REV. B
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
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
a
AD9708
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700 World Wide Web Site: http://www.analog.com
Fax: 781/326-8703 © Analog Devices, Inc., 1999
8-Bit, 100 MSPS+
TxDAC
®
D/A Converter
FUNCTIONAL BLOCK DIAGRAM
+1.20V REF
REFLO
REF IO
FS ADJ
50pF
COMP1
0.1mF
CURRENT
SOURCE
ARRAY
+5V
AVDD
SEGMENTED
SWITCHES
LATCHES
DIGITAL DATA INPUTS (DB7–DB0)
DVDD
DCOM
CLOCKSLEEP
IOUTA
IOUTB
COMP2
ACOM
0.1mF
+5V
RSET
CLOCK
0.1mFAD9708
FEATURES
Member of Pin-Compatible TxDAC Product Family
125 MSPS Update Rate
8-Bit Resolution
Linearity: 1/4 LSB DNL
Linearity: 1/4 LSB INL
Differential Current Outputs
SINAD @ 5 MHz Output: 50 dB
Power Dissipation: 175 mW @ 5 V to 45 mW @ 3 V
Power-Down Mode: 20 mW @ 5 V
On-Chip 1.20 V Reference
Single +5 V or +3 V Supply Operation
Packages: 28-Lead SOIC and 28-Lead TSSOP
Edge-Triggered Latches
Fast Settling: 35 ns Full-Scale Settling to 0.1%
APPLICATIONS
Communications
Signal Reconstruction
Instrumentation
PRODUCT DESCRIPTION
The AD9708 is the 8-bit resolution member of the TxDAC
series of high performance, low power CMOS digital-to-analog
converters (DACs). The TxDAC family, which consists of pin
compatible 8-, 10-, 12-, and 14-bit DACs, was specifically opti-
mized for the transmit signal path of communication systems. All
of the devices share the same interface options, small outline
package and pinout, thus providing an upward or downward
component selection path based on performance, resolution and
cost. The AD9708 offers exceptional ac and dc performance
while supporting update rates up to 125 MSPS.
The AD9708’s flexible single-supply operating range of +2.7 V
to +5.5 V and low power dissipation are well suited for portable
and low power applications. Its power dissipation can be
further reduced to 45 mW, without a significant degradation in
performance, by lowering the full-scale current output. In addi-
tion, a power-down mode reduces the standby power dissipa-
tion to approximately 20 mW.
The AD9708 is manufactured on an advanced CMOS process.
A segmented current source architecture is combined with a
proprietary switching technique to reduce spurious components
and enhance dynamic performance. Edge-triggered input latches
and a temperature compensated bandgap reference have been inte-
grated to provide a complete monolithic DAC solution. Flexible
supply options support +3 V and +5 V CMOS logic families.
The AD9708 is a current-output DAC with a nominal full-scale
output current of 20 mA and > 100 kΩ output impedance.
TxDAC is a registered trademark of Analog Devices, Inc.
Differential current outputs are provided to support single-
ended or differential applications. The current outputs may be
directly tied to an output resistor to provide two complemen-
tary, single-ended voltage outputs. The output voltage compliance
range is 1.25 V.
The AD9708 contains a 1.2 V on-chip reference and reference
control amplifier, which allows the full-scale output current to
be simply set by a single resistor. The AD9708 can be driven by
a variety of external reference voltages. The AD9708’s full-scale
current can be adjusted over a 2 mA to 20 mA range without
any degradation in dynamic performance. Thus, the AD9708
may operate at reduced power levels or be adjusted over a 20 dB
range to provide additional gain ranging capabilities.
The AD9708 is available in 28-lead SOIC and 28-lead TSSOP
packages. It is specified for operation over the industrial tem-
perature range.
PRODUCT HIGHLIGHTS
1. The AD9708 is a member of the TxDAC product family, which
provides an upward or downward component selection path
based on resolution (8 to 14 bits), performance and cost.
2. Manufactured on a CMOS process, the AD9708 uses a pro-
prietary switching technique that enhances dynamic perfor-
mance well beyond 8- and 10-bit video DACs.
3. On-chip, edge-triggered input CMOS latches readily interface
to +3 V and +5 V CMOS logic families. The AD9708 can
support update rates up to 125 MSPS.
4. A flexible single-supply operating range of +2.7 V to +5.5 V
and a wide full-scale current adjustment span of 2 mA to
20 mA allows the AD9708 to operate at reduced power levels
(i.e., 45 mW) without any degradation in dynamic performance.
5. A temperature compensated, 1.20 V bandgap reference is
included on-chip providing a complete DAC solution. An
external reference may be used.
6. The current output(s) of the AD9708 can easily be config-
ured for various single-ended or differential applications.
DC SPECIFICATIONS
Parameter Min Typ Max Units
RESOLUTION 8 Bits
MONOTONICITY GUARANTEED OVER SPECIFIED TEMPERATURE RANGE
DC ACCURACY
1
Integral Linearity Error (INL) –1/2 ±1/4 +1/2 LSB
Differential Nonlinearity (DNL) –1/2 ±1/4 +1/2 LSB
ANALOG OUTPUT
Offset Error –0.025 +0.025 % of FSR
Gain Error
(Without Internal Reference) –10 ±2 +10 % of FSR
Gain Error
(With Internal Reference) –10 ±1 +10 % of FSR
Full-Scale Output Current
2
2.0 20.0 mA
Output Compliance Range –1.0 1.25 V
Output Resistance 100 kΩ
Output Capacitance 5 pF
REFERENCE OUTPUT
Reference Voltage 1.08 1.20 1.32 V
Reference Output Current
3
100 nA
REFERENCE INPUT
Input Compliance Range 0.1 1.25 V
Reference Input Resistance 1 MΩ
Small Signal Bandwidth (w/o C
COMP1
)
4
1.4 MHz
TEMPERATURE COEFFICIENTS
Offset Drift 0 ppm of FSR/°C
Gain Drift
(Without Internal Reference) ±50 ppm of FSR/°C
Gain Drift
(With Internal Reference) ±100 ppm of FSR/°C
Reference Voltage Drift ±50 ppm/°C
POWER SUPPLY
Supply Voltages
AVDD
5
2.7 5.0 5.5 V
DVDD 2.7 5.0 5.5 V
Analog Supply Current (I
AVDD
)2530mA
Digital Supply Current (I
DVDD
)
6
36mA
Supply Current Sleep Mode (I
AVDD
) 8.5 mA
Power Dissipation
6
(5 V, I
OUTFS
= 20 mA) 140 175 mW
Power Dissipation
7
(5 V, I
OUTFS
= 20 mA) 190 mW
Power Dissipation
7
(3 V, I
OUTFS
= 2 mA) 45 mW
Power Supply Rejection Ratio—AVDD –0.4 +0.4 % of FSR/V
Power Supply Rejection Ratio—DVDD –0.025 +0.025 % of FSR/V
OPERATING RANGE –40 +85 °C
NOTES
1
Measured at IOUTA, driving a virtual ground.
