HI5805(1999) Ver la hoja de datos (PDF) - Intersil
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HI5805 Datasheet PDF : 12 Pages
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HI5805
TABLE 1.
CODE CENTER
DESCRIPTION
DIFFERENTIAL
INPUT VOLTAGE† MSB
(USING INTERNAL
REFERENCE) D11 D10 D9
OFFSET BINARY OUTPUT CODE
LSB
D8 D7 D6 D5 D4 D3 D2 D1 D0
+Full Scale (+FS) - 1/4 LSB +1.99976V
1
1
1
1
1
1
1
1
1
1
1
1
+FS - 11/4 LSB
1.99878V
1
1
1
1
1
1
1
1
1
1
1
0
+ 3/4 LSB
732.4µV
1
0
0
0
0
0
0
0
0
0
0
0
- 1/4 LSB
-244.1µV
0
1
1
1
1
1
1
1
1
1
1
1
-FS + 13/4 LSB
-1.99829V
0
0
0
0
0
0
0
0
0
0
0
1
-Full Scale (-FS) + 3/4 LSB -1.99927V
0
0
0
0
0
0
0
0
0
0
0
0
† The voltages listed above represent the ideal center of each offset binary output code shown.
Analog Input, Differential Connection
The analog input to the HI5805 can be configured in various
ways depending on the signal source and the required level
of performance. A fully differential connection (Figure 15) will
give the best performance for the converter.
VIN
VIN+
HI5805
VDC
-VIN
VIN-
FIGURE 15. AC COUPLED DIFFERENTIAL INPUT
Since the HI5805 is powered off a single +5V supply, the
analog input must be biased so it lies within the analog input
common mode voltage range of 1.0V to 4.0V. The
performance of the ADC does not change significantly with
the value of the analog input common mode voltage.
A 2.3V DC bias voltage source, VDC, half way between the
top and bottom internal reference voltages, is made
available to the user to help simplify circuit design when
using a differential input. This low output impedance voltage
source is not designed to be a reference but makes an
excellent bias source and stays within the analog input
common mode voltage range over temperature.
The difference between the converter’s two internal voltage
references is 2V. For the AC coupled differential input,
(Figure 15), if VIN is a 2VP-P sinewave with -VIN being 180
degrees out of phase with VIN , then VIN+ is a 2VP-P
sinewave riding on a DC bias voltage equal to VDC and
VIN- is a 2VP-P sinewave riding on a DC bias voltage equal
to VDC. Consequently, the converter will be at positive full
scale, all 1s digital data output code, when the VIN+ input is
at VDC +1V and the VIN- input is at VDC -1V (VIN+ - VIN- =
2V). Conversely, the ADC will be at negative full scale, all
0s digital data output code, when the VIN+ input is equal to
VDC - 1V and VIN- is at VDC + 1V (VIN+ - VIN- = -2V). From
this, the converter is seen to have a peak-to-peak
differential analog input voltage range of ±2V.
The analog input can be DC coupled (Figure 16) as long as
the inputs are within the analog input common mode voltage
range (1.0V ≤ VDC ≤ 4.0V).
VIN
VDC
-VIN
VDC
VIN+
R
C
HI5805
VDC
R
VIN-
FIGURE 16. DC COUPLED DIFFERENTIAL INPUT
The resistors, R, in Figure 16 are not absolutely necessary
but may be used as load setting resistors. A capacitor, C,
connected from VIN+ to VIN- will help filter any high
frequency noise on the inputs, also improving performance.
Values around 20pF are sufficient and can be used on AC
coupled inputs as well. Note, however, that the value of
capacitor C chosen must take into account the highest
frequency component of the analog input signal.
Analog Input, Single-Ended Connection
The configuration shown in Figure 17 may be used with a
single ended AC coupled input. Sufficient headroom must be
provided such that the input voltage never goes above +5V
or below AGND.
124
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