DAC1221

16-Bit Low Power

DIGITAL-TO-ANALOG CONVERTER

FEATURES

16-BIT MONOTONICITY GUARANTEED

OVER 40

C TO +85

LOW POWER: 1.2mW

VOLTAGE OUTPUT

SETTLING TIME: 2ms to 0.012%

MAX LINEARITY ERROR: 30ppm

ON-CHIP CALIBRATION

APPLICATIONS

PROCESS CONTROL

ATE PIN ELECTRONICS

CLOSED-LOOP SERVO-CONTROL

SMART TRANSMITTERS

PORTABLE INSTRUMENTS

VCO CONTROL

DESCRIPTION

The DAC1221 is a Digital-to-Analog (D/A) converter
offering 16-bit monotonic performance over the speci-
fied temperature range. It utilizes delta-sigma technol-
ogy to achieve inherently linear performance in a
small package at very low power. The output range is
two times the external reference voltage. On-chip
calibration circuitry dramatically reduces offset and
gain errors.

The DAC1221 features a synchronous serial interface.
In single converter applications, the serial interface can
be accomplished with just two wires, allowing low-
cost isolation. For multiple converters, a CS signal
allows for selection of the appropriate D/A converter.

The DAC1221 has been designed for closed-loop
control applications in the industrial process control
market, and high resolution applications in the test and
measurement market. It is also ideal for remote appli-
cations, battery-powered instruments, and isolated sys-
tems. The DAC1221 is available in a SSOP-16 package.

PDS-1519B

Printed in U.S.A. May, 2000

International Airport Industrial Park · Mailing Address: PO Box 11400, Tucson, AZ 85734 · Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 · Tel: (520) 746-1111

Twx: 910-952-1111 · Internet: http://www.burr-brown.com/ · Cable: BBRCORP · Telex: 066-6491 · FAX: (520) 889-1510 · Immediate Product Info: (800) 548-6132

DAC1221

For most current data sheet and other product

information, visit www.burr-brown.com

Clock Generator

Serial

Interface

Second-Order

Modulator

Instruction Register
Command Register

Data Register

Offset Register

Full-Scale Register

Microcontroller

First-Order

Switched

Capacitor Filter

Second-Order

Continuous

Time Post Filter

Modulator Control

OUT

REF

DGND

AGND

SDIO

OUT

SCLK

DAC1221

SPECIFICATIONS

All specifications T

MIN

to T

MAX

, AV

= DV

= +3V, f

XIN

= 2.5MHz, V

REF

= +1.25V, C

= 2.2nF, C

= 150pF, C

= 6.8nF, unless otherwise noted.

DAC1221E

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

ACCURACY
Monotonicity

Bits

Linearity Error

(1)

ppm of FSR

Offset Error

(2)

OUT

= 20mV, CALPIN = 1

(6)

190

Offset Error Drift

(3)

Midscale Error

(2)

OUT

= V

REF

, CALPIN = 1

(6)

Midscale Error Drift

(3)

Gain Error

(2)

CALPIN = 1

(6)

0.015

Gain Error Drift

(3)

ppm/

Power-Supply Rejection Ratio

at DC, dB = 20log(

OUT

)

ANALOG OUTPUT
Output Voltage

(4)

2 · V

REF

Output Current

(1)

0.25

Capacitive Load

500

Short-Circuit Current

Short-Circuit Duration

GND or V

Indefinite

DYNAMIC PERFORMANCE
Settling Time

(1,5)

0.012%

1.8

Output-Noise Voltage

1Hz to 2kHz

Vrms

REFERENCE INPUT
Input Voltage

1.125

1.25

1.375

Input Impedance

DIGITAL INPUT/OUTPUT
Logic Family

TTL-Compatible CMOS

Logic Levels (all except X

)

2.0

+ 0.3

0.3

0.8

= 0.8mA

2.4

= 1.6mA

0.4

Input-Leakage Current

Frequency Range (f

XIN

)

1.0

2.5

MHz

Data Format

User Programmable

Offset Two's Complement

or Straight Binary

POWER SUPPLY REQUIREMENTS
Power-Supply Voltage

2.7

3.3

Supply Current

Analog Current

320

Digital Current

Power Dissipation

Normal Mode

1.2

1.6

Sleep Mode

0.25

TEMPERATURE RANGE
Specified Performance

+85

NOTES: (1) Valid from AGND + 20mV to 2 · V

REF

. (2) Applies after calibration. (3) Recalibration can remove these errors. (4) Ideal output voltage. (5) Using external

low-pass filter with 2kHz corner frequency. (6) See Command Register for description of CALPIN.