2
Nominal full-scale current, I
OUTFS
, is 32 × the I
REF
current.
3
Use an external buffer amplifier to drive any external load.
4
Reference bandwidth is a function of external cap at COMP1 pin.
5
For operation below 3 V, it is recommended that the output current be reduced to 12 mA or less to maintain optimum performance.
6
Measured at f
CLOCK
= 50 MSPS and f
OUT
= 1.0 MHz.
7
Measured as unbuffered voltage output into 50 Ω R
LOAD
at IOUTA and IOUTB, f
CLOCK
= 100 MSPS and f
OUT
= 40 MHz.
Specifications subject to change without notice.
(TMIN to TMAX , AVDD = +5 V, DVDD = +5 V, IOUTFS = 20 mA, unless otherwise noted)
–2– REV. B
AD9708–SPECIFICATIONS
DYNAMIC SPECIFICATIONS
P
arameter Min Typ Max Units
DYNAMIC PERFORMANCE
Maximum Output Update Rate (f
CLOCK
) 100 125 MSPS
Output Settling Time (t
ST
) (to 0.1%)
1
35 ns
Output Propagation Delay (t
PD
)1ns
Glitch Impulse 5 pV-s
Output Rise Time (10% to 90%)
1
2.5 ns
Output Fall Time (10% to 90%)
1
2.5 ns
Output Noise (I
OUTFS
= 20 mA) 50 pA/√Hz
Output Noise (I
OUTFS
= 2 mA) 30 pA/√Hz
AC LINEARITY TO NYQUIST
Signal-to-Noise and Distortion Ratio
f
CLOCK
= 10 MSPS; f
OUT
= 1.00 MHz 50 dB
f
CLOCK
= 50 MSPS; f
OUT
= 1.00 MHz 50 dB
f
CLOCK
= 50 MSPS; f
OUT
= 12.51 MHz 48 dB
f
CLOCK
= 100 MSPS; f
OUT
= 5.01 MHz 50 dB
f
CLOCK
= 100 MSPS; f
OUT
= 25.01 MHz 45 dB
Total Harmonic Distortion
f
CLOCK
= 10 MSPS; f
OUT
= 1.00 MHz –67 dBc
f
CLOCK
= 50 MSPS; f
OUT
= 1.00 MHz –67 –62 dBc
f
CLOCK
= 50 MSPS; f
OUT
= 12.51 MHz –59 dBc
f
CLOCK
= 100 MSPS; f
OUT
= 5.01 MHz –64 dBc
f
CLOCK
= 100 MSPS; f
OUT
= 25.01 MHz –48 dBc
Spurious-Free Dynamic Range to Nyquist
f
CLOCK
= 10 MSPS; f
OUT
= 1.00 MHz 68 dBc
f
CLOCK
= 50 MSPS; f
OUT
= 1.00 MHz 62 68 dBc
f
CLOCK
= 50 MSPS; f
OUT
= 12.51 MHz 63 dBc
f
CLOCK
= 100 MSPS; f
OUT
= 5.01 MHz 67 dBc
f
CLOCK
= 100 MSPS; f
OUT
= 25.01 MHz 50 dBc
NOTES
1
Measured single ended into 50 Ω load.
Specifications subject to change without notice.
DIGITAL SPECIFICATIONS
P
arameter Min Typ Max Units
DIGITAL INPUTS
Logic “1” Voltage @ DVDD = +5 V 3.5 5 V
Logic “1” Voltage @ DVDD = +3 V 2.1 3 V
Logic “0” Voltage @ DVDD = +5 V 0 1.3 V
Logic “0” Voltage @ DVDD = +3 V 0 0.9 V
Logic “1” Current –10 +10 µA
Logic “0” Current –10 +10 µA
Input Capacitance 5pF
Input Setup Time (t
S
)2.0ns
Input Hold Time (t
H
)1.5ns
Latch Pulsewidth (t
LPW
)
3.5 ns
Specifications subject to change without notice.
0.1%
0.1%
tS tH
tLPW
tPD tST
DB0–DB7
CLOCK
IOUTA
OR
IOUTB
Figure 1. Timing Diagram
(TMIN to TMAX , AVDD = +5 V, DVDD = +5 V, IOUTFS = 20 mA, Single-Ended Output, IOUTA, 50 ⍀ Doubly
Terminated, unless otherwise noted)
AD9708
–3–
REV. B
(TMIN to TMAX, AVDD = +5 V, DVDD = +5 V, IOUTFS = 20 mA unless otherwise noted)
AD9708
–4– REV. B
ABSOLUTE MAXIMUM RATINGS*
With
Parameter Respect to Min Max Units
AVDD ACOM –0.3 +6.5 V
DVDD DCOM –0.3 +6.5 V
ACOM DCOM –0.3 +0.3 V
AVDD DVDD –6.5 +6.5 V
CLOCK, SLEEP DCOM –0.3 DVDD + 0.3 V
Digital Inputs DCOM –0.3 DVDD + 0.3 V
IOUTA, IOUTB ACOM –1.0 AVDD + 0.3 V
COMP1, COMP2 ACOM –0.3 AVDD + 0.3 V
REFIO, FSADJ ACOM –0.3 AVDD + 0.3 V
REFLO ACOM –0.3 +0.3 V
Junction Temperature +150 °C
Storage Temperature –65 +150 °C
Lead Temperature
(10 sec) +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
sections of this specification is not implied. Exposure to absolute maximum
ratings for extended periods may effect device reliability.
