Rainbow-electronics MAX552 Bedienungsanleitung PDF herunterladen (Seite 8)

MAX551/MAX552

+3V/+5V, 12-Bit, Serial, Multiplying DACs

in 10-Pin µMAX Package

8 _______________________________________________________________________________________

DIN

SCLK

LOAD

BIT 11

MSB

BIT 0

LSB

BIT 10 BIT 1

1 2

LOAD SERIAL DATA INTO INPUT REGISTER

CLR

Figure 2. Write-Cycle Timing Diagram

MAX551

MAX552

+5V (+3V)

( ) ARE FOR MAX552

REF

50Ω

15pF

OUT

100Ω

DIN

REF

RFB

OUT

GND

AGND

SCLK

LOAD

Table 1. Unipolar Binary-Code Table

for Circuit of Figure 3

DIGITAL INPUT

MSB LSB

ANALOG OUTPUT

1111 1111 1111

1000 0000 0000

0000 0000 0001

0000 0000 0000 0

−













REF

4095

4096

−













= −V

REF

2048

4096 2

−













REF

4096

Figure 3. Unipolar Operation

Detailed Description

The MAX551/MAX552 digital-to-analog converter (DAC)

circuits consist of a laser-trimmed, thin-film R-2R resis-

tor array with NMOS current switches (Figure 1).

Binary-weighted currents are switched to either OUT or

AGND, depending on the status of each input data bit.

Although the currents at OUT and AGND depend on

the digital input code, the sum of the two output cur-

rents is always equal to the input current at REF.

The output current (I

OUT

) can be converted into a volt-

age by adding an external output amplifier (Figure 3).

The REF input accepts a wide range of signals, includ-

ing fixed and time-varying voltage or current inputs. If a

current source is used at the reference input, use a

low-tempco, external feedback resistor in place of the

internal feedback resistor (R

) to minimize gain varia-

tion with temperature.

The internal feedback resistor (R

) is compensated

with an NMOS switch that matches the NMOS switches

used in the R-2R array, resulting in excellent supply

rejection and gain-temperature coefficient.

The OUT pin output capacitance (C

OUT

) is code

dependent. C

OUT

is typically

14pF at 000hex and 20pF

at FFFhex.

Serial Interface

The MAX551/MAX552 serial interface is compatible

with the SPI/QSPI and Microwire serial-interface stan-

dards. These devices accept serial clocks up to

12.5MHz (50% duty cycle). If the SCLK input is not

1 2 3 4 5 6 7 8 9 10 11 12

MAX551/MAX552 1

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