DAC1221

The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes
no responsibility for the use of this information, and all use of such information shall be entirely at the user's own risk. Prices and specifications are subject to change
without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant
any BURR-BROWN product for use in life support devices and/or systems.

ABSOLUTE MAXIMUM RATINGS

(1)

to DV

...................................................................................

0.3V

to AGND ........................................................................ 0.3V to 4V

to DGND ....................................................................... 0.3V to 4V

AGND to DGND ...............................................................................

0.3V

REF

Voltage to AGND .......................................................... 1.0V to 1.5V

Digital Input Voltage to DGND .............................. 0.3V to DV

+ 0.3V

Digital Output Voltage to DGND ........................... 0.3V to DV

+ 0.3V

Package Power Dissipation ............................................. (T

JMAX

) /

Maximum Junction Temperature (T

JMAX

) ..................................... +150

Thermal Resistance,

SSOP-16 ............................................................................... 200

C/ W

Lead Temperature (soldering, 10s) ............................................... +300

NOTE: (1) Stresses above those listed under "Absolute Maximum Ratings"
may cause permanent damage to the device. Exposure to absolute maximum
conditions for extended periods may affect device reliability.

ELECTROSTATIC
DISCHARGE SENSITIVITY

This integrated circuit can be damaged by ESD. Burr-Brown
recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling
and installation procedures can cause damage.

ESD damage can range from subtle performance degradation
to complete device failure. Precision integrated circuits may
be more susceptible to damage because very small parametric
changes could cause the device not to meet its published
specifications.

PIN CONFIGURATION

Top View

SSOP

PIN DESCRIPTIONS

PIN

NAME

DESCRIPTION

Digital Supply, +3V nominal

OUT

Digital, System Clock Output

Digital, System Clock Input

DGND

Digital Ground

Analog Supply, +3V nominal

DNC

Do Not Connect

Analog, Filter Capacitor

OUT

Analog Output Voltage

REF

Analog, Reference Input

AGND

Analog Ground

Digital, Chip Select Input

SDIO

Digital, Serial Data Input/Output

SCLK

Digital, Clock Input for Serial Data Transfer

OUT

DGND

DNC

SCLK

SDIO

AGND

REF

OUT

DAC1221E

PACKAGE

SPECIFIED

DRAWING

TEMPERATURE

PACKAGE

ORDERING

TRANSPORT

PRODUCT

PACKAGE

NUMBER

RANGE

MARKING

NUMBER

(1)

MEDIA

DAC1221E

SSOP-16

322

C to +85

DAC1221E

Rails

DAC1221E/2K5

Tape and Reel

NOTE: (1) Models with a slash (/) are available only in Tape and Reel in the quantities indicated (e.g., /2K5 indicates 2500 devices per reel). Ordering 2500 pieces
of "DAC1221E/2K5" will get a single 2500-piece Tape and Reel.

PACKAGE/ORDERING INFORMATION

DAC1221

TYPICAL PERFORMANCE CURVES

At T

= +25

C, AV

= DV

= +3.0V, f

XIN

= 2.5MHz, V

REF

= 1.25V, C

= 2.2nF, C

= 150pF and C

= 6.8nF.

POWER SUPPLY REJECTION RATIO vs FREQUENCY

Frequency (Hz)

100

1000

10000

100000

PSRR (dB)

FULL SCALE OUTPUT SWING

Time (ms)

Output (V)

3.0

2.5

2.0

1.5

1.0

0.5

Time (ms)

SETTLING TIME: 20mV to FS

Around FS (

300

600

900

1200

1500

SETTLING TIME: FS to 20mV

Time (ms)

Around 20mV (

1500

1200

900

600

300

OFFSET vs TEMPERATURE

Temperature (

100

Offset (mV)

(can be corrected with calibration)

OUTPUT NOISE VOLTAGE vs FREQUENCY

Frequency (Hz)

100

1000

10000

Noise (nv/

Hz)

10000

1000

100

DAC1221

FIGURE 1. Capacitor Connections.

THEORY OF OPERATION

The DAC1221 is a precision, high dynamic range, self-
calibrating, 16-bit, delta-sigma digital-to-analog converter.
It contains a second-order delta-sigma modulator, a first-
order switched-capacitor filter, a second-order continuous-
time post filter, a microcontroller including the Instruction,
Command and Calibration registers, a serial interface, and a
clock generator circuit.