THERMAL CHARACTERISTICS
Thermal Resistance
28-Lead 300 mil SOIC
θ
JA
= 71.4°C/W
θ
JC
= 23°C/W
28-Lead TSSOP
θ
JA
= 97.9°C/W
θ
JC
= 14.0°C/W
PIN CONFIGURATION
14
13
12
11
17
16
15
20
19
18
10
9
8
1
2
3
4
7
6
5
TOP VIEW
(Not to Scale)
28
27
26
25
24
23
22
21
AD9708
NC = NO CONNECT
(MSB) DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
NC
NC
NC
NC
NC
NC
CLOCK
DVDD
DCOM
NC
AVDD
COMP2
IOUTA
IOUTB
ACOM
COMP1
FS ADJ
REFIO
REFLO
SLEEP
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 AD9708 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.
PIN FUNCTION DESCRIPTIONS
Pin No. Name Description
1 DB7 Most Significant Data Bit (MSB).
2–7 DB6–DB1 Data Bits 1–6.
8 DB0 Least Significant Data Bit (LSB).
9–14, 25 NC No Internal Connection.
15 SLEEP Power-Down Control Input. Active
High. Contains active pull-down circuit,
thus may be left unterminated if not
used.
16 REFLO Reference Ground when Internal 1.2 V
Reference Used. Connect to AVDD to
disable internal reference.
17 REFIO Reference Input/Output. Serves as
reference input when internal reference
disabled (i.e., Tie REFLO to AVDD).
Serves as 1.2 V reference output when
internal reference activated (i.e., Tie
REFLO to ACOM). Requires 0.1 µF
capacitor to ACOM when internal
reference activated.
18 FS ADJ Full-Scale Current Output Adjust.
19 COMP1 Bandwidth/Noise Reduction Node.
Add 0.1 µF to AVDD for optimum
performance.
20 ACOM Analog Common.
21 IOUTB Complementary DAC Current Output.
Full-scale current when all data bits
are 0s.
22 IOUTA DAC Current Output. Full-scale
current when all data bits are 1s.
23 COMP2 Internal Bias Node for Switch Driver
Circuitry. Decouple to ACOM with
0.1 µF capacitor.
24 AVDD Analog Supply Voltage (+2.7 V to
+5.5 V).
26 DCOM Digital Common.
27 DVDD Digital Supply Voltage (+2.7 V to
+5.5 V).
28 CLOCK Clock Input. Data latched on positive
edge of clock.
ORDERING GUIDE
Temperature Package Package
Model Range Descriptions Options*
AD9708AR –40°C to +85°C 28-Lead 300 Mil SOIC R-28
AD9708ARU –40°C to +85°C 28-Lead TSSOP RU-28
AD9708-EB Evaluation Board
*R = Small Outline IC; RU = Thin Small Outline IC.
WARNING!
ESD SENSITIVE DEVICE
AD9708
–5–
REV. B
DEFINITIONS OF SPECIFICATIONS
Linearity Error (Also Called Integral Nonlinearity or INL)
Linearity error is defined as the maximum deviation of the
actual analog output from the ideal output, determined by a
straight line drawn from zero to full scale.
Differential Nonlinearity (or DNL)
DNL is the measure of the variation in analog value, normalized
to full scale, associated with a 1 LSB change in digital input code.
Monotonicity
A D/A converter is monotonic if the output either increases or
remains constant as the digital input increases.
Offset Error
The deviation of the output current from the ideal of zero is
called offset error. For IOUTA, 0 mA output is expected when
the inputs are all 0s. For IOUTB, 0 mA output is expected
when all inputs are set to 1s.
Gain Error
The difference between the actual and ideal output span. The
actual span is determined by the output when all inputs are set
to 1s minus the output when all inputs are set to 0s.
Output Compliance Range
The range of allowable voltage at the output of a current-output
DAC. Operation beyond the maximum compliance limits may
cause either output stage saturation or breakdown resulting in
nonlinear performance.
Temperature Drift
Temperature drift is specified as the maximum change from the
ambient (+25°C) value to the value at either T
MIN
or T
MAX
. For
offset and gain drift, the drift is reported in ppm of full-scale
range (FSR) per degree C. For reference drift, the drift is
reported in ppm per degree C.
Power Supply Rejection
The maximum change in the full-scale output as the supplies
are varied from nominal to minimum and maximum specified
voltages.
Settling Time
The time required for the output to reach and remain within a
specified error band about its final value, measured from the
start of the output transition.
Glitch Impulse
Asymmetrical switching times in a DAC give rise to undesired
output transients that are quantified by a glitch impulse. It is
specified as the net area of the glitch in pV-s.
Spurious-Free Dynamic Range
The difference, in dB, between the rms amplitude of the output
signal and the peak spurious signal over the specified bandwidth.
Signal-to-Noise and Distortion (S/N+D, SINAD) Ratio
S/N+D is the ratio of the rms value of the measured output
signal to the rms sum of all other spectral components below the
Nyquist frequency, including harmonics but excluding dc. The
value for S/N+D is expressed in decibels.
Total Harmonic Distortion
THD is the ratio of the rms sum of the first six harmonic
components to the rms value of the measured output signal. It is
expressed as a percentage or in decibels (dB).
DVDD
DCOM
RETIMED
CLOCK
OUTPUT* DIGITAL
DATA
TEKTRONIX
AWG-2021
LECROY 9210
PULSE GENERATOR
CLOCK
OUTPUT
50V20pF
50V20pF
TO HP3589A
SPECTRUM/
NETWORK
ANALYZER
50V INPUT
* AWG2021 CLOCK RETIMED
SUCH THAT DIGITAL DATA
TRANSITIONS ON FALLING EDGE
OF 50% DUTY CYCLE CLOCK.
