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RDC19220 Datasheet(PDF) 6 Page - List of Unclassifed Manufacturers

Part No. RDC19220
Description  16-BIT MONOLITHIC TRACKING RESOLVER (LVDT)-TO-DIGITAL CONVERTERS
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Maker  ETC1 [List of Unclassifed Manufacturers]
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4) The BIT output which is active low is activated by an error of
approximately 100 LSBs. During normal operation for step
inputs or on power up, a large error can exist.
5) This device has several high impedance amplifier inputs (+C,
-C, +S, -S, -VCO and -VSUM). These nodes are sensitive to
noise and coupling components should be connected as
close as possible.
6) Setup of bandwidth and velocity scaling for the optimized crit-
ically damped case should proceed as follows:
Note: DDC has software available to perform the previous calcu-
lations. Contact DDC to request software or visit our web-
site at www.ddc-web.com to download software.
- Select the desired f BW (closed loop) based on overall
system dynamics.
- Select f carrier
≥ 3.5f BW
- Select the applications tracking rate (in accordance with TABLE 3),
and use appropriate values for R SET and R CLK
- Compute Rv =
- Compute CBW (pF) =
- Where Fs = 67 kHz for R CLK = 30 K
100 kHz for R CLK = 20 K
125 kHz for R CLK = 15 K
- Compute RB =
- Compute
3.2 x Fs (Hz) x 108
Rv x (f BW)2
Full Scale Velocity Voltage
Tracking Rate (rps) x 2 resolution x 50 pF x 1.25 V
0.9
CBW x f BW
CBW
10
As an example:
Calculate component values for a 16-bit converter with 100Hz
bandwidth, a tracking rate of 10RPS and a full scale velocity
of 4 volts.
- Rv =
= 97655
- Compute CBW (pF) =
= 21955 pF
- Compute RB =
= 410 k
4 V
10 rps x 216 x 50 pF x 1.25 V
0.9
21955 x 10 -12 x 100 Hz
3.2 x 67 kHz x 108
97655 x 100 Hz2
6
Data Device Corporation
www.ddc-web.com
RDC-19220 SERIES
R-12/05-0
7) Selecting a fBW that is too low relative to the maximum appli-
cation tracking rate can create a spin-around condition in
which the converter never settles. The relationship to insure
against
spin-around
is
as
follows
(TABLE
3):
8) For RDC-19222 & RDC-19224; package’s only.
This version is capable of +5V only operation. It accomplish-
es this with a charge pump technique that inverts the +5V
supply for use as -5V, hence the +5V supply current doubles.
The built-in -5 V inverter can be used by connecting pin 2 to
26, pin 17 to 22, a 10 µF/10 Vdc capacitor from pin 23 (nega-
tive terminal) to pin 25 (positive terminal), and a 47 µF/10 Vdc
capacitor from -5 V to GND. The current drain from the +5 V
supply doubles. No external -5 V supply is needed (SEE FIG-
URE 5).
When using the -5 V inverter, the max. tracking rate should be
scaled for a velocity output of 3.5 V max. Use the following equa-
tion to determine tracking rate used in the formula on page 5:
TR (required) x (4.0) = Tracking rate used in calculation
(3.5)
Note: When using the highest BW and Tracking Rates, using
the -5 V inverter is not recommended.
HIGHER TRACKING RATES AND CARRIER FREQUENCIES
Tracking rate (nominally 4 V) is limited by two factors: velocity
voltage saturation and maximum internal clock rate (nominally
1,333,333 Hz). An understanding of their interaction is essential
to extending performance.
The General Setup Considerations section makes note of the
selection of Rv for the desired velocity scaling. Rv is the input resis-
RDC-19222/4
10uF
+CAP
-CAP
.01uF
(-5c)
-5V
.01uF
(+5c) +5V
47uF
47uF
+
+
FIGURE 5. -5V BUILT-IN INVERTER
TABLE 3. TRACKING/BW RELATIONSHIP
RPS (MAX)/BW
RESOLUTION
1
10
0.45
12
0.25
14
0.125
16


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