CS5581

20

DS796PP1

3/25/08

14:34

3.7 AIN & VREF Sampling Structures

The CS5581 uses on-chip buffers on the AIN and the VREF+ inputs. Buffers provide much higher input

impedance and therefore reduce the amount of drive current required from an external source. This helps

minimize errors.

The Buffer Enable (BUFEN) pin determines if the on-chip buffers are used or not. If the BUFEN pin is

connected to the V1+ supply, the buffers will be enabled. If the BUFEN pin is connected to the V1- pin,

the buffers are off. The converter will consume about 30 mW less power when the buffers are off, but the

input impedances of AIN, ACOM and VREF+ will be significantly less than with the buffers enabled.

3.8 Converter Performance

The CS5581 achieves excellent differential nonlinearity (DNL) as shown in Figures 9 and 10. Figure 9

illustrates the code widths on the typical scale of ±1 LSB. Figure 10 illustrates a zoomed scale of ±0.1

LSB. The DNL error histogram in Figure 10 indicates that more than half the codes are accurate to better

than ±0.01 LSB.

Figure 9. CS5581 DNL Plot

Figure 10. CS5581 DNL Error Plot with DNL Histogram

-1.00

-0.75

-0.50

-0.25

0.00

0.25

0.50

0.75

1.00

1

65535

Codes

2k

4k

6k

8k

10k

12k

14k

16k

18k

0

0

+0.08

+0.07

+0.06

+0.05

+0.04

+0.03

+0.02

+0.01

-0.01

-0.02

-0.03

-0.04

-0.05

-0.06

-0.07

-0.08

-0.09

-0.1

+0.09

+0.1

Counts per 0.01 LSB Error

-0.10

-0.08

-0.06

-0.04

-0.02

0

+0.02

+0.04

+0.06

+0.08

+0.10

1

65535

Codes