+1.20V REF
REFLO
REF IO
FS ADJ
50pF
COMP1
0.1mF
CURRENT
SOURCE
ARRAY
+5V
AVDD
SEGMENTED
SWITCHES
LATCHES
DVDD
DCOM
CLOCK
SLEEP
IOUTA
IOUTB
COMP2
ACOM
0.1mF
+5V
RSET
2kV
0.1mF
AD9708
50V
Figure 2. Basic AC Characterization Test Setup
AD9708
–6– REV. B
Typical AC Characterization Curves
FREQUENCY – MHz
SINAD/THD – dB
70
60
40
0.1 1 100
10
50
65
55
45
THD @ 10MSPS THD @ 50MSPS
THD
@ 100MSPS
SINAD @ 10MSPS
SINAD @ 100MSPS
SINAD @ 50MSPS
Figure 3. SINAD/THD vs. f
OUT
(AVDD
and DVDD = 5.0 V)
FREQUENCY – MHz
SINAD/THD – dB
70
60
40
0.1 1 100
10
50
65
55
45
THD @ 10MSPS
THD @ 50MSPS
THD
@ 100MSPS
SINAD @ 10MSPS
SINAD @ 100MSPS
SINAD @ 50MSPS
Figure 6. SINAD/THD vs. f
OUT
(AVDD
and DVDD = 3.0 V)
fCLOCK = 25MSPS
fOUT = 7.81MHz
SFDR = +60.7dBc
AMPLITUDE = 0dBFS
0
–100
START: 0Hz STOP: 12.5MHz
10dB – Div
Figure 9. Single-Tone Spectral Plot
@ 25 MSPS
FREQUENCY – MHz
SINAD/THD – dB
70
60
40
0.1 1 100
10
50
65
55
45
THD @ 10MSPS
THD @ 50MSPS
THD
@ 100MSPS
SINAD @ 10MSPS
SINAD @ 100MSPS
SINAD @ 50MSPS
Figure 4. SINAD/THD vs. f
OUT
(Differ-
ential Output, AVDD and DVDD = 5.0 V)
FREQUENCY – MHz
SINAD/THD – dB
70
60
40
0.1 1 100
10
50
65
55
45
THD
@ 10MSPS THD
@ 50MSPS
THD @ 100MSPS
SINAD @ 10MSPS
SINAD @ 100MSPS
SINAD @ 50MSPS
Figure 7. SINAD/THD vs. f
OUT
(Differ-
ential Output, AVDD and DVDD = 3.0 V)
fCLOCK = 125MSPS
fOUT = 27.0MHz
SFDR = +52.7dBc
AMPLITUDE = 0dBc
0
START: 0Hz STOP: 62.5MHz
–100
10dB – Div
Figure 10. Single-Tone Spectral
Plot @ 125 MSPS
FREQUENCY – MHz
SINAD – dB
55
50
301 100
10
40
45
35
IOUTFS = 20mA
IOUTFS = 10mA
IOUTFS = 5mA
IOUTFS = 2.5mA
Figure 5. SINAD vs. I
OUTFS
@ 100 MSPS
FREQUENCY – MHz
SINAD – dB
52
50
42
0.1 10
1
46
48
44
IOUTFS = 20mA
IOUTFS = 5mA
IOUTFS = 2.5mA
IOUTFS = 10mA
Figure 8. SINAD vs. I
OUTFS
@ 20 MSPS
TIME – 5ns/Div
VOLTS
0.5
0.4
0.3
0.2
0.1
0.0
–0.1
0.6
–0.2
Figure 11. Step Response
(AVDD = +5 V or +3 V, DVDD = +5 V or +3 V, 50 ⍀ Doubly Terminated Load,
Single-Ended Output, IOUTA, IOUTFS = 20 mA, TA = +25ⴗC, unless otherwise noted)
AD9708
–7–
REV. B
FUNCTIONAL DESCRIPTION
Figure 12 shows a simplified block diagram of the AD9708. The
AD9708 consists of a large PMOS current source array capable of
providing up to 20 mA of total current. The array is divided into
31 equal currents that make up the five most significant bits
(MSBs). The remaining 3 LSBs are also implemented with equally
weighted current sources whose sum total equals 7/8th of an
MSB current source. Implementing the upper and lower bits
with current sources helps maintain the DAC’s high output
impedance (i.e. > 100 kΩ). All of these current sources are
switched to one or the other of the two output nodes (i.e., IOUTA
or IOUTB) via PMOS differential current switches. The switches
are based on a new architecture that drastically improves
distortion performance.
The analog and digital sections of the AD9708 have separate
power supply inputs (i.e., AVDD and DVDD) that can operate
independently over a 2.7 volt to 5.5 volt range. The digital section,
which is capable of operating up to a 125 MSPS clock rate,
consists of edge-triggered latches and segment decoding logic
circuitry. The analog section includes the PMOS current
sources, the associated differential switches, a 1.20 V bandgap
voltage reference and a reference control amplifier.
The full-scale output current is regulated by the reference con-
trol amplifier and can be set from 2 mA to 20 mA via an exter-
nal resistor, R
SET
. The external resistor, in combination with
both the reference control amplifier and voltage reference
V
REFIO
, sets the reference current I
REF
, which is mirrored over to
the segmented current sources with the proper scaling factor.
The full-scale current, I
OUTFS
, is thirty-two times the value of I
REF
.
DAC TRANSFER FUNCTION
The AD9708 provides complementary current outputs, IOUTA
and IOUTB. IOUTA will provide a near full-scale current output,
I
OUTFS
, when all bits are high (i.e., DAC CODE = 255), while
IOUTB, the complementary output, provides no current. The
current output appearing at IOUTA and IOUTB are a function
of both the input code and I
OUTFS
and can be expressed as:
I
OUTA
= (DAC CODE/256) × I
OUTFS
(1)
I
OUTB
= (255 – DAC CODE)/256 × I
OUTFS
(2)
where DAC CODE = 0 to 255 (i.e., Decimal Representation).
As previously mentioned, I
OUTFS
is a function of the reference
current I
REF
, which is nominally set by a reference voltage
V
REFIO
and external resistor R
SET
. It can be expressed as:
I
OUTFS
= 32 × I
REF
(3)
where
I
REF
= V
REFIO
/R
SET
(4)
The two current outputs will typically drive a resistive load
directly. If dc coupling is required, IOUTA and IOUTB should
be directly connected to matching resistive loads, R
LOAD
, which
are tied to analog common, ACOM. Note, R
LOAD
may repre-
sent the equivalent load resistance seen by IOUTA or IOUTB
as would be the case in a doubly terminated 50 Ω or 75 Ω cable.
The single-ended voltage output appearing at the IOUTA and
IOUTB nodes is simply:
V
OUTA
= I
OUTA
× R
LOAD
(5)
V
OUTB
= I
OUTB
× R
LOAD
(6)
Note the full-scale value of V
OUTA
and V
OUTB
should not exceed
the specified output compliance range to maintain specified
distortion and linearity performance.
