REV. A
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties that
may result from its use. No license is granted by implication or otherwise
under any patent or patent rights of Analog Devices.
a
AD7390/AD7391
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700 www.analog.com
Fax: 781/326-8703 © Analog Devices, Inc., 2002
3 V Serial-Input
Micropower 10-Bit and 12-Bit DACs
FUNCTIONAL BLOCK DIAGRAM
EN
AD7390
DAC REGISTER
12-BIT DAC
12
12
SERIAL REGISTER
REF
V
DD
CLR
LD
CLK
SDI
GND
V
OUT
FEATURES
Micropower—100 A
Single-Supply—2.7 V to 5.5 V Operation
Compact 1.75 mm Height SO-8 Package
and 1.1 mm Height TSSOP-8 Package
AD7390—12-Bit Resolution
AD7391—10-Bit Resolution
SPI and QSPI Serial Interface Compatible with Schmitt
Trigger Inputs
APPLICATIONS
Automotive 0.5 V to 4.5 V Output Span Voltage
Portable Communications
Digitally Controlled Calibration
GENERAL DESCRIPTION
The AD7390/AD7391 family of 10-bit and 12-bit voltage-
output digital-to-analog converters is designed to operate
from a single 3 V supply. Built using a CBCMOS process,
these monolithic DACs offer the user low cost, and ease-of-use
in single-supply 3 V systems. Operation is guaranteed over the
supply voltage range of 2.7 V to 5.5 V consuming less than 100 µA
making this device ideal for battery operated applications.
The full-scale voltage output is determined by the external
reference input voltage applied. The rail-to-rail REF
IN
to
DAC
OUT
allows for a full-scale voltage set equal to the positive
supply V
DD
or any value in between.
A doubled-buffered serial-data interface offers high-speed,
3-wire, SPI and microcontroller compatible inputs using data
in (SDI), clock (CLK) and load strobe (LD) pins. Addition-
ally, a CLR input sets the output to zero scale at power on or
upon user demand.
Both parts are offered in the same pinout to allow users to select
the amount of resolution appropriate for their application without
circuit card redesign.
The AD7390/AD7391 are specified over the extended industrial
(40°C to 85°C) temperature range. The AD7391AR is
specified for the 40°C to 125°C automotive temperature
range. The AD7390/AD7391s are available in plastic DIP, and
low profile 1.75 mm height SO-8 surface mount packages. The
AD7391ARU is available for ultracompact applications in a thin
1.1 mm TSSOP-8 package.
CODE – Decimal
1.00
1.00 0 4096512
DNL – LSB
1024 1536 2048 2560 3072 3584
0.75
0.00
0.25
0.50
0.75
0.50
0.25
AD7390
V
DD
= 3.0V
T
A
= 55C, +25C, +85C
SUPERIMPOSED
Figure 1. Differential Nonlinearity Error vs. Code
AD7390
V
DD
= 3.0V
V
REF
= 2.5V
+25C, +85C
CODE – Decimal
0 4096512 1024 1536 2048 2560 3072 2584
2.0
2.0
INL – LSB
1.5
0.0
0.5
1.0
1.5
1.0
0.5
55C
Figure 2. INL Error vs. Code and Temperature
REV. A
–2–
AD7390/AD7391–SPECIFICATIONS
Parameter Symbol Conditions 3 V 10% 5 V 10% Unit
STATIC PERFORMANCE
Resolution
1
N 12 12 Bits
Relative Accuracy
2
INL T
A
= 25°C±1.6 ±1.6 LSB max
INL T
A
= 40°C, 85°C±2.0 ±2 LSB max
Differential Nonlinearity
2
DNL T
A
= 25°C, Monotonic ±0.9 ±0.9 LSB max
DNL Monotonic ±1±1 LSB max
Zero-Scale Error V
ZSE
Data = 000
H
4.0 4.0 mV max
Full-Scale Voltage Error V
FSE
T
A
= 25°C, 85°C, Data = FFF
H
±8±8mV max
V
FSE
T
A
= 40°C, Data = FFF
H
±20 ±20 mV max
Full-Scale Tempco
3
TCV
FS
16 16 ppm/°C typ
REFERENCE INPUT
V
REF IN
Range V
REF
0/V
DD
0/V
DD
V min/max
Input Resistance R
REF
2.5 2.5 MΩ typ
4
Input Capacitance
3
C
REF
5 5 pF typ
ANALOG OUTPUT
Output Current (Source) I
OUT
Data = 800
H
, ∆V
OUT
= 5 LSB 1 1 mA typ
Output Current (Sink) I
OUT
Data = 800
H
, ∆V
OUT
= 5 LSB 3 3 mA typ
Capacitive Load
3
C
L
No Oscillation 100 100 pF typ
LOGIC INPUTS
Logic Input Low Voltage V
IL
0.5 0.8 V max
Logic Input High Voltage V
IH
V
DD
0.6 V
DD
0.6 V min
Input Leakage Current I
IL
10 10 µA max
Input Capacitance
3
C
IL
10 10 pF max
