DAC7631 datasheet(12/24 Pages) TI2

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DAC7631

ANALOG OUTPUTS

When VSS = –5V (dual supply operation), the output ampli-

fier can swing to within 2.25V of the supply rails, guaran-

teed over the –40

°C to +85°C temperature range. When

VSS = 0V (single-supply operation), and with RLOAD also

connected to ground, the output can swing to ground. Care

must also be taken when measuring the zero-scale error

when VSS = 0V. Since the output voltage cannot swing

below ground, the output voltage may not change for the

first few digital input codes (0000H, 0001H, 0002H, etc.) if

the output amplifier has a negative offset. At the negative

limit of –2mV, the first specified output starts at code 0040H.

Due to the high accuracy of these D/A converters, system

design problems such as grounding and contact resistance

become very important. A 16-bit converter with a 2.5V full-

scale range has a 1LSB value of 38

µV. With a load current

of 1mA, series wiring and connector resistance of only

40m

Ω (R

W2) will cause a voltage drop of 40µV, as shown in

Figure 4. To understand what this means in terms of a

system layout, the resistivity of a typical 1 ounce copper-

clad printed circuit board is 1/2 m

Ω per square. For a 1mA

FIGURE 2. Basic Single-Supply Operation.

FIGURE 3. Basic Dual-Supply Operation.

load, a 10 milli-inch wide printed circuit conductor 600

milli-inches long will result in a voltage drop of 30

µV.

The DAC7631 offers a force and sense output configuration

for the high open-loop gain output amplifier. This feature

allows the loop around the output amplifier to be closed at

the load (as shown in Figure 4), thus ensuring an accurate

output voltage.

REFERENCE INPUTS

The reference inputs, VREFL and VREFH, can be any voltage

between VSS + 2.5V and VCC – 2.5V, provided that VREFH

is at least 1.25V greater than VREFL. The minimum output of

each DAC is equal to VREFL plus a small offset voltage

(essentially, the offset of the output op amp). The maximum

output is equal to VREFH plus a similar offset voltage. Note

that VSS (the negative power supply) must either be

connected to ground or must be in the range of –4.75V to

–5.25V. The voltage on VSS sets several bias points within

the converter. If VSS is not in one of these two configura-

tions, the bias values may be in error and proper operation

of the device is not guaranteed.

Reset DAC Registers

Chip Select

DGND

SDI

CLK

AGND

DAC7631

REFH Sense

REFH

REFL Sense

REFL

SDO

OUT Sense

OUT

RSTSEL

RST

LOAD

Serial Data In

Clock

Load DAC Registers

Load

LDAC

Serial Data Out

0.1

µF1µF

+5V

+2.5000V

0V to +2.5V

Reset DAC Registers

Chip Select

DGND

SDI

CLK

AGND

DAC7631

REFH Sense

REFH

REFL Sense

REFL

SDO

OUT Sense

OUT

RSTSEL

RST

Serial Data In

Clock

Load DAC Registers

Load

LDAC

LOAD

Serial Data Out

0.1

µF

0.1

µF1µF

+5V

µF

0.1

µF1µF

+5V

–5V

+2.5000V

–2.5000V

–2.5V to +2.5V

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