The design topology provides low system noise and good
power-supply rejection. The modulator frequency of the
delta-sigma D/A converter is controlled by the system clock.

The DAC1221 also includes complete onboard calibration
that can correct for internal offset and gain errors.
The calibration registers are fully readable and writable.
This feature allows for system calibration. The various
settings, modes, and registers of the DAC1221 are read or
written via a synchronous serial interface. This interface
operates as an externally clocked interface.

DEFINITION OF TERMS

Differential Nonlinearity Error--The differential
nonlinearity error is the difference between an actual step
width and the ideal value of 1 LSB. If the step width is
exactly 1 LSB, the differential nonlinearity error is zero.
A differential nonlinearity specification of less than 1 LSB
guarantees monotonicity.

Drift--The drift is the change in a parameter over tempera-
ture.

Full-Scale Range (FSR)--This is the magnitude of the
typical analog output voltage range which is 2 · V

REF

For example, when the converter is configured with a 1.25V
reference, the full-scale range is 2.5V.

Gain Error--This error represents the difference in the
slope between the actual and ideal transfer functions.

Linearity Error--The linearity error is the deviation of the
actual transfer function from an ideal straight line between
the data end points.

Least Significant Bit (LSB) Weight--This is the ideal
change in voltage that the analog output will change with a
change in the digital input code of 1 LSB.

Monotonicity--Monotonicity assures that the analog output
will increase or stay the same for increasing digital input
codes.

Offset Error--The offset error is the difference between the
expected and actual output, when the output is zero. The
value is calculated from measurements made when
V

OUT

= 20mV.

Settling Time--The settling time is the time it takes the
output to settle to its new value after the digital code has
been changed.

XIN

--The frequency of the crystal oscillator or CMOS-

compatible input signal at the X

input of the DAC1221.

ANALOG OPERATION

The system clock is divided down to provide the sample
clock for the modulator. The sample clock is used by the
modulator to convert the multi-bit digital input into a 1-bit
digital output stream. The use of a 1-bit DAC provides
inherent linearity. The digital output stream is then con-
verted into an analog signal via the 1-bit DAC and then
filtered by the 1st-order switched-capacitor filter.

The output of the switched-capacitor filter feeds into the
continuous time filter. The continuous time filter uses exter-
nal capacitors, C

and C

, to adjust the settling time. The

connections for capacitors are shown in Figure 1. C

con-

nects to V

REF

. C

connects between the C

pins. C

connected between C

and V

REF

, and is used for calibration.

CALIBRATION

The DAC1221 offers a self-calibration mode which auto-
matically calibrates the output offset and gain. The calibra-
tion is performed once and then normal operation is re-
sumed. In general, calibration is recommended immediately
after power-on and whenever there is a "significant" change
in the operating environment. The amount of change which
should cause re-calibration is dependent on the application.
Where high accuracy is important, re-calibration should be
done on changes in temperature and power supply.

After a calibration has been accomplished, the Offset Cali-
bration Register (OCR) and the Full-Scale Calibration Reg-
ister (FCR) contain the results of the calibration.

Note that the values in the calibration registers will vary
from configuration to configuration and from part to part.

REF

DAC1221

6.8nF

2.2nF

150pF

NOTE: C

and C

should be NPO type capacitors.

DAC1221

OPA336

+3V

87.6k

REF1004-1.2

20k

0.10

0.1

0.10

To V

REF

100

FIGURE 2. Recommended External Voltage Reference Circuit for Best Low Noise Operation with the DAC1221.

Self Calibration

A self-calibration is performed after the bits "01" have been
written to the Command Register Operation Mode bits
(MD1 and MD0). This initiates a self-calibration on the next
clock cycle. The offset correction code is determined by a
repeated sequence of auto-zeroing the calibration compara-
tor to the offset reference and then comparing the DAC
output to the offset reference value. The end result is the
averaged, Offset Two's Complement adjusted, and placed in
the OCR. The gain correction is done in a similar fashion,
except the correction is done against V

REF

to eliminate

common-mode errors. The FCR result represents the gain
code and is not Offset Two's Complement adjusted.

The calibration function takes between 300ms and 500ms
(for f

XIN

= 2.5MHz) to complete. Once calibration is initi-

ated, further writing of register bits is disabled until calibra-
tion completes. The status of calibration can be verified by
reading the status of the Command Register Operation Mode
bits (MD1 and MD0). These bits will return to normal mode
"00" when calibration is complete.

