DAC7562T Datasheet, PDF (40/60 Pages) Texas Instruments – Internal Reference

DAC7562T, DAC7563T, DAC8162T
DAC8163T, DAC8562T, DAC8563T
SLASE61A – SEPTEMBER 2015 – REVISED OCTOBER 2015
www.ti.com
Application Information (continued)
9.1.1.3 Noise Performance
Typical 0.1-Hz to 10-Hz voltage noise and noise spectral density performance are listed in the Electrical
Characteristics. Additional filtering can be used to improve output noise levels, although care should be taken to
ensure the output impedance does not degrade the ac performance. The output noise spectrum at the
V_REFIN/V_REFOUT pin, both unloaded and with an external 4.7-µF load capacitor, is shown in Figure 6. Internal
reference noise impacts the DAC output noise when the internal reference is used.
9.1.1.4 Load Regulation
Load regulation is defined as the change in reference output voltage as a result of changes in load current. The
load regulation of the internal reference is measured using force and sense contacts as shown in Figure 95. The
force and sense lines reduce the impact of contact and trace resistance, resulting in accurate measurement of
the load regulation contributed solely by the internal reference. Measurement results are shown in Figure 4.
Force and sense lines should be used for applications that require improved load regulation.
Output Pin
Contact and
Trace Resistance
V_OUT
Sense Line
Meter
Force Line
I_L
Load
Figure 95. Accurate Load Regulation of the DAC756xT, DAC816xT, and DAC856xT Internal Reference
9.1.1.4.1 Long-Term Stability
Long-term stability or aging refers to the change of the output voltage of a reference over a period of months or
years. This effect lessens as time progresses. The typical drift value for the internal reference is listed in the
Electrical Charateristics and measurement results are shown in Figure 5. This parameter is characterized by
powering up multiple devices and measuring them at regular intervals.
9.1.1.5 Thermal Hysteresis
Thermal hysteresis for a reference is defined as the change in output voltage after operating the device at 25°C,
cycling the device through the operating temperature range, and returning to 25°C. Hysteresis is expressed by
Equation 4:
V_HYST =
é
ê
V_{REF_PRE}
-
V_{REF_POST}
ù
ú
êë
V_{REF_NOM}
úû
´ 10⁶(ppm/°C)
(4)
where:
V_HYST = thermal hysteresis.
V_{REF_PRE} = output voltage measured at 25°C pre-temperature cycling.
V_{REF_POST} = output voltage measured after the device cycles through the temperature range of –40°C to
aaa 125°C, and returns to 25°C.
V_{REF_NOM} = 2.5 V, target value for reference output voltage.
9.1.2 DAC Noise Performance
Output noise spectral density at the V_OUT-n pin versus frequency is depicted in Figure 45 and Figure 46 for full-
scale, mid-scale, and zero-scale input codes. The typical noise density for mid-scale code is 90 nV/√Hz at 1 kHz.
High-frequency noise can be improved by filtering the reference noise. Integrated output noise between 0.1 Hz
and 10 Hz is close to 2.5 µV_PP (mid-scale), as shown in Figure 47.
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