MAX5158 Datasheet, PDF(9/16 Page) Maxim Integrated Products – Low-Power, Dual, 10-Bit, Voltage-Output DACs with Serial Interface

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MAX5158 Datasheet, PDF (9/16 Pages) Maxim Integrated Products – Low-Power, Dual, 10-Bit, Voltage-Output DACs with Serial Interface

◁

Low-Power, Dual, 10-Bit, Voltage-Output DACs

with Serial Interface

_____________________Pin Description

OS_

PIN NAME

FUNCTION

AGND Analog Ground

OUTA DAC A Output Voltage

OUT_

OSA DAC A Offset Adjustment

REFA Reference for DAC A

Active-Low Clear Input. Resets all reg-

isters to zero. DAC outputs go to 0V.

Chip-Select Input

DIN

Serial-Data Input

2R 2R

REF_

AGND

SCLK Serial Clock Input

DGND Digital Ground

SHOWN FOR ALL 1s ON DAC

Figure 1. Simplified DAC Circuit Diagram

DOUT Serial-Data Output

UPO User-Programmable Output

PDL

Power-Down Lockout. The device can-

not be powered down when PDL is low.

REFB Reference for DAC B

OSB DAC B Offset Adjustment

OUTB DAC B Output Voltage

VDD

Positive Power Supply

_______________Detailed Description

The MAX5158/MAX5159 dual, 10-bit, voltage-output

DACs are easily configured with a 3-wire serial inter-

face. These devices include a 16-bit data-in/data-out

shift register, and each DAC has a double-buffered

input composed of an input register and a DAC register

(see Functional Diagram). In addition, trimmed internal

resistors produce an internal gain of +2V/V that maxi-

mizes output voltage swing. The amplifierâs offset-adjust

pin allows for a DC shift in the DACâs output.

Both DACs use an inverted R-2R ladder network that

produces a weighted voltage proportional to the input

voltage value. Each DAC has its own reference input to

facilitate independent full-scale values. Figure 1

depicts a simplified circuit diagram of one of the two

DACs.

Reference Inputs

The reference inputs accept both AC and DC values

with a voltage range extending from 0V to (VDD - 1.4V).

Determine the output voltage using the following equa-

tion (OS_ = AGND):

VOUT = (VREF x NB / 1024) x 2

where NB is the numeric value of the DACâs binary input

code (0 to 1023) and VREF is the reference voltage.

The reference input impedance ranges from 18kâ¦

(1558 hex) to several giga ohms (with an input code of

0000 hex). The reference input capacitance is code

dependent and typically ranges from 15pF with an

input code of all zeros to 50pF with a full-scale input

code.

Output Amplifier

The output amplifiers on the MAX5158/MAX5159 have

internal resistors that provide for a gain of +2V/V when

OS_ is connected to AGND. These resistors are

trimmed to minimize gain error. The output amplifiers

have a typical slew rate of 0.75V/Âµs and settle to

1/2LSB within 8Âµs, with a load of 10kâ¦ in parallel with

100pF. Loads less than 2kâ¦ degrade performance.

The OS_ pin can be used to produce an adjustable off-

set voltage at the output. For instance, to achieve a 1V

offset, apply -1V to the OS_ pin to produce an output

range from 1V to (1V + VREF x 2). Note that the DACâs

output range is still limited by the maximum output volt-

age specification.

Power-Down Mode

The MAX5158/MAX5159 feature a software-program-

mable shutdown mode that reduces the typical supply

current to 2ÂµA. The two DACs can be shutdown inde-

pendently, or simultaneously using the appropriate pro-

gramming command. Enter shutdown mode by writing

the appropriate input-control word (Table 1). In shut-

down mode, the reference inputs and amplifier out-

puts become high impedance, and the serial interface

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