DAC7678SPW datasheet(38/52 Pages) TI

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OUT

CLR

OUT

REFIN

REFOUT

DAC7678

SCL

SDA

GND

OUT

LDAC

ADDR0

OUT

1 F

100nF

Output Pin

Meter

Load

Force Line

Sense Line

Contact and

Trace Resistance

OUT

REF_MAX

REF_MIN

REF

RANGE

Drift Error =

10 (ppm/°C)

DAC7678

SBAS493A – FEBRUARY 2010 – REVISED AUGUST 2010

www.ti.com

APPLICATION INFORMATION

INTERNAL REFERENCE

Where:

The internal reference of the DAC7678 does not

VREF_MAX = maximum reference voltage observed

require

external

load

capacitor

for

stability

within temperature range TRANGE.

because it is stable with any capacitive load.

VREF_MIN = minimum reference voltage observed

However,

for

improved

noise

performance,

within temperature range TRANGE.

external load capacitor of 100nF or larger connected

VREF = 2.5V, target value for reference output

the

VREFIN/VREFOUT output is recommended.

voltage.

Figure 94 shows the typical connections required for

The

internal

reference

features

exceptional

operation of the DAC7678 internal reference. A

maximum drift coefficient of 25ppm/°C from –40°C to

supply bypass capacitor at the AVDD input is also

125°C. Temperature drift results are summarized in

recommended.

the Typical Characteristics.

Noise Performance

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

Figure 7, 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

VREFIN/VREFOUT without any

external components is depicted in Figure 6, Internal

Reference Noise Density vs Frequency. Internal

reference noise impacts the DAC output noise; see

the DAC Noise Performance section for more details.

Load Regulation

Load regulation is defined as the change in reference

output voltage as a result of changes in load current.

Figure 94. Typical Connections for Operating the

The load regulation of the internal reference is

DAC7678 Internal Reference

measured using force and sense contacts as shown

in Figure 5. The force and sense lines reduce the

impact of contact and trace resistance, resulting in

Supply Voltage

accurate

measurement

the

load

regulation

The internal reference features an extremely low

contributed

solely

the

internal

reference.

dropout voltage. It can be operated with a supply of

Measurement results are summarized in the Typical

only 5mV above the reference output voltage in an

Characteristics. Force and sense lines should be

unloaded condition. For loaded conditions, refer to

used for applications that require improved load

the Load Regulation section. The stability of the

regulation.

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 VREFIN/VREFOUT is less than 100 µV/V;

see the Typical Characteristics.

Temperature Drift

The internal reference is designed to exhibit minimal

drift error, defined as the change in reference output

voltage

over

varying

temperature.

The

drift

calculated using the box method described by

Equation 3:

Figure 95. Accurate Load Regulation of the

DAC7678 Internal Reference

(3)

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