The differential voltage, V
DIFF
, appearing across IOUTA and
IOUTB is:
V
DIFF
= (I
OUTA
– I
OUTB
) × R
LOAD
(7)
Substituting the values of I
OUTA
, I
OUTB
, and I
REF
; V
DIFF
can be
expressed as:
V
DIFF
= {(2 DAC CODE – 255)/256}/ × (32 R
LOAD
/R
SET
)
× V
REFIO
(8)
VOLTAGE REFERENCE AND CONTROL AMPLIFIER
The AD9708 contains an internal 1.20 V bandgap reference
that can be easily disabled and overridden by an external refer-
ence. REFIO serves as either an input or output depending on
whether the internal or an external reference is selected. If
REFLO is tied to ACOM, as shown in Figure 13, the internal
reference is activated and REFIO provides a 1.20 V output. In
this case, the internal reference must be compensated externally
with a ceramic chip capacitor of 0.1 µF or greater from REFIO
to REFLO. Note that REFIO is not designed to drive any ex-
ternal load. It should be buffered with an external amplifier
having an input bias current less than 100 nA if any additional
loading is required.
+1.20V REF
REFLO
REFIO
FS ADJ
50pF
COMP1
0.1mF
CURRENT
SOURCE
ARRAY
+5V
AVDD
SEGMENTED
SWITCHES
LATCHES
DVDD
DCOM
CLOCK
SLEEP
IOUTA
IOUTB
COMP2
ACOM
0.1mF
+5V
RSET
2kV
0.1mF
AD9708
IOUTB VOUTB
RLOAD
50V
VOUTA
RLOAD
50V
IOUTA
VDIFF = VOUTA – VOUTB
CLOCK
IREF
VREFIO
DIGITAL DATA INPUTS (DB7–DB0)
Figure 12. Functional Block Diagram
AD9708
–8– REV. B
50pF
COMP1
+1.2V REF
AVDD
REFLO
CURRENT
SOURCE
ARRAY
0.1mF
+5V
REFIO
FS ADJ
2kV
0.1mF
AD9708
ADDITIONAL
LOAD
OPTIONAL
EXTERNAL
REF BUFFER
Figure 13. Internal Reference Configuration
The internal reference can be disabled by connecting REFLO to
AVDD. In this case, an external reference may then be applied
to REFIO as shown in Figure 14. The external reference may
provide either a fixed reference voltage to enhance accuracy and
drift performance or a varying reference voltage for gain control.
Note that the 0.1 µF compensation capacitor is not required
since the internal reference is disabled, and the high input
impedance (i.e., 1 MΩ) of REFIO minimizes any loading of the
external reference.
50pF
COMP1
+1.2V REF
AVDD
REFLO
CURRENT
SOURCE
ARRAY
0.1mF
AVDD
REFIO
FS ADJ
RSET
AD9708
EXTERNAL
REF
IREF =
VREFIO/RSET
AVDD
REFERENCE
CONTROL
AMPLIFIER
VREFIO
Figure 14. External Reference Configuration
The AD9708 also contains an internal control amplifier that is
used to regulate the DAC’s full-scale output current, I
OUTFS
.
The control amplifier is configured as a V-I converter, as shown
in Figure 14, such that its current output, I
REF
, is determined by
the ratio of the V
REFIO
and an external resistor, R
SET
, as stated
in Equation 4. The control amplifier allows a wide (10:1)
adjustment span of I
OUTFS
over a 2 mA to 20 mA range by setting
I
REF
between 62.5 µA and 625 µA. The wide adjustment span of
I
OUTFS
provides several application benefits. The first benefit
relates directly to the power dissipation of the AD9708, which is
proportional to I
OUTFS
(refer to the POWER DISSIPATION
section). The second benefit relates to the 20 dB adjustment,
which is useful for system gain control purposes.
The small signal bandwidth of the reference control amplifier is
approximately 1.8 MHz and can be reduced by connecting an
external capacitor between COMP1 and AVDD. The output of
the control amplifier, COMP1, is internally compensated via a
50 pF capacitor that limits the control amplifier small-signal
bandwidth and reduces its output impedance. Any additional
external capacitance further limits the bandwidth and acts as
a filter to reduce the noise contribution from the reference
amplifier. If I
REF
is fixed for an application, a 0.1 µF ceramic chip
capacitor is recommended.
I
REF
can be varied for a fixed R
SET
by disabling the internal
reference and varying the common-mode voltage over its
compliance range of 1.25 V to 0.10 V. REFIO can be driven by
a single-supply amplifier or DAC, thus allowing I
REF
to be var-
ied for a fixed R
SET
. Since the input impedance of REFIO is
approximately 1 MΩ, a simple R-2R ladder DAC configured in
the voltage mode topology may be used to control the gain. This
circuit is shown in Figure 15 using the AD7524 and an external
1.2 V reference, the AD1580. Note another AD9708 could also
be used as the gain control DAC since it can also provide a
programmable unipolar output up to 1.2 V.
ANALOG OUTPUTS AND OUTPUT CONFIGURATIONS
The AD9708 produces two complementary current outputs,
I
OUTA
and I
OUTB
, which may be converted into complementary
single-ended voltage outputs, V
OUTA
and V
OUTB
, via a load resistor,
R
LOAD
, as described in the DAC TRANSFER FUNCTION
section. Figure 16 shows the AD9708 configured to provide a
positive unipolar output range of approximately 0 V to +0.5 V
for a double terminated 50 Ω cable for a nominal full-scale
current, I
OUTFS
, of 20 mA. In this case, R
LOAD
represents the
equivalent load resistance seen by IOUTA or IOUTB and is
equal to 25 Ω. The unused output (IOUTA or IOUTB) can be
connected to ACOM directly or via a matching R
LOAD
. Different
values of I
OUTFS
and R
LOAD
can be selected as long as the posi-
tive compliance range is adhered to.
AD9708
IOUTA
IOUTB 21
50V
25V
50V
VOUTA = 0 TO +0.5V
IOUTFS = 20mA
22
Figure 16. 0 V to +0.5 V Unbuffered Voltage Output
Alternatively, an amplifier could be configured as an I-V converter
thus converting IOUTA or IOUTB into a negative unipolar
1.2V 50pF
COMP1
+1.2V REF
AVDD
REFLO
CURRENT
SOURCE
ARRAY
AVDD
REFIO
FS ADJ
RSET AD9708
IREF =
VREF/RSET
AVDD OPTIONAL
BANDLIMITING
CAPACITOR
VREF
VDD
RFB
OUT1
OUT2
AGND
DB7–DB0
AD7524
AD1580
0.1V TO 1.2V
Figure 15. Single-Supply Gain Control Circuit
AD9708
–9–
REV. B
voltage. Figure 17 shows a buffered singled-ended output con-
figuration in which the op amp, U1, performs an I-V conversion
on the AD9708 output current. U1 provides a negative unipolar
output voltage and its full-scale output voltage is simply the
product of R
FB
and I
OUTFS
. The full-scale output should be set
within U1’s voltage output swing capabilities by scaling I
OUTFS
and/or R
FB
. An improvement in ac distortion performance may
result with a reduced I
OUTFS
, since the signal current U1 will be
required to sink and will be subsequently reduced. Note, the ac
distortion performance of this circuit at higher DAC update
rates may be limited by U1’s slewing capabilities.
