LTC1289CCSW(RevB) View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
LTC1289CCSW Datasheet PDF : 28 Pages
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LTC1289
APPLICATI S I FOR ATIO
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.
capacitor. The noise and ripple is approximately 0.5mV.
Figure 8b shows the response of a lithium battery with a 10µF
bypass capacitor. The noise and ripple is kept below 0.5mV.
2. Bypassing
For good performance, VCC must be free of noise and
ripple. Any changes in the VCC voltage with respect to
analog ground during a conversion cycle can induce
errors or noise in the output code. VCC noise and ripple can
be kept below 0.5mV by bypassing the VCC pin directly to
the analog ground plane with a 22µF tantalum capacitor
and leads as short as possible. The lead from the device to
the VCC supply should also be kept to a minimum and the
VCC 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 VCC pin. A
battery placed close to the device will only require 10µF to
adequately bypass the supply pin. Figure 7 shows the
effect of poor VCC bypassing. Figure 8a shows the settling
of a LT1117 low dropout regulator with a 22µF bypass
HORIZONTAL: 10µs/DIV
Figure 7. Poor VCC Bypassing.
Noise and Ripple Can Cause A/D Errors.
5V/DIV
CS
0.1µF
VCC
22µF
TANTALUM
ANALOG
GROUND
PLANE
1
20
2
19
3
18
4
17
5
16
6
15
7
14
8
13
9
12
10
11
V–
0.1µF
CERAMIC
DISK
LTC1289 AIF06
Figure 6. Example Ground Plane for the LTC1289
16
VCC
0.5mV/DIV
HORIZONTAL: 20µs/DIV
Figure 8a. LT1117 Regulator with 22µF Bypassing on VCC
5V/DIV
CS
0.5mV/DIV
VCC
HORIZONTAL: 20µs/DIV
Figure 8b. Lithium Battery with 10µF Bypassing on VCC
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