DAC108S085
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SNAS423B – AUGUST 2007 – REVISED MARCH 2013
DAC108S085 10-Bit Micro Power OCTAL Digital-to-Analog Converter with Rail-to-Rail
Outputs
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FEATURES
DESCRIPTION
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The DAC108S085 is a full-featured, general purpose
OCTAL
10-bit
voltage-output
digital-to-analog
converter (DAC) that can operate from a single +2.7V
to +5.5V supply and consumes 1.95 mW at 3V and
4.85 mW at 5V. The DAC108S085 is packaged in a
16-lead WQFN package and a 16-lead TSSOP
package. The WQFN package makes the
DAC108S085 the smallest OCTAL DAC in its class.
The on-chip output amplifiers allow rail-to-rail output
swing and the three wire serial interface operates at
clock rates up to 40 MHz over the entire supply
voltage range. Competitive devices are limited to 25
MHz clock rates at supply voltages in the 2.7V to
3.6V range. The serial interface is compatible with
standard SPI™, QSPI, MICROWIRE and DSP
interfaces. The DAC108S085 also offers daisy chain
operation
where
an
unlimited
number
of
DAC108S085s can be updated simultaneously using
a single serial interface.
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Ensured Monotonicity
Low Power Operation
Rail-to-Rail Voltage Output
Daisy Chain Capability
Power-on Reset to 0V
Simultaneous Output Updating
Individual Channel Power Down Capability
Wide power supply range (+2.7V to +5.5V)
Dual Reference Voltages with Range of 0.5V to
VA
Operating Temperature Range of −40°C to
+125°C
Industry's Smallest Package
APPLICATIONS
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Battery-Powered Instruments
Digital Gain and Offset Adjustment
Programmable Voltage & Current Sources
Programmable Attenuators
Voltage Reference for ADCs
Sensor Supply Voltage
Range Detectors
KEY SPECIFICATIONS
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Resolution: 10 Bits
INL: ±2 LSB (Max)
DNL: +0.35/-0.2 LSB (Max)
Settling Time: 6 µs (Max)
Zero Code Error : +15mV (Max)
Full-Scale Error: -0.75% FSR (Max)
Supply Power
– Normal: 1.95 mW (3V)/4,85 mW (5V) (Typ)
– Power Down: 0.3 µW (3V)/1 W (5V) (Typ)
There are two references for the DAC108S085. One
reference input serves channels A through D while
the other reference serves channels E through H.
Each reference can be set independently between
0.5V and VA, providing the widest possible output
dynamic range. The DAC108S085 has a 16-bit input
shift register that controls the mode of operation, the
power-down condition, and the DAC channels'
register/output value. All eight DAC outputs can be
updated simultaneously or individually.
A power-on reset circuit ensures that the DAC
outputs power up to zero volts and remain there until
there is a valid write to the device. The power-down
feature of the DAC108S085 allows each DAC to be
independently
powered
with
three
different
termination options. With all the DAC channels
powered down, power consumption reduces to less
than 0.3 µW at 3V and less than 1 µW at 5V. The low
power consumption and small packages of the
DAC108S085 make it an excellent choice for use in
battery operated equipment.
1
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3
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
SPI is a trademark of Motorola, Inc..
All other trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2007–2013, Texas Instruments Incorporated
DAC108S085
SNAS423B – AUGUST 2007 – REVISED MARCH 2013
www.ti.com
DESCRIPTION (CONTINUED)
The DAC108S085 is one of a family of pin compatible DACs, including the 8-bit DAC088S085 and the 12-bit
DAC128S085. All three parts are offered with the same pinout, allowing system designers to select a resolution
appropriate for their application without redesigning their printed circuit board. The DAC108S085 operates over
the extended industrial temperature range of −40°C to +125°C.
Block Diagram
VREF1
DAC108S085
REF
10 BIT DAC
VOUTA
BUFFER
10
2.5k
100k
REF
10 BIT DAC
VOUTB
BUFFER
10
POWER-ON
RESET
2.5k
100k
REF
10 BIT DAC
VOUTC
BUFFER
10
2.5k
100k
REF
10 BIT DAC
VOUTD
BUFFER
10
2.5k
100k
REF
10 BIT DAC
DAC
REGISTER
VOUTE
BUFFER
10
2.5k
100k
REF
10 BIT DAC
VOUTF
BUFFER
10
2.5k
100k
REF
10 BIT DAC
VOUTG
BUFFER
10
2.5k
100k
10
REF
10 BIT DAC
VOUTH
BUFFER
10
2.5k
DOUT
2
SYNC
SCLK
100k
POWER-DOWN
CONTROL
LOGIC
INPUT
CONTROL
LOGIC
DIN
VREF2
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Pin Configuration
SYNC
13
4
14
VOUTD
SCLK
2
3
16
VOUTB
VOUTC
15
1
DIN
DOUT
VOUTA
1
16
DOUT
2
15
SYNC
VOUTA
3
14
VOUTE
DIN
12
VOUTE
11
VOUTF
10
VOUTG
9
VOUTH
DAC108S085
SCLK
8
7
6
5
VREF2
GND
VREF1
VA
VOUTB
4
13
VOUTF
VOUTC
5
12
VOUTG
VOUTD
6
11
VOUTH
VA
7
10
GND
VREF1
8
9
DAC108S085
VREF2
PIN DESCRIPTIONS
WQFN
Pin No.
TSSOP
Pin No.
Symbol
Type
1
3
VOUTA
Analog Output
Channel A Analog Output Voltage.
2
4
VOUTB
Analog Output
Channel B Analog Output Voltage.
3
5
VOUTC
Analog Output
Channel C Analog Output Voltage.
4
6
VOUTD
Analog Output
Channel D Analog Output Voltage.
5
7
VA
Supply
6
8
VREF1
Analog Input
Unbuffered reference voltage shared by Channels A, B, C, and D.
Must be decoupled to GND.
7
9
VREF2
Analog Input
Unbuffered reference voltage shared by Channels E, F, G, and H.
Must be decoupled to GND.
8
10
GND
Ground
9
11
VOUTH
Analog Output
Channel H Analog Output Voltage.
10
12
VOUTG
Analog Output
Channel G Analog Output Voltage.
11
13
VOUTF
Analog Output
Channel F Analog Output Voltage.
12
14
VOUTE
Analog Output
Channel E Analog Output Voltage.
Description
Power supply input. Must be decoupled to GND.
Ground reference for all on-chip circuitry.
13
15
SYNC
Digital Input
Frame Synchronization Input. When this pin goes low, data is written
into the DAC's input shift register on the falling edges of SCLK. After
the 16th falling edge of SCLK, a rising edge of SYNC causes the
DAC to be updated. If SYNC is brought high before the 15th falling
edge of SCLK, the rising edge of SYNC acts as an interrupt and the
write sequence is ignored by the DAC.
14
16
SCLK
Digital Input
Serial Clock Input. Data is clocked into the input shift register on the
falling edges of this pin.
15
1
DIN
Digital Input
Serial Data Input. Data is clocked into the 16-bit shift register on the
falling edges of SCLK after the fall of SYNC.
16
2
DOUT
Digital Output
Serial Data Output. DOUT is utilized in daisy chain operation and is
connected directly to a DIN pin on another DAC108S085. Data is not
available at DOUT unless SYNC remains low for more than 16 SCLK
cycles.
