Max5548, Detailed description, Serial interface – Rainbow Electronics MAX5548 User Manual

Page 8: Pin description

MAX5548

Detailed Description

Architecture

The MAX5548 8-bit, dual current-steering DAC (see the
Functional Diagram) operates with DAC update rates
up to 10Msps in SPI mode and 400ksps in I

C mode.

The converter consists of a 16-bit shift register and
input DAC registers, followed by a current-steering
array. The current-steering array generates full-scale
currents up to 30mA per DAC. An integrated +1.25V
bandgap reference, control amplifier, and an external
resistor determine each data converter’s full-scale
output range.

Reference Architecture and Operation

The MAX5548 provides an internal +1.25V bandgap ref-
erence or accepts an external reference voltage source
between +0.5V and +1.5V. REFIN serves as the input for
an external low-impedance reference source. Leave
REFIN unconnected in internal reference mode. Internal
or external reference mode is software selectable
through the SPI/I

C serial interface.

The MAX5548’s reference circuit (

Figure 1) employs a

control amplifier to regulate the full-scale current (I

)

for the current outputs of the DAC. This device has a
software-selectable full-scale current range (see the
command summary in Table 4). After selecting a cur-
rent range, an external resistor (R

FSADJ

_) sets the full-

scale current. See Table 1 for a matrix of I

and

FSADJ

selections.

During startup, when the power is first applied, the
MAX5548 defaults to the external reference mode, and
to the 1mA–2mA full-scale current-range mode.

DAC Data

The 8-bit DAC data is decoded as offset binary, MSB
first, with 1 LSB = I

/ 256, and converted into the cor-

responding current as shown in Table 2.

Serial Interface

The MAX5548 features a pin-selectable SPI/I

C serial

interface. Connect SPI/I2C to GND to select I

C mode,

or connect SPI/I2C to V

to select SPI mode. SDA

and SCL (I

C mode) and DIN, SCLK, and CS (SPI

Dual, 8-Bit, Programmable, 30mA
High-Output-Current DAC

_______________________________________________________________________________________

Pin Description

PIN

NAME

FUNCTION

SCLK/SCL

Serial Clock Input. Connect SCL to V

through a 2.4k

Ω resistor in I

C mode.

DIN/SDA

Serial Data Input. Connect SDA to V

through a 2.4k

Ω resistor in I

C mode.

CS/A0

Chip-Select Input in SPI Mode/Address Select 0 in I

C Mode. CS is an active-low input. Connect A0 to

or GND to set the device address in I

C mode.

SPI/I2C

SPI/I2C Select Input. Connect SPI/I2C to V

to select SPI mode, or connect SPI/I2C to GND to select

C mode.

DOUT/A1

Serial Data Output in SPI Mode/Address Select 1 in I

C Mode. Use DOUT to daisy chain the MAX5548 to

other devices or to read back in SPI mode. The digital data is clocked out on SCLK’s falling edge.
Connect A1 to V

or GND to set the device address in I

C mode.

6, 13, 15

N.C.

No Connection. Leave unconnected or connect to GND.

REFIN

Reference Input. Drive REFIN with an external reference source between +0.5V and +1.5V. Leave REFIN
unconnected in internal reference mode. Bypass REFIN with a 0.1µF capacitor to GND as close to the
device as possible.

8, 16

GND

Ground

OUTB

DACB Output. OUTB provides up to 30mA of output current.

FSADJB

D AC B Ful l - S cal e Ad j ust Inp ut. For m axi m um ful l - scal e outp ut cur r ent, connect a 20k

Ω r esi stor b etw een

FS AD JB and G N D . For m i ni m um ful l - scal e cur r ent, connect a 40k

Ω r esi stor b etw een FS AD JB and G N D .

FSADJA

D AC A Ful l - S cal e Ad j ust Inp ut. For m axi m um ful l - scal e outp ut cur r ent, connect a 20k

Ω r esi stor b etw een

FS AD JA and G N D . For m i ni m um ful l - scal e cur r ent, connect a 40k

Ω r esi stor b etw een FS AD JA and G N D .

OUTA

DACA Output. OUTA provides up to 30mA of output current.

Power-Supply Input. Connect V

to a +2.7 to +5.25V power supply. Bypass V

to GND with a 0.1µF

capacitor as close to the device as possible.