DRC1746_15 Datasheet, PDF (6/8 Pages) Analog Devices – HIGH POWER OUTPUT HYBRID DIGITAL TO SYNCHRO RESOLVER CONVERTERS

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Page 15
DRC1745/DRC1746
SIN SENSE
SIN
In the case of an inductive load under similar conditions, 500
milliohms would produce the same error.
DRC174511748
SIGGND
LOA!>
e STM1683
T"""SFOAME"
Using the remote sense facility as shown in Figure 7 will half
this error or allow twice the distance to be driven for the same
additional error.
If the remote sense is not used, then "COS SENSE" should be
joined to "COS" and "SIN SENSE" should be joined to "SIN"
at the PCB edge connector.
COS
c:os SENSE
NOTE, THE "EMOTE SENSE E,ooLiTY 1$ SHOWN .. THE ABOVE DIAGRAM.
C, IS THE TUNING CAPACITOIO.
Figure 6. Incorporating a Resistor in the Tuning CircUIt
Note also that when output transformers are used with the
converters they should be regarded as the load and the remote
sense wires taken to the transformer primary inputs.
Sense wiring may employ minimum wire gauge; it does not
carry load current.
Care must be taken in tolerancing the tuning capacitors when
OBSOLETE ^{using secondary tuning since the significant output impedance}
of typical output transformers can give rise to capacitive balance
related angular errors.
The use of these precaurions enables the converters to drive
fully tuned 2VA loads.
For more informarion please send for relevant application note.
SHORT CIRCUIT PROTECTION
The short circuit current limit is set at <600mA maximum.
Under short circuit or excessive current conditions, the overcurrent
protection circuit will trip and reduce the output current to
zero. In order to minimize power dissipated under current limit
conditions the device goes into a switching mode, testing the
load condition at a high frequency.
When the overload conditions are removed, the output is auto-
matically restored to its normal condition.
VECTOR ERRORS AND EFFECTS
cas
DflC1745/1746 SIN
COS SENSE
lOAD
CDS GND
SIN GOO
Figure 7. Using the Remote Sense Facility
The ground returns from the load should be individually wired
and star-poim connected at the converter's signal ground. Any
common resistance in the signal returns will produce errors due
to the summation of the sin and cos outputs. With a resistive
load of 33 ohms at lAVA, and at the worst angles of 0 and 90°,
there will be 1.3 arc-minutes of extra error introduced for every
12.5 milliohms of common signal return resistance.
TRANSZORBTM OUTPUT PROTECTION
The error law used in the converter has no inherent vector
As an option, the outpUt stages of the converter can be internally
errors. The figure of 0.03% given in the specification is accounted
for by tolerances in some of the thin-film resistor netWorks used
in the converter.
fined with TransZorb protection. This form of protection can
be advantageous and significantly increase the Mean Time BetWeen
Failures when driving inductive loads. The TransZorbs, which
These very low vector errors make the conveners ideally suited
for applications such as displays, or metal cutting control where
perfect circles have to be generated.
are effectively back to back zener diodes, give full protection
against transient voltages generated by an inductive load in
response to an abrupt change in load current. Such a change
can occur at switch off or as a consequence of external power
BANDWIDTH
The open loop gain bandwidth product of the DRC1745 and
DRC1746hasbeentailoredto ensurethat the fullangularaccuracy
is maintained over the broadband range of dc to 2.6kHz. This
results in a closed loop bandwidth of 300kHz.
supply fault conditions. The TransZorbs are rated to give pro.
tection against worst case transients corresponding to an instan.
taneous interruption of the converter when driving into a full
2VA pure inducrive load with the converter operating at the
maximum case temperature of 125°C.
Figure 8 shows a simplifieddiagramof the converter output
REMOTE SENSE FACILITY AND ADDITIONAL
OUTPUT ERRORS
.
stage indicating the action of the TransZorb when the 15 volt
supply is interrupted.
A remote sense facility is included in the DRC1745 and DRC1746 It is important to appreciate that destructively high voltages can
in order to reduce errors caused by the output interconnection
be generated (given by E = Ldi/dt) even for modest inductive
wiring when driving large loads. The magnitude of this error is
illustrated by tWo examples below.
.
loading, under many fault conditions, since diJdt is effectively
uncontrolled. Internal TransZorb protection is a bener and
Assume that the sine and cosine load impedances are perfectly
matched and the sine output wiring resistance matches the
cosine output wiring resistance to within 5%. Then for a resistive
load of lAVA (33 ohms) and the worst case angle of 45 degrees,
there will be 1.3 arc-minUtes of extra error introduced for every
250 milliohms of resistance for the loop wiring betWeen the
more direct solution to the problem than employing a pair of
reverse biased diodes to the output stage power supplies. This is
because the transient is contained within the specific load disturbed
and does not escape into the power supply wiring and hence
cause possible damage to other equipments and devices. A domino
effect of catastrophic failure is therefore prevented.
converter and the load. (AWG2Z "" 17m!l/ft, 1 oz PCB copper
= 4OOmfl/ft.)
Tr~rb is a registt:M trademark of General Semiconductor
ladustries, la".
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REV. A