PAD
(WQFN only)
Ground
Exposed die attach pad can be connected to ground or left floating.
Soldering the pad to the PCB offers optimal thermal performance
and enhances package self-alignment during reflow.
17
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
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Absolute Maximum Ratings (1) (2) (3)
Supply Voltage, VA
6.5V
−0.3V to 6.5V
Voltage on any Input Pin
Input Current at Any Pin (4)
10 mA
Package Input Current (4)
30 mA
Power Consumption at TA = 25°C
See (5)
Human Body Model
ESD Susceptibility (6)
Machine Model
Charge Device Mode
2500V
250V
1000V
Junction Temperature
+150°C
Storage Temperature
−65°C to +150°C
(1)
(2)
(3)
(4)
(5)
(6)
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is functional, but do not specify specific performance limits. For ensured specifications and test conditions, see the
Electrical Characteristics. The ensured specifications apply only for the test conditions listed. Some performance characteristics may
degrade when the device is not operated under the listed test conditions. Operation of the device beyond the maximum Operating
Ratings is not recommended.
All voltages are measured with respect to GND = 0V, unless otherwise specified.
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and
specifications.
When the input voltage at any pin exceeds 5.5V or is less than GND, the current at that pin should be limited to 10 mA. The 30 mA
maximum package input current rating limits the number of pins that can safely exceed the power supplies with an input current of 10
mA to three.
The absolute maximum junction temperature (TJmax) for this device is 150°C. The maximum allowable power dissipation is dictated by
TJmax, the junction-to-ambient thermal resistance (θJA), and the ambient temperature (TA), and can be calculated using the formula
PDMAX = (TJmax − TA) / θJA. The values for maximum power dissipation will be reached only when the device is operated in a severe
fault condition (e.g., when input or output pins are driven beyond the operating ratings, or the power supply polarity is reversed). Such
conditions should always be avoided.
Human body model is 100 pF capacitor discharged through a 1.5 kΩ resistor. Machine model is 220 pF discharged through 0 Ω. Charge
device model simulates a pin slowly acquiring charge (such as from a device sliding down the feeder in an automated assembler) then
rapidly being discharged.
Operating Ratings (1) (2)
−40°C ≤ TA ≤ +125°C
Operating Temperature Range
Supply Voltage, VA
+2.7V to 5.5V
Reference Voltage, VREF1,2
+0.5V to VA
Digital Input Voltage (3)
0.0V to 5.5V
Output Load
0 to 1500 pF
SCLK Frequency
(1)
(2)
(3)
Up to 40 MHz
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is functional, but do not specify specific performance limits. For ensured specifications and test conditions, see the
Electrical Characteristics. The ensured specifications apply only for the test conditions listed. Some performance characteristics may
degrade when the device is not operated under the listed test conditions. Operation of the device beyond the maximum Operating
Ratings is not recommended.
All voltages are measured with respect to GND = 0V, unless otherwise specified.
The inputs are protected as shown below. Input voltage magnitudes up to 5.5V, regardless of VA, will not cause errors in the conversion
result. For example, if VA is 3V, the digital input pins can be driven with a 5V logic device.
I/O
TO INTERNAL
CIRCUITRY
GND
4
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Package Thermal Resistances (1) (2)
(1)
(2)
Package
θJA
16-Lead WQFN
38°C/W
16-Lead TSSOP
130°C/W
Soldering process must comply with Texas Instruments' Reflow Temperature Profile specifications. Refer to
http://www.ti.com/packaging.
Reflow temperature profiles are different for lead-free packages.
Electrical Characteristics
The following specifications apply for VA = +2.7V to +5.5V, VREF1 = VREF2 = VA, CL = 200 pF to GND, fSCLK = 30 MHz, input
code range 12 to 1011. Boldface limits apply for TMIN ≤ TA ≤ TMAX and all other limits are at TA = 25°C, unless otherwise
specified.
Limits (1)
Units
(Limits)
Resolution
10
Bits (min)
Monotonicity
10
Bits (min)
±0.5
±2
LSB (max)
+0.08
+0.35
LSB (max)
−0.04
−0.2
LSB (min)
Symbol
Parameter
Conditions
Typical
STATIC PERFORMANCE
INL
Integral Non-Linearity
DNL
Differential Non-Linearity
ZE
Zero Code Error
IOUT = 0
+5
+15
mV (max)
FSE
Full-Scale Error
IOUT = 0
−0.1
−0.75
% FSR (max)
GE
Gain Error
−0.2
−1.0
% FSR (max)
ZCED
Zero Code Error Drift
−20
µV/°C
TC GE
Gain Error Tempco
−1.0
ppm/°C
OUTPUT CHARACTERISTICS
Output Voltage Range
IOZ
ZCO
FSO
Zero Code Output
Full Scale Output
V (min)
V (max)
±1
µA (max)
VA = 3V, IOUT = 200 µA
10
mV
VA = 3V, IOUT = 1 mA
45
mV
VA = 5V, IOUT = 200 µA
8
mV
VA = 5V, IOUT = 1 mA
34
mV
VA = 3V, IOUT = 200 µA
2.984
V
VA = 3V, IOUT = 1 mA
2.933
V
VA = 5V, IOUT = 200 µA
4.987
V
VA = 5V, IOUT = 1 mA
4.955
V
Output Short Circuit Current
(source) (3)
VA = 3V, VOUT = 0V, Input Code = 3FFh
−50
mA
VA = 5V, VOUT = 0V, Input Code = 3FFh
−60
mA
IOS
Output Short Circuit Current
(sink) (3)
VA = 3V, VOUT = 3V, Input Code = 000h
50
mA
VA = 5V, VOUT = 5V, Input Code = 000h
70
IO
Continuous Output Current per
channel (2)
TA = 105°C
IOS
CL
ZOUT
(1)
(2)
(3)
High-Impedance Output Leakage
Current (2)
0
VREF1,2
Maximum Load Capacitance
TA = 125°C
mA
10
mA (max)
6.5
mA (max)
RL = ∞
1500
pF
RL = 2kΩ
1500
pF
8
Ω
DC Output Impedance
Test limits are specified to AOQL (Average Outgoing Quality Level).
This parameter is specified by design and/or characterization and is not tested in production.
This parameter does not represent a condition which the DAC can sustain continuously. See the continuous output current specification
for the maximum DAC output current per channel.
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Electrical Characteristics (continued)
The following specifications apply for VA = +2.7V to +5.5V, VREF1 = VREF2 = VA, CL = 200 pF to GND, fSCLK = 30 MHz, input
code range 12 to 1011. Boldface limits apply for TMIN ≤ TA ≤ TMAX and all other limits are at TA = 25°C, unless otherwise
specified.