It is recommended that the output be connected during
calibration. The output isolation is controlled by the CALPIN
bit in the CMR register. Setting the CALPIN bit will connect
the output and clearing the bit will disconnect and isolate the
output. Although it is recommended to connect the output
during calibration, the load impedance should be such that
the DAC1221 is not required to sink any current, but is able
to source up to the specified maximum.

Output Mode

The output of the DAC1221 can be synchronously reset.
By setting the CLR bit in the CMR, the data input register
is cleared to zero. This will result in an output of 0V when
DF = 1, or V

REF

when DF = 0.

The settling time is determined by the DISF and ADPT bits
of the command register. The default state of DISF = 0 and
ADPT = 0 enables fast settling, unless the output step is
small (

40mV). However, the DAC1221 can be forced to

always use fast settling if the ADPT bit is set to 1. If DISF
is set to 1, all fast settling is disabled.

The CRST bit of the CMR can be used to reset the offset and
calibration registers. By setting the CRST bit, the contents of
the calibration registers are reset to 0.

REFERENCE INPUT

The reference input voltage of 1.25V can be directly con-
nected to V

REF

pin.

The recommended reference circuit for the DAC1221 is
shown in Figure 2.

DIGITAL OPERATION

SYSTEM CONFIGURATION

The DAC1221 is controlled by 8-bit instruction codes (INSR)
and 16-bit command codes (CMR) via the serial interface,
which is externally clocked.

The DAC1221 Microcontroller (MC) consists of an ALU
and a register bank. The MC has three states: power-on
reset, calibration, and normal operation. In the power-on
reset state, the MC resets all the registers to their default
states. In the calibration state, the MC performs offset and
gain self-calibration. In the normal state, the MC performs
D/A conversions.

The DAC1221 has five internal registers, as shown in Table I.
Two of these, the Instruction Register (INSR) and the
Command Register (CMR), control the operation of the
converter. The Instruction Register utilizes an 8-bit instruc-
tion code to control the serial interface to determine whether
the next operation is either a read or a write, to control the
word length, and to select the appropriate register to
read/write. Communication with the DAC1221 is controlled
via the INSR. Under normal operation, the INSR is written
as the first part of each serial communication. The instruc-
tion that is sent determines what type of communication will
occur next. It is not possible to read the INSR. The Com-
mand Register has a 16-bit command code to set up the

INSR

Instruction Register

8 Bits

DIR

Data Input Register

16 Bits

CMR

Command Register

16 Bits

OCR

Offset Calibration Register

24 Bits

FCR

Full-Scale Calibration Register

24 Bits

TABLE I. DAC1221 Registers.

DAC1221

TABLE II. Instruction Register.

MSB

LSB

R/W

MB1

MB0

NOTE: INSR is a write-only register with the MSB (Most Significant Byte and
Bit) written first, independent of the BD bit.

Data Input Register Byte 1 MSB

Data Input Register Byte 0 LSB

Reserved

Command Register Byte 1 MSB

Command Register Byte 0 LSB

Reserved

Offset Cal Register Byte 2 MSB

Offset Cal Register Byte 1

Offset Cal Register Byte 0 LSB

Reserved

Full-Scale Cal Register Byte 2 MSB

Full-Scale Cal Register Byte 1

Full-Scale Cal Register Byte 0 LSB

Reserved

TABLE III. A3 - A0 Addressing.

MSB

Byte 1

ADPT

CALPIN

CRST

Byte 0

LSB

CLR

DISF

MSB

MD1

MD0

TABLE IV. Command Register.

R/W

Write

Read

MB1

MB0

1 Byte

2 Bytes

3 Bytes

DAC1221 operation mode, settling mode and data format.
The Data Input Register (DIR) contains the value for the
next conversion. The Offset and Full-Scale Calibration Reg-
isters (OCR and FCR) contain data used for correcting the
internal conversion value after it is placed into the DIR. The
data in these two registers may be the result of a calibration
routine, or they may be values which have been written
directly via the serial interface.

INSTRUCTION REGISTER (INSR)

Each serial communication starts with the 8 bits of INSR
being sent to the DAC1221. The read/write bit, the number
of bytes (n), and the starting register address are defined in
Table II. When the n bytes have been transferred, the
instruction is complete. A new communication cycle is
initiated by sending a new INSR (under restrictions outlined
in the Interfacing section).

