HI-7159A 데이터 시트보기 (PDF) - Renesas Electronics
부품명
상세내역
제조사
HI-7159A Datasheet PDF : 14 Pages
| |||
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--C-----L---O----C-----K------7---1----5---9----A-----
Divider 7159 A
=
f--C-----R----Y----S----T---A----L------H----o----s---t---U----A----R-----T----
DividerHost UART
=
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
=
---------C-----------
fCLOCK
where the constant C is determined from Table 13.
TABLE 13. CONVERSION TIMES
51/2
COMP
CONVERSION TYPE
51/2
UNCOMP
41/2
COMP
41/2
UNCOMP
f = 2.4MHz
C
133ms
320,000
66.7ms
160,000
33.3ms
80,000
16.7ms
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
VREF LO
VIN HI
VIN LO
AGND
+5V
VCC
1
-5V
XTAL
27 VEE
14
2 INT OUT CINT
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
400k
CINT
0.01F
CREF
1.0F
1.2MHz
360k
0.022F
2.2F
600kHz
330k
0.047F
4.7F
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 1F
capacitor is recommended. The equation for other
frequencies is:
CREF
=
-------2---.--5---------
fCLOCK
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
=
---V----I--N----
RINT
so
RINT
=
-V----I--N---
IINT
,
where VIN = VIN HI - VIN LO = 2 x VREF .
FN2936 Rev 4.00
January 1999
Page 11 of 14
Share Link: 