LTC2637 LINER [Linear Technology], LTC2637 Datasheet - Page 24

• Manufacturer Part Number: LTC2637
• Description: Mobile Communications
• Manufacturer: LINER [Linear Technology]

LTC2637
operation
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

V
SDA
SCL
OUT
NEGATIVE
START
OFFSET
X = DON’ T CARE
VOLTAGE
OUTPUT
A6
A6
1
0V
A5
A5
2
A4
A4
3
SLAVE ADDRESS
A3
A3 A2
4
A2
5
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
A1
A1
INPUT CODE
6
Figure 4. Typical LTC2637 Input Waveform—Programming DAC Output for Full-Scale
A0
(b)
A0
7
W
8
ACK
9
C3
C3
1
C2
C2
2
COMMAND/ADDRESS
C1
C1
3
C0
C0
4
VOLTAGE
OUTPUT
A3
A3
5
0V
A2
A2
0
6
A1
A1
7
A0
A0
8
ACK
9
INPUT CODE
V
D11 D10 D9
REF
1
2,048
(a)
= V
2
CC
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.
3
MS DATA
D8
4
D7
5
4,095
D6
6
D5
7
D4
8
ACK
9
D3 D2
1
2
D1
3
D0
V
LS DATA
4
REF
INPUT CODE
= V
X
5
CC
(c)
X
6
X
7
X
8
ACK
9
2637 F04
OUTPUT
VOLTAGE
POSITIVE
FSE
FULL-SCALE
VOLTAGE
ZERO-SCALE
VOLTAGE
2637 F04
STOP
2637fa