TLC876M, TLC876I, TLC876C

10-BIT 20 MSPS PARALLEL OUTPUT CMOS

ANALOG-TO-DIGITAL CONVERTERS

SLAS140D – JULY 1997 – REVISED MAY 2000

16

POST OFFICE BOX 655303

PRINCIPLES OF OPERATION

dc considerations (continued)

5

Ω

5

Ω

RARRAY

500

Ω

C (Equivalent)

CLK

CLK

TLC876

REFTF

REFTS

REFBS

REFBF

DAC

10

Ω

5

Ω

5

Ω

5

Ω

10

Ω

5

Ω

5

Ω

5

Ω

Figure 17. TLC876 Equivalent Reference Structure

The REFTS and REFBS terminals should not be connected in configurations that do not use a force-sense

reference. Connecting the force and sense lines together allows current to flow in the sense lines. Any current

allowed to flow through these lines must be negligibly small. Current flow causes voltage drops across the

resistance in the sense lines. Because the internal DACs tap different points along the sense lines, each DAC

would receive a slightly different reference voltage if current were flowing in these lines. To avoid this undesirable

condition, leave the sense lines unconnected. Any current allowed to flow through these lines must be negligibly

small (< 100

µA).

Input Voltage Span = V(REFTS) – V(REFBS)

(3)

Therefore, a full-scale input span is approximately 2 V when [V(REFTS) – V(REFBS)] = 2 V. The external

reference must provide approximately 4 mA for a 2-V drop across the internal resistor array.

Figure 18 shows the flexibility in determining both the full-scale span of the analog input and where to center

this voltage without degrading the typical performance.