AN-1359: Low Noise, Dual-Supply Solution Using the ADP5070 for the Precision AD5761R Bipolar DAC in Single-Supply Systems (Rev. A) PDF

AN-1359
APPLICATION NOTE
One Technology Way • P.O. Box 9106 • Norwood, MA 02062-9106, U.S.A. • Tel: 781.329.4700 • Fax: 781.461.3113 • www.analog.com
Low Noise, Dual-Supply Solution Using the ADP5070 for the Precision AD5761R
Bipolar DAC in Single-Supply Systems
by Estibaliz Sanz Obaldia and James Jasper Macasaet
INTRODUCTION
This application note describes how a system with a single
unipolar supply can be used to power components requiring
dual (bipolar) power supplies. The AD5761R, a bipolar digitalto-analog converter (DAC), requires dual supplies to provide
bipolar output voltage ranges. The examples shown in this
application note use the ADP5070 dc-to-dc switching regulator
with the ADP7142 and ADP7182 complementary metal-oxide
semiconductor (CMOS) low dropout (LDO) linear regulators,
LC filters, and resistor dividers to generate dual supplies from a
5 V single voltage supply to power the AD5761R.
Together, the 5 V power supply and combination of the ADP5070,
ADP7142, ADP7182, and/or LC filters provide a power supply
solution for DACs that output unipolar and bipolar voltage ranges.
This solution provides noise performance similar to that of a
DAC being supplied by a dual bench power supply.
The power spectrum analysis, voltage output noise, and ac
performance data included in this application note support the
performance of this solution.
The proposed supply configurations yield different results
depending on which tests a user performs on the system. For
instance, a configuration that incorporates the ADP5070 supply
and additional LC filters is optimal for reducing the spectral
noise from 10 Hz to 10 kHz when the internal reference of the
DAC is used. An external supply, on the other hand, provides
the best result for a spectral analysis using an external reference.
Results gathered with the external supply were used as the
baseline measurement for all the supply configurations. For a
higher frequency bandwidth (10 kHz to 10 MHz), adding
CMOS LDO linear regulators to the ADP5070 supply offers the
best spectral noise performance. The resulting output spectrum
of the DAC for an LC filter and LDO configuration, which is
used to reduce the switching noise from the ADP5070, is
comparable to an external supply configuration.
The sensitivity to noise of the system determines the amount of
circuitry required to reduce the noise to acceptable levels. No
significant difference is observable between the output noise
measurements at 0.1 Hz to 10 Hz due to the inherent noise
rejection capabilities of the AD5761R. Using additional LDOs
significantly reduces the AD5761R output noise, resulting in a
performance comparable to the baseline measurement.
For the ac performance tests, the AD5761R performs within the
data sheet specifications under all presented supply configurations.
The AD5761R is a 16-bit DAC that integrates an output amplifier,
a reference buffer, and a maximum 5 ppm/°C temperature
coefficient internal reference. The AD5761R operates from a
unipolar supply of up to 30 V or a bipolar supply of −16.5 V to
0 V for VSS and 4.75 V to 16.5 V for VDD. The AD5761R offers
eight programmable output ranges, 35 nV/√Hz noise, and a
7.5 µs settling time on selected ranges.
The ADR4525, a 2.5 V voltage reference, is used across the tests
presented in this application note as an external reference to cover
applications that require ultralow noise voltage references.
The ADP5070 is a dual, high performance, dc-to-dc regulator
that generates independently regulated positive and negative rails.
The input voltage range of 2.85 V to 15 V supports a wide variety
of applications. The integrated main switch in both regulators
enables generation of an adjustable positive output voltage up to
+39 V and a negative output voltage down to −39 V below input
voltage. The ADP5070 operates at a pin selected 1.2 MHz/2.4 MHz
switching frequency. In addition, the regulator has slew rate
control circuitry for the metal-oxide semiconductor field effect
transistor (MOSFET) driver stage to reduce electromagnetic
interference (EMI).
The ADP7142 is an LDO linear regulator that operates from 2.7 V
to 40 V and provides up to 200 mA of output current. This high
input voltage LDO linear regulator is ideal for regulating high
performance analog and mixed-signal circuits operating rails
from 40 V down to 1.2 V. Using a proprietary architecture, the
device provides high power supply rejection, low noise, and
achieves excellent line and load transient response. The ADP7142
regulator output noise is 11 μV rms at 5 V or less with the
ability to adjust the output voltage on the 5 V option to 15 V.
The ADP7182 is an LDO linear regulator that operates from
−2.7 V to −28 V and provides up to −200 mA of output current.
This high negative input voltage LDO linear regulator is ideal
for regulating high performance analog and mixed-signal
circuits operating rails from −27 V down to −1.2 V.