R/W (Read/Write) Bit--For a write operation to occur, this
bit of the INSR must be 0. For a read, this bit must be 1, as
shown:

MB1, MB0 (Multiple Bytes) Bits--These two bits are used
to control the word length (number of bytes) of the read or
write operation, as shown:

A3 A0 (Address) Bits--These four bits select the begin-
ning register location that will be read from or written to, as
shown in Table III. Each subsequent byte will be read from
or written to the next higher location (increment address). If
the BD bit in the Command register is set, each subsequent
byte will be read from or written to the next lower location
(decrement address). This bit does not affect INSR register

or the write operation for the CMR register. If the next
location is reserved in Table III, the results are unknown.
Reading or writing continues until the number of bytes
specified by MB1 and MB0 have been transferred.

COMMAND REGISTER (CMR)

The CMR controls all of the functionality of the DAC1221.
The new configuration is latched in on the negative transi-
tion of SCLK for the last bit of the last byte of data being
written to the command register. The organization of the
CMR is comprised of 16 bits of information in 2 bytes of 8
bits each.

ADPT (Adaptive Filter Disable) Bit--The ADPT bit de-
termines if the adaptive filter is enabled or disabled. When
the Adaptive Filter is enabled, the DAC1221 does fast
settling only when there is an output step of larger than

40mV. For small changes in the data, fast settling is not

necessary. When ADPT = 1, the Adaptive Filter is disabled
and the DAC1221 will not look at the size of a step to
determine the necessity of using fast settling. In either case,
fast settling can be defeated if DISF = 1.

ADPT

Enabled (default)

Disabled

DAC1221

CALPIN (Calibration Pin) Bit--The CALPIN bit deter-
mines if the output is isolated or connected during calibration.

CRST

OFF (default)

Reset

CRST (Calibration Reset) Bit--The CRST bit resets the
offset and full-scale calibration registers, as shown:

Offset Two's

Straight

Complement

Binary

OUT

DF = 0

DF = 1

(default)

8000

0000

8000

REF

7FFF

FFFF

2 · V

REF

Input Code

DISF (Disable Fast Settling) Bit--The DISF bit disables
the fast settling option. If this bit is zero the fast settling
performance is determined by the ADPT bit.

DISF

Fast Settling (default)

Disable Fast Settling

BD (Byte Order) Bit--The BD bit controls the order in
which bytes of data are transferred (either most significant
byte first (MSBF) or least significant byte first (LSBF)), as
shown:

BD bit:

0 (default)

INSR

write only

MSBF

CMR

MSBF

LSBF

MSBF

DIR

MSBF

LSBF

MSBF

LSBF

OCR

MSBF

LSBF

MSBF

LSBF

FCR

MSBF

LSBF

MSBF

LSBF

read

write

Care must be observed in reading the Command Register if
the state of the BD bit is unknown. If a two byte read is
started at address 0100 with BD = 0, it will read 0100, then
0101. However, if BD = 1, it will read 0100, then 0011. If
the BD bit is unknown, all reads of the command register are
best performed as read commands of one byte.

MSB (Bit Order) Bit--The MSB bit controls the order in
which bits within a byte of data are read or written (either
most significant bit first or least significant bit first), as
follows:

MD1

MD0

Normal Mode

Self-Cal

Sleep (default)

Reserved

MSB

MSB First (default)

LSB First

MD1 MD0 (Operating Mode) Bits--The Operating
Mode bits control the calibration functions of the DAC1221.
The Normal Mode is used to perform conversions. The Self-
Calibration Mode is a one-step calibration sequence that
calibrates both the offset and full scale.

Offset Calibration Register (OCR)

The OCR is a 24-bit register containing the offset correction
factor that is used to apply a correction to the digital input
before it is transferred to the modulator. The results of the
self-calibration process will be written to this register.

The OCR is both readable and writable via the serial inter-
face. For applications requiring a more accurate calibration,
a calibration can be performed, the results averaged, and a
more precise offset calibration value written back to the
OCR.

The actual OCR value will change from part to part and with
configuration, temperature, and power supply.

In addition, be aware that the contents of the OCR are not
used to directly correct the digital input. Rather, the correc-
tion is a function of the OCR value. This function is linear
and two known points can be used as a basis for interpolat-
ing intermediate values for the OCR.

The results of calibration are averaged, Offset Two's Comple-
ment adjusted, and placed in the OCR.

