19

LTC1609

1609fa

Output Data Format

The SB/BTC pin controls the format of the serial digital

output word. With the pin tied high the format is straight

binary. With the pin tied low the data format is two’s

complement. See Table 1c.

Board Layout, Power Supplies and Decoupling

Wire wrap boards are not recommended for high resolu-

tion or high speed A/D converters. To obtain the best

performance from the LTC1609, a printed circuit board is

required. Layout for the printed circuit board should

ensure the digital and analog signal lines are separated as

much as possible. In particular, care should be taken not

to run any digital track alongside an analog signal track or

underneath the ADC. The analog input should be screened

by AGND.

APPLICATIO S I FOR ATIO

B15

0

123456789

10

11

12

13

14

15

16

17

18

19

20

21

22

23

• • •

• • •

R/C

BUSY

DCLK

DATA

OUT

B14

B13

B12

B11

B10

B9

B8

B7

B6

B5

B4

B3

DEVICE DATA #1

DEVICE DATA #2

B2

B1

B0

NULL

BIT

B14

B13

B12

B11

B10

1609 F14

B15

Figure 14. Data Output from Cascading Two (CS = Low, TAG (#2) = Low) LTC1609s Together

Pay particular attention to the design of the analog and

digital ground planes. Placing the bypass capacitor as

and reference buffer output is very important. Low imped-

ance common returns for these bypass capacitors are

essential to low noise operation of the ADC, and the foil

width for these tracks should be as wide as possible. Also,

since any potential difference in grounds between the

signal source and ADC appears as an error voltage in

series with the input signal, attention should be paid to

reducing the ground circuit impedance as much as pos-

sible. The digital output latches and the onboard sampling

clock have been placed on the digital ground plane. The

two ground planes are tied together at the power supply

ground connection.

A “postage stamp” (1.6in

× 1.5in) evaluation board is

available and allows fast in-situ evaluation of the LTC1609.

See Figures 15a through 15d, inclusive.