Rev. A | Page 1 of 16
AN-1359
Application Note
TABLE OF CONTENTS
Introduction ...................................................................................... 1
ADP5070 Configuration ..............................................................7
Revision History ............................................................................... 2
AD5761R Power Supply Configurations ...................................7
Bipolar DACs .................................................................................... 3
DAC Output Spectral Response ..................................................7
Bipolar Range Generation ........................................................... 3
AD5761R Output Voltage Noise .............................................. 11
Single-Supply Systems Configured to Support the AD5761R .... 4
AC Performance ......................................................................... 15
Circuit Description....................................................................... 4
Conclusion....................................................................................... 16
Measurements and Results .............................................................. 7
REVISION HISTORY
3/16—Rev. 0 to Rev. A
Changes to Introduction Section.................................................... 1
Changes to Bipolar Range Generation Section ............................ 3
Changes to DC-to-DC Switching Regulator Section and
Figure 3 .............................................................................................. 4
Changes to Linear Regulators Section ........................................... 5
Changes to DVCC Digital Supply Section and Figure 6 Caption ....... 6
Changed Power Supply Spectrum Analysis Section to DAC
Output Spectral Response Section ................................................. 7
Changes to AD5761R Power Supply Configurations Section and
DAC Output Spectral Response Section ....................................... 7
Changes to External Supply and AD5761R Configuration
Section, Figure 7 Caption, Figure 8 Caption, Figure 9 Caption,
and Figure 10 Caption...................................................................... 8
Changes to DC-to-DC Switching Regulator and LC Output Filters
Supply Configuration Section, and Figure 11 to Figure 14...............9
Changes to DC-to-DC Switching Regulator and CMOS LDO
Linear Regulators Supply Configuration Section, Figure 15,
Figure 16, DC-to-DC Switching Regulator, LC Output Filters,
and CMOS LDO Linear Regulators Supply Configuration
Section, and Figure 17 to Figure 19 ............................................. 10
Changes to Figure 20 and AD5761R Output Voltage Noise
Section .......................................................................................................... 11
Added Conclusion Section ............................................................ 16
12/15—Revision 0: Initial Version
Rev. A | Page 2 of 16
Application Note
AN-1359
BIPOLAR DACs
BIPOLAR RANGE GENERATION
output buffer, or a reference buffer to provide a complete solution.
In these cases, design time, factor form, and the selection process
of the correct devices increase the complexity of the application.
For example, selecting a voltage reference for a bipolar DAC
that meets the required specifications increases design and
evaluation time. Selecting an integrated solution removes this
overhead.
Applications such as test and measurement, data acquisition,
actuator control, and industrial automation require a variety of
voltage ranges because the voltage range can vary during operation.
Single-supply DACs, such as multiplying DACs or nanoDACs,
can be used to generate bipolar output ranges. However, generating
bipolar output ranges using these DACs requires the addition of
external discrete components such as op amps or resistors. In
this type of solution, the basic configuration consists of a generalpurpose DAC followed by an amplifying stage and an offset stage.
Figure 1 shows an example of a discrete solution using a singlesupply DAC. A discrete solution is acceptable in applications for
which minimum board area, overall system high performance, and
low cost are not essential. An estimated area of 23 mm2 is required
to implement the circuit in Figure 1. This estimate takes into
account any errors resulting from the increasing number of external components that degrade the quality of the final output signal.
Adding expensive precision resistors to optimize the system performance increases cost. Bipolar DACs are capable of generating
bipolar outputs but require bipolar power supplies to do so.
Additionally, not all bipolar DACs integrate a reference, an
+5V
+5V
+15V
RFB
VDD
REFF
REFS
CS
DIN
SCLK
The AD5761R is a complete solution that provides all the required
functionality and integrates a buffered reference and an output
buffer. Decoupling capacitors are the only external components
required. The proposed configurations support applications in
which only a single 5 V supply is available. A dc-to-dc switching
regulator, LC filters, LDO linear regulators, and/or resistor dividers
are used to support the operation of the AD5761R. Figure 2 shows
the AD5761R, which integrates the external components required
in Figure 1 to generate the bipolar ranges. The AD5761R is
available in a small, 3 mm × 3 mm LFCSP.
RFB
RINV
±5V BIPOLAR
OUTPUT
INV
+15V
±10V BIPOLAR
OUTPUT
VOUT
AD5542
LDAC
–15V
DGND AGNDF AGNDS
–15V
13102-001
R
R
Figure 1. Single-Supply DAC Configured in ±10 V
VREFIN/VREFOUT
VDD
AD5761R
2.5V
REFERENCE
DVCC
ALERT
SDI
SCLK
SYNC
SDO
INPUT SHIFT
REGISTER
AND
CONTROL
LOGIC
12/16
INPUT
REG
DAC
REG
REFERENCE
BUFFERS
12/16
12-BIT/
16-BIT
DAC
RESET
VOUT
0V TO 5V
0V TO 10V
0V TO 16V
0V TO 20V
±3V
±5V
±10V
−2.5V TO +7.5V
DNC
AGND
DGND
VSS
LDAC
NOTES
1. DNC = DO NOT CONNECT. DO NOT CONNECT TO THIS PIN.
Figure 2. AD5761R Functional Block Diagram
Rev. A | Page 3 of 16
13102-002
CLEAR
AN-1359
Application Note
SINGLE-SUPPLY SYSTEMS CONFIGURED TO SUPPORT THE AD5761R
CIRCUIT DESCRIPTION
Table 1. Link Details for Supply Configuration Selection
The AD5761R DAC shown in Figure 2 provides four unipolar
output ranges (0 V to 5 V, 0 V to 10 V, 0 V to 16 V, and 0 V to
20 V) and four bipolar output ranges (±3 V, ±5 V, ±10 V, and
−2.5 V to +7.5 V).