INTERFACE TIMING
3, 5
Clock Width High t
CH
50 30 ns min
Clock Width Low t
CL
50 30 ns min
Load Pulsewidth t
LDW
30 20 ns min
Data Setup t
DS
10 10 ns min
Data Hold t
DH
30 15 ns min
Clear Pulsewidth t
CLRW
15 15 ns min
Load Setup t
LD1
30 15 ns min
Load Hold t
LD2
40 20 ns min
AC CHARACTERISTICS
6
Output Slew Rate SR Data = 000
H
to FFF
H
to 000
H
0.05 0.05 V/µs typ
Settling Time t
S
To 0.1% of Full Scale 70 60 µs typ
DAC Glitch Q Code 7FF
H
to 800
H
to 7FF
H
65 65 nVs typ
Digital Feedthrough Q 15 15 nVs typ
Feedthrough V
OUT
/V
REF
V
REF
= 1.5 V
DC
1 V p-p
,
63 63 dB typ
Data = 000
H
, f = 100 kHz
SUPPLY CHARACTERISTICS
Power Supply Range V
DD RANGE
DNL < ±1 LSB 2.7/5.5 2.7/5.5 V min/max
Positive Supply Current I
DD
V
IL
= 0 V, No Load, T
A
= 25°C55 55 µA typ
I
DD
V
IL
= 0 V, No Load 100 100 µA max
Power Dissipation P
DISS
V
IL
= 0 V, No Load 300 500 µW max
Power Supply Sensitivity PSS ∆V
DD
= ±5% 0.006 0.006 %/% max
NOTES
1
One LSB = V
REF
/4096 V for the 12-bit AD7390.
2
The first two codes (000
H
, 001
H
) are excluded from the linearity error measurement.
3
These parameters are guaranteed by design and not subject to production testing.
4
Typicals represent average readings measured at 25°C.
5
All input control signals are specified with
t
R
=
t
F
= 2 ns (10% to 90% of 3 V) and timed from a voltage level of 1.6 V.
6
The settling time specification does not apply for negative going transitions within the last 3 LSBs of ground.
Specifications subject to change without notice.
AD7390 ELECTRICAL CHARACTERISTICS
(@ VREF IN = 2.5 V, –40C < TA < +85C unless otherwise noted.)
REV. A –3–
AD7390/AD7391
AD7391 ELECTRICAL CHARACTERISTICS
Parameter Symbol Conditions 3 V 10% 5 V 10% Unit
STATIC PERFORMANCE
Resolution
1
N 10 10 Bits
Relative Accuracy
2
INL T
A
= 25°C±1.75 ±1.75 LSB max
INL T
A
= 40°C, 85°C, 125°C±2.0 ±2.0 LSB max
INL T
A
= 55°C, S Grade ±3 LSB max
Differential Nonlinearity
2
DNL Monotonic ±0.9 ±0.9 LSB max
DNL T
A
= 55°C, S Grade ±2 LSB max
Zero-Scale Error V
ZSE
Data = 000
H
9.0 9.0 mV max
V
ZSE
T
A
= 55°C, S Grade 20 mV max
Full-Scale Error V
FSE
T
A
= 25°C, 85°C, 125°C, ±32 ±32 mV max
Data = 3FF
H
V
FSE
T
A
= 55°C, S Grade ±55 mV max
Full-Scale Tempco
3
TCV
FS
16 16 ppm/°C typ
TCV
FS
T
A
= 55°C, S Grade 32 ppm/°C typ
REFERENCE INPUT
V
REF IN
Range V
REF
0/V
DD
0/V
DD
V min/max
Input Resistance R
REF
2.5 2.5 MΩ typ
4
Input Capacitance
3
C
REF
5 5 pF typ
ANALOG OUTPUT
Output Current (Source) I
OUT
Data = 800
H
, ∆V
OUT
= 5 LSB 1 1 mA typ
Output Current (Sink) I
OUT
Data = 800
H
, ∆V
OUT
= 5 LSB 3 3 mA typ
Capacitive Load
3
C
L
No Oscillation 100 100 pF typ
LOGIC INPUTS
Logic Input Low Voltage V
IL
0.5 0.8 V max
Logic Input High Voltage V
IH
V
DD
0.6 V
DD
0.6 V min
Input Leakage Current I
IL
10 10 µA max
Input Capacitance
3
C
IL
10 10 pF max
INTERFACE TIMING
3, 5
Clock Width High t
CH
50 30 ns
Clock Width Low t
CL
50 30 ns
Load Pulsewidth t
LDW
30 20 ns
Data Setup t
DS
10 10 ns
Data Hold t
DH
30 15 ns
Clear Pulsewidth t
CLRW
15 15 ns
Load Setup t
LD1
30 15 ns
Load Hold t
LD2
40 20 ns
AC CHARACTERISTICS
6
Output Slew Rate SR Data = 000
H
to 3FF
H
to 000
H
0.05 0.05 V/µs typ
Settling Time t
S
To 0.1% of Full Scale 70 60 µs typ
t
S
T
A
= –55°C, S Grade 100 µs typ
DAC Glitch Q Code 7FF
H
to 800
H
to 7FF
H
65 65 nVs typ
Digital Feedthrough Q 15 15 nVs typ
Feedthrough V
OUT
/V
REF
V
REF
= 1.5 V
DC
1 V p-p, 63 63 dB typ
Data = 000
H
, f = 100 kHz
SUPPLY CHARACTERISTICS
Power Supply Range V
DD RANGE
DNL < ±1 LSB 2.7/5.5 2.7/5.5 V min/max
Positive Supply Current I
DD
V
IL
= 0 V, No Load, T
A
= 25°C55 55 µA typ
I
DD
V
IL
= 0 V, No Load 100 100 µA max
Power Dissipation P
DISS
V
IL
= 0 V, No Load 300 500 µW max
Power Supply Sensitivity PSS ∆V
DD
= ±5% 0.006 0.006 %/% max
NOTES
1
One LSB = V
REF
/1024 V for the 10-bit AD7391.
