MAX551 Просмотр технического описания (PDF) - Maxim Integrated

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MAX551

+3V/+5V, 12-Bit, Serial, Multiplying DACs in 10-Pin µMAX Package

Maxim Integrated 

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

in 10-Pin µMAX Package

DIN

BIT 11

MSB

BIT 10

BIT 1

BIT 0

LSB

tDS

tDH

1

2

11

tCH

tCL

SCLK

LOAD SERIAL DATA INTO INPUT REGISTER

tLC

tSL

tLD

LOAD

CLR

tCLR

Figure 2. Write-Cycle Timing Diagram

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 (IOUT) 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 (RFB) to minimize gain varia-

tion with temperature.

The internal feedback resistor (RFB) 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 (COUT) is code

dependent. COUT 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

standards. These devices accept serial clocks up to

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

Table 1. Unipolar Binary-Code Table

for Circuit of Figure 3

DIGITAL INPUT

MSB

LSB

1111 1111 1111

1000 0000 0000

0000 0000 0001

ANALOG OUTPUT

−VREF

 4095

 4096

−VREF





2048 

4096 

=

−

VREF

2

−VREF

 1

 4096

VREF

R1

100Ω

+5V (+3V)

REF

VDD

R2

50Ω

DIN

RFB

C1

15pF

MAX551

2

SCLK

MAX552 OUT

LOAD

3

GND

AGND

6

VOUT

0000 0000 0000

0

( ) ARE FOR MAX552

Figure 3. Unipolar Operation

8 _______________________________________________________________________________________

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