Link
LK7
Link Inserted
21.1 V
Link Removed
23.2 V
In this application note, the AD5761R is powered up with specific
supply voltages to cover all eight possible output ranges. Because
the AD5761R requires a minimum 1 V headroom/footroom in
addition to the voltage supply, apply a minimum VDD of 21 V and
maximum VSS of −11 V to the DAC. When the DAC is used to
output lower output ranges, lower supply voltages can be supplied.
LK8
−11 V
−13 V
The ADR4525 can also externally supply the 2.5 V reference
voltage. Refer to Figure 6.
DC-to-DC Switching Regulator
The ADP5070 output voltages are adjusted to +21.1 V and
−11 V when LK7 and LK8 are inserted, respectively. These
supply voltages are required for the AD5761R to cover all eight
possible programmable output ranges from the DAC.
This application note presents two supply configurations that
provide the required VDD and VSS voltages. The level of acceptable
noise in the system determines the best approach for supplying
the DAC. The two configurations comprise the following:
•
Figure 3 shows two filter components mainly intended for
switching ripple reduction. Inductor L1 and Capacitors C14, C16,
and C19 form an LC filter for the positive output, whereas Inductor
L2 and Capacitors C15, C17 and C20 are configured on the negative output. These LC filters, located inside the control loop of
the regulator, contain values that result in a considerable attenuation at the ripple frequency. Optional second-stage LDO linear
regulators are available at the output stage of the switching regulator for further ripple reduction. With the LC filter alone, the
AD5761R performs within the data sheet specifications. For
applications that require better noise performance, an LDO can
be used at the output stage.
The ADP5070 in conjunction with the resistor ladders. In
this case, insert the LK1, LK2, LK7, and LK8 links.
The ADP5070 in conjunction with the resistor ladders and
the linear regulators (ADP7142 and ADP7182). In this case,
remove the LK1, LK2, LK7, and LK8 links.
•
Test Conditions/
Comments
Voltage measured at
Test Point A
Voltage measured at
Test Point B
The LK1 and LK2 links bypass the linear regulators in the circuit,
and the LK7 and LK8 links determine the voltage available right
before these linear regulators. Table 1 lists the voltages available
at Test Point A and Test Point B for the LK7 and LK8 link
configurations.
Figure 3 shows the power supply configuration for the AD5761R,
where VDD and VSS are generated by different means from an
initial unipolar 5 V single supply.
U7
ADP5070ACPZ
LK1
8
6
7
14
INBK
SS
1
EN1
VREG
OUTPUT FILTERS
L4
6.8µH
COMP1
SW1
A
D1
R22
NSR0240HT1G
SOD-323
6.65Ω
L1
U2
ADP7142ACPZN5.0-R7
6
20
15
PVIN1
17
16 PVIN2
PVINSYS
C25
2.2µF
C19
C16
FB1
PGND
COMP2
VREF
1
VDD = +21V
10µF
10µF
10µF
R26
47.5kΩ
1.5µH
2.2µF
4
7
R27
5
19
C32
12
1µF
EP(GND)
R31
1.87kΩ
2
SS
C3
2.2µF
R4
5.1kΩ
C7
R7
50kΩ
1nF
LK7
C2
0.47µF
R5
160kΩ
5
GND
3
4.87kΩ
LK8
R28
5.9kΩ
2
SYNC/FREQ
4
3 SLEW
11
SEQ
FB2
SENSE/ADJ
EN
R29
LK2
15.4kΩ
D2
AGND
SW2
EP
13
21
R30
86.6kΩ
18
U3
ADP7182ACPZ
R23
NSR0240HT1G
SOD-323
L3
6.8µH
C26
2.2µF
7
6.98Ω
L2
C20
C17
C15
8
C11
10µF
1µH
10µF
9
10µF
B
AGND
2.2µF
VIN
VOUT
VIN
VOUT
EP(GND)
NC
4
EN
OUTPUT FILTERS
GND ADJ
6
1
VSS = –11V
2
5
3
C4
2.2µF
R3
82kΩ
C1
2.2µF
R2
887Ω
R1
10kΩ
13102-003
10
EN2
VOUT
C8
AGND
9
VIN
C14
Figure 3. AD5761R Power Supply Configuration
Rev. A | Page 4 of 16
Application Note
AN-1359
Linear Regulators
sheets, two additional components need to be added to the
output voltage setting resistor divider to obtain ultralow output
noise. CNR (C1, C2) and RNR (R2, R4) are connected in parallel
with RFB1 (R3, R5) to reduce the ac gain of the error amplifier.
The ADP5070, in conjunction with the ADP7182 and ADP7142
linear regulators, provides the lowest noise +21 V and −11 V
voltage supplies. Note that for this approach, LK1, LK2, LK7,
and LK8 are removed.