2
The first two codes (000
H
, 001
H
) are excluded from the linearity error measurement.
3
These parameters are guaranteed by design and not subject to production testing.
4
Typicals represent average readings measured at 25°C.
5
All input control signals are specified with t
R
= t
F
= 2 ns (10% to 90% of 3 V) and timed from a voltage level of 1.6 V.
6
The settling time specification does not apply for negative going transitions within the last 3 LSBs of ground.
Specifications subject to change without notice.
(@ V
REF IN
= 2.5 V, 40
C < T
A
< 85
C unless otherwise noted.)
REV. A
AD7390/AD7391
–4–
PIN DESCRIPTIONS
Pin No. Name Function
1LD Load Strobe. Transfers shift register
data to DAC register while active low.
See truth table for operation.
2 CLK Clock Input. Positive edge clocks data
into shift register.
3 SDI Serial Data Input. Data loads directly
into the shift register.
4CLR Resets DAC register to zero condition.
Active low input.
5 GND Analog and Digital Ground.
6V
OUT
DAC Voltage Output. Full-scale output
1 LSB less than reference input voltage REF.
7V
DD
Positive Power Supply Input. Specified
range of operation 2.7 V to 5.5 V.
8V
REF
DAC Reference Input Pin. Establishes
DAC full-scale voltage.
ABSOLUTE MAXIMUM RATINGS*
V
DD
to GND . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.3 V, 8 V
V
REF
to GND . . . . . . . . . . . . . . . . . . . . . . 0.3 V, V
DD
0.3 V
Logic Inputs to GND . . . . . . . . . . . . . . . . . . . . .0.3 V, 8 V
V
OUT
to GND . . . . . . . . . . . . . . . . . . . . 0.3 V, V
DD
0.3 V
I
OUT
Short Circuit to GND . . . . . . . . . . . . . . . . . . . . . . 50 mA
Package Power Dissipation . . . . . . . . . . . . . (T
J MAX
T
A
)/θ
JA
Thermal Resistance θ
JA
8-Lead Plastic DIP Package (N-8) . . . . . . . . . . . . . 103°C/W
8-Lead SOIC Package (SO-8) . . . . . . . . . . . . . . . . 158°C/W
TSSOP-8 Package (RU-8) . . . . . . . . . . . . . . . . . . . 240°C/W
Maximum Junction Temperature (T
J MAX
) . . . . . . . . . . 150°C
Operating Temperature Range . . . . . . . . . . 40°C to 85°C
AD7391AR . . . . . . . . . . . . . . . . . . . . . . . . 40°C to 125°C
Storage Temperature Range . . . . . . . . . . . 65°C to 150°C
Lead Temperature (Soldering, 10 secs) . . . . . . . . . . . . . 300°C
*Stresses above those listed under Absolute Maximum Ratings may cause perma-
nent damage to the device. This is a stress rating only; functional operation of the
device at these or any other conditions above those indicated in the operational
specification is not implied. Exposure to the above maximum rating conditions for
extended periods may affect device reliability.
DAC
REGISTER
RESET
LOAD
CLK
12-BIT AD7390*
SHIFT REGISTER
D
CLR
LD
CLK
SDI
12
*AD7391 HAS A 10-BIT SHIFT REGISTER
Figure 3. Digital Control Logic
PIN CONFIGURATIONS
TOP VIEW
(Not to
Scale)
1
2
3
4
8
7
6
5
TOP VIEW
(Not to Scale)
8
7
6
5
1
2
3
4
TOP VIEW
(Not to Scale)
8
7
6
5
1
2
3
4
LD
CLK
CLR
SDI
GND
VREF
VDD
VOUT
TSSOP-8 SO-8
P-DIP-8
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection. Although
the AD7390/AD7391 features proprietary ESD protection circuitry, permanent damage may occur
on devices subjected to high-energy electrostatic discharges. Therefore, proper ESD precautions
are recommended to avoid performance degradation or loss of functionality.
WARNING!
