Datasheet
MAX5222
Dual, 8-Bit, Voltage-Output
Serial DAC in 8-Pin SOT23
8 _______________________________________________________________________________________
Figure 1. DAC Simplified Circuit Diagram
2R 2R 2R 2R 2R
RRR
REF
GND
OUT
SHOWN FOR ALL 1s ON DAC
Table 1. Input Shift Register
Serial Interface
An active-low chip select (
–
C
—
S
–
) enables the shift register
to receive data from the serial data input. Data is
clocked into the shift register on every rising edge of
the serial clock signal (SCLK). The clock frequency can
be as high as 25MHz.
Data is sent most significant bit (MSB) first and can be
transmitted in one 16-bit word. The write cycle can be
segmented when
–
C
—
S
–
is kept active (low) to allow, for
example, two 8-bit-wide transfers. After clocking all 16
bits into the input shift register, the rising edge of
–
C
—
S
–
updates the DAC outputs and the shutdown status.
Because of their single buffered structure, DACs cannot
be simultaneously updated to different digital values.
Serial-Input Data Format and Control Codes
Table 2 lists the serial-input data format. The 16-bit
input word consists of an 8-bit control byte and an 8-bit
data byte. The 8-bit control byte is not decoded inter-
nally. Every control bit performs one function. Data is
clocked in starting with UB1 (uncommitted bit), followed
by the remaining control bits and the data byte. The
least significant bit (LSB) of the data byte (B0) is the
last bit clocked into the shift register (Figure 2).
Table 3 is an example of a 16-bit input word. It per-
forms the following functions:
• 80 hex (128 decimal) loaded into DAC registers
A and B.
• DAC A and DAC B are active.
*Clocked in last.
**Clocked in first.
Uncommitted Bit 1
UB1**
Uncommitted Bit 2UB2
Uncommitted Bit 3UB3
Shut Down, Active HighSB
Shut Down, Active HighSA
Uncommitted Bit 4UB4
Load Reg DAC B, Active HighLB
Load Reg DAC A, Active HighLA
DAC Data Bit 7 (MSB)B7
DAC Data Bit 6B6
DAC Data Bit 5B5
DAC Data Bit 4B4
DAC Data Bit 3B3
DAC Data Bit 2B2
DAC Data Bit 1B1
DAC Data Bit 0 (LSB)B0*
DATA BITSCONTROL BITS