11

LTC1410

1

2

3

4

5

0.1

µF

10

µF

ANALOG

INPUT

1410 F08b

LT1019A-2.5

5V

REFCOMP

AGND

LTC1410

Figure 8b. Using the LT1019-2.5 as an External Reference

easily overdriven in applications where an external refer-

ence is required. The reference amplifier provides buffer-

ing between the internal reference and the capacitive DAC.

The reference amplifier compensation pin REFCOMP

(Pin 4), must be bypassed with a capacitor to ground. The

reference amplifier is stable with capacitors of 1

µF or

greater. For the best noise performance, a 10

µF tantalum

in parallel with 0.1

µF ceramic is recommended.

(Figure 8b), a DAC or other means to provide input span

to 2.75V for specified linearity.

Full-Scale and Offset Adjustment

Figure 9 shows the ideal input/output characteristics for

the LTC1410. The code transitions occur midway between

successive integer LSB values (i.e., – FS + 0.5LSB,

– FS + 1.5LSB, – FS + 2.5LSB, . . . FS – 1.5LSB,

FS – 0.5LSB).The output is two’s complement binary

with 1LSB = [(+FS) – (– FS)]/4096 = 5V/4096 = 1.22mV.

In applications where absolute accuracy is important,

offset and full-scale errors can be adjusted to zero. Offset

error must be adjusted before full-scale error. Figure 10

shows the extra components required for full-scale error

adjustment. Zero offset is achieved by adjusting the offset

0000 0000 and 1111 1111 1111. For full-scale adjust-

ment, an input voltage of 2.49817V (FS – 1.5LSBs) is

flickers between 0111 1111 1110 and 0111 1111 1111.

BOARD LAYOUT AND BYPASSING

Wire wrap boards are not recommended for high resolu-

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

performance from the LTC1410, a printed circuit board

with ground plane is required. Layout for the printed

circuit board should ensure that digital and analog signal

lines are separated as much as possible. 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.

ANALOG

INPUT

1410 F10

1

2

3

R4

100

Ω

R2

50k

R3

47k

–5V

R6

24k

R1

50k

R5

47k

4

5

0.1

µF

10

µF

REFCOMP

AGND

LTC1410

Figure 10. Offset and Full-Scale Adjust Circuit

0V

–1

LSB

1410 F09

011...111

011...110

000...001

000...000

100...000

100...001

111...110

1

LSB

BIPOLAR

ZERO

111...111

FS – LSB

–FS

FS = 2.5V

1LSB =

2FS

4096

Figure 9. LTC1410 Transfer Characteristics