ESD SENSITIVE DEVICE
ORDERING GUIDE
1
Temperature Package Package Top Number of Devices
Model Resolution Range Description Option Mark
2
Per Container
AD7390AN 12 40°C to 85°C 8-Lead P-DIP N-8 AD7390
2
50
AD7390AR 12 40°C to 85°C 8-Lead SOIC SO-8 AD7390
3
196
AD7390AR-REEL7 12 40°C to 85°C 8-Lead SOIC SO-8 AD7390
3
1000
AD7391AN 10 40°C to 85°C 8-Lead P-DIP N-8 AD7391
2
50
AD7391AR 10 40°C to 125°C 8-Lead SOIC SO-8 AD7391
3
196
AD7391SR 10 55°C to 125°C 8-Lead SOIC SO-8 AD7391
3
39
AD7391ARU-REEL 10 40°C to 85°C TSSOP-8 RU-8 AD7391A
4
2500
NOTES
1
The AD7390 contains 588 transistors. The die size measures 70 mm 68 mm.
2
Line 1 contains ADI logo symbol and part number. Line 2 contains grade and date code YWW. Line 3 contains the letter G plus the 4-digit lot number.
3
Line 1 contains part number. Line 2 contains grade and date code YWW. Line 3 contains the letter G plus the 4-digit lot number and the ADI logo symbol.
4
Line 1 contains the date code YWW. Line 2 contains the 4-digit part number plus grade.
REV. A
AD7390/AD7391
–5–
DAC REGISTER LOAD
CLK
CLR
LD
CLK
SDI
AD7391AD7390
tLD1
D11
tLD1
D10 D9 D7 D5 D4 D3 D2 D1 D0
tLD2
tDS tDH
tCL tCH
tLDW
tS
tCLRW
tS
0.1% FS
ERROR BAND
SDI
LD
FS
ZS
V
OUT
Figure 4. Timing Diagram
Table I. Control-Logic Truth Table
CLK CLR LD Serial Shift Register Function DAC Register Function
↑H H Shift-Register-Data Advanced One-Bit Latched
X H L Disables Updated with Current Shift Register Contents
X L X No Effect Loaded with all Zeros
X↑H No Effect Latched with all Zeros
X↑L Disabled Previous SR Contents Loaded (Avoid usage of CLR
when LD is logic low, since SR data could be corrupted
if a clock edge takes place, while CLR returns high.)
↑ = Positive logic transition.
X = Don’t care.
Table II. AD7390 Serial Input Register Data Format, Data is Loaded in the MSB-First Format
MSB LSB
B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0
AD7390 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
Table III. AD7391 Serial Input Register Data Format, Data is Loaded in the MSB-First Format
MSB LSB
B9 B8 B7 B6 B5 B4 B3 B2 B1 B0
AD7391 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
REV. A
AD7390/AD7391–Typical Performance Characteristics
–6–
TOTAL UNADJUSTED ERROR – LSB
FREQUENCY
25
05.0
10
5
20
15
5.8 6.6 7.3 8.1 8.9 9.7 10.5 11.2 12.0
SS = 100 UNITS
TA = 25C
VDD = 2.7V
VREF = 2.5V
TPC 1. AD7390 Total Unadjusted
Error Histogram
FREQUENCY – Hz
OUTPUT VOLTAGE NOISE – VHz
10
8
01 10 100k
100 1k 10k
6
4
2
12
14
16
V
DD
= 5V
V
REF
= 2.5V
T
A
= 25C
TPC 4. AD7390 Voltage Noise
Density vs. Frequency
TEMPERATURE – C
SUPPLY CURRENT – A
100
20
55 35 125
15 5 25 65 85 10545
90
60
50
40
30
80
70
SAMPLE SIZE = 300 UNITS
V
DD
= 5.0V, V
LOGIC
= 0V
V
DD
= 3.0V, V
LOGIC
= 0V
V
DD
= 3.6V, V
LOGIC
= 2.4V
TPC 7. AD7390 Supply Current
vs. Temperature
TOTAL UNADJUSTED ERROR – LSB
FREQUENCY
100
0–10
40
20
80
60
–3.3 3.3 10 16 23 30 36 43 50
SS = 300 UNITS
T
A
= 25C
V
DD
= 2.7V
V
REF
= 2.5V
90
70
50
30
10
TPC 2. AD7391 Total Unadjusted
Error Histogram
V
IN
– V
0.0 0.5 3.0
1.0 1.5 2.0 2.5
SUPPLY CURRENT – A
100
95
50
70
65
60
55
90
75
80
85
V
LOGIC
FROM
3.0V TO 0V
V
LOGIC
FROM
0V TO 3.0V
T
A
= 25C
V
DD
= 3.0V
TPC 5. AD7390 Supply Current vs.
