PRODUCT SPECIFICATION
TMC1175A
Regulated +5V
+5V
0.1µF
0.1µF
1kΩ
LM385
V
V
DDD
+5V
DDA
0.1µF
Gain Adjust
VR+
R
T
20Ω
2V
+
2kΩ
0.1mF
-
1kΩ
0.1µF
TMC1175A
R
B
D
7-0
1kΩ
VR-
Wideband
Op-amp
+
-
OE
Video
Input
V
IN
CONV
455Ω
75Ω
A
D
GND
GND
455Ω
+5V
27056A
Figure 12. Typical Interface Circuit-High Performance
Grounding
+5V
0.1µF
0.1µF
The TMC1175A has separate analog and digital
circuits. To keep digital system noise from the A/D
converter, it is recommended that power supply voltages
V
V
DDD
DDA
Offset
Adjust
+5V
2.2kΩ
VR+
(V
and V
) originate from separate sources with
and
) be made to the analog ground plane. Power supply
DDD
DDA
R
T
V
A
regulated, and that ground connections (D
GND
DDA
GND
0.1µF
TMC1175A
2kΩ
R
pins should be individually decoupled at the pin. The digital
circuitry that gets its input from the TMC1175A should be
referred to the system digital ground plane.
B
D
7-0
0.1µF
VR-
560Ω
0.1µF
OE
Video
Input
CONV
V
IN
Printed Circuit Board Layout
10µF
75Ω
A
D
GND
GND
Designing with high performance mixed-signal circuits
demands printed circuits with ground planes. Wire-wrap is
not an option, even for breadboarding. Overall system per-
formance is strongly influenced by the board layout. Capac-
itive coupling from digital to analog circuits may result in
poor A/D conversion. Consider the following suggestions
when doing the layout:
24458A
Figure 13. Typical Interface Circuit – Low Cost
+5V
0.1µF
0.1µF
1. Keep the critical analog traces (V , R , R , VR+,
V
V
DDD
IN
T
B
DDA
VR-) as short as possible and as far as possible from all
digital signals. The TMC1175A should be located near
the board edge, close to the analog input connectors.
VR+
R
T
TMC1175A
0.1µF
LM385
2. The power plane for the TMC1175A should be sepa-
rate from that which supplies the rest of the digital cir-
cuitry. A single power plane should be used for all of
R
B
1kΩ
D
7-0
VR-
10µF
RF
Input
OE
V
IN
the V
DD
pins. If the power supply for the TMC1175A
CONV
is the same as that of the system's digital circuitry,
power to the TMC1175A should be decoupled with
ferrite beads and 0.1µF capacitors to reduce noise.
56Ω
1kΩ
A
D
GND
GND
24457A
Figure 14. Typical Interface Circuit – Stabilized Reference
3. The ground plane should be solid, not cross-hatched.
Connections to the ground plane should have very
short leads.
REV. 1.3.3 2/28/02
13
CADEKA [ CADEKA MICROCIRCUITS LLC. ]