Adding linear regulators to the output stage of the switching
regulator helps to reduce noise in the DAC output due to the
switching regulator that is not removed by the passive filter.
The ADP5070 provides a positive output voltage of +39 V and a
negative output voltage of –39 V. Figure 4 shows the value of the
resistors forming the resistor dividers (R26, R27, and R31; and
R28, R29, and R30) needed to adjust these voltages to acceptable
input voltages for the ADP7142 and ADP7182. Note that a minimum headroom/footroom of 2 V is needed on top of the desired
output voltage of the linear regulators.
Resistor Dividers
Figure 5 shows, by means of resistor dividers, the option to adjust
the positive and negative output voltages of the ADP5070 to the
required +21 V VDD and −11 V VSS voltage supplies for the
AD5761R. There are no linear regulators involved in this configuration, for which the LK1, LK2, LK7, and LK8 links are
inserted.
Both linear regulators, the ADP7142 and the ADP7182, are
configured to achieve an output voltage signal with noise as low
as possible. As explained in the ADP7182 and ADP7142 data
+23.2V
U2
ADP7142ACPZN5.0-R7
6
SW1
VOUT
VIN
1
VDD = +21V
C8
R26
47.5kΩ
2.2µF
4
7
R27
SENSE/ADJ
EN
EP(GND)
FB1
C32
1µF
R31
1.87kΩ
R5
160kΩ
5
GND
3
4.87kΩ
VREF = 1.60V
SS
2
C2
0.47µF
C3
2.2µF
R4
5.1kΩ
C7
R7
50kΩ
1nF
R28
5.9kΩ
R29
FB2
–13V
15.4kΩ
R30
86.6kΩ
U3
ADP7182ACPZ
7
SW2
C11
8
9
2.2µF
VIN
VOUT
VIN
VOUT
EP(GND)
NC
4
EN
GND ADJ
6
1
VSS = –11V
2
5
C4
2.2µF
C1
2.2µF
R3
82kΩ
R2
3
887Ω
13102-004
R1
10kΩ
Figure 4. AD5761R Supply Configuration with ADP5070 and Linear Regulators
LK1 INSERTED
VDD = +21V
SW1
LK7 INSERTED
R26
47.5kΩ
FB1
VREF = 1.60V
C32
R28
5.9kΩ
1µF
R31
1.87kΩ
LK8 INSERTED
R30
86.6kΩ
LK2 INSERTED
VSS = –11V
SW2
Figure 5. AD5761R Supply Configuration with ADP5070 and Resistor Dividers
Rev. A | Page 5 of 16
13102-005
FB2
AN-1359
Application Note
DVCC Digital Supply
external sources to supply the DAC depending on the position
of LK4.
Figure 6 shows how to digitally supply the AD5761R from the
external 5 V voltage signal. A less noisy voltage signal generated by
the ADP5070 and adjusted by an ADP7142 regulator can also
be considered.
Reference Voltage
LK4 can be shorted to Position A, where an external voltage is
input to the VREFIN/VREFOUT SMB connector. When using the
internal reference, 2.5 V is available in this connector for
external use.
The AD5761R offers a 2.5 V, 5 ppm/°C internal voltage reference,
which is on by default. Alternatively, Figure 6 shows two possible
If LK4 is shorted to Position C, the reference voltage is sourced
by the ADR4525 ultralow noise, high accuracy voltage reference.
+5V_LDO
+5V
0.1µF
C24
0.1µF
C23
R20
R21
0Ω
R19
0Ω
DNP
VDD
A
LK3
10µF
C12
B
+
+
0.1µF
C13
VDD
4
VREFIN/VREFOUT
DVCC
SDO
C27
DNC
VOUT
U1
AD5761RBRUZ
LDAC
CLEAR
RESET
ALERT
9
TP2
0.1µF
VOUT
+VIN
2
+5V_LDO
GND
4
VOUT
7
1
TP8
ALERT
R15
10kΩ
DVCC
DGND
0.1µF
C9
10µF
C10
13102-006
2
3
SDI
AGND
11
SCLK
VSS
10
SYNC
5
CLR
RESET
14
12
6
C
6
SDO
LDAC
13
8
U6
ADR4525BRZ
+
SDIN
LK4
A
DGND
SCLK
VREFIN/VREFOUT
DVCC
16
SYNC
TP10
0.1µF
C6
15
DGND
10µF
C5
VSS
Figure 6. AD5761R Connections
Rev. A | Page 6 of 16
Application Note
AN-1359
MEASUREMENTS AND RESULTS
ADP5070 CONFIGURATION
DAC OUTPUT SPECTRAL RESPONSE
To provide the highest possible ripple amplitude and obtain
results for the worst case scenario, the switching frequency of
the ADP5070 is set to 1.2 MHz with a fast slew mode.
The results detailed in this section show how the DAC output
noise spectrum varies depending on the supply configuration
selected. Table 2 and Table 3 show the maximum output spectral
response level from the spectral analysis presented in Figure 7
to Figure 20.