AD9708
22
IOUTA
IOUTB 21
COPT
200V
U1 VOUT = IOUTFS 3 RFB
IOUTFS = 10mA
RFB
200V
Figure 17. Unipolar Buffered Voltage Output
IOUTA and IOUTB also have a negative and positive voltage
compliance range that must be adhered to in order to achieve
optimum performance. The positive output compliance range is
slightly dependent on the full-scale output current, I
OUTFS
. It
degrades slightly from its nominal 1.25 V for an I
OUTFS
= 20 mA
to 1.00 V for an I
OUTFS
= 2 mA. Applications requiring the
AD9708’s output (i.e., V
OUTA
and/or V
OUTB
) to extend up to its
output compliance range should size R
LOAD
accordingly. Operation
beyond this compliance range will adversely affect the AD9708’s
linearity.
The differential voltage, V
DIFF
, existing between V
OUTA
and
V
OUTB
may also be converted to a single-ended voltage via a
transformer or differential amplifier configuration. Refer to the
DIFFERENTIAL OUTPUT CONFIGURATION section for
more information.
DIGITAL INPUTS
The AD9708’s digital input consists of eight data input pins and
a clock input pin. The 8-bit parallel data inputs follow standard
positive binary coding where DB7 is the most significant bit
(MSB) and DB0 is the least significant bit (LSB). The digital
interface is implemented using an edge-triggered master slave
latch. The DAC output is updated following the rising edge of
the clock as shown in Figure 1 and is designed to support a
clock rate as high as 125 MSPS. The clock can be operated at
any duty cycle that meets the specified latch pulsewidth. The
setup-and-hold times can also be varied within the clock cycle as
long as the specified minimum times are met; although the
location of these transition edges may affect digital feedthrough
and distortion performance.
The digital inputs are CMOS compatible with logic thresholds,
V
THRESHOLD
set to approximately half the digital positive supply
(DVDD) or
V
THRESHOLD
= DVDD/2 (±20%)
Figure 18 shows the equivalent digital input circuit for the data
and clock inputs. The sleep mode input is similar, except that
it contains an active pull-down circuit, thus ensuring that the
AD9708 remains enabled if this input is left disconnected. The
internal digital circuitry of the AD9708 is capable of operating
over a digital supply range of 2.7 V to 5.5 V. As a result, the
digital inputs can also accommodate TTL levels when DVDD is
set to accommodate the maximum high level voltage, V
OH(MAX)
,
of the TTL drivers. A DVDD of 3 V to 3.3 V will typically
ensure upper compatibility of most TTL logic families.
DVDD
DIGITAL
INPUT
Figure 18. Equivalent Digital Input
Since the AD9708 is capable of being updated up to 125 MSPS,
the quality of the clock and data input signals are important in
achieving the optimum performance. The drivers of the digital
data interface circuitry should be specified to meet the minimum
setup-and-hold times of the AD9708 as well as its required min/
max input logic level thresholds. Typically, the selection of the
slowest logic family that satisfies the above conditions will result
in the lowest data feedthrough and noise.
Digital signal paths should be kept short and run lengths matched
to avoid propagation delay mismatch. The insertion of a low
value resistor network (i.e., 20 Ω to 100 Ω) between the AD9708
digital inputs and driver outputs may be helpful in reducing any
overshooting and ringing at the digital inputs that contribute to
data feedthrough. For longer run lengths and high data update
rates, strip line techniques with proper termination resistors
should be considered to maintain “clean” digital inputs. Also,
operating the AD9708 with reduced logic swings and a corre-
sponding digital supply (DVDD) will also reduce data feedthrough.
The external clock driver circuitry should provide the AD9708
with a low jitter clock input meeting the min/max logic levels
while providing fast edges. Fast clock edges will help minimize
any jitter that will manifest itself as phase noise on a recon-
structed waveform. However, the clock input could also be
driven by via a sine wave, which is centered around the digital
threshold (i.e., DVDD/2), and meets the min/max logic threshold.
This may result in a slight degradation in the phase noise, which
becomes more noticeable at higher sampling rates and output
frequencies. Note, at higher sampling rates the 20% tolerance
of the digital logic threshold should be considered since it will
affect the effective clock duty cycle and subsequently cut into
the required data setup-and-hold times.
SLEEP MODE OPERATION
The AD9708 has a power-down function that turns off the
output current and reduces the supply current to less than 8.5 mA
over the specified supply range of 2.7 V to 5.5 V and tempera-
ture range. This mode can be activated by applying a logic level
“1” to the SLEEP pin. This digital input also contains an active
pull-down circuit that ensures the AD9708 remains enabled if
this input is left disconnected. The SLEEP input with active
pull-down requires <40 µA of drive current.
The power-up and power-down characteristics of the AD9708
are dependent on the value of the compensation capacitor con-
nected to COMP2 (Pin 23). With a nominal value of 0.1 µF, the
AD9708 takes less than 5 µs to power down and approximately
3.25 ms to power back up.
AD9708
–10– REV. B
POWER DISSIPATION
The power dissipation, P
D
, of the AD9708 is dependent on
several factors, including: (1) AVDD and DVDD, the power
supply voltages; (2) I
OUTFS
, the full-scale current output; (3)
f
CLOCK
, the update rate; (4) and the reconstructed digital input
waveform. The power dissipation is directly proportional to the
analog supply current, I
AVDD
, and the digital supply current,
I
DVDD.
I
AVDD
is directly proportional to I
OUTFS
, as shown in
Figure 19, and is insensitive to f
CLOCK
.
Conversely, I
DVDD
is dependent on both the digital input wave-
form, f
CLOCK
, and digital supply DVDD. Figures 20 and 21
show I
DVDD
as a function of full-scale sine wave output ratios
(f
OUT
/f
CLOCK
) for various update rates with DVDD = 5 V and
DVDD = 3 V, respectively. Note, how I
DVDD
is reduced by more
than a factor of 2 when DVDD is reduced from 5 V to 3 V.