Symbol
Parameter
Conditions
Units
(Limits)
Typical
Limits (1)
0.5
2.7
V (min)
VA
V (max)
REFERENCE INPUT CHARACTERISTICS
Input Range Minimum
VREF1,2
Input Range Maximum
Input Impedance
30
kΩ
LOGIC INPUT CHARACTERISTICS
Input Current (4)
IIN
VIL
Input Low Voltage
VIH
Input High Voltage
CIN
Input Capacitance (4)
±1
µA (max)
VA = 2.7V to 3.6V
1.0
0.6
V (max)
VA = 4.5V to 5.5V
1.1
0.8
V (max)
VA = 2.7V to 3.6V
1.4
2.1
V (min)
VA = 4.5V to 5.5V
2.0
2.4
V (min)
3
pF (max)
POWER REQUIREMENTS
VA
Supply Voltage Minimum
2.7
V (min)
Supply Voltage Maximum
5.5
V (max)
fSCLK = 30 MHz,
output unloaded
VA = 2.7V to 3.6V
460
585
µA (max)
VA = 4.5V to 5.5V
650
855
µA (max)
Normal Supply Current for VREF1 or
VREF2
fSCLK = 30 MHz,
output unloaded
VA = 2.7V to 3.6V
95
135
µA (max)
VA = 4.5V to 5.5V
160
225
µA (max)
Static Supply Current for supply pin
VA
fSCLK = 0,
output unloaded
VA = 2.7V to 3.6V
370
µA
VA = 4.5V to 5.5V
440
µA
fSCLK = 0,
output unloaded
VA = 2.7V to 3.6V
95
µA
Normal Supply Current for supply
pin VA
IN
IST
Static Supply Current for VREF1 or
VREF2
IPD
Total Power Consumption (output
unloaded)
PN
PPD
(4)
6
Total Power Down Supply Current
for all PD Modes (4)
Total Power Consumption in all PD
Modes (4)
VA = 4.5V to 5.5V
160
fSCLK = 30 MHz,
VA = 2.7V to 3.6V
SYNC = VA and DIN =
0V after PD mode
VA = 4.5V to 5.5V
loaded
0.2
1.5
µA (max)
µA
0.5
3.0
µA (max)
fSCLK = 0, SYNC = VA VA = 2.7V to 3.6V
and DIN = 0V after PD
VA = 4.5V to 5.5V
mode loaded
0.1
1.0
µA (max)
0.2
2.0
µA (max)
fSCLK = 30 MHz
output unloaded
VA = 2.7V to 3.6V
1.95
3.1
mW (max)
VA = 4.5V to 5.5V
4.85
7.2
mW (max)
fSCLK = 0
output unloaded
VA = 2.7V to 3.6V
1.68
mW
VA = 4.5V to 5.5V
3.80
fSCLK = 30 MHz,
VA = 2.7V to 3.6V
SYNC = VA and DIN =
0V after PD mode
VA = 4.5V to 5.5V
loaded
0.6
5.4
µW (max)
mW
2.5
16.5
µW (max)
fSCLK = 0, SYNC = VA VA = 2.7V to 3.6V
and DIN = 0V after PD
VA = 4.5V to 5.5V
mode loaded
0.3
3.6
µW (max)
1
11
µW (max)
This parameter is specified by design and/or characterization and is not tested in production.
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A.C. and Timing Characteristics
The following specifications apply for VA = +2.7V to +5.5V, VREF1,2 = VA, CL = 200 pF to GND, fSCLK = 30 MHz, input code
range 12 to 1011. Boldface limits apply for TMIN ≤ TA ≤ TMAX and all other limits are at TA = 25°C, unless otherwise
specified.
Symbol
fSCLK
ts
Limits
(1)
Units
(Limits)
40
30
MHz (max)
100h to 300h code change
RL = 2kΩ, CL = 200 pF
4.5
6.0
µs (max)
1
V/µs
Code change from 200h to 1FFh
40
nV-sec
Parameter
Conductions
Typical
SCLK Frequency
Output Voltage Settling Time (2)
SR
Output Slew Rate
GI
Glitch Impulse
DF
Digital Feedthrough
0.5
nV-sec
DC
Digital Crosstalk
0.5
nV-sec
1
nV-sec
CROSS
DAC-to-DAC Crosstalk
MBW
Multiplying Bandwidth
VREF1,2 = 2.5V ± 2Vpp
360
kHz
ONSD
Output Noise Spectral Density
DAC Code = 200h, 10kHz
40
nV/sqrt(Hz)
ON
Output Noise
BW = 30kHz
14
µV
tWU
Wake-Up Time
VA = 3V
3
µsec
VA = 5V
20
1/fSCLK
25
33
ns (min)
tCH
SCLK High time
7
10
ns (min)
tCL
SCLK Low Time
7
10
ns (min)
tSS
SYNC Set-up Time prior to SCLK
Falling Edge
3
10
ns (min)
1 / fSCLK - 3
ns (max)
tDS
Data Set-Up Time prior to SCLK Falling
Edge
1.0
2.5
ns (min)
tDH
Data Hold Time after SCLK Falling
Edge
1.0
2.5
ns (min)
tSH
SYNC Hold Time after the 16th falling
edge of SCLK
0
SYNC High Time
5
tSYNC
(1)
(2)
µsec
SCLK Cycle Time
3
ns (min)
1 / fSCLK - 3
ns (max)
15
ns (min)
Test limits are specified to AOQL (Average Outgoing Quality Level).
This parameter is specified by design and/or characterization and is not tested in production.
Timing Diagrams
|
1 / fSCLK
SCLK
1
2
13
tSS
tSYNC
tCL
14
15
16
tCH
tSH
|
SYNC
| |
tDH
DB15
DIN
DB0
tDS
Figure 1. Serial Timing Diagram
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Specification Definitions
DIFFERENTIAL NON-LINEARITY (DNL) is the measure of the maximum deviation from the ideal step size of 1
LSB, which is VREF / 1024 = VA / 1024.
DAC-to-DAC CROSSTALK is the glitch impulse transferred to a DAC output in response to a full-scale change
in the output of another DAC.
DIGITAL CROSSTALK is the glitch impulse transferred to a DAC output at mid-scale in response to a full-scale
change in the input register of another DAC.
DIGITAL FEEDTHROUGH is a measure of the energy injected into the analog output of the DAC from the digital
inputs when the DAC outputs are not updated. It is measured with a full-scale code change on the data bus.
FULL-SCALE ERROR is the difference between the actual output voltage with a full scale code (3FFh) loaded
into the DAC and the value of VA x 1023 / 1024.
GAIN ERROR is the deviation from the ideal slope of the transfer function. It can be calculated from Zero and
Full-Scale Errors as GE = FSE - ZE, where GE is Gain error, FSE is Full-Scale Error and ZE is Zero Error.
GLITCH IMPULSE is the energy injected into the analog output when the input code to the DAC register
changes. It is specified as the area of the glitch in nanovolt-seconds.
INTEGRAL NON-LINEARITY (INL) is a measure of the deviation of each individual code from a straight line
through the input to output transfer function. The deviation of any given code from this straight line is measured
from the center of that code value. The end point method is used. INL for this product is specified over a limited
range, per the Electrical Tables.
LEAST SIGNIFICANT BIT (LSB) is the bit that has the smallest value or weight of all bits in a word. This value is
LSB = VREF / 2n
(1)
where VREF is the supply voltage for this product, and "n" is the DAC resolution in bits, which is 10 for the
DAC108S085.
MAXIMUM LOAD CAPACITANCE is the maximum capacitance that can be driven by the DAC with output
stability maintained.
MONOTONICITY is the condition of being monotonic, where the DAC has an output that never decreases when
the input code increases.
MOST SIGNIFICANT BIT (MSB) is the bit that has the largest value or weight of all bits in a word. Its value is
1/2 of VA.
MULTIPLYING BANDWIDTH is the frequency at which the output amplitude falls 3dB below the input sine wave
on VREF1,2 with the DAC code at full-scale.