AD5761R POWER SUPPLY CONFIGURATIONS
The series of measurements presented in this section show the
AD5761R DAC tested at three data codes (zero-scale, half-scale,
and full-scale) for a ±10 V output voltage range, which is a representative output range for this bipolar DAC. The AD5761R is
powered up under four different supply configurations across
the series of measurements.
•
•
•
•
External supply
DC-to-dc switching regulator (ADP5070) and LC output filter
DC-to-dc switching regulator (ADP5070) followed by
CMOS LDO linear regulators (ADP7142 and ADP7182)
(this supply configuration is not included on the ac
performance test)
DC-to-dc switching regulator (ADP5070) with LC output
filter, followed by CMOS LDO linear regulators (ADP7142
and ADP7182)
Table 4 shows the maximum DAC output spectral response
level at a 1.2 MHz switching frequency over a 10 kHz to 10 MHz
frequency range. Adding an LC filter to the supply configuration
maintains the AD5761R within the set specification of 20.6 dBµV,
which represents a 0.1 LSB level. Adding an LDO as a secondstage filter further reduces the ripple to a level comparable to an
external supply operation, allowing the DAC to perform with a
minimal noise output.
The performance of the AD5761R is also tested with the internal
reference of the DAC and with the ADR4525.
Table 2. AD5761R Maximum Output Spectral Response Level per DAC Data Code (dBµV), 10 Hz to 10 kHz
Power Supply Configuration
External Supply
ADP5070 and LC Output Filters
ADP5070, LC Output Filters, and CMOS LDO Linear Regulators
Internal Reference
Zero-Scale Half-Scale Full-Scale
8.00
3.63
7.04
6.57
2.41
8.01
7.4
3.91
5.96
External Reference
Zero-Scale Half-Scale Full-Scale
2.60
3.39
1.45
2.58
3.34
3.59
1.68
2.49
3.32
Table 3. AD5761R Maximum Output Spectral Response Level per DAC Code (dBµV), 10 kHz to 10 MHz
Power Supply Configuration
External Supply
ADP5070 and LC Output Filters
ADP5070 and CMOS LDO Linear Regulators
ADP5070, LC Output Filters, and CMOS LDO Linear Regulators
Internal Reference
Zero-Scale Half-Scale Full-Scale
2.23
−1.57
0.58
1.19
−0.62
4.37
1.85
−0.93
0.69
1.94
−2.20
−0.06
External Reference
Zero-Scale Half-Scale Full-Scale
9.33
−1.55
10.55
10.27
1.73
9.64
9.89
−0.98
9.22
9.99
−1.60
10.03
Table 4. AD5761R 1.2 MHz Maximum Spectral Output Response Level per DAC Data Code (dBµV), 10 kHz to 10 MHz
Power Supply Configuration
External Supply
ADP5070 and LC Output Filters
ADP5070 and CMOS LDO Linear Regulators
ADP5070, LC Output Filters, and CMOS LDO Linear Regulators
Internal Reference
Zero-Scale Half-Scale Full-Scale
−17.07
−17.06
−16.96
−14.99
−11.47
−2.44
−16.78
−17.93
−16.68
−17.07
−18.39
−17.64
Rev. A | Page 7 of 16
External Reference
Zero-Scale Half-Scale Full-Scale
−16.49
−17.48
−17.5
−15.69
−10.34
−3.62
−17.51
−18.37
−16.63
−16.53
−16.43
−17.01
AN-1359
Application Note
External Supply and AD5761R Configuration
60
The spectral traces shown in Figure 7 to Figure 10 are used as
baseline plots for the subsequent AD5761R DAC and ADP5070
direct switching regulator evaluations. The red dashed line in
Figure 7 to Figure 10 represents a threshold limit for the spectral
levels. The threshold level is set at 20.6 dBµV, which represents a
value of approximately 0.1 LSB. In Figure 7 to Figure 20, RBW is
the resolution bandwidth, VBW is the video bandwidth, and
REF is the reference value. The VBW, generally associated with
the video filter of the measurement equipment, leads to better
display of the signals of interest; it reduces the noise on the trace
while maintaining the floor noise.
