIOS
BAUD RATE SELECTED
CRYSTAL DIVIDER
“300”
512
“1200”
128
“9600”
16
“19200”
8
The following equation determines the divider needed to
operate the HI-7159A at any given crystal frequency:
-f-DC----i-L-v--O-i-d--C-e----Kr--(--(-7-7--1-1--5--5--9-9--A--A---)-)- = f--C---D--R---i-Yv---i-Sd----Te---rA---(-L-H---(-o-H---s-o--t--s-U--t--A-U---R-A----TR----)-T----) = Data Clock
Once determined, the new divider must be written directly to
the Host’s UART. Most PC compatibles use an 8250 UART with
a 1.8432MHz crystal, so the proper divider for the 2MHz
example given above would be 15. Again, these considerations
apply only to Serial Modes 1 and 2. Parallel and Serial Mode 0
communication rates are independent of crystal frequency.
Conversion Time
The conversion time of the HI-7159A is a function of the
crystal frequency and the type of conversion being made.
The conversion times for fCLOCK = 2.4MHz are shown in
Table 13. At other clock frequencies the times may be
calculated from the following formula:
tCONV = f--C-----L--C-O----C-----K--
where the constant C is determined from Table 13.
f = 2.4MHz
C
TABLE 13. CONVERSION TIMES
51/2
COMP
CONVERSION TYPE
51/2
UNCOMP
41/2
COMP
41/2
UNCOMP
133ms 66.7ms 33.3ms 16.7ms
320,000 160,000 80,000 40,000
Component Selection
Three external passive components must be chosen for the
HI-7159A: the integrating capacitor (CINT), the integrating
resistor (RINT), and the reference capacitor (CREF). They are
chosen based on the crystal frequency, the reference voltage
(VREF), and the desired integrating current. Figure 8 illustrates
the analog components necessary for the HI-7159A to function.
VREF HI
REF LO
VIN HI
VIN LO
AGND
+5V
VCC
1
-5V
XTAL
27 VEE
14
INT OUT CINT
2
9
10
HI-7159A
12
13
INT IN
3
BUF OUT RINT
4
CREF - GUARD
5
CREF-
6
CREF+
7
CREF
REFERENCE
CAPACITOR
GUARD
RINGS
11
26
8 CREF+ GUARD
DGND
AGND
DGND
FIGURE 8. ANALOG COMPONENTS AND INPUTS
TABLE 14. RECOMMENDED COMPONENT VALUES vs
CLOCK FREQUENCY
fCLOCK
2.4MHz
RINT
400kΩ
CINT
0.01µF
CREF
1.0µF
1.2MHz
360kΩ
0.022µF
2.2µF
600kHz
330kΩ
0.047µF
4.7µF
NOTE: CINT MUST be a high quality polypropylene capacitor or
performance may be degraded.
The reference capacitor and integrating components can
either be selected from Table 14, or calculated from the
following equations.
CREF acts as a voltage source at different times during a
conversion. Its value is determined by two considerations: it
must be small enough to be fully charged from its
discharged state at power-on; yet it also must be large
enough to supply current to the circuit during conversion
without significantly drooping from its initial value. For
2.4MHz operation, a 1µF capacitor is recommended. The
equation for other frequencies is:
CREF = -f-C-----L2---O.--5--C-----K--
The values of RINT and CINT are selected by choosing the
maximum integration current and the maximum integrator
output voltage swing. The maximum integration current and
voltage swing occurs when VIN = full scale = 2 X VREF. The
recommended integration current for the HI-7159A is
5mA - 10mA. This will help determine the value of RINT,
since:
IINT = R--V---I--IN--N--T-- so RINT = I-V-I--N-I--N-T-- ,
where VIN = VIN HI - VIN LO = 2 x VREF.
11
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