MC33765_06 Datasheet, PDF (9/12 Pages) ON Semiconductor – Very Low Dropout/Ultra Low Noise 5 Outputs Voltage Regulator

MC33765
DESIGN HINTS
Reducing the cross−talk between the MC33765 outputs
One of the origin of the DC shift finds its seat in the layout
surrounding the integrated circuit. Particular care has to be
taken when routing the output ground paths. Star grounding
or a ground plane are the absolute conditions to reduce the
noise or shift associated to common impedance situations,
as depicted by Figure 17.
1
16
2
15
WRONG
3
14
4
13
5
12
6
11
7
10
8
9
common impedance shift
Load1 Load2
1
16
2
15
3
14
4
13
5
12
6
11
7
10
8
9
Star cabling
CORRECT
Load1 Load2
Rlayout
Figure 17. Star Cabling Avoids Coupling by Common Ground Impedance
The first left cabling will generate a voltage shift which will
superimpose on the output voltages, thus creating an
undesirable offset. By routing the return grounds to a single
low impedance point, you naturally shield the circuit against
common impedance disturbances. Figure 18 portraits the text
fixture implemented to test the response of the MC33765.
V_CC
10k 10k
1
10nF
2
3
4
5
6
10k
7
8
16
15
14
470nF
13
12
Output 3
11
+
56
10
1mF
9
18
100nF
Output 4
Figure 18. DC Shift Text Fixture
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