Logic Input Voltage
CLOCK FREQUENCY – Hz
SUPPLY CURRENT – A
1000
800
0
1k 10k 10M
100k 1M
600
400
200
a. V
DD
= 5.5V, CODE = 155
H
b. V
DD
= 5.5V, CODE = 3FF
H
c. V
DD
= 2.7V, CODE = 155
H
d
. V
DD
= 2.7V, CODE = 355
H
ab
c
d
V
LOGIC
= 0V TO V
DD
TO 0V
V
REF
= 2.5V
T
A
= 25C
TPC 8. AD7391 Supply Current
vs. Clock Frequency
FULL-SCALE TEMPCO – ppm/ C
FREQUENCY
0–33
12
6
24
18
–30 –26 –23 –20 –16 –13 –10 –6–3
30
0
SS = 100 UNITS
T
A
= 40C TO +85C
V
DD
= 2.7V
V
REF
= 2.5V
TPC 3. AD7391 Full-Scale Output
Tempco Histogram
SUPPLY VOLTAGE – V
12 7
34 56
THRESHOLD VOLTAGE – V
5.0
4.5
0.0
2.0
1.5
1.0
0.5
4.0
2.5
3.0
3.5
V
LOGIC
FROM
HIGH TO LOW
V
LOGIC
FROM
LOW TO HIGH
CODE = FFF
H
V
REF
= 2V
RS LOGIC VOLTAGE
VARIED
TPC 6. AD7390 Logic Threshold
vs. Supply Voltage
FREQUENCY – Hz
PSRR – dB
60
50
010 100 10k
1k
30
20
10
40
V
DD
= 3V 5%
V
DD
= 5V 5%
T
A
= 25C
TPC 9. Power Supply Rejection
vs. Frequency
REV. A –7–
AD7390/AD7391
V
OUT
– V
I
OUT
– mA
40
30
001 5
23 4
20
10
V
DD
= 5V
V
REF
= 3V
CODE = ØØØ
H
TPC 10. I
OUT
at Zero Scale vs. V
OUT
100
s
1V
TIME – 100s/DIV
V
OUT
(1V/DIV)
LD
(5V/DIV)
V
DD
= 5V
V
REF
= 2.5V
f
CLK
= 50kHz
TPC 13. AD7390 Large Signal
Settling Time
HOURS OF OPERATION AT 150C
NOMINAL CHANGE IN VOLTAGE – mV
1.2
0.00 100 600
200 300 400 500
1.0
0.8
0.6
0.4
0.2
SAMPLE SIZE = 50
CODE = FFF
H
CODE = 000
H
TPC 16. AD7390 Long-Term Drift
Accelerated by Burn-In
2
s
20mV
VDD = 5V
VREF = 2.5V
fCLK = 50kHz
CODE: 7FH to 80H
TIME – 2s/DIV
VOUT
(5mV/DIV)
LD
(5V/DIV)
TPC 11. AD7390 Midscale Transi-
tion Performance
FREQUENCY – Hz
GAIN – dB
100 1k 100k10k
0
–5
V
DD
= 5V
V
REF
= 50mV 2V dc
DATA = FFF
H
5
10
–10
–15
–20
–25
–30
–35
–40
TPC 14. AD7390 Gain vs.
Frequency
5
s
5mV
VDD = 5V
VREF = 2.5V
fCLK = 50kHz
LD = HIGH
TIME – 5s/DIV
VOUT
(5mV/DIV)
CLK
(5V/DIV)
TPC 12. Digital Feedthrough
REFERENCE VOLTAGE – V
05
1324
INTEGRAL NONLINEARITY – LSB
2.0
1.8
0.0
0.8
0.6
0.4
0.2
1.6
1.0
1.2
1.4
V
DD
= 5V
CODE = 768
H
T
A
= 25C
TPC 15. AD7390 INL Error vs.
Reference Voltage
REV. A
AD7390/AD7391
–8–
OPERATION
The AD7390 and AD7391 are a set of pin compatible, 12-bit/
10-bit digital-to-analog converters. These single-supply opera-
tion devices consume less than 100 microamps of current while
operating from power supplies in the 2.7 V to 5.5 V range mak-
ing them ideal for battery operated applications. They contain a
voltage-switched, 12-bit/10-bit, laser-trimmed digital-to-analog
converter, rail-to-rail output op amps, serial-input register, and
a DAC register. The external reference input has constant input
resistance independent of the digital code setting of the DAC.
In addition, the reference input can be tied to the same supply
voltage as V
DD
resulting in a maximum output voltage span of
0 to V
DD
. The SPI compatible, serial-data interface consists of
a serial data input (SDI), clock (CLK), and load (LD) pins.
A CLR pin is available to reset the DAC register to zero-scale.
This function is useful for power-on reset or system failure
recovery to a known state.
D/A CONVERTER SECTION
The voltage switched R-2R DAC generates an output voltage
dependent on the external reference voltage connected to the
V
REF
pin according to the following equation:
VV D
OUT REF N
=×
2
(1)
where D is the decimal data word loaded into the DAC register,
and N is the number of bits of DAC resolution. In the case of the
10-bit AD7391 using a 2.5 V reference, Equation 1 simplifies to:
VD
OUT =×25 1024
.
(2)
Using Equation 2 the nominal midscale voltage at V
OUT
is
1.25 V for D = 512; full-scale voltage is 2.497 V. The LSB step
size is = 2.5 1/1024 = 0.0024 V.
For the 12-bit AD7390 operating from a 5.0 V reference
Equation 1 becomes:
VD
OUT =×50 4096
.
