1400 データシートの表示（PDF） - Linear Technology

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1400

Complete SO-8, 12-Bit, 400ksps ADC with Shutdown

Linear Technology 

LTC1400

APPLICATIO S I FOR ATIO

trimmed to 2.42V. It is internally connected to the DAC

and is available at Pin 3 to provide up to 1mA of current to

an external load. For minimum code transition noise, the

reference output should be decoupled with a capacitor to

filter wideband noise from the reference (10μF tantalum in

parallel with a 0.1μF ceramic). The VREF pin can be driven

with a DAC or other means to provide input span adjust-

ment in bipolar mode. The VREF pin must be driven to at

least 2.45V to prevent conflict with the internal reference.

The reference should not be driven to more than 5V.

Figure 6 shows an LT1360 op amp driving the reference

pin. Figure 7 shows a typical reference, the LT1019A-5

connected to the LTC1400. This will provide an improved

drift (equal to the maximum 5ppm/°C of the LT1019A-

5) and a ±4.231V full scale. If VREF is forced lower than

2.42V, the REFRDY bit in the serial data output will be

forced to low.

INPUT RANGE

±0.846 • VREF(OUT)

+

LT1360

–

VREF(OUT) ≥ 2.45V

3Ω

10µF

5V

AIN VCC

LTC1400

VREF

GND VSS

–5V

1400 F06

Figure 6. Driving the VREF with the LT1360 Op Amp

INPUT RANGE ±4.231V

(= ±0.846 • VREF)

10V

VIN

VOUT

LT1019A-5

GND

3Ω

10µF

5V

AIN VCC

LTC1400

VREF

GND VSS

–5V

1400 F07

Figure 7. Supplying a 5V Reference Voltage

to the LTC1400 with the LT1019A-5

Unipolar/Bipolar Operation and Adjustment

Figure 8 shows the ideal input/output characteristics for

the LTC1400. The code transitions occur midway between

successive integer LSB values (i.e., 0.5LSB, 1.5LSB,

2.5LSB, … FS – 1.5LSB). The output code is straight

binary with 1LSB = 4.096V/4096 = 1mV. Figure 9 shows

the input/output transfer characteristics for the bipolar

mode in two’s complement format.

111...111

111...110

111...101

111...100

1LSB

=

FS

4096

UNIPOLAR

ZERO

000...011

000...010

000...001

000...000

0V 1

LSB

INPUT VOLTAGE (V)

FS – 1LSB

1400 F08

Figure 8. LTC1400 Unipolar Transfer Characteristics

011...111

011...110

000...001

000...000

111...111

111...110

BIPOLAR

ZERO

100...001

100...000

– FS/2

–1 0V 1

LSB LSB

INPUT VOLTAGE (V)

FS/2 – 1LSB

11400 F09

Figure 9. LTC1400 Bipolar Transfer Characteristics

Unipolar Offset and Full-Scale Error Adjustments

In applications where absolute accuracy is important,

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

10a shows the extra components required for full-scale

1400fa

10

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