LTC1595_15 Datasheet, PDF (11/16 Pages) Linear Technology – Serial 16-Bit Multiplying DACs

LTC1595/LTC1596/LTC1596-1
Applications Information
Bipolar (4-Quadrant Multiplying) Mode
(V_OUT = – V_REF to V_REF)
The LTC1595/LTC1596 can be used with a dual op amp
and three external resistors to provide 4-quadrant multi-
plying operation as shown in Figure 2 (last page). With a
fixed 10V reference, the circuits shown give a precision
bipolar –10V to 10V output swing. Using the LTC1596-1
will cause the power-on reset and clear pin to reset the
DAC to mid-scale (bipolar zero).
Op Amp Selection
Because of the extremely high accuracy of the 16-bit
LTC1595/LTC1596, thought should be given to op amp
selection in order to achieve the exceptional performance
of which the part is capable. Fortunately, the sensitivity of
INL and DNL to op amp offset has been greatly reduced
compared to previous generations of multiplying DACs.
Op amp offset will contribute mostly to output offset and
gain and will have minimal effect on INL and DNL. For
example, a 500µV op amp offset will cause about 0.55LSB
INL degradation and 0.15LSB DNL degradation with a 10V
full-scale range. The main effects of op amp offset will
be a degradation of zero-scale error equal to the op amp
offset, and a degradation of full-scale error equal to twice
the op amp offset. For example, the same 500µV op amp
offset will cause a 3.3LSB zero-scale error and a 6.5LSB
full-scale error with a 10V full-scale range.
Op amp input bias current (I_BIAS) contributes only a zero-
scale error equal to I_BIAS(R_FB) = I_BIAS(R_REF) = I_BIAS(7k).
Table 2 shows a selection of LTC op amps which are
suitable for use with the LTC1595/LTC1596. For a thor-
ough discussion of 16-bit DAC settling time and op amp
selection, refer to Application Note 74, “Component and
Measurement Advances Ensure 16-Bit DAC Settling Time. ”
Grounding
As with any high resolution converter, clean grounding
is important. A low impedance analog ground plane and
star grounding should be used. I_OUT2 (LTC1596) and GND
(LTC1595) must be tied to the star ground with as low a
resistance as possible.
Table 2. 16-Bit Settling Time for Various Amplifiers Driven by the LT1595 DAC. LT1468 (Shaded) Offers Fastest Settling Time While
Maintaining Accuracy Over Temperature
AMPLIFIER
CONSERVATIVE SETTLING TIME AND COMPENSATION VALUE COMMENTS
LT1001
120µs
100pF
Good Low Speed Choice
LT1007
LT1013
LT1077
19µs
75µs
200µs
100pF
150pF
100pF
I_B Gives ≈1LSB Error at 25°C
≈1LSB Error Due to V_OS Over Temperature
LT1097
120µs
75pF
Good Low Speed Choice
LT1112
120µs
100pF
Good Low Speed Choice Dual
LT1178
450µs
100pF
Low Power Dual
LT1468
2.5µs
30pF
Fastest Settling with 16-Bit Performance
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