NOISE SPECTRAL DENSITY is the internally generated random noise. It is measured by loading the DAC to
mid-scale and measuring the noise at the output.
POWER EFFICIENCY is the ratio of the output current to the total supply current. The output current comes from
the power supply. The difference between the supply and output currents is the power consumed by the device
without a load.
SETTLING TIME is the time for the output to settle to within 1/2 LSB of the final value after the input code is
updated.
TOTAL HARMONIC DISTORTION PLUS NOISE (THD+N) is the ratio of the harmonics plus the noise present at
the output of the DACs to the rms level of an ideal sine wave applied to VREF1,2 with the DAC code at mid-scale.
WAKE-UP TIME is the time for the output to exit power-down mode. This is the time from the rising edge of
SYNC to when the output voltage deviates from the power-down voltage of 0V.
ZERO CODE ERROR is the output error, or voltage, present at the DAC output after a code of 000h has been
entered.
8
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Transfer Characteristic
FSE
1023 x VA
1024
GE = FSE - ZE
FSE = GE + ZE
OUTPUT
VOLTAGE
ZE
0
0
1023
DIGITAL INPUT CODE
Figure 2. Input / Output Transfer Characteristic
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Typical Performance Characteristics
VA = +2.7V to +5.5V, VREF1,2 = VA, fSCLK = 30 MHz, TA = 25°C, unless otherwise stated
10
INL vs Code
DNL vs Code
Figure 3.
Figure 4.
INL/DNL vs VREF
INL/DNL vs fSCLK
Figure 5.
Figure 6.
INL/DNL vs VA
INL/DNL vs Temperature
Figure 7.
Figure 8.
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Typical Performance Characteristics (continued)
VA = +2.7V to +5.5V, VREF1,2 = VA, fSCLK = 30 MHz, TA = 25°C, unless otherwise stated
Zero Code Error vs. VA
Zero Code Error vs. VREF
Figure 9.
Figure 10.
Zero Code Error vs. fSCLK
Zero Code Error vs. Temperature
Figure 11.
Figure 12.
Full-Scale Error vs. VA
Full-Scale Error vs. VREF
Figure 13.
Figure 14.
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Typical Performance Characteristics (continued)
VA = +2.7V to +5.5V, VREF1,2 = VA, fSCLK = 30 MHz, TA = 25°C, unless otherwise stated
12
Full-Scale Error vs. fSCLK
Full-Scale Error vs. Temperature
Figure 15.
Figure 16.
IVA vs. VA
IVA vs. Temperature
Figure 17.
Figure 18.
IVREF vs. VREF
IVREF vs. Temperature
Figure 19.
Figure 20.
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Typical Performance Characteristics (continued)
VA = +2.7V to +5.5V, VREF1,2 = VA, fSCLK = 30 MHz, TA = 25°C, unless otherwise stated
Settling Time
Glitch Response
Figure 21.
Figure 22.
Wake-Up Time
DAC-to-DAC Crosstalk
Figure 23.
Figure 24.
Power-On Reset
Multiplying Bandwidth
Figure 25.
Figure 26.
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FUNCTIONAL DESCRIPTION
DAC ARCHITECTURE
The DAC108S085 is fabricated on a CMOS process with an architecture that consists of switches and resistor
strings that are followed by an output buffer. The reference voltages are externally applied at VREF1 for DAC
channels A through D and VREF2 for DAC channels E through H.
For simplicity, a single resistor string is shown in Figure 27. This string consists of 1024 equal valued resistors
with a switch at each junction of two resistors, plus a switch to ground. The code loaded into the DAC register
determines which switch is closed, connecting the proper node to the amplifier. The input coding is straight
binary with an ideal output voltage of:
VOUTA,B,C,D = VREF1 x (D / 1024)
VOUTE,F,G,H = VREF2 x (D / 1024)
(2)
where
•
D is the decimal equivalent of the binary code that is loaded into the DAC register
(3)
D can take on any value between 0 and 1023. This configuration ensures that the DAC is monotonic.
VREF
R
S2 n
R
S2 n-1
R
VOUT
S2 n-2
S2
R
S1
R
S0
Figure 27. DAC Resistor String
Since all eight DAC channels of the DAC108S085 can be controlled independently, each channel consists of a
DAC register and a 10-bit DAC. Figure 28 is a simple block diagram of an individual channel in the
DAC108S085. Depending on the mode of operation, data written into a DAC register causes the 10-bit DAC
output to be updated or an additional command is required to update the DAC output. Further description of the
modes of operation can be found in the Serial Interface description.
VREF
REF
DAC
REGISTER
10 BIT DAC
BUFFER
10
VOUT
Figure 28. Single Channel Block Diagram
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OUTPUT AMPLIFIERS
The output amplifiers are rail-to-rail, providing an output voltage range of 0V to VA when the reference is VA. All
amplifiers, even rail-to-rail types, exhibit a loss of linearity as the output approaches the supply rails (0V and VA,
in this case). For this reason, linearity is specified over less than the full output range of the DAC. However, if the
reference is less than VA, there is only a loss in linearity in the lowest codes.
The output amplifiers are capable of driving a load of 2 kΩ in parallel with 1500 pF to ground or to VA. The zerocode and full-scale outputs for given load currents are available in the Electrical Characteristics.
REFERENCE VOLTAGE
The DAC108S085 uses dual external references, VREF1 and VREF2, that are shared by channels A, B, C, D and
channels E, F, G, H respectively. The reference pins are not buffered and have an input impedance of 30 kΩ. It
is recommended that VREF1 and VREF2 be driven by voltage sources with low output impedance. The reference
voltage range is 0.5V to VA, providing the widest possible output dynamic range.
SERIAL INTERFACE
The three-wire interface is compatible with SPI™, QSPI and MICROWIRE, as well as most DSPs and operates
at clock rates up to 40 MHz. A valid serial frame contains 16 falling edges of SCLK. See the Timing Diagrams for
information on a write sequence.
A write sequence begins by bringing the SYNC line low. Once SYNC is low, the data on the DIN line is clocked
into the 16-bit serial input register on the falling edges of SCLK. To avoid mis-clocking data into the shift register,
it is critical that SYNC not be brought low on a falling edge of SCLK (see minimum and maximum setup times for
SYNC in the Timing Characteristics and Figure 29). On the 16th falling edge of SCLK, the last data bit is clocked
into the register. The write sequence is concluded by bringing the SYNC line high. Once SYNC is high, the
programmed function (a change in the DAC channel address, mode of operation and/or register contents) is
executed. To avoid mis-clocking data into the shift register, it is critical that SYNC be brought high between the
16th and 17th falling edges of SCLK (see minimum and maximum hold times for SYNC in the Timing
Characteristics and Figure 29).
SCLK
1
15
tSS
17
16
tSH
SYNC
Figure 29. CS Setup and Hold Times
If SYNC is brought high before the 15th falling edge of SCLK, the write sequence is aborted and the data that
has been shifted into the input register is discarded. If SYNC is held low beyond the 17th falling edge of SCLK,
the serial data presented at DIN will begin to be output on DOUT. More information on this mode of operation can
be found in Daisy Chain Operation. In either case, SYNC must be brought high for the minimum specified time
before the next write sequence is initiated with a falling edge of SYNC.