CALPIN

Output Isolated (default)

Output Connected

CLR (Clear) Bit--The CLR bit synchronously resets the
data input register to zero. The analog output will be based
on the DF bit--if 1, the output will be 0V; if 0, the output
will be V

REF

DF (Data Format) Bit--The DF bit controls the format of
the input data, shown in hexadecimal (either Offset Two's
Complement or Straight Binary), as shown:

MSB

Byte 2

OCR23

OCR22

OCR21

OCR20

OCR19

OCR18

OCR17

OCR16

Byte 1

OCR15

OCR14

OCR13

OCR12

OCR11

OCR10

OCR9

OCR8

Byte 0

LSB

OCR7

OCR6

OCR5

OCR4

OCR3

OCR2

OCR1

OCR0

TABLE V. Offset Calibration Register.

DAC1221

MSB

Byte 2

FCR23

FCR22

FCR21

FCR20

FCR19

FCR18

FCR17

FCR16

Byte 1

FCR15

FCR14

FCR13

FCR12

FCR11

FCR10

FCR9

FCR8

Byte 0

LSB

FCR7

FCR6

FCR5

FCR4

FCR3

FCR2

FCR1

FCR0

TABLE VI. Full-Scale Calibration Register.

MSB

Byte 1

DIR15

DIR14

DIR13

DIR12

DIR11

DIR10

DIR9

DIR8

Byte 0

LSB

DIR7

DIR6

DIR5

DIR4

DIR3

DIR2

DIR1

DIR0

TABLE VII. Data Input Register.

Full-Scale Calibration Register (FCR)

The FCR is a 24-bit register which contains the full-scale
correction factor that is applied to the digital input before it
is transferred to the modulator. The contents of this register
will be the result of a self-calibration, or written to by the
user.

The FCR is both readable and writable via the serial inter-
face. For applications requiring a more accurate calibration,
a calibration can be performed, the results averaged, and a
more precise value written back to the FCR.

The actual FCR value will change from part to part and with
configuration, temperature, and power supply.

In addition, be aware that the contents of the FCR are not
used to directly correct the digital input. Rather, the correc-
tion is a function of the FCR value. This function is linear
and two known points can be used as a basis of interpolating
intermediate values for the FCR. The contents of the FCR
are in unsigned binary format. This is not affected by the DF
bit in the Command Register.

Data Input Register (DIR)

The DIR is a 16-bit register which contains the digital input
value (see Table VII). The register is latched on the falling
edge of the last bit of the last byte sent. The contents of the
DIR are then loaded into the modulator. This means that the
DIR register can be updated after sending 1 or 2 bytes, which
is determined by the MB1 and MB0 bits in the Instruction
Register. The contents of the DIR can be Offset Two's
Complement or Straight Binary.

SLEEP MODE

The Sleep Mode is entered after the bit combination 10 has
been written to the CMR Operation Mode bits (MD1 and
MD0). This mode ends when these bits are changed to a
value other than 10.

Communication with the DAC1221 can continue during
Sleep Mode. When a new mode (other than Sleep) has been
entered, the DAC1221 will execute a very brief internal
power-up sequence of the analog and digital circuitry. In
addition, the settling of the external V

REF

and other circuitry

must be taken into account to determine the amount of time
required to resume normal operation.

Once serial communication is resumed, the Sleep Mode is
exited by changing the MD1 - MD0 bits to any other mode.
When a new mode (other than Sleep) has been entered, the
DAC1221 will execute a very brief internal power-up se-
quence of the analog and digital circuitry. In addition, the
settling of the external V

REF

and other circuitry must be

taken into account to determine the amount of time required
to resume normal operation.

SERIAL INTERFACE

The DAC1221 includes a flexible serial interface which can
be connected to microcontrollers and digital signal proces-
sors in a variety of ways. Along with this flexibility, there is
also a good deal of complexity. This section describes the
trade-offs between the different types of interfacing methods
in a top-down approach--starting with the overall flow and
control of serial data, moving to specific interface examples,
and then providing information on various issues related to
the serial interface.

Reset, Power-On Reset and Brown-Out

The DAC1221 contains an internal power-on reset circuit. If
the power supply ramp rate is greater than 50mV/ms, this
circuit will be adequate to ensure the device powers up
correctly. Due to oscillator settling considerations, commu-
nication to and from the DAC1221 should not occur for at
least 25ms after power is stable.

If this requirement cannot be met or if the circuit has brown-
out considerations, the timing diagram of Figure 3 can be
used to reset the DAC1221. This accomplishes the reset by
controlling the duty cycle of the SCLK input.