50
LEVEL (dBµV)
40
30
20
CODE = 0xFFFF
CODE = 0x7FFF
CODE = 0x0
10
0
–10
–30
10k
13102-009
–20
60
50
RBW: 30Hz; VBW: 10Hz
REF: 60dBµV
100k
10M
1M
FREQUENCY (Hz)
RBW: 3Hz; VBW: 1Hz
REF: 60dBµV
Figure 9. External Supply and AD5761R Configuration Output Spectral
Response, Internal Reference (10 kHz to 10 MHz)
40
50
20
CODE = 0xFFFF
CODE = 0x7FFF
CODE = 0x0
10
0
–10
–30
10
13102-007
–20
100
30
20
CODE = 0xFFFF
CODE = 0x7FFF
CODE = 0x0
10
0
10k
1k
RBW: 3Hz; VBW: 1Hz
REF: 60dBµV
40
LEVEL (dBµV)
LEVEL (dBµV)
60
30
–10
FREQUENCY (Hz)
–30
10k
60
50
LEVEL (dBµV)
1M
10M
Figure 10. External Supply and AD5761R Configuration Output Spectral
Response, External Reference (10 kHz to 10 MHz)
30
20
CODE = 0xFFFF
CODE = 0x7FFF
CODE = 0x0
10
0
–10
13102-008
–20
100
100k
FREQUENCY (Hz)
RBW: 3Hz; VBW: 1Hz
REF: 60dBµV
40
–30
10
13102-010
–20
Figure 7. External Supply and AD5761R Configuration Output Spectral
Response, Internal Reference (10 Hz to 10 kHz)
1k
10k
FREQUENCY (Hz)
Figure 8. External Supply and AD5761R Configuration Output Spectral
Response, External Reference (10 Hz to 10 kHz)
Rev. A | Page 8 of 16
Application Note
AN-1359
DC-to-DC Switching Regulator and LC Output Filters
Supply Configuration
60
50
In this supply configuration, LC filters are used for initial ripple
rejection in addition to the ADP5070 direct switching regulator
used to generate the bipolar supply ranges. Figure 11 and Figure 12
show the ripple level for a frequency bandwidth of 10 Hz to
10 kHz, and Figure 13 and Figure 14 show the ripple level for a
frequency bandwidth of 10 kHz to 10 MHz.
LEVEL (dBµV)
40
SLEW: FAST
SEQUENCE: VDD TO VSS
SWITCHING FREQUENCY: 1.2MHz
RBW: 30Hz; VBW: 10Hz
REF: 60dBµV
30
20
CODE = 0xFFFF
CODE = 0x7FFF
CODE = 0x0
10
0
60
LEVEL (dBµV)
40
–10
SLEW: FAST
SEQUENCE: VDD TO VSS
SWITCHING FREQUENCY: 1.2MHz
RBW: 3Hz; VBW: 1Hz
REF: 60dBµV
–20
–30
10k
30
13102-013
50
100k
1M
10M
FREQUENCY (Hz)
20
Figure 13. ADP5070, LC Filters, and AD5761R Supply Configuration Output
Spectral Response, Internal Reference (10 kHz to 10 MHz)
CODE = 0xFFFF
CODE = 0x7FFF
CODE = 0x0
10
60
0
50
–10
100
1k
LEVEL (dBµV)
–30
10
40
13102-011
–20
10k
FREQUENCY (Hz)
Figure 11. ADP5070, LC Filters, and AD5761R Supply Configuration Output
Spectral Response, Internal Reference (10 Hz to 10 kHz)
SLEW: FAST
SEQUENCE: VDD TO VSS
SWITCHING FREQUENCY: 1.2MHz
RBW: 30Hz; VBW: 10Hz
REF: 60dBµV
30
20
CODE = 0xFFFF
CODE = 0x7FFF
CODE = 0x0
10
0
60
LEVEL (dBµV)
40
–10
SLEW: FAST
SEQUENCE: VDD TO VSS
SWITCHING FREQUENCY: 1.2MHz
RBW: 3Hz; VBW: 1Hz
REF: 60dBµV
–20
–30
10k
30
13102-014
50
100k
1M
10M
FREQUENCY (Hz)
20
Figure 14. ADP5070, LC Filters, and AD5761R Supply Configuration Output
Spectral Response, External Reference (10 kHz to 10 MHz)
CODE = 0xFFFF
CODE = 0x7FFF
CODE = 0x0
10
DC-to-DC Switching Regulator and CMOS LDO Linear
Regulators Supply Configuration
0
–10
–30
10
13102-012
–20
100
1k
10k
FREQUENCY (Hz)
Figure 12. ADP5070, LC Filters, and AD5761R Supply Configuration Output
Spectral Response, External Reference (10 Hz to 10 kHz)
Figure 13 and Figure 14 show a frequency spike at 1 MHz in the
frequency bandwidth of 10 kHz to 10 MHz. The LC filter does
not sufficiently reduce the amplitude of this ripple coming from
the ADP5070 dc-to-dc regulator; therefore, the performance of
this power supply solution is not ideal from a spectrum analysis
point of view.
Adding LDOs to the output of the ADP5070 dc-to-dc regulator
considerably reduces the spike observed at a 1 MHz frequency
(see the DC-to-DC Switching Regulator and LC Output Filters
Supply Configuration section). This reduction demonstrates
that adding an LC filter to the supply circuit is not necessary to
obtain an improved performance.
Figure 15 and Figure 16 show the performance of the ADP5070,
LDOs, and AD5761R supply configuration at high frequency.