Since the DIN buffer draws more current when it is high, it should be idled low between write sequences to
minimize power consumption. On the other hand, SYNC should be idled high to avoid the activation of daisy
chain operation where DOUT is active.
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DAISY CHAIN OPERATION
Daisy chain operation allows communication with any number of DAC108S085s using a single serial interface.
As long as the correct number of data bits are input in a write sequence (multiple of sixteen bits), a rising edge of
SYNC will properly update all DACs in the system.
To support multiple devices in a daisy chain configuration, SCLK and SYNC are shared across all DAC108S085s
and DOUT of the first DAC in the chain is connected to DIN of the second. Figure 30 shows three DAC108S085s
connected in daisy chain fashion. Similar to a single channel write sequence, the conversion for a daisy chain
operation begins on a falling edge of SYNC and ends on a rising edge of SYNC. A valid write sequence for n
devices in a chain requires n times 16 falling edges to shift the entire input data stream through the chain. Daisy
chain operation is specifed for a maximum SCLK speed of 30MHz.
SYNC
SCLK
DIN
SYNC
SCLK
SYNC
SCLK
SYNC
SCLK
DIN DOUT
DIN DOUT
DIN DOUT
DAC 1
DAC 2
DAC 3
Figure 30. Daisy Chain Configuration
The serial data output pin, DOUT, is available on the DAC108S085 to allow daisy-chaining of multiple
DAC108S085 devices in a system. In a write sequence, DOUT remains low for the first fourteen falling edges of
SCLK before going high on the fifteenth falling edge. Subsequently, the next sixteen falling edges of SCLK will
output the first sixteen data bits entered into DIN. Figure 31 shows the timing of three DAC108S085s in
Figure 30. In this instance, It takes forty-eight falling edges of SCLK followed by a rising edge of SYNC to load all
three DAC108S085s with the appropriate register data. On the rising edge of SYNC, the programmed function is
executed in each DAC108S085 simultaneously.
48 SCLK Cycles (16 X 3)
SYNC
DIN1
DAC 3
DIN2/DOUT1
th
15 SCLK Cycle
DAC 2
DAC 1
DAC 3
DAC 2
st
31 SCLK Cycle
DIN3/DOUT2
DAC 3
Data Loaded into the DACs
Figure 31. Daisy Chain Timing Diagram
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SERIAL INPUT REGISTER
The DAC108S085 has two modes of operation plus a few special command operations. The two modes of
operation are Write Register Mode (WRM) and Write Through Mode (WTM). For the rest of this document, these
modes will be referred to as WRM and WTM. The special command operations are separate from WRM and
WTM because they can be called upon regardless of the current mode of operation. The mode of operation is
controlled by the first four bits of the control register, DB15 through DB12. See Table 1 for a detailed summary.
Table 1. Write Register and Write Through Modes
DB[15:12]
DB[11:0]
Description of Mode
1000
XXXXXXXXXXXX
WRM: The registers of each DAC Channel can be written to without causing
their outputs to change.
1001
XXXXXXXXXXXX
WTM: Writing data to a channel's register causes the DAC output to change.
When the DAC108S085 first powers up, the DAC is in WRM. In WRM, the registers of each individual DAC
channel can be written to without causing the DAC outputs to be updated. This is accomplished by setting DB15
to "0", specifying the DAC register to be written to in DB[14:12], and entering the new DAC register setting in
DB[11:0] (see Table 2).The DAC108S085 remains in WRM until the mode of operation is changed to WTM. The
mode of operation is changed from WRM to WTM by setting DB[15:12] to "1001". Once in WTM, writing data to a
DAC channel's register causes the DAC's output to be updated as well. Changing a DAC channel's register in
WTM is accomplished in the same manner as it is done in WRM. However, in WTM the DAC's register and
output are updated at the completion of the command (see Table 2). Similarly, the DAC108S085 remains in
WTM until the mode of operation is changed to WRM by setting DB[15:12] to "1000".
Table 2. Commands Impacted by WRM and WTM
DB15
DB[14:12]
DB[11:0]
Description of Mode
0
000
D11 D10 ... D2 X X
WRM: D[11:0] written to ChA's data register only
WTM: ChA's output is updated by data in D[11:0]
0
001
D11 D10 ... D2 X X
WRM: D[11:0] written to ChB's data register only
WTM: ChB's output is updated by data in D[11:0]
0
010
D11 D10 ... D2 X X
WRM: D[11:0] written to ChC's data register only
WTM: ChC's output is updated by data in D[11:0]
0
011
D11 D10 ... D2 X X
WRM: D[11:0] written to ChD's data register only
WTM: ChD's output is updated by data in D[11:0]
0
100
D11 D10 ... D2 X X
WRM: D[11:0] written to ChE's data register only
WTM: ChE's output is updated by data in D[11:0]
0
101
D11 D10 ... D2 X X
WRM: D[11:0] written to ChF's data register only
WTM: ChF's output is updated by data in D[11:0]
0
110
D11 D10 ... D2 X X
WRM: D[11:0] written to ChG's data register only
WTM: ChG's output is updated by data in D[11:0]
0
111
D11 D10 ... D2 X X
WRM: D[11:0] written to ChH's data register only
WTM: ChH's output is updated by data in D[11:0]
As mentioned previously, the special command operations can be exercised at any time regardless of the mode
of operation. There are three special command operations. The first command is exercised by setting data bits
DB[15:12] to "1010". This allows a user to update multiple DAC outputs simultaneously to the values currently
loaded in their respective control registers. This command is valuable if the user wants each DAC output to be at
a different output voltage but still have all the DAC outputs change to their appropriate values simultaneously
(see Table 3).
The second special command allows the user to alter the DAC output of channel A with a single write frame.
This command is exercised by setting data bits DB[15:12] to "1011" and data bits DB[11:0] to the desired control
register value. It also has the added benefit of causing the DAC outputs of the other channels to update to their
current control register values as well. A user may choose to exercise this command to save a write sequence.
For example, the user may wish to update several DAC outputs simultaneously, including channel A. In order to
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accomplish this task in the minimum number of write frames, the user would alter the control register values of all
the DAC channels except channel A while operating in WRM. The last write frame would be used to exercise the
special command "Channel A Write Mode". In addition to updating channel A's control register and output to a
new value, all of the other channels would be updated as well. At the end of this sequence of write frames, the
DAC108S085 would still be operating in WRM (see Table 3).
The third special command allows the user to set all the DAC control registers and outputs to the same level.
This command is commonly referred to as "broadcast" mode since the same data bits are being broadcast to all
of the channels simultaneously. This command is exercised by setting data bits DB[15:12] to "1100" and data bits
DB[11:0] to the value that the user wishes to broadcast to all the DAC control registers. Once the command is
exercised, each DAC output is updated by the new control register value. This command is frequently used to set
all the DAC outputs to some known voltage such as 0V, VREF/2, or Full Scale. A summary of the commands can
be found in Table 3.
Table 3. Special Command Operations
DB[15:12]
DB[11:0]
Description of Mode
1010
XXXXHGFEDCBA
1011
D11 D10 ... D3 D2 X X
Channel A Write: Channel A's control register and DAC output are updated to
the data in DB[11:0]. The outputs of the other seven channels are also
updated according to their respective control register values.
1100
D11 D10 ... D3 D2 X X
Broadcast: The data in DB[11:0] is written to all channels' control register and
DAC output simultaneously.
