LTC1277CSW データシートの表示（PDF） - Linear Technology

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LTC1277CSW

12-Bit, 10mW, 100ksps ADCs with 1µA Shutdown

Linear Technology 

LTC1274/LTC1277

APPLICATI S I FOR ATIO

DIGITAL INTERFACE

The ADCs are designed to interface with microproces-

sors as a memory mapped device. The CS and RD control

inputs are common to all peripheral memory interfacing.

A separate CONVST is used to initiate a conversion.

Figures 10a to 10c are the input/output characteristics of

the ADCs. The code transitions occur midway between

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

2.5LSB…FS – 1.5LSV). The output code is scaled such

that 1.0LSB = FS/4096 = 4.096V/4096 = 1.0mV.

Unipolar Offset and Full-Scale Error Adjustments

In applications where absolute accuracy is important, then

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

error must be adjusted before full-scale error. Figure 11a

shows the extra components required for full-scale error

adjustment. If both offset and full-scale adjustments are

needed, the circuit in Figure 11b can be used. For zero

offset error, apply 0.50mV (i.e., 0.5LSB) at the input and

adjust the offset trim until the LTC1274/LTC1277 output

code flickers between 0000 0000 0000 and 0000 0000

0001. For zero full-scale error, apply an analog input of

4.0945V (i.e., FS – 1.5LSB or last code transition) at the

input and adjust R5 until the ADC output code flickers

between 1111 1111 1110 and 1111 1111 1111.

Bipolar Offset and Full-Scale Error Adjustments

Bipolar offset and full-scale errors are adjusted in a similar

fashion to the unipolar case. Again, bipolar offset must be

111...111

111...110

111...101

111...100

1LSB = FS = 4.096V = 1mV

4096 4096

UNIPOLAR

ZERO

000...011

000...010

000...001

000...000

0V 1

LSB

INPUT VOLTAGE (V)

FS – 1LSB

LTC1274/77 F10a

Figure 10a. LTC1274/LTC1277 Unipolar

Transfer Characteristics

011...111

011...110

000...001

000...000

111...111

111...110

BIPOLAR

ZERO

100...001

100...000

1LSB

=

FS

4096

=

4.096V

4096

=

1mV

– FS/2

–1 0V 1

LSB LSB

INPUT VOLTAGE (V)

FS/2 – 1LSB

LTC1274/77 • F10b

Figure 10b. LTC1274 Bipolar Transfer

Characteristics (2’s Complement)

111...111

111...110

100...001

100...000

011...111

011...110

BIPOLAR

Z ERO

000...001

000...000

– FS/2

1LSB =

FS

4096

=

4.096V

4096

= 1mV

–1 0V 1

LSB LSB

INPUT VOLTAGE (V)

FS/2 – 1LSB

LTC1274/77 • F10c

Figure 10c. LTC1277 Bipolar Transfer Characteristics

(Offset Binary)

15

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