Datasheet

1
2
3
4
8
7
6
5
GND
D
IN
SCLK
SYNC
V
DD
V
REF
V
FB
V
OUT
V
DD
V
REF
DAC8560
1 Fm
150nF
Drift Error +
ǒ
V
REF_MAX
* V
REF_MIN
V
REF
T
RANGE
Ǔ
10
6
(ppmń°C)
OutputPin
Meter
Load
ForceLine
SenseLine
Contactand
TraceResistance
I
L
V
OUT
DAC8560
SLAS464B –DECEMBER 2006–REVISED NOVEMBER 2011 www.ti.com
APPLICATION INFORMATION
INTERNAL REFERENCE
The DAC8560 internal reference (grades C and D)
The DAC8560 internal reference does not require an features an exceptional typical drift coefficient of
external load capacitor for stability because it is 2ppm/°C from –40°C to +120°C. Characterizing a
stable with any capacitive load. However, for large number of units, a maximum drift coefficient of
improved noise performance, an external load 5ppm/°C (grades C and D) is observed. Temperature
capacitor of 150nF or larger connected to the V
REF
drift results are summarized in the Typical
output is recommended. Figure 67 shows the typical Characteristics.
connections required for operation of the DAC8560
internal reference. A supply bypass capacitor at the Noise Performance
V
DD
input is also recommended.
Typical 0.1Hz to 10Hz voltage noise can be seen in
Figure 8, Internal Reference Noise. 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 V
REF
without any external
components is depicted in Figure 7, Internal
Reference Noise Density vs Frequency. Another
noise density spectrum is also shown in Figure 7,
which was obtained using a 4μF load capacitor at
V
REF
for noise filtering. Internal reference noise
impacts the DAC output noise; see the DAC Noise
Figure 67. Typical Connections for Operating the
DAC8560 Internal Reference Performance section for more details.
Load Regulation
Supply Voltage
Load regulation is defined as the change in reference
The DAC8560 internal reference features an
output voltage as a result of changes in load current.
extremely low dropout voltage. It can be operated
The load regulation of the DAC8560 internal
with a supply of only 5mV above the reference output
reference is measured using force and sense
voltage in an unloaded condition. For loaded
contacts as pictured in Figure 68. The force and
conditions, refer to the Load Regulation section. The
sense lines reduce the impact of contact and trace
stability of the DAC8560 internal reference with
resistance, resulting in accurate measurement of the
variations in supply voltage (line regulation, DC
load regulation contributed solely by the DAC8560
PSRR) is also exceptional. Within the specified
internal reference. Measurement results are
supply voltage range of 2.7V to 5.5V, the variation at
summarized in the Typical Characteristics. Force and
V
REF
is smaller than 10μV/V; see the Typical
sense lines should be used for applications requiring
Characteristics.
improved load regulation.
Temperature Drift
The DAC8560 internal reference is designed to
exhibit minimal drift error, defined as the change in
reference output voltage over varying temperature.
The drift is calculated using the box method, which is
described by Equation 2:
(2)
Where:
V
REF_MAX
= maximum reference voltage observed
within temperature range T
RANGE
.
Figure 68. Accurate Load Regulation of the
V
REF_MIN
= minimum reference voltage observed
DAC8560 Internal Reference
within temperature range T
RANGE
.
V
REF
= 2.5V, target value for reference output
voltage.
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