Update Select: The DAC outputs of the channels selected with a "1" in
DB[7:0] are updated simultaneously to the values in their respective control
registers.
POWER-ON RESET
The power-on reset circuit controls the output voltages of the eight DACs during power-up. Upon application of
power, the DAC registers are filled with zeros and the output voltages are set to 0V. The outputs remain at 0V
until a valid write sequence is made.
POWER-DOWN MODES
The DAC108S085 has three power-down modes where different output terminations can be selected (see
Table 4). With all channels powered down, the supply current drops to 0.1 µA at 3V and 0.2 µA at 5V. By
selecting the channels to be powered down in DB[7:0] with a "1", individual channels can be powered down
separately or multiple channels can be powered down simultaneously. The three different output terminations
include high output impedance, 100k ohm to ground, and 2.5k ohm to ground.
The output amplifiers, resistor strings, and other linear circuitry are all shut down in any of the power-down
modes. The bias generator, however, is only shut down if all the channels are placed in power-down mode. The
contents of the DAC registers are unaffected when in power-down. Therefore, each DAC register maintains its
value prior to the DAC108S085 being powered down unless it is changed during the write sequence which
instructed it to recover from power down. Minimum power consumption is achieved in the power-down mode with
SYNC idled high, DIN idled low, and SCLK disabled. The time to exit power-down (Wake-Up Time) is typically 3
µsec at 3V and 20 µsec at 5V.
Table 4. Power-Down Modes
DB[15:12]
DB[11:8]
7
6
4
3
2
1
0
Output Impedance
1101
XXXX
H
G
F
5
E
D
C
B
A
High-Z outputs
1110
XXXX
H
G
F
E
D
C
B
A
100 kΩ outputs
1111
XXXX
H
G
F
E
D
C
B
A
2.5 kΩ outputs
Applications Information
EXAMPLES PROGRAMMING THE DAC108S085
This section will present the step-by-step instructions for programming the serial input register.
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Updating DAC Outputs Simultaneously
When the DAC108S085 is first powered on, the DAC is operating in Write Register Mode (WRM). Operating in
WRM allows the user to program the registers of multiple DAC channels without causing the DAC outputs to be
updated. As an example, here are the steps for setting Channel A to a full scale output, Channel B to threequarters full scale, Channel C to half-scale, Channel D to one-quarter full scale and having all the DAC outputs
update simultaneously.
As stated previously, the DAC108S085 powers up in WRM. If the device was previously operating in Write
Through Mode (WTM), an extra step to set the DAC into WRM would be required. First, the DAC registers need
to be programmed to the desired values. To set Channel A to an output of full scale, write "0FFC" to the control
register. This will update the data register for Channel A without updating the output of Channel A. Second, set
Channel B to an output of three-quarters full scale by writing "1C00" to the control register. This will update the
data register for Channel B. Once again, the output of Channel B and Channel A will not be updated since the
DAC is operating in WRM. Third, set Channel C to half scale by writing "2800" to the control register. Fourth, set
Channel D to one-quarter full scale by writing "3400" to the control register. Finally, update all four DAC channels
simultaneously by writing "A00F" to the control register. This procedure allows the user to update four channels
simultaneously with five steps.
Since Channel A was one of the DACs to be updated, one command step could have been saved by writing to
Channel A last. This is accomplished by writing to Channel B, C, and D first and using the the special command
"Channel A Write" to update Channel A's DAC register and output. This special command has the added benefit
of updating all DAC outputs while updating Channel A. With this sequence of commands, the user was able to
update four channels simultaneously with four steps. A summary of this command can be found in Table 3.
Updating DAC Outputs Independently
If the DAC108S085 is currently operating in WRM, change the mode of operation to WTM by writing "9XXX" to
the control register. Once the DAC is operating in WTM, any DAC channel can be updated in one step. For
example, if a design required Channel G to be set to half scale, the user can write "6800" to the control register
and Channel G's data register and DAC output will be updated. Similarly, if Channel F's output needed to be set
to full scale, "5FFC" would need to be written to the control register. Channel A is the only channel that has a
special command that allows its DAC output to be updated in one command regardless of the mode of operation.
Setting Channel A's DAC output to full scale could be accomplished in one step by writing "BFFF" to the control
register.
USING REFERENCES AS POWER SUPPLIES
While the simplicity of the DAC108S085 implies ease of use, it is important to recognize that the path from the
reference input (VREF1,2) to the DAC outputs will have zero Power Supply Rejection Ratio (PSRR). Therefore, it is
necessary to provide a noise-free supply voltage to VREF1,2. In order to utilize the full dynamic range of the
DAC108S085, the supply pin (VA) and VREF1,2 can be connected together and share the same supply voltage.
Since the DAC108S085 consumes very little power, a reference source may be used as the reference input
and/or the supply voltage. The advantages of using a reference source over a voltage regulator are accuracy and
stability. Some low noise regulators can also be used. Listed below are a few reference and power supply
options for the DAC108S085.
LM4132
The LM4132, with its ±0.05% accuracy over temperature, is a good choice as a reference source for the
DAC108S085. The 4.096V version is useful if a 0V to 4.095V output range is desirable. Bypassing the LM4132
voltage input pin with a 4.7µF capacitor and the voltage output pin with a 4.7µF capacitor will improve stability
and reduce output noise. The LM4132 comes in a space-saving 5-pin SOT23.
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Input
Voltage
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LM4132-4.1
C1 +
4.7 PF
C3
0.1 PF
+ C2
4.7 PF
VA VREF1,2
DAC108S085
SYNC
DIN
VOUT = 0V
to 4.095V
SCLK
Figure 32. The LM4132 as a power supply
LM4050
Available with accuracy of ±0.1%, the LM4050 shunt reference is also a good choice as a reference for the
DAC108S085. It is available in 4.096V and 5V versions and comes in a space-saving 3-pin SOT23.
Input
Voltage
R
VZ
IDAC
IZ
0.1 PF
1 PF
LM4050-4.1
or
LM4050-5.0
VA VREF1,2
DAC108S085
SYNC
DIN
VOUT = 0V
to 5V
SCLK
Figure 33. The LM4050 as a power supply
The minimum resistor value in the circuit of must be chosen such that the maximum current through the LM4050
does not exceed its 15 mA rating. The conditions for maximum current include the input voltage at its maximum,
the LM4050 voltage at its minimum, and the DAC108S085 drawing zero current. The maximum resistor value
must allow the LM4050 to draw more than its minimum current for regulation plus the maximum DAC108S085
current in full operation. The conditions for minimum current include the input voltage at its minimum, the LM4050
voltage at its maximum, the resistor value at its maximum due to tolerance, and the DAC108S085 draws its
maximum current. These conditions can be summarized as
R(min) = ( VIN(max) − VZ(min) ) /IZ(max)
(4)
and
R(max) = ( VIN(min) − VZ(max) ) / ( (IDAC(max) + IZ(min) )
where
•
•
•
VZ(min) and VZ(max) are the nominal LM4050 output voltages ± the LM4050 output tolerance over
temperature
IZ(max) is the maximum allowable current through the LM4050, IZ(min) is the minimum current required by the
LM4050 for proper regulation
IDAC(max) is the maximum DAC108S085 supply current
(5)
LP3985
The LP3985 is a low noise, ultra low dropout voltage regulator with a ±3% accuracy over temperature. It is a
good choice for applications that do not require a precision reference for the DAC108S085. It comes in 3.0V,
3.3V and 5V versions, among others, and sports a low 30 µV noise specification at low frequencies. Since low
frequency noise is relatively difficult to filter, this specification could be important for some applications. The
LP3985 comes in a space-saving 5-pin SOT-23 and 5-bump DSBGA packages.
