MAX547 Просмотр технического описания (PDF) - Maxim Integrated

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MAX547

Octal, 13-Bit Voltage-Output DAC with Parallel Interface

Maxim Integrated 

Octal, 13-Bit Voltage-Output

DAC with Parallel Interface

Table 5. Reference, AGND– and Output Relationships

PARAMETER

BIPOLAR OPERATION

(AGND_ = 0V)

POSITIVE UNIPOLAR

OPERATION

(AGND_ = REF_/2)

Bipolar Zero Level, or

Unipolar Mid-scale,

(Code = 1000000000000)

AGND_ (=0V)

( ) AGND–

=

—R—EF—_

2

Differential Reference Voltage

(VDR)

REF–

REF–/2

Negative Full-scale Output

(Code = All 0s)

-REF–

0V

Positive Full-Scale Output

(Code = All 1s)

( ) ( ) —4—09—5 REF_

4096

( ) ( ) —8—19—1 REF_

8192

LSB Weight

—RE—F—_

4096

( ) —RE—F—_

8192

VOUT– as a Function of

Digital Code (D, 0 to 8191)

( ) ( ) ——D— - 1 REF_

4096

( ) ( ) ——D— REF_

8192

CUSTOM OPERATION

AGND–

REF– - AGND–

AGND– - VDR

( ) ( ) AGND _ +

—40—9—5

4096

VDR

—VD—R—

4096

( ) ( ) AGND _ +

—D--—- - 1

4096

VDR

load regulation is specified to 20ppm/mA max over

temperature, resulting in a maximum error of 36ppm

(90µV). This corresponds to a maximum error caused

by reference load regulation of only 0.147LSB

[0.147LSB = 90µV/(5V/8192)LSB] over temperature.

If you want a ±4.096V full-scale output swing (1LSB =

1mV), you can use the calibrated, low-drift, low-dropout

MAX676. Operating from a 5V supply, it is fully speci-

fied to drive two REF_ inputs with less than 60.4µV error

(0.0604LSB) over temperature, caused by the maxi-

mum load step.

Reference Buffering

Another way to obtain high accuracy is to buffer a refer-

ence with an op amp. When driving all reference inputs

simultaneously, keep the closed-loop output imped-

ance of the op amp below 0.03Ω to ensure an error of

less than 0.1LSB. The op amp must also drive the

capacitive load (typically 500pF to 1200pF).

Each reference input can also be buffered separately

by using the circuit in Figure 6. A reference load step

caused by a digital transition only affects the DAC pair

where the code transition occurs. It also allows the use

of references with little drive capability. Keep the

closed-loop output impedance of each op amp below

0.12Ω, to ensure an error of less than 0.1LSB. Figure 6

shows the op amp’s inverting input directly connected

to the MAX547’s reference terminal. This eliminates the

VSS

1N5817

SYSTEM GND

VSS

MAX547

GND

Figure 5. Optional Schottky Diode between VSS and GND

influence of board lead resistance by sensing the volt-

age with a low-current path sense line directly at the

reference input.

Adding feedback resistors to individual reference

buffer amplifiers enables different reference voltages to

be generated from a single reference.

______________________________________________________________________________________ 11

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