Rev. A | Page 9 of 16
AN-1359
Application Note
60
40
LEVEL (dBµV)
30
20
CODE = 0xFFFF
CODE = 0x7FFF
CODE = 0x0
10
20
–10
–10
–20
–20
100k
1M
–30
10
10M
CODE = 0xFFFF
CODE = 0x7FFF
CODE = 0x0
10
0
–30
10k
SLEW: FAST
SEQUENCE: VDD TO VSS
SWITCHING FREQUENCY: 1.2MHz
RBW: 3Hz; VBW: 1Hz
REF: 60dBµV
30
0
13102-015
LEVEL (dBµV)
40
50
13102-017
50
60
SLEW: FAST
SEQUENCE: VDD TO VSS
SWITCHING FREQUENCY: 1.2MHz
RBW: 30Hz; VBW: 10Hz
REF: 60dBµV
100
Figure 15. ADP5070, LDOs, and AD5761R Supply Configuration Output
Spectral Response, Internal Reference (10 kHz to 10 MHz)
60
50
40
LEVEL (dBµV)
30
20
CODE = 0xFFFF
CODE = 0x7FFF
CODE = 0x0
30
20
0
0
–10
–10
–20
–20
–30
10k
100k
1M
–30
10
10M
CODE = 0xFFFF
CODE = 0x7FFF
CODE = 0x0
10
FREQUENCY (Hz)
100
1k
10k
FREQUENCY (Hz)
Figure 16. ADP5070, LDOs,and AD5761R Supply Configuration Output
Spectral Response, External Reference (10 kHz to 10 MHz)
Figure 18. ADP5070, LC Filters, LDOs, and AD5761R Supply Configuration
Output Spectral Response, External Reference (10 Hz to 10 kHz)
DC-to-DC Switching Regulator, LC Output Filters, and
CMOS LDO Linear Regulators Supply Configuration
60
50
Adding two LDOs to the dc-to-dc switching regulator and LC
output filters supply configuration further filters the ripple at
the analog supplies of the AD5761R. The ADP7142 is used on
the analog positive supply (VDD), while the ADP7182 is placed at
the analog negative supply (VSS).
LEVEL (dBµV)
As explained in the DC-to-DC Switching Regulator and CMOS
LDO Linear Regulators Supply Configuration section, adding
LDOs to the ADP5070 dc-to-dc switch output when working at
high frequencies is enough to obtain a good DAC output
spectral response performance with no added spikes at any
undesired frequency. The LC filters can still contribute to
output noise rejection, but the LDO is the most significant factor
in reducing the output noise. However, the LC filter is still a
recommended option for sufficient high frequency ripple
filtering.
40
SLEW: FAST
SEQUENCE: VDD TO VSS
SWITCHING FREQUENCY: 1.2MHz
RBW: 30Hz; VBW: 10Hz
REF: 60dBµV
30
20
CODE = 0xFFFF
CODE = 0x7FFF
CODE = 0x0
10
0
–10
–20
–30
10k
13102-019
10
SLEW: FAST
SEQUENCE: VDD TO VSS
SWITCHING FREQUENCY: 1.2MHz
RBW: 3Hz; VBW: 1Hz
REF: 60dBµV
13102-018
SLEW: FAST
SEQUENCE: VDD TO VSS
SWITCHING FREQUENCY: 1.2MHz
RBW: 30Hz; VBW: 10Hz
REF: 60dBµV
13102-016
LEVEL (dBµV)
40
10k
Figure 17. ADP5070, LC Filters, LDOs, and AD5761R Supply Configuration
Output Spectral Response, Internal Reference (10 Hz to 10 kHz)
60
50
1k
FREQUENCY (Hz)
FREQUENCY (Hz)
100k
1M
10M
FREQUENCY (Hz)
Figure 19. ADP5070, LC Filters, LDOs, and AD5761R Supply Configuration
Output Spectral Response, Internal Reference (10 kHz to 10 MHz)
Rev. A | Page 10 of 16
Application Note
AN-1359
60
50
LEVEL (dBµV)
40
Table 5. External Supply and AD5761R Maximum Peak-toPeak Output Noise (µV p-p), 0.1 Hz to 10 Hz Frequency
Bandwidth
SLEW: FAST
SEQUENCE: VDD TO VSS
SWITCHING FREQUENCY: 1.2MHz
RBW: 30Hz; VBW: 10Hz
REF: 60dBµV
30
20
Code
Zero-Scale
Half-Scale
Full-Scale
CODE = 0xFFFF
CODE = 0x7FFF
CODE = 0x0
10
0
Maximum Peak-to-Peak Output Noise
AD5761R
Internal Reference
ADR4525
41 µV p-p, 0.13 LSB p-p
12 µV p-p, 0.04 LSB p-p
4.8 µV p-p, 0.016 LSB p-p
6.2 µV p-p, 0.02 LSB p-p
40 µV p-p, 0.13 LSB p-p
14 µV p-p, 0.04 LSB p-p
–10
1M
CODE = 0xFFFF
CODE = 0x7FFF
CODE = 0x0
10M
FREQUENCY (Hz)
To provide a high precision response, it is recommended to
maintain the peak-to-peak noise obtained at the output of the
DAC below 1 LSB, which is 305.17 µV for 16-bit resolution and a
20 V peak-to-peak voltage range. The AD5761R offers a typical
output noise of 15 µV p-p for the 0.1 Hz to 10 Hz frequency bandwidth and 35 µV rms (which is equivalent to approximately
100 µV p-p) for the 100 kHz frequency bandwidth. The noise at
the output of the AD5761R for a ±10 V range is measured over
a period of 100 seconds, across the 0.1 Hz to 10 Hz frequency
range and a 100 kHz bandwidth.