(3)
Using Equation 3 the AD7390 provides a nominal midscale
voltage of 2.5 V for D = 2048, and a full-scale output of 4.998 V.
The LSB step size is = 5.0 1/4096 = 0.0012 V.
AMPLIFIER SECTION
The internal DAC’s output is buffered by a low power con-
sumption precision amplifier. The op amp has a 60 µs typical
settling time to 0.1% of full scale. There are slight differences in
settling time for negative slewing signals versus positive. Also,
negative transition settling time to within the last 6 LSBs of zero
volts has an extended settling time. The rail-to-rail output stage
of this amplifier has been designed to provide precision perfor-
mance while operating near either power supply. Figure 5
shows an equivalent output schematic of the rail-to-rail ampli-
fier with its N-channel pull-down FETs that will pull an output
load directly to GND. The output sourcing current is provided
by a P-channel pull-up device that can source current to GND
terminated loads.
AGND
V
OUT
V
DD
P-CH
N-CH
Figure 5. Equivalent Analog Output Circuit
The rail-to-rail output stage provides ±1 mA of output current.
The N-channel output pull-down MOSFET shown in Figure 5
has a 35 Ω ON resistance, which sets the sink current capability
near ground. In addition to resistive load driving capability, the
amplifier has also been carefully designed and characterized for
up to 100 pF capacitive load driving capability.
REFERENCE INPUT
The reference input terminal has a constant input-resistance
independent of digital code which results in reduced glitches on
the external reference voltage source. The high 2 MΩ input-
resistance minimizes power dissipation within the AD7390/
AD7391 D/A converters. The V
REF
input accepts input voltages
ranging from ground to the positive-supply voltage V
DD
. One of
the simplest applications which saves an external reference
voltage source is connection of the V
REF
terminal to the positive
V
DD
supply. This connection results in a rail-to-rail voltage
output span maximizing the programmed range. The reference
input will accept ac signals as long as they are kept within the
supply voltage range, 0 < V
REF IN
< V
DD
. The reference band-
width and integral nonlinearity error performance are plotted in
the typical performance section (see TPCs 14 and 15). The
ratiometric reference feature makes the AD7390/AD7391 an
ideal companion to ratiometric analog-to-digital converters such
as the AD7896.
POWER SUPPLY
The very low power consumption of the AD7390/AD7391 is a
direct result of a circuit design optimizing the use of a CBCMOS
process. By using the low power characteristics of CMOS for the
logic, and the low noise, tight-matching of the complementary
bipolar transistors, excellent analog accuracy is achieved. One
advantage of the rail-to-rail output amplifiers used in the AD7390/
AD7391 is the wide range of usable supply voltage. The part is
fully specified and tested for operation from 2.7 V to 5.5 V.
POWER SUPPLY BYPASSING AND GROUNDING
Precision analog products, such as the AD7390/AD7391, require
a well filtered power source. Since the AD7390/AD7391 operates
from a single 3 V to 5 V supply, it seems convenient to simply tap
into the digital logic power supply. Unfortunately, the logic sup-
ply is often a switch-mode design, which generates noise in the
20 kHz to 1 MHz range. In addition, fast logic gates can generate
glitches hundred of millivolts in amplitude due to wiring resis-
tance and inductance. The power supply noise generated thereby
means that special care must be taken to assure that the inherent
precision of the DAC is maintained. Good engineering judgment
should be exercised when addressing the power supply ground-
ing and bypassing of the AD7390.
REV. A
AD7390/AD7391
–9–
The AD7390 should be powered directly from the system
power supply. This arrangement, shown in Figure 6, employs an
LC filter and separate power and ground connections to isolate
the analog section from the logic switching transients.
FERRITE BEAD:
TWO TURNS, FAIR-RITE
#2677006301
TTL/CMOS
LOGIC
CIRCUITS
5V
POWER SUPPLY
100F
ELECT.
10F–22F
TANTALUM
0.1F
CERAMIC
CAPACITOR
5V
5V
RETURN
Figure 6. Use Separate Traces to Reduce Power
Supply Noise
Whether or not a separate power supply trace is available, how-
ever, generous supply bypassing will reduce supply-line induced
errors. Local supply bypassing consisting of a 10 µF tantalum
electrolytic in parallel with a 0.1 µF ceramic capacitor is recom-
mended in all applications (Figure 7).
AD7390
OR
AD7391
0.1F
CLK V
OUT
REF V
DD
GND
C
*
10F
6
78
5
1
2
3
4
SDI
CLR
LD
*OPTIONAL EXTERNAL
REFERENCE BYPASS
2.7V TO 5.5V
Figure 7. Recommended Supply Bypassing
INPUT LOGIC LEVELS
All digital inputs are protected with a Zener-type ESD protection
structure (Figure 8) that allows logic input voltages to exceed the
V
DD
supply voltage. This feature can be useful if the user is driving
one or more of the digital inputs with a 5 V CMOS logic input-
voltage level while operating the AD7390/AD7391 on a 3 V power
supply. If this mode of interface is used, make sure that the V
OL
of the 5 V CMOS meets the V
IL
input requirement of the AD7390/
AD7391 operating at 3 V. See TPC 6 for a graph for digital
logic input threshold versus operating V
DD
supply voltage.
