Datasheet

DriftError=
´ 10 (ppm/ C)°
6
V V-
REF_MAX REF_MIN
V T´
REF RANGE
5
6
7
8
12
11
10
9
V D
OUT
V F
OUT
V H
OUT
CLR
V C
OUT
V E
OUT
V G
OUT
V IN/V OUT
REF REF
AV
DD
DAC7568
DAC8168
DAC8568
1
2
3
4
16
15
14
13
SCLK
D
IN
GND
V B
OUT
LDAC
SYNC
AV
DD
V A
OUT
1 Fm
150nF
DAC7568
DAC8168
DAC8568
SBAS430D –JANUARY 2009–REVISED MAY 2012 www.ti.com
APPLICATION INFORMATION
INTERNAL REFERENCE
Temperature Drift
The internal reference of the DAC7568, DAC8168,
The internal reference is designed to exhibit minimal
and DAC8568 does not require an external load
drift error, defined as the change in reference output
capacitor for stability because it is stable with any
voltage over varying temperature. The drift is
capacitive load. However, for improved noise
calculated using the box method described by
performance, an external load capacitor of 150nF or
Equation 2:
larger connected to the V
REF
H/V
REF
OUT output is
recommended. Figure 125 shows the typical
connections required for operation of the DAC7568,
DAC8168, and DAC8568 internal reference. A supply
(2)
bypass capacitor at the AV
DD
input is also
recommended.
Where:
V
REF_MAX
= maximum reference voltage observed
within temperature range T
RANGE
.
V
REF_MIN
= minimum reference voltage observed
within temperature range T
RANGE
.
V
REF
= 2.5V, target value for reference output
voltage.
The internal reference (grade C only) features an
exceptional typical drift coefficient of 2ppm/°C from
–40°C to +125°C. Characterizing a large number of
units, a maximum drift coefficient of 5ppm/°C (grade
C only) is observed. Temperature drift results are
summarized in the Typical Characteristics.
Noise Performance
Typical 0.1Hz to 10Hz voltage noise can be seen in
Figure 9, Internal Reference Noise. Additional filtering
can be used to improve output noise levels, although
care should be taken to ensure the output impedance
Figure 125. Typical Connections for Operating
the DAC7568/DAC8168/DAC8568 Internal
does not degrade the ac performance. The output
Reference (16-Pin Version Shown)
noise spectrum at V
REF
H/V
REF
OUT without any
external components is depicted in Figure 8, Internal
Reference Noise Density vs Frequency. A second
Supply Voltage
noise density spectrum is also shown in Figure 8.
This spectrum was obtained using a 4.8μF load
The internal reference features an extremely low
capacitor at V
REF
H/V
REF
OUT for noise filtering.
dropout voltage. It can be operated with a supply of
Internal reference noise impacts the DAC output
only 5mV above the reference output voltage in an
noise; see the DAC Noise Performance section for
unloaded condition. For loaded conditions, refer to
more details.
the Load Regulation section. The stability of the
internal reference with variations in supply voltage
(line regulation, dc PSRR) is also exceptional. Within
the specified supply voltage range of 2.7V to 5.5V,
the variation at V
REF
H/V
REF
OUT is less than 10μV/V;
see the Typical Characteristics.
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