Sleep mode is the default state after power on or reset. The
output is high impedance during sleep mode.

DAC1221

SCLK

Reset On

Falling Edge

FIGURE 3. Resetting the DAC1221.

: > 512 · t

XIN

< 800 · t

XIN

: > 10 · t

XIN

: > 1024 · t

XIN

< 1800 · t

XIN

2048 · t

XIN

< 2400 · t

XIN

I/O Recovery

If serial communication stops during an instruction or data
transfer for longer than 100ms (for f

XIN

= 2.5MHz), the

DAC1221 will reset its serial interface. This will not affect
the internal registers. The main controller must not continue
the transfer after this event, but must restart the transfer from
the beginning. This feature is very useful if the main control-
ler can be reset at any point. After reset, simply wait 200ms
(for f

XIN

= 2.5MHz) before starting serial communication.

Isolation

The serial interface of the DAC1221 provides for simple
isolation methods. An example of an isolated two-wire
interface is shown in Figure 4.

Using CS

The serial interface may make use of the CS signal, or this
input may simply be tied LOW. There are several issues
associated with choosing to do one or the other. The CS
signal does not directly control the tri-state condition of the
SDIO output. These signals are normally in the tri-state

condition. They only become active when serial data is
being transmitted from the DAC1221. If the DAC1221 is in
the middle of a serial transfer and the SDIO is an output,
taking CS HIGH will not tri-state the output signal.

If there are multiple serial peripherals utilizing the same
serial I/O lines and communication may occur with any
peripheral at any time, the CS signal must be used. The CS
signal is then used to enable communication with the
DAC1221.

TIMING

The maximum serial clock frequency cannot exceed the
DAC1221 X

frequency divided by 10. Table VIII and

Figures 5 through 9 define the basic digital timing character-
istics of the DAC1221. Figure 5 and the associated timing
symbols apply to the X

input signal. Figures 6 through 9

and associated timing symbols apply to the serial interface
signals (SCLK, SDIO, and CS). The serial interface is
discussed in detail in the Serial Interface section.

OUT

DGND

DNC

SCLK

SDIO

AGND

REF

OUT

DAC1221

5.6pF

XTAL

REF

P1.1

P1.0

8051

Opto

Coupler

Opto

Coupler

Isolated

Power

= DGND

= AGND

= Isolated

FIGURE 4. Isolation for Two-Wire Interface.

DAC1221

SYMBOL

DESCRIPTION

MIN

NOM

MAX

UNITS

XIN

Clock Frequency

2.5

MHz

XIN

Clock Period

400

1000

Clock High

0.4 · t

XIN

Clock LOW

0.4 · t

XIN

SCLK HIGH

5 · t

XIN

SCLK LOW

5 · t

XIN

Data In Valid to SCLK Falling Edge (Setup)

SCLK Falling Edge to Data In Not Valid (Hold)

Data Out Valid After Rising Edge of SCLK (Hold)

SCLK Rising Edge to New Data Out Valid (Delay)

(1)

Falling Edge of Last SCLK for INSR to Rising Edge of First

13 · t

XIN

SCLK for Register Data

Falling Edge of CS to Rising Edge of SCLK

11 · t

XIN

Falling Edge of Last SCLK for INSR to SDIO as Output

8 · t

XIN

10 · t

XIN

SDIO as Output to Rising Edge of First SCLK for Register Data

4 · t

XIN

Falling Edge of Last SCLK for Register Data to SDIO Tri-State

4 · t

XIN

6 · t

XIN

Falling Edge of Last SCLK for Register Data to Rising Edge

41 · t

XIN

of First SCLK of next INSR (CS Tied LOW)

Rising Edge of CS to Falling Edge of CS (Using CS)

22 · t

XIN

NOTE: (1) With 10pF load.

TABLE VIII. Digital Timing Characteristics.

XIN

SCLK

SDIO

IN7

IN0

IN1

INM

IN1

IN0

IN7

Write Register Data

IN7

OUT0

OUT1

OUTM

IN1

IN0

IN7

Read Register Data

SCLK

SDIO

SCLK

SDIO

IN7

IN0

IN1

IN0

IN1

IN7

INM

Write Register Data

SDIO

IN7

OUT0

OUT1

IN0

IN1

IN7

OUTM

Read Register Data

FIGURE 5. X

Clock Timing.

FIGURE 6. Serial Input/Output Timing.