LOGIC
IN
VDD
GND
Figure 8. Equivalent Digital Input ESD Protection
In order to minimize power dissipation from input-logic levels
that
are near the V
IH
and V
IL
logic input voltage specifications,
a
Schmitt trigger design was used that minimizes the input-buffer
current consumption compared to traditional CMOS input
stages. TPC 5 shows a plot of incremental input voltage versus
supply current showing that negligible current consumption
takes place when logic levels are in their quiescent state. The
normal crossover current still occurs during logic transitions. A
secondary advantage of this Schmitt trigger is the prevention of
false triggers that would occur with slow moving logic transi-
tions when a standard CMOS logic interface or opto isolators
are used. The logic inputs SDI, CLK, LD, CLR all contain the
Schmitt trigger circuits.
DIGITAL INTERFACE
The AD7390/AD7391 have a double-buffered serial data input.
The serial-input register is separate from the DAC register,
which allows preloading of a new data value into the serial regis-
ter without disturbing the present DAC values. A functional
block diagram of the digital section is shown in Figure 4, while
Table I contains the truth table for the control logic inputs.
Three pins control the serial data input. Data at the Serial Data
Input (SDI) is clocked into the shift register on the rising edge
of CLK. Data is entered in MSB-first format. Twelve clock
pulses are required to load the 12-bit AD7390 DAC value. If
additional bits are clocked into the shift register, for example
when a microcontroller sends two 8-bit bytes, the MSBs are
ignored (Figure 9). The CLK pin is only enabled when Load
(LD) is high. The lower resolution 10-bit AD7391 contains a
10-bit shift register. The AD7391 is also loaded MSB first with
10 bits of data. Again if additional bits are clocked into the shift
register, only the last 10 bits clocked in are used.
The Load pin (LD) controls the flow of data from the shift
register to the DAC register. After a new value is clocked into
the serial-input register, it will be transferred to the DAC register
by the negative transition of the Load pin (LD).
BYTE 1 BYTE 0
MSB LSB MSB LSB
B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0
X X X X D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
X X X X X X D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
D11–D0: 12-BIT AD7390 DAC VALUE; D9–D0: 10-BIT AD7391 DAC VALUE
X = DON’T CARE
THE MSB OF BYTE 1 IS THE FIRST BIT THAT IS LOADED INTO THE DAC
Figure 9. Typical AD7390-Microprocessor Serial Data
Input Forms
RESET (CLR) PIN
Forcing the CLR pin low will set the DAC register to all zeros
and the DAC output voltage will be zero volts. The reset function
is useful for setting the DAC outputs to zero at power-up or
after a power supply interruption. Test systems and motor
controllers are two of many applications which benefit from
powering up to a known state. The external reset pulse can be
generated by the microprocessor’s power-on RESET signal, by
an output from the microprocessor, or by an external resistor
and capacitor. CLR has a Schmitt trigger input which results in
a clean reset function when using external resistor/capacitor
generated pulses. The CLR input overrides other logic inputs,
specifically LD. However, LD should be set high before CLR
goes high. If CLR is kept low, then the contents of the shift
register will be transferred to the DAC register as soon as CLR
returns high. See the Control-Logic Truth Table I.
REV. A
AD7390/AD7391
–10–
UNIPOLAR OUTPUT OPERATION
This is the basic mode of operation for the AD7390. As shown
in Figure 10, the AD7390 has been designed to drive loads as
low as 5 kΩ in parallel with 100 pF. The code table for this
operation is shown in Table IV.
AD7390
0.1F
CLK
V
OUT
REF V
DD
GND
R
10F
6
7
5
1
2
3
4
SDI
CLR
LD
2.7V TO 5.5V
R
L
5k
C
L
100pF
C
RS
EXT
REF
0.01F
Figure 10. AD7390 Unipolar Output Operation
Table IV. AD7390 Unipolar Code Table
Hexadecimal Decimal Output
Number Number Voltage (V)
in DAC Register in DAC Register V
REF
= 2.5 V
FFF 4095 2.4994
801 2049 1.2506
800 2048 1.2500
7FF 2047 1.2494
000 0 0
The circuit can be configured with an external reference plus
power supply, or powered from a single dedicated regulator or
reference, depending on the application performance requirements.
BIPOLAR OUTPUT OPERATION
Although the AD7391 has been designed for single-supply opera-
tion, the output can be easily configured for bipolar operation.
A typical circuit is shown in Figure 11. This circuit uses a clean
regulated 5 V supply for power, which also provides the circuit’s
reference voltage. Since the AD7391 output span swings from
ground to very near 5 V, it is necessary to choose an external
amplifier with a common-mode input voltage range that extends
to its positive supply rail. The micropower consumption OP196 has
been designed just for this purpose and results in only 50 micro-
amps of maximum current consumption. Connection of the equally
valued 470 kΩ resistors results in a differential amplifier mode
of operation with a voltage gain of two, which results in a circuit
output span of ten volts, that is, 25 V to 15 V. As the DAC is
programmed with zero-code 000
H
to midscale 200
H
to full-scale
3FF
H
, the circuit output voltage V
O
is set at 25 V, 0 V and 15 V
(minus 1 LSB). The output voltage V
O
is coded in offset binary
according to Equation 4.
