Single-Supply Linearity

As with any amplifier, the MAX504/MAX515’s output

buffer offset can be positive or negative. When the off-

set is positive, it is easily accounted for (Figure 10).

However, when the offset is negative, the buffer output

cannot follow linearly when there is no negative supply.

In that case, the amplifier output (VOUT) remains at

ground until the DAC voltage is sufficient to overcome

the offset and the output becomes positive.

Normally, linearity is measured after accounting for

zero error and gain error. Since, in single-supply opera-

tion, the actual value of a negative offset is unknown, it

cannot be accounted for during test. Additionally, the

output buffer amplifier exhibits a nonlinearity near-zero

output when operating with a single supply. To account

for this nonlinearity in the MAX504/MAX515, linearity

and gain error are measured from code 3 to code

1023. The output buffer’s offset and nonlinearity do not

affect monotonicity, and these DACs are guaranteed

monotonic starting with code zero. In dual-supply oper-

ation, linearity and gain error are measured from code

0 to 1023.

Power-Supply Bypassing and

Ground Management

Best system performance is obtained with printed cir-

cuit boards that use separate analog and digital

ground planes. Wire-wrap boards are not recommend-

ed. The two ground planes should be connected

together at the low-impedance power-supply source.

DGND and AGND should be connected together at the

chip. For the MAX504 in single-supply applications,

connection may be achieved by connecting the DAC's

DGND and AGND pins together and connecting that

point to the system analog ground plane. If the DAC's

DGND is connected to the system digital ground, digi-

tal noise may get through to the DAC’s analog portion.

short leads close to the device. Ferrite beads may also

be used to further isolate the analog and digital power

supplies.

Figures 11a and 11b illustrate the grounding and

bypassing scheme described.

Saving Power

When the DAC is not being used by the system, mini-

mize power consumption by setting the appropriate

code to minimize load current. For example, in bipolar

mode, with a resistive load to ground, set the DAC

code to mid-scale (see Table 3). If there is no output

load, minimize internal loading on the reference by set-

ting the DAC to all 0s (on the MAX504, use CLR).

Under this condition, REFIN is high impedance and the

op amp operates at its minimum quiescent current.

Due to these low currents, the output settling time for a

zero input code typically increases to 60µs (100µs

max).

5V, Low-Power, Voltage-Output,

Serial 10-Bit DACs

12

______________________________________________________________________________________

Figure 8. Bipolar Configuration (-2.048V to +2.048V Output)

Table 3. Bipolar (Offset Binary) Code

33µF

REFIN

REFOUT

AGND

DGND

BIPOFF

RFB

VOUT

-5V

+5V

MAX504

INPUT*

OUTPUT

1111

1111

11(00)

1000

0000

01(00)

1000

0000

00(00)

0111

1111

11(00)

0000

0000

01(00)

0000

0000

00(00)

511

512

1

512

1

512

511

512

0V

512

512

*

Write 10-bit data words with two sub-LSB 0s because the

DAC input latch is 12 bits wide.