FIGURE 7. Serial Interface Timing (CS always LOW).

FIGURE 8. Serial Interface Timing (using CS).

DAC1221

OUT MSB

OUT0

SDIO is an input

SDIO is an output

IN7

IN0

SCLK

SDIO

Start

Writing

Start

Reading

External device

generates 8

serial clock cycles

and transmits

instruction register

data via SDIO

CS taken HIGH

for t

periods

minimum

(or CS tied LOW)

External device

generates n

serial clock cycles

and transmits

specified

via SDIO

state

instructions?

End

HIGH

Yes

LOW

Is next

instruction

a read?

Yes

state

From Read

flowchart

HIGH

LOW

To Read

flowchart

External device

generates 8 serial

clock cycles and

transmits instruction

via SDIO

SDIO input to

output transition

state

instructions?

End

HIGH

Yes

LOW

Is next

instruction

a Write?

Yes

state

To Write

flowchart

HIGH

LOW

To Write

flowchart

External device

generates n serial

clock cycles and

receives specified

SDIO transitions to

tri-state condition

CS taken HIGH

for t

periods

minimum

(or CS tied LOW)

FIGURE 9. SDIO Input to Output Transition Timing.

FIGURE 10. Flowchart for Writing and Reading Register Data.

DAC1221

LAYOUT

POWER SUPPLIES

The DAC1221 requires the digital supply (DV

) to be no

greater than the analog supply (AV

) +0.3V. In the majority

of systems, this means that the analog supply must come up
first, followed by the digital supply and V

REF

. Failure to

observe this condition could cause permanent damage to the
DAC1221.

Inputs to the DAC1221, such as SDIO or V

REF

, should not

be present before the analog and digital supplies are on.
Violating this condition could cause latch-up. If these sig-
nals are present before the supplies are on, series resistors
should be used to limit the input current.

The best scheme is to power the analog section of the design
and AV

of the DAC1221 from one +3V supply, and the

digital section (and DV

) from a separate +3V supply. The

analog supply should come up first. This will ensure that
SCLK, SDIO, CS and V

REF

do not exceed AV

, that the

digital inputs are present only after AV

has been estab-

lished, and that they do not exceed DV

The analog supply should be well regulated and low noise.
For designs requiring very high resolution from the DAC1221,
power supply rejection will be a concern. See the "PSRR vs
Frequency" curve in the Typical Performance Curves sec-
tion of this data sheet for more information.

The requirements for the digital supply are not as strict.
However, high frequency noise on DV

can capacitively

couple into the analog portion of the DAC1221. This noise
can originate from switching power supplies, very fast
microprocessors, or digital signal processors.

If one supply must be used to power the DAC1221, the
AV

supply should be used to power DV

. This connec-

tion can be made via a 10

resistor which, along with the

decoupling capacitors, will provide some filtering between
DV

and AV

. In some systems, a direct connection can

be made. Experimentation may be the best way to determine
the appropriate connection between AV

and DV

GROUNDING

The analog and digital sections of the design should be
carefully and cleanly partitioned. Each section should have
its own ground plane with no overlap between them. AGND
should be connected to the analog ground plane, as well as
all other analog grounds. DGND should be connected to the
digital ground plane, and all digital signals referenced to this
plane.

The DAC1221 pinout is such that the converter is cleanly
separated into an analog and digital portion. This should
allow simple layout of the analog and digital sections of the
design.

For a single converter system, AGND and DGND of the
DAC1221 should be connected together, underneath the
converter. Do not join the ground planes. Instead, connect
the two with a moderate signal trace. For multiple convert-
ers, connect the two ground planes at one location, as central
to all of the converters as possible. In some cases, experi-
mentation may be required to find the best point to connect
the two planes together. The printed circuit board can be
designed to provide different analog/digital ground connec-
tions via short jumpers. The initial prototype can be used to
establish which connection works best.

DECOUPLING

Good decoupling practices should be used for the DAC1221
and for all components in the design. All decoupling capaci-
tors, and specifically the 0.1

F ceramic capacitors, should

be placed as close as possible to the pin being decoupled. A
1

F to 10

F capacitor, in parallel with a 0.1

F ceramic

capacitor, should be used to decouple AV

to AGND. At a

minimum, a 0.1

F ceramic capacitor should be used to

decouple DV

to DGND, as well as for the digital supply

on each digital component.

Ð­Ð»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: DAC1221

ÐÐ»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: DAC1221