artisan DAC128V, Hardware Reference Manual

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PRODUCT OVERVIEW
Copyright 2001 2-6 DAC128V HARDWARE REFERENCE
2.7.2 Low Reference For QDAC#1
The low-side reference for the first four DAC outputs generated by QDAC#1 at U17 is
selected by placing the jumper shunt designated as H5 onto one pair of the three jumper
pads designated as J8 (ground or 0.000 V), J9 (-5.000 V), or J10 (-10.000 V). The
Operational Amplifier at U14 buffers the selection, which provides the low-side reference
voltage for QDAC#1. Using J9 or J10 is valid for any configuration. Use of J8 should
occur if, and only if, J5 is not used for the high reference for QDAC#1 (see subsection
2.7.1, above).
2.7.3 High Reference For QDAC#2
The high-side reference for the last four DAC outputs generated by QDAC#2 at U18 is
selected by placing the jumper shunt designated as H6 onto one pair of three jumper pads
designated as J11 (ground or 0.000 V), J12 (+5.000 V), or J13 (+10.000 V). The
Operational Amplifier at U15 buffers the selection, which in turn provides the high-side
reference voltage for QDAC#2. Using J12 or J13 is valid for any configuration. Use of
J11 should occur if, and only if, J14 is not used for the low reference for QDAC#2 (see
2.7.4, below).
2.7.4 Low Reference For QDAC#2
The low-side reference for the last four DAC outputs generated by QDAC#2 at U18 is
selected by placing the jumper shunt designated as H7 onto one pair of the three jumper
pads designated as J14 (ground or 0.000 V), J15 (-5.000 V), or J16 (-10.000 V). The
Operational Amplifier at U16 buffers the selection, which provides the low-side reference
voltage for QDAC#2. Using J15 or J16 is valid for any configuration. Use of J14 should
occur if, and only if, J11 is not used for the high reference for QDAC#2 (see 2.7.3,
above).
2.8 Reference Voltage Generation
The principle voltage reference is the LM369DM device at U8, and is based upon a
buried zener reference technology. Its nominal output voltage is +10.000 V, with a typical
error of ±70 ppm or ±700
µ
V. Its temperature coefficient over the product's specified
operating range is typically 5 ppm/
°
C. The multi-reference generator places a constant
load on this voltage reference, regardless of the demands of the DACs or the user’s loads
for the reference voltages supplied to the I/O connector. That load is a constant 500
µ
A.
The 0.1
µ
F capacitor at C16 provides additional noise filtering such that the noise voltage
is reduced to a typical value of 4
µ
Vrms for the spectrum of 10 Hz through 10 kHz.
This reference has a relatively low drop-out voltage ceiling which enables proper
operation even when running the DAC128V from a carrier-sourced ±12 V supply. At
25
°
C, the minimum supply voltage is about +11 V, with it increasing to about +11.5 V for
the low temperature operations of the DAC128V, and down to about +10.5 V for the high
temperature end. The reference generator’s power supply connections are identical to
those of the remaining analog circuitry, and are switched to the externally supplied power
sources when jumpered to do so (see section 2.9, below).
The resistor divider network located at U7, in conjunction with the three Operational
Amplifiers at U10, U11, and U12 derive the remaining three reference voltages (not
supplied by U8): +5.000 V, -5.000 V, and -10.000 V. U7 contains four 10 K
Ω
resistors
that have an absolute tolerance (not very important for this application) of ±0.1%, and a
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