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Input
Voltage
LP3985-5.0
1 PF
1 PF
0.1 PF
0.01 PF
VA
VREF1,2
DAC108S085
SYNC
VOUT = 0V
DIN
to 5V
SCLK
Figure 34. Using the LP3985 regulator
An input capacitance of 1.0µF without any ESR requirement is required at the LP3985 input, while a 1.0µF
ceramic capacitor with an ESR requirement of 5mΩ to 500mΩ is required at the output. Careful interpretation
and understanding of the capacitor specification is required to ensure correct device operation.
LP2980
The LP2980 is an ultra low dropout regulator with a ±0.5% or ±1.0% accuracy over temperature, depending upon
grade. It is available in 3.0V, 3.3V and 5V versions, among others.
VIN
Input
Voltage
VOUT
LP2980
ON /OFF
+
4.7 PF
0.1 PF
VA VREF1,2
DAC108S085
SYNC
DIN
VOUT = 0V
to 5V
SCLK
Figure 35. Using the LP2980 regulator
Like any low dropout regulator, the LP2980 requires an output capacitor for loop stability. This output capacitor
must be at least 1.0µF over temperature, but values of 2.2µF or more will provide even better performance. The
ESR of this capacitor should be within the range specified in the LP2980 data sheet. Surface-mount solid
tantalum capacitors offer a good combination of small size and low ESR. Ceramic capacitors are attractive due to
their small size but generally have ESR values that are too low for use with the LP2980. Aluminum electrolytic
capacitors are typically not a good choice due to their large size and high ESR values at low temperatures.
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BIPOLAR OPERATION
The DAC108S085 is designed for single supply operation and thus has a unipolar output. However, a bipolar
output may be achieved with the circuit in. This circuit will provide an output voltage range of ±5 Volts. A rail-torail amplifier should be used if the amplifier supplies are limited to ±5V.
10 pF
R2
+5V
R1
+5V
10 PF
+
-
0.1 PF
±5V
+
VA / VREF1,2
-5V
DAC108S085
VOUT
SYNC
DIN
SCLK
Figure 36. Bipolar Operation
The output voltage of this circuit for any code is found to be
VO = (VA x (D / 1024) x ((R1 + R2) / R1) - VA x R2 / R1)
VO = (10 x D / 1024) - 5V
(6)
where
•
D is the input code in decimal form. With VA = 5V and R1 = R2
(7)
A list of rail-to-rail amplifiers suitable for this application are indicated in .
Table 5. Some Rail-to-Rail Amplifiers
AMP
PKGS
LMP7701
SOT23-5
±37 µV
Typ VOS
Typ ISUPPLY
0.79 mA
LMV841
SOT23-5
−17 µV
1.11 mA
LMC7111
SOT23-5
900 µV
25 µA
LM7301
SOT23-5
30 µV
620 µA
LM8261
SOT23-5
700 µV
1 mA
VARIABLE CURRENT SOURCE OUTPUT
The DAC108S085 is a voltage output DAC but can be easily converted to a current output with the addition of an
opamp. In Figure 37, one of the channels of the DAC108S085 is converted to a variable current source capable
of sourcing up to 40mA.
R1
R2
LMV710
+5V
10 PF
+
-
0.1 PF
+
VREF
DIN
RB
R3 (= R1)
SYNC
VOUT
IO
RA
SCLK
Load
DAC108S085
Figure 37. Variable Current Source
22
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The output current of this circuit (IO) for any DAC code is found to be
IO = (VREF x (D / 1024) x (R2) / (R1 x RB)
where
•
•
D is the input code in decimal form
R2 = RA + RB
(8)
APPLICATION CIRCUITS
The following figures are examples of the DAC108S085 in typical application circuits. These circuits are basic
and will generally require modification for specific circumstances.
Industrial Application
Figure 38 shows the DAC108S085 controlling several different circuits in an industrial setting. Channel A is
shown providing the reference voltage to the ADC101S625, one of TI's general purpose Analog-to-Digital
Converters (ADCs). The reference for the ADC121S625 may be set to any voltage from 0.2V to 5.5V, providing
the widest dynamic range possible. Typically, the ADC121S625 will be monitoring a sensor and would benefit
from the ADC's reference voltage being adjustable. Channel B is providing the drive or supply voltage for a
sensor. By having the sensor supply voltage adjustable, the output of the sensor can be optimized to the input
level of the ADC monitoring it. Channel C is defined to adjust the offset or gain of an amplifier stage in the
system. Channel D is configured with an opamp to provide an adjustable current source. Being able to convert
one of the eight channels of the DAC108S085 to a current output eliminates the need for a separate current
output DAC to be added to the circuit. Channel E, in conjunction with an opamp, provides a bipolar output swing
for devices requiring control voltages that are centered around ground. Channel F and G are used to set the
upper and lower limits for a range detector. Channel H is reserved for providing voltage control or acting as a
voltage setpoint.
ADC121S625
Sensor
Signal
Set ADC Reference
VREF
VOUTA
Setting Sensor Drive or Supply
(Add buffer for sensor with low
input impedance)
VOUTB
Set offset and gain
VOUTC
SCLK
SYNC
DIN
Output to Another
DAC (Daisy Chain)
VOUTD
Programmable ISOURCE
+V
DAC108S085
Bipolar Output Swing
VOUTE
-V
+
-
Set Limits for Range Detector
Control (Valve, Damper, Robotics,
Process Ctrl) or Voltage Setpoint
(Battery Ctrl, Signal Trigger)
DOUT
VOUTF
VIN
+
-
VREF1
(Ch A - Ch D)
3V or 5V Reference
VREF2
(Ch E - Ch H)
3V or 5V Reference
VOUTG
VOUTH
Figure 38. Industrial Application
ADC Reference
Figure 39 shows Channel A of the DAC108S085 providing the drive or supply voltage for a bridge sensor. By
having the sensor supply voltage adjustable, the output of the sensor can be optimized to the input level of the
ADC monitoring it. The output of the sensor is amplified by a fixed gain amplifier stage with a differential gain of 1
+ 2 × (RF / RI). The advantage of this amplifier configuration is the high input impedance seen by the output of
the bridge sensor. The disadvantage is the poor common-mode rejection ratio (CMRR). The common-mode
voltage (VCM) of the bridge sensor is half of Channel A's DAC output. The VCM is amplified by a gain of 1V/V by
the amplifier stage and thus becomes the bias voltage for the input of the ADC121S705. Channel B of the
DAC108S085 is providing the reference voltage to the ADC121S705. The reference for the ADC121S705 may
be set to any voltage from 1V to 5V, providing the widest dynamic range possible.
