rdc19220 ETC-unknow, rdc19220 Datasheet - Page 7

• Manufacturer Part Number: rdc19220
• Description: 16-bit Monolithic Tracking Resolver Lvdt -to-digital Converters
• Manufacturer: ETC-unknow

bring it to 0 V. The output counts per second per volt input is there-
fore:
As an example:
For a 12-bit converter there are 2
1,333,333/4096 = 325 rotations per second or 333,333 counts
per second per volt.
The maximum rate capability of the RDC-19220 is set by R
When R
equates to 325 rps (rotations per second). This is the absolute
maximum rate; it is recommended to only run at <90% of this rate
(as seen in TABLE 3), therefore the minimum R v will be limited
to 55 k
50% in the 16- and 14-bit modes and 100% in the 12- and 10-bit
modes by increasing the supply current from 12 to 15 mA (by
using an R
changing R
12- and 10-bit resolution (see TABLE 4).
The maximum carrier frequency can, in the same way, increase
from: 5 to 10 kHz in the 16-bit mode, 7 to 14 kHz in the 14-bit
mode, 11 to 32 kHz in the 12-bit mode, and 20 to 40 kHz in the
10-bit mode (see TABLE 5).
The maximum tracking rate and carrier frequency for full perfor-
mance are set by the power supply current control resistor (R
per the following tables:
The carrier frequency should be 1/10, or less, of the sampling fre-
quency in order to have many samples per carrier cycle. The con-
verter will work with reduced quadrature rejection at a carrier fre-
quency up to 1/4 the sampling frequency. Carrier frequency should
be at least 3.5 times the BW in order to eliminate the chance of jitter.
REDUCED POWER SUPPLY CURRENTS
When R
supply current can be cut from 14 to 9 mA by setting R
Data Device Corporation
www.ddc-web.com
Calculate Rv for the maximum counting rate, at a VEL voltage
of 4 V.
Rv =
(333,333 x 50 pF x 1.25)
s
s
= 30 k (tracking rate is not being pushed), nominal power
The converter maximum tracking rate can be increased
= 30 k
c
s
to 20 k for 16- and 14-bit resolution or to 15 k for
= 23 k ), and by increasing the sampling rate by
(R v x 50 pF x 1.25)
1
it is nominally 1,333,333 counts/sec, which
1
= 48 k
12
or 4096 counts per rotation.
c
= 53 k .
c
s
)
.
7
TRANSFORMER ISOLATION
System requirements often include electrical isolation. There are
transformers available for reference and synchro/resolver signal
isolation. TABLE 6 includes a listing of the most common trans-
formers. The synchro/resolver transformers reduce the voltage
to 2 Vrms for a direct connection to the converter. See FIGURES
5A, 5B, 5C and 5D for transformer layouts and schematics, and
FIGURE 6 for typical connections.
DC INPUTS
As noted in TABLE 1, the RD-19220/2/4 will accept DC inputs.
• Operation from 0° to 180° or 180° to 359° only. This is due to
the possibility of a unstable false null. IE: 180° hang-up. This
180° hang-up is unstable and once the converter moves it will go
to the correct answer. In real world applications where an instan-
taneous 180° change are not possible the converter will always
be correct within 360°. The problem arises at power-up in real
systems. If the converter angle powers up at exactly 180° from
the applied input the converter will not move. This is very unlike-
ly although it is theoretically possible. This condition is most often
encountered during wrap around verification tests, simulations
or troubleshooting.
• Set the REF input to DC by tying RH to +5V and RL to GND or
-5V.
• Set the COS and SIN inputs such that max signal will be equal
to 1.8VDC. IE: For 90°, the SIN input will equal 1.8VDC. This will
keep the BW hysteresis consistant with AC operation.
• Input offsets will affect accuracy. Verify the COS and SIN inputs
do not have DC offsets. If offsets are present , a differential op
amp configuration can be used to minimize differential offset
problems.
• With DC inputs the converter BIT will remain at logic 0.
• The Bandwidth value of the converter should be chosen based
on the rate of change of the system’s input amplitude variation,
and should be large enough so to minimize it’s effect on the sys-
tem dynamics. Note that if the bandwidth is too high the system
will be more susceptible to noise.
• The accuracy of the converter using a DC input will be degrad-
ed from the rated accuracy. Consider the best case where the
input is single ended and no additional DC offsets are present on
the input converter - the accuracy will degrade by about 2 arc
minutes. IE:, If a part is rated at 2 arc minutes, a DC input will
degrade the accuracy to approximately 4 arc minutes.
RDC-19220 SERIES
R-12/05-0