LTC2637



2637fa

analog section of the ground plane. The resistance from

the LTC2637 GND pin to the ground plane should be as

low as possible. Resistance here will add directly to the

effective DC output impedance of the device (typically

0.1Ω). Note that the LTC2637 is no more susceptible to

this effect than any other parts of this type; on the con-

trary, it allows layout-based performance improvements

to shine rather than limiting attainable performance with

excessive internal resistance.

Another technique for minimizing errors is to use a sepa-

rate power ground return trace on another board layer.

The trace should run between the point where the power

supply is connected to the board and the DAC ground pin.

Thus the DAC ground pin becomes the common point for

analog ground, digital ground, and power ground. When

the LTC2637 is sinking large currents, this current flows

out the ground pin and directly to the power ground trace

without affecting the analog ground plane voltage.

It is sometimes necessary to interrupt the ground plane

to confine digital ground currents to the digital portion of

the plane. When doing this, make the gap in the plane only

as long as it needs to be to serve its purpose and ensure

that no traces cross over the gap.

operation

A6

A5 A4 A3 A2 A1 A0

W

C3

C3

ACK

SLAVE ADDRESS

ACK

ACK

ACK

C2 C1 C0 A3 A2 A1 A0

D11 D10 D9 D8 D7 D6 D5 D4

D3 D2 D1 D0

X

X

X

X

A6

START

STOP

FULL-SCALE

VOLTAGE

ZERO-SCALE

VOLTAGE

SDA

SCL

X = DON’T CARE

A5 A4 A3

A2 A1 A0

C2 C1 C0 A3

A2 A1 A0

8

9

1

2

3

4

5

6

7

1

2

3

4

5

6

7

8

9

1

2

3

4

5

6

7

8

9

1

2

3

4

5

6

7

8

9

COMMAND/ADDRESS

MS DATA

LS DATA

2637 F04

Figure 4. Typical LTC2637 Input Waveform—Programming DAC Output for Full-Scale

Figure 5. Effects of Rail-to-Rail Operation On a DAC Transfer Curve (Shown for 12 Bits).

(a) Overall Transfer Function

(b) Effect of Negative Offset for Codes Near Zero

(c) Effect of Positive Full-Scale Error for Codes Near Full-Scale

2637 F04

INPUT CODE

(b)

OUTPUT

VOLTAGE

NEGATIVE

OFFSET

0V

0V

2,048

0

4,095

INPUT CODE

OUTPUT

VOLTAGE

(a)

(c)

INPUT CODE

OUTPUT

VOLTAGE

POSITIVE

FSE