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The reference voltage for Channel A and B is powered by an external 5V power supply. Since the 5V supply is
common to the sensor supply voltage and the reference voltage of the ADC, fluctuations in the value of the 5V
supply will have a minimal effect on the digital output code of the ADC. This type of configuration is often referred
to as a "Ratio-metric" design. For example, an increase of 5% to the 5V supply will cause the sensor supply
voltage to increase by 5%. This causes the gain or sensitivity of the sensor to increase by 5%. The gain of the
amplifier stage is unaffected by the change in supply voltage. The ADC121S705 on the other hand, also
experiences a 5% increase to its reference voltage. This causes the size of the ADC's least significant bit (LSB)
to increase by 5%. As a result of the sensor's gain increasing by 5% and the LSB size of the ADC increasing by
the same 5%, there is no net effect on the circuit's performance. It is assumed that the amplifier gain is set low
enough to allow for a 5% increase in the sensor output. Otherwise, the increase in the sensor output level may
cause the output of the amplifiers to clip.
+5V
Channel A
REF
SYNCB
DIN
Channel B
LMP7702
Controller
+
-
DAC108S085
+5V
RF
Bridge
Sensor
REF
REF
ADC121S705
RI
RF
+
Av = 1 + 2
SCLK
SCLK
DOUT
CSB
RF
RI
Figure 39. Driving an ADC Reference
Programmable Attenuator
shows one of the channels of the DAC108S085 being used as a single-quadrant multiplier. In this configuration,
an AC or DC signal can be driven into one of the reference pins. The SPI interface of the DAC can be used to
digitally attenuate the signal to any level from 0dB (full scale) to 0V. This is accomplished without adding any
noticeable level of noise to the signal. An amplifier stage is shown in as a reference for applications where the
input signal requires amplification. Note how the AC signal in this application is ac-coupled to the amplifier before
being amplified. A separate bias voltage is used to set the common-mode voltage for the DAC108S085's
reference input to VA / 2, allowing the largest possible input swing. The multiplying bandwidth of VREF1,2 is
360kHz with a VCM of 2.5V and a peak-to-peak signal swing of 2V.
4.7 PF
20 k:
20 k:
+5V
VBIAS
+5V
Controller
+
LMP7731
VA REF
DAC108S085
Figure 40. Programmable Attenuator
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DSP/MICROPROCESSOR INTERFACING
Interfacing the DAC108S085 to microprocessors and DSPs is quite simple. The following guidelines are offered
to hasten the design process.
ADSP-2101/ADSP2103 Interfacing
Figure 41 shows a serial interface between the DAC108S085 and the ADSP-2101/ADSP2103. The DSP should
be set to operate in the SPORT Transmit Alternate Framing Mode. It is programmed through the SPORT control
register and should be configured for Internal Clock Operation, Active Low Framing and 16-bit Word Length.
Transmission is started by writing a word to the Tx register after the SPORT mode has been enabled.
ADSP-2101/
ADSP2103
TFS
DT
SCLK
DAC108S085
SYNC
DIN
SCLK
Figure 41. ADSP-2101/2103 Interface
80C51/80L51 Interface
A serial interface between the DAC108S085 and the 80C51/80L51 microcontroller is shown in Figure 42. The
SYNC signal comes from a bit-programmable pin on the microcontroller. The example shown here uses port line
P3.3. This line is taken low when data is transmitted to the DAC108S085. Since the 80C51/80L51 transmits 8-bit
bytes, only eight falling clock edges occur in the transmit cycle. To load data into the DAC, the P3.3 line must be
left low after the first eight bits are transmitted. A second write cycle is initiated to transmit the second byte of
data, after which port line P3.3 is brought high. The 80C51/80L51 transmit routine must recognize that the
80C51/80L51 transmits data with the LSB first while the DAC108S085 requires data with the MSB first.
80C51/80L51
DAC108S085
P3.3
SYNC
TXD
SCLK
RXD
DIN
Figure 42. 80C51/80L51 Interface
68HC11 Interface
A serial interface between the DAC108S085 and the 68HC11 microcontroller is shown in Figure 43. The SYNC
line of the DAC108S085 is driven from a port line (PC7 in the figure), similar to the 80C51/80L51.
The 68HC11 should be configured with its CPOL bit as a zero and its CPHA bit as a one. This configuration
causes data on the MOSI output to be valid on the falling edge of SCLK. PC7 is taken low to transmit data to the
DAC. The 68HC11 transmits data in 8-bit bytes with eight falling clock edges. Data is transmitted with the MSB
first. PC7 must remain low after the first eight bits are transferred. A second write cycle is initiated to transmit the
second byte of data to the DAC, after which PC7 should be raised to end the write sequence.
68HC11
DAC108S085
PC7
SYNC
SCK
SCLK
MOSI
DIN
Figure 43. 68HC11 Interface
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Microwire Interface
Figure 44 shows an interface between a Microwire compatible device and the DAC108S085. Data is clocked out
on the rising edges of the SK signal. As a result, the SK of the Microwire device needs to be inverted before
driving the SCLK of the DAC108S085.
MICROWIRE
DEVICE
CS
SYNC
SK
SCLK
SO
DIN
DAC108S085
Figure 44. Microwire Interface
LAYOUT, GROUNDING, AND BYPASSING
For best accuracy and minimum noise, the printed circuit board containing the DAC108S085 should have
separate analog and digital areas. The areas are defined by the locations of the analog and digital power planes.
Both of these planes should be located in the same board layer. A single ground plane is preferred if digital
return current does not flow through the analog ground area. Frequently a single ground plane design will utilize
a "fencing" technique to prevent the mixing of analog and digital ground current. Separate ground planes should
only be utilized when the fencing technique is inadequate. The separate ground planes must be connected in
one place, preferably near the DAC108S085. Special care is required to ensure that digital signals with fast edge
rates do not pass over split ground planes. They must always have a continuous return path below their traces.
For best performance, the DAC108S085 power supply should be bypassed with at least a 1µF and a 0.1µF
capacitor. The 0.1µF capacitor needs to be placed right at the device supply pin. The 1µF or larger valued
capacitor can be a tantalum capacitor while the 0.1µF capacitor needs to be a ceramic capacitor with low ESL
and low ESR. If a ceramic capacitor with low ESL and low ESR is used for the 1µF value and it can be placed
right at the supply pin, the 0.1µF capacitor can be eliminated. Capacitors of this nature typically span the same
frequency spectrum as the 0.1µF capacitor and thus eliminate the need for the extra capacitor. The power supply
for the DAC108S085 should only be used for analog circuits.
It is also advisable to avoid the crossover of analog and digital signals. This helps minimize the amount of noise
from the transitions of the digital signals from coupling onto the sensitive analog signals such as the reference
pins and the DAC outputs.
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REVISION HISTORY
Changes from Revision A (March 2013) to Revision B
•
Page
Changed layout of National Data Sheet to TI format .......................................................................................................... 26
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PACKAGE OPTION ADDENDUM
www.ti.com
30-Sep-2021
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
DAC108S085CIMT
NRND
TSSOP
PW
16
92
Non-RoHS
& Green
Call TI
Level-1-260C-UNLIM
-40 to 125
X80C
DAC108S085CIMT/NOPB
ACTIVE
TSSOP
PW
16
92
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
X80C
DAC108S085CIMTX/NOPB
ACTIVE
TSSOP
PW
16
2500
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
X80C
DAC108S085CISQ/NOPB
ACTIVE
WQFN
RGH
16
1000
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
108S085
DAC108S085CISQX/NOPB
ACTIVE
WQFN
RGH
16
4500
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
108S085
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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