LTC1289 Linear Technology, LTC1289 Datasheet - Page 16

• Manufacturer Part Number: LTC1289
• Description: 3 Volt Single Chip 12-Bit Data Acquisition System
• Manufacturer: Linear Technology

LTC1289
Figure 6 shows an example of an ideal ground plane design
for a two-sided board. Of course, this much ground plane
will not always be possible, but users should strive to get
as close to this ideal as possible.
2. Bypassing
For good performance, V
Any changes in the V
ground during a conversion cycle can induce errors or
noise in the output code. V
below 0.5mV by bypassing the V
ground plane with a 22 F tantalum capacitor and leads as
short as possible. The lead from the device to the V
supply should also be kept to a minimum and the V
supply should have a low output impedance such as that
obtained from a voltage regulator (e.g., LT1117). Using a
battery to power the LTC1289 will help reduce the amount
of bypass capacitance required on the V
placed close to the device will only require 10 F to ad-
equately bypass the supply pin. Figure 7 shows the effect of
poor V
LT1117 low dropout regulator with a 22 F bypass capaci-
16
A
PPLICATI
CC
Figure 6. Example Ground Plane for the LTC1289
GROUND
ANALOG
PLANE
bypassing. Figure 8a shows the settling of a
O
U
10
1
2
3
4
5
6
7
8
9
CC
S
0.1 F
CC
voltage with respect to analog
I FOR ATIO
CC
must be free of noise and ripple.
U
noise and ripple can be kept
20
19
18
17
16
15
14
13
12
11
CC
pin directly to the analog
V
CC
W
22 F
TANTALUM
CC
pin. A battery
0.1µF
CERAMIC
DISK
V
–
U
LTC1289 AIF06
CC
CC
tor. The noise and ripple is approximately 0.5mV. Figure 8b
shows the response of a lithium battery with a 10 F bypass
capacitor. The noise and ripple is kept below 0.5mV.
0.5mV/DIV
0.5mV/DIV
Figure 8a. LT1117 Regulator with 22 F Bypassing on V
5V/DIV
5V/DIV
Figure 8b. Lithium Battery with 10 F Bypassing on V
Figure 7. Poor V
Noise and Ripple Can Cause A/D Errors.
HORIZONTAL: 10 s/DIV
HORIZONTAL: 20 s/DIV
HORIZONTAL: 20 s/DIV
CC
Bypassing.
CS
CS
V
V
CC
CC
CC
CC