TMC1175A datasheet(13/18 Pages) CADEKA

13 / 18 page

PRODUCT SPECIFICATION

TMC1175A

REV. 1.3.3 2/28/02

Figure 12. Typical Interface Circuit-High Performance

+5V

0.1

µF

0.1mF

0.1

µF

VDDA

VDDD

VR+

VR-

VIN

AGND

DGND

CONV

D7-0

TMC1175A

0.1

µF

0.1

µF

Ω

LM385

Ω

455

Ω

455

Ω

Video

Input

+5V

Regulated +5V

Gain Adjust

+5V

27056A

Wideband

Op-amp

Figure 13. Typical Interface Circuit – Low Cost

Figure 14. Typical Interface Circuit – Stabilized Reference

0.1

µF

0.1

µF

0.1

µF

+5V

2.2k

Ω

560

Ω

Video

Input

24458A

Offset

Adjust

+5V

0.1

µF

0.1

µF

VDDA

VDDD

VR+

VR-

VIN

AGND

DGND

CONV

D7-0

TMC1175A

0.1

µF

Ω

Input

24457A

+5V

0.1

µF

0.1

µF

VDDA

VDDD

VR+

VR-

VIN

AGND

DGND

CONV

D7-0

TMC1175A

LM385

Grounding

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

(VDDD and VDDA) originate from separate sources with

VDDA regulated, and that ground connections (DGND and

AGND) be made to the analog ground plane. Power supply

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.

Printed Circuit Board Layout

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:

1. Keep the critical analog traces (VIN, RT, RB, VR+,

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.

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

the VDD pins. If the power supply for the TMC1175A

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.

3. The ground plane should be solid, not cross-hatched.

Connections to the ground plane should have very

short leads.

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