DAC8564IBPWR datasheet(34/46 Pages) TI

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APPLICATION INFORMATION

INTERNAL REFERENCE

Temperature Drift

DriftError=

´ 10 (ppm/ C)

REF_MAX

REF_MIN

REF

RANGE

(2)

IOV

SCLK

SYNC

REF

GND

OUT

DAC8564

LDAC

ENABLE

OUT

H/V

OUT

REF

Noise Performance

Supply Voltage

DAC8564

SBAS403A – JUNE 2007 – REVISED NOVEMBER 2007

The internal reference of the DAC8564 does not

The internal reference is designed to exhibit minimal

require

external

load

capacitor

for

stability

drift error, defined as the change in reference output

because it is stable with any capacitive load.

voltage

over

varying

temperature.

The

drift

However,

for

improved

noise

performance,

calculated using the box method described by

external load capacitor of 150nF or larger connected

Equation 2:

to the VREFH/VREFOUT output is recommended.

Figure 97 shows the typical connections required for

operation of the DAC8564 internal reference. A

supply bypass capacitor at the AVDD input is also

recommended.

Where:

VREF_MAX = maximum reference voltage observed

within temperature range TRANGE.

VREF_MIN = minimum reference voltage observed

within temperature range TRANGE.

VREF = 2.5V, target value for reference output

voltage.

The internal reference (grades C and D) features an

exceptional typical drift coefficient of 2ppm/

°C from

–40

°C to +120°C. Characterizing a large number of

units, a maximum drift coefficient of 5ppm/

°C (grades

C and D) is observed. Temperature drift results are

summarized in the Typical Characteristics.

Figure 97. Typical Connections for Operating the

Typical 0.1Hz to 10Hz voltage noise can be seen in

DAC8564 Internal Reference

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

The internal reference features an extremely low

noise spectrum at

VREFH/VREFOUT without any

dropout voltage. It can be operated with a supply of

external components is depicted in Figure 7, Internal

only 5mV above the reference output voltage in an

Reference Noise Density vs Frequency. Another

unloaded condition. For loaded conditions, refer to

noise density spectrum is also shown in Figure 7.

the Load Regulation section. The stability of the

This spectrum was obtained using a 4.8

µF load

internal reference with variations in supply voltage

capacitor

VREFH/VREFOUT for noise filtering.

(line regulation, dc PSRR) is also exceptional. Within

Internal reference noise impacts the DAC output

the specified supply voltage range of 2.7V to 5.5V,

noise; see the DAC Noise Performance section for

the variation at VREFH/VREFOUT is less than 10µV/V;

more details.

see the Typical Characteristics.

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