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LTC1603

1603f

APPLICATIONS INFORMATION

LTC1603

AIN

ANALOG INPUT

2V TO 2.7V

DIFFERENTIAL

AIN

–

VREF

REFCOMP

AGND

1603 F13

µF

LTC1450

2V TO 2.7V

Figure 14a. CMRR vs Input Frequency

INPUT FREQUENCY (Hz)

10k

100k

1603 G14a

Figure 13. Driving VREF with a DAC

can not exceed the AVDD or VSS power supply voltages.

Integral nonlinearity errors (INL) and differential nonlin-

earity errors (DNL) are independent of the common mode

voltage, 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 96dB

with a common mode of 0V to 86dB with a common mode

of 2.5V or – 2.5V.

Differential inputs allow greater flexibility for accepting

different input ranges. Figure 14b shows a circuit that

converts a 0V to 5V analog input signal with only an

additional buffer that is not in the signal path.

LTC1603

AIN

–

VREF

0V TO

±2.5V

REFCOMP

AGND

1603 F14b

µF

ANALOG INPUT

–

Figure 14b. Selectable 0V to 5V or

±2.5V Input Range

Full-Scale and Offset Adjustment

Figure 15a shows the ideal input/output characteristics

for the LTC1603. 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)/65536 = 5V/65536 = 76.3

µV.

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 15b

shows the extra components required for full-scale error

adjustment. Zero offset is achieved by adjusting the offset

applied to the AIN– input. For zero offset error apply

1603 F15a

011...111

011...110

000...001

000...000

111...111

111...110

100...001

100...000

FS – 1LSB

– (FS – 1LSB)

INPUT VOLTAGE (AIN

+ – A

–)

Figure 15a. LTC1603 Transfer Characteristics

LTC1603 Datasheet(PDF) 14 Page - Linear Technology

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