APPLYING THE AD9708
Power and Grounding Considerations
In systems seeking to simultaneously achieve high speed and
high performance, the implementation and construction of the
printed circuit board design is often as important as the circuit
design. Proper RF techniques must be used in device selection
placement and routing and supply bypassing and grounding.
The evaluation board for the AD9708, which uses a four layer
PC board, serves as a good example for the above mentioned
considerations. The evaluation board provides an illustration of
the recommended printed circuit board ground, power and
signal plane layouts.
Proper grounding and decoupling should be a primary objective
in any high speed system. The AD9708 features separate analog
and digital supply and ground pins to optimize the management
of analog and digital ground currents in a system. In general,
AVDD, the analog supply, should be decoupled to ACOM, the
analog common, as close to the chip as physically possible. Simi-
larly, DVDD, the digital supply, should be decoupled to DCOM
as close as physically as possible.
For those applications requiring a single +5 V or +3 V supply
for both the analog and digital supply, a clean analog supply
may be generated using the circuit shown in Figure 22. The
circuit consists of a differential LC filter with separate power
supply and return lines. Lower noise can be attained using low
ESR type electrolytic and tantalum capacitors.
IOUTFS – mA
30
02204681012141618
25
20
15
10
5
IAVDD – mA
Figure 19. I
AVDD
vs. I
OUTFS
RATIO (fOUT/fCLK)
18
16
0
0.01 10.1
IDVDD – mA
8
6
4
2
12
10
14
5MSPS
25MSPS
50MSPS
100MSPS
125MSPS
Figure 20. I
DVDD
vs. Ratio
@ DVDD = 5 V
100mF
ELECT. 10-22mF
TANT. 0.1mF
CER.
TTL/CMOS
LOGIC
CIRCUITS
+5V OR +3V
POWER SUPPLY
FERRITE
BEADS
AVDD
ACOM
Figure 22. Differential LC Filter for Single +5 V or +3 V
Applications
Maintaining low noise on power supplies and ground is critical
to obtaining optimum results from the AD9708. If properly
implemented, ground planes can perform a host of functions on
high speed circuit boards: bypassing, shielding, current trans-
port, etc. In mixed signal design, the analog and digital portions
of the board should be distinct from each other, with the analog
ground plane confined to the areas covering the analog signal
traces, and the digital ground plane confined to areas covering
the digital interconnects.
All analog ground pins of the DAC, reference and other analog
components, should be tied directly to the analog ground plane.
The two ground planes should be connected by a path 1/8 to
1/4 inch wide underneath or within 1/2 inch of the DAC to
maintain optimum performance. Care should be taken to ensure
that the ground plane is uninterrupted over crucial signal paths.
On the digital side, this includes the digital input lines running
to the DAC as well as any clock signals. On the analog side, this
includes the DAC output signal, reference signal and the supply
feeders.
The use of wide runs or planes in the routing of power lines is
also recommended. This serves the dual role of providing a low
series impedance power supply to the part, as well as providing
some “free” capacitive decoupling to the appropriate ground
plane. It is essential that care be taken in the layout of signal and
power ground interconnects to avoid inducing extraneous
voltage drops in the signal ground paths. It is recommended that
all connections be short, direct and as physically close to the
package as possible in order to minimize the sharing of conduc-
tion paths between different currents. When runs exceed an inch
in length, strip line techniques with proper termination resistor
RATIO (fOUT/fCLK)
8
0
0.01 10.1
IDVDD – mA
6
4
2
5MSPS
25MSPS
50MSPS
100MSPS
125MSPS
Figure 21. I
DVDD
vs. Ratio
@ DVDD = 3 V
AD9708
–11–
REV. B
should be considered. The necessity and value of this resistor
will be dependent upon the logic family used.
For a more detailed discussion of the implementation and
construction of high speed, mixed signal printed circuit boards,
refer to Analog Devices’ application notes AN-280 and AN-333.
DIFFERENTIAL OUTPUT CONFIGURATIONS
For applications requiring the optimum dynamic performance
and/or a bipolar output swing, a differential output configura-
tion is suggested. A differential output configuration may con-
sists of either an RF transformer or a differential op amp
configuration. The transformer configuration is well suited for
ac coupling applications. It provides the optimum high fre-
quency performance due to its excellent rejection of common-
mode distortion (i.e., even-order harmonics) and noise over a
wide frequency range. It also provides electrical isolation and
the ability to deliver twice the power to the load (i.e., assuming
no source termination). The differential op amp configuration is
suitable for applications requiring dc coupling, a bipolar output,
signal gain, and/or level shifting.
Figure 23 shows the AD9708 in a typical transformer coupled
output configuration. The center-tap on the primary side of the
transformer must be connected to ACOM to provide the necessary
dc current path for both IOUTA and IOUTB. The complemen-
tary voltages appearing at IOUTA and IOUTB (i.e., V
OUTA
and
V
OUTB
) swing symmetrically around ACOM and should be
maintained within the specified output compliance range of the
AD9708. A differential resistor, R
DIFF
, may be inserted in
applications in which the output of the transformer is connected
to the load, R
LOAD
, via a passive reconstruction filter or cable.
R
DIFF
is determined by the transformer’s impedance ratio and
provides the proper source termination. Note that approxi-
mately half the signal power will be dissipated across R
DIFF
.
RLOAD
AD9708
22
21
MINI-CIRCUITS
T1-1T
OPTIONAL RDIFF
IOUTA
IOUTB
Figure 23. Differential Output Using a Transformer
An op amp can also be used to perform a differential to single-
ended conversion as shown in Figure 24. The AD9708 is
configured with two equal load resistors, R
LOAD
, of 25 Ω. The
differential voltage developed across IOUTA and IOUTB is
converted to a single-ended signal via the differential op amp
configuration. An optional capacitor can be installed across
IOUTA and IOUTB forming a real pole in a low-pass filter.
The addition of this capacitor also enhances the op amps distortion
performance by preventing the DACs high slewing output from
overloading the op amp’s input.