VD
O=
×
512 15–
(4)
where D is the decimal code loaded in the AD7391 DAC register.
Note that the LSB step size is 10/1024 = 10 mV. This circuit has
been optimized for micropower consumption including the 470 kΩ
gain setting resistors, which should have low temperature coeffi-
cients to maintain accuracy and matching (preferably the same
material, such as metal film). If better stability is required, the power
supply could be substituted with a precision reference voltage such
as the low dropout REF195, which can easily supply the circuit’s
162 µA of current, and still provide additional power for the
load connected to V
O
. The micropower REF195 is guaranteed
to source 10 mA output drive current, but only consumes 50 µA
internally. If higher resolution is required, the AD7390 can be
used with the addition of two more bits of data inserted into the
software coding, which would result in a 2.5 mV LSB step size.
Table V shows examples of nominal output voltages V
O
provided
by the Bipolar Operation circuit application.
C
ISY < 162A
BIPOLAR
OUTPUT
SWING
VO
+5V
–5V
–5V
VOUT
AD7391
VDD
REF
GND
+5V
< 100A
470k470k
< 50A
OP196
DIGITAL INTERFACE CIRCUITRY OMITTED FOR CLARITY
Figure 11. Bipolar Output Operation
Table V. Bipolar Code Table
Hexadecimal Decimal Analog
Number Number Output
in DAC Register in DAC Register Voltage (V)
3FF 1023 4.9902
201 513 0.0097
200 512 0.0000
1FF 511 –0.0097
000 0 –5.0000
MICROCOMPUTER INTERFACES
The AD7390 serial data input provides an easy interface to a
variety of single-chip microcomputers (µCs). Many µCs have a
built-in serial data capability which can be used for communi-
cating with the DAC. In cases where no serial port is provided,
or it is being used for some other purpose (such as an RS-232
communications interface), the AD7390/AD7391 can easily be
addressed in software.
Twelve data bits are required to load a value into the AD7390.
If more than 12 bits are transmitted before the load LD input
goes high, the extra (i.e., the most-significant) bits are ignored.
This feature is valuable because most µCs only transmit data
in 8-bit increments. Thus, the µC sends 16 bits to the DAC
instead of 12 bits. The AD7390 will only respond to the last
12 bits clocked into the SDI input, however, so the serial-data
interface is not affected.
Ten data bits are required to load a value into the AD7391. If
more than 10 bits are transmitted before load LD returns high,
the extra bits are ignored.
REV. A
AD7390/AD7391
–11–
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
8-Lead SOIC
(R-8)
0.0098 (0.25)
0.0075 (0.19)
0.0500 (1.27)
0.0160 (0.41)
8
0
0.0196 (0.50)
0.0099 (0.25) 45
85
41
0.1968 (5.00)
0.1890 (4.80)
0.2440 (6.20)
0.2284 (5.80)
PIN 1
0.1574 (4.00)
0.1497 (3.80)
0.0500 (1.27)
BSC
0.0688 (1.75)
0.0532 (1.35)
SEATING
PLANE
0.0098 (0.25)
0.0040 (0.10)
0.0192 (0.49)
0.0138 (0.35)
8-Lead Plastic DIP
(N-8)
SEATING
PLANE
0.060 (1.52)
0.015 (0.38)
0.210
(5.33)
MAX
0.022 (0.558)
0.014 (0.356)
0.160 (4.06)
0.115 (2.93)
0.070 (1.77)
0.045 (1.15)
0.130
(3.30)
MIN
8
14
5
PIN 1
0.280 (7.11)
0.240 (6.10)
0.100 (2.54)
BSC
0.430 (10.92)
0.348 (8.84)
0.195 (4.95)
0.115 (2.93)
0.015 (0.381)
0.008 (0.204)
0.325 (8.25)
0.300 (7.62)
8-Lead TSSOP
(RU-8)
85
41
0.256 (6.50)
0.246 (6.25)
0.177 (4.50)
0.169 (4.30)
PIN 1
0.0256 (0.65)
BSC
0.122 (3.10)
0.114 (2.90)
SEATING
PLANE
0.006 (0.15)
0.002 (0.05)
0.0118 (0.30)
0.0075 (0.19)
0.0433
(1.10)
MAX
0.0079 (0.20)
0.0035 (0.090)
0.028 (0.70)
0.020 (0.50)
8
0
REV. A
–12–
C01120–0–2/02(A)
PRINTED IN U.S.A.
AD7390/AD7391
Revision History
Location Page
Data Sheet changed from REV. 0 to REV. A.
Edits to SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Edits to ABSOLUTE MAXIMUM RATINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Edits to ORDERING GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Edit to Figure 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Edit to TPC 14 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
