HI5808BIB Просмотр технического описания (PDF) - Intersil
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HI5808BIB Datasheet PDF : 12 Pages
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HI5808
TABLE 1. A/D CODE TABLE
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
+FS - 11/4 LSB
+ 3/4 LSB
- 1/4 LSB
-FS + 13/4 LSB
-Full Scale (-FS) + 3/4 LSB
+1.99976V
1.99878V
732.4µV
-244.1µV
-1.99829V
-1.99927V
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0
1
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
0
1
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.
Internal Reference Generator, VROUT and VRIN
The HI5808 has an internal reference generator, therefore, no
external reference voltage is required. VROUT must be
connected to VRIN when using the internal reference voltage.
The HI5808 can be used with an external reference. The
converter requires only one external reference voltage
connected to the VRIN pin with VROUT left open.
The HI5808 is tested with VRIN equal to 3.5V. Internal to the
converter, two reference voltages of 1.3V and 3.3V are
generated for a fully differential input signal range of ±2V.
In order to minimize overall converter noise, it is
recommended that adequate high frequency decoupling be
provided at the reference voltage input pin, VRIN.
Analog Input, Differential Connection
The analog input to the HI5808 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.
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 1’s 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 0’s 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
VIN+
HI5808
VDC
-VIN
VIN-
FIGURE 15. AC COUPLED DIFFERENTIAL INPUT
Since the HI5808 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
9
VIN
VDC
VDC
-VIN
VIN+
R
C
HI5808
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.
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