13

LTC1409

S

APPLICATI

I FOR ATIO

INPUT FREQUENCY (Hz)

1

80

70

60

50

40

30

20

10

0

10

100

LTC1409 • TPC09

1000

10000

Figure 10a. CMRR vs Input Frequency

The output is two’s complement binary with 1LSB =

FS – (– FS)/4096 = 5V/4096 = 1.22mV.

Figure 10b. Selectable 0V to 5V or

±2.5V Input Range

however, the bipolar zero error (BZE) will vary. The change

in BZE is typically less than 0.1% of the common mode

voltage. Dynamic performance is also affected by the

common mode voltage. THD will degrade as the inputs

approach either power supply rail, from 86dB with a

common mode of 0V to 75dB with a common mode of

2.5V or – 2.5V.

Differential inputs allow greater flexibility for accepting

different input ranges. Figure 10b shows a circuit that

converts a 0V to 5V analog input signal with no additional

translation circuitry.

Full-Scale and Offset Adjustment

Figure 11a shows the ideal input/output characteristics for

the LTC1409. 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).

INPUT RANGE

LTC1409 • F11a

111...111

111...110

111...101

000...000

000...001

000...010

FS – 1LSB

–(FS – 1LSB)

Figure 11a. LTC1409 Transfer Characteristics

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 11b

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/2 – 1.5LSBs) is

flickers between 0111 1111 1110 and 0111 1111 1111.

LTC1409

ANALOG INPUT

REFCOMP

AGND

LTC1409 • F11b

1

2

3

R4

100

Ω

R2

50k

R3

24k

–5V

R6

24k

R1

50k

R5

47k

4

5

10

µF

Figure 11b. Offset and Full-Scale Adjust Circuit

LTC1409

ANALOG INPUT

REFCOMP

AGND

LTC1409 • F10b

1

2

3

4

5

10

µF

2.5V

0V TO 5V

RANGE

1

µF

±2.5V RANGE