AD9708
22
IOUTA
IOUTB 21 COPT
500V
225V
225V
500V
25V25V
AD8072
Figure 24. DC Differential Coupling Using an Op Amp
The common-mode rejection of this configuration is typically
determined by the resistor matching. In this circuit, the differ-
ential op amp circuit is configured to provide some additional
signal gain. The op amp must operate off a dual supply since its
output is approximately ±1.0 V. A high speed amplifier capable
of preserving the differential performance of the AD9708 while
meeting other system level objectives (i.e., cost, power) should
be selected. The op amps differential gain, its gain setting resis-
tor values and full-scale output swing capabilities should all be
considered when optimizing this circuit.
The differential circuit shown in Figure 25 provides the neces-
sary level-shifting required in a single supply system. In this
case, AVDD, which is the positive analog supply for both the
AD9708 and the op amp, is also used to level-shift the differ-
ential output of the AD9762 to midsupply (i.e., AVDD/2).
AD9708
22
IOUTA
IOUTB 21 COPT
500V
225V
225V
1kV25V
25V
AD8072
1kVAVDD
Figure 25. Single-Supply DC Differential Coupled Circuit
AD9708 EVALUATION BOARD
General Description
The AD9708-EB is an evaluation board for the AD9708 8-bit
D/A converter. Careful attention to layout and circuit design,
combined with a prototyping area, allows the user to easily and
effectively evaluate the AD9708 in any application where high
resolution, high speed conversion is required.
This board allows the user the flexibility to operate the AD9708
in various configurations. Possible output configurations include
transformer coupled, resistor terminated, inverting/noninverting
and differential amplifier outputs. The digital inputs are
designed to be driven directly from various word generators,
with the on-board option to add a resistor network for proper
load termination. Provisions are also made to operate the
AD9708 with either the internal or external reference, or to
exercise the power-down feature.
Refer to the application note AN-420 “Using the AD9760/
AD9762/AD9764-EB Evaluation Board” for a thorough
description and operating instructions for the AD9708 evalua-
tion board.
AD9708
–12– REV. B
1098765432
1
R4
10
98765432
1
R7
DVDD
10
98765432
1
R3
1098765432
1
DVDD
R6
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
1
3
5
7
9
11
13
15
17
19
21
23
25
27
29
31
33
35
37
39
P1 10
98765432
1
R5
DVDD
10
98765432
1
R1
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
C19
C1
C2
C25
C26
C27
C28
C29
16 PINDIP
RES PK
16
15
14
13
12
11
10
1
2
3
4
5
6
7
C30
C31
C32
C33
C34
C35
C36
16 PINDIP
RES PK
1
2
3
4
5
6
7
8
9
10
11
12
13
14
28
27
26
25
24
23
22
21
20
19
18
17
16
15
DB13
DB12
DB11
DB10
DB9
DB8
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
CLOCK
DVDD
DCOM
NC
AVDD
COMP2
IOUTA
IOUTB
ACOM
COMP1
FS ADJ
REFIO
REFLO
SLEEP
U1
AD9708
AVDD
CT1
A1
A
R15
49.9V
CLK
JP1
AB
3
2
1
J1 TP1
EXTCLK
C7
1mFC8
0.1mF
AVDD
A
C9
0.1mF
TP8
2
AVDD
TP11
C11
0.1mF
TP10 TP9
R16
2kV
TP14
JP4
C10
0.1mF
OUT 1 OUT 2
TP13
R17
49.9V
PDIN
J2 A A A AVDD
3
JP2
TP12
TP7
A
C6
10mF
AVCC
B6
TP6
A
C5
10mF
AVEE
B5
TP19
A
AGND
B4
TP18
TP5
C4
10mF
TP4
AVDD
B3
TP2
DGND
B2
C3
10mF
TP3
DVDD
B1
R20
49.9V
J3
C12
22pF
A A
R14
0
A
4
5
61
3
T1
J7
R38
49.9V
J4
A A
JP6A
JP6B
A
R13
OPEN
C13
22pF
C20
0
R12
OPEN
A
B
A
JP7B
B
A
JP7A
R10
1kV
B
A
JP8
R9
1kVA
B
A
R35
1kV
JP9
R18
1kV
A
376
24
AD8047
C21
0.1mF
A
C22
1mF
R36
1kV
C23
0.1mF
A
C24
1mF
AVEE
AVCC
R37
49.9V
J6
A
376
24
123
JP5
C15
0.1mF
A
AVEE
R46
1kV
C17
0.1mF
A
1
2
3
JP3
A
B
AVCC
A
CW
R43
5kV
R45
1kV
C14
1mF
A
R44
50V
EXTREFIN
J5
A
R42
1kV
C16
1mF
A
AVCC
C18
0.1mF
U7
6
2
4
A
VIN VOUT
GND
REF43
98765432
1
R2
10
A
1098765432
1
DVDD
R8
U6
A
AD8047
OUT2
OUT1 U4
Figure 26. Evaluation Board Schematic
AD9708
–13–
REV. B
Figure 27. Silkscreen Layer—Top
Figure 28. Component Side PCB Layout (Layer 1)
AD9708
–14– REV. B
Figure 30. Power Plane PCB Layout (Layer 3)
Figure 29. Ground Plane PCB Layout (Layer 2)
AD9708
–15–
REV. B
Figure 31. Solder Side PCB Layout (Layer 4)
Figure 32. Silkscreen Layer—Bottom
–16–
C2979b–1–4/99
PRINTED IN U.S.A.
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
28-Lead, 300 Mil SOIC
(R-28)
0.0125 (0.32)
0.0091 (0.23)
88
08
0.0291 (0.74)
0.0098 (0.25)3 458
0.0500 (1.27)
0.0157 (0.40)
28 15
14
1
0.7125 (18.10)
0.6969 (17.70)
0.4193 (10.65)
0.3937 (10.00)
0.2992 (7.60)
0.2914 (7.40)
PIN 1
SEATING
PLANE
0.0118 (0.30)
0.0040 (0.10) 0.0192 (0.49)
0.0138 (0.35)
0.1043 (2.65)
0.0926 (2.35)
0.0500
(1.27)
BSC
28-Lead TSSOP
(RU-28)
28 15
14
1
0.386 (9.80)
0.378 (9.60)
0.256 (6.50)
0.246 (6.25)
0.177 (4.50)
0.169 (4.30)
PIN 1
SEATING
PLANE
0.006 (0.15)
0.002 (0.05)
0.0118 (0.30)
0.0075 (0.19)
0.0256 (0.65)
BSC
0.0433
(1.10)
MAX
0.0079 (0.20)
0.0035 (0.090)
0.028 (0.70)
0.020 (0.50)
8°
0°
AD9708
REV. B