The test results for the three different configurations show the
DAC performing within the specifications of the AD5761R data
sheet. Figure 21 to Figure 34 show the noise at the output of the
DAC for each configuration and frequency bandwidth, and Table 5
to Table 11 summarize the maximum peak-to-peak noise on the
output of the DAC for the available power configurations.
The data in Table 2 to Table 12 and Figure 7 to Figure 37 show a
common trend for all power supply configurations detailed in
this application note. At the lower frequency bandwidth, the
ADR4525 external reference produces a lower DAC output
noise compared to using the AD5761R internal reference. In
contrast, the DAC output noise is lower when the internal
reference is used at a higher frequency bandwidth. This
behavior correlates with the DAC output spectral response
results previously presented.
10
–10
–30
–50
0
20
40
60
TIME (Seconds)
80
100
Figure 21. External Supply and AD5761R Peak-to-Peak Noise (Voltage
Output Noise), 0.1 Hz to 10 Hz Bandwidth, Internal Reference
50
CODE = 0xFFFF
CODE = 0x7FFF
CODE = 0x0
30
AMPLITUDE (µV)
AD5761R OUTPUT VOLTAGE NOISE
AMPLITUDE (µV)
30
Figure 20. ADP5070, LC Filters, LDOs, and AD5761R Supply Configuration
Output Spectral Response, External Reference (10 kHz to 10 MHz)
13102-021
100k
50
10
–10
–30
13102-022
–30
10k
13102-020
–20
–50
0
20
40
60
TIME (Seconds)
80
100
Figure 22. External Supply and AD5761R Peak-to-Peak Noise (Voltage
Output Noise), 0.1 Hz to 10 Hz Bandwidth, External Reference
Adding LDOs to the supply configuration affects performance
slightly at a low frequency bandwidth for the DAC output noise
presented in Figure 31 and Figure 32.
In contrast, at a high frequency bandwidth, adding an LDO to
the supply configuration helps maintain a low noise overall
performance. Figure 29 and Figure 30 show the AD5761R output
noise when the DAC is powered by the ADP5070 and LDOs for
a high frequency bandwidth of up to 100 kHz.
Rev. A | Page 11 of 16
AN-1359
Application Note
Table 6. External Supply and AD5761R Maximum Peak-toPeak Output Noise (µV p-p), 100 kHz Frequency Bandwidth
Code
Zero Scale
Half-Scale
Full-Scale
Maximum Peak-to-Peak Output Noise
AD5761R Internal
ADR4525
Reference
33.6 µV p-p, 0.11 LSB p-p 63.2 µV p-p, 0.21 LSB p-p
21 µV p-p, 0.07 LSB p-p
22 µV p-p, 0.07 LSB p-p
32 µV p-p, 0.10 LSB p-p
58.4 µV p-p, 0.19 LSB p-p
Table 7. ADP5070, LC Filters, and AD5761R Maximum Peakto-Peak Output Noise (µV p-p), 0.1 Hz to 10 Hz Frequency
Bandwidth
Code
Zero-Scale
Half-Scale
Full-Scale
Maximum Peak-to-Peak Output Noise
AD5761R Internal
Reference
ADR4525
41 µV p-p, 0.13 LSB p-p
13 µV p-p, 0.04 LSB p-p
6.6 µV p-p, 0.02 LSB p-p
4.4 µV p-p, 0.014 LSB p-p
38 µV p-p, 0.12 LSB p-p
13 µV p-p, 0.04 LSB p-p
50
CODE = 0xFFFF
CODE = 0x7FFF
CODE = 0x0
50
CODE = 0xFFFF
CODE = 0x7FFF
CODE = 0x0
30
10
AMPLITUDE (µV)
AMPLITUDE (µV)
30
–10
10
–10
–30
–50
0
20
40
60
TIME (Seconds)
80
100
13102-025
13102-023
–30
–50
0
Figure 23. External Supply and AD5761R Peak-to-Peak Noise
(Voltage Output Noise), 100 kHz Bandwidth, Internal Reference
20
40
60
TIME (Seconds)
80
100
Figure 25. ADP5070, LC Filters, and AD5761R Peak-to-Peak Noise
(Voltage Output Noise), 0.1 Hz to 10 Hz Bandwidth, Internal Reference
50
CODE = 0xFFFF
CODE = 0x7FFF
CODE = 0x0
50
CODE = 0xFFFF
CODE = 0x7FFF
CODE = 0x0
30
AMPLITUDE (µV)
10
–10
10
–10
–30
–50
0
20
40
60
TIME (Seconds)
80
100
Figure 24. External Supply and AD5761R Peak-to-Peak Noise
(Voltage Output Noise), 100 kHz Bandwidth, External Reference
13102-026
–30
13102-024
AMPLITUDE (µV)
30
–50
0
20
40
60
TIME (Seconds)
80
100
Figure 26. ADP5070, LC Filters, and AD5761R Peak-to-Peak Noise
(Voltage Output Noise), 0.1 Hz to 10 Hz Bandwidth, External Reference
Rev. A | Page 12 of 16
Application Note
AN-1359
Table 8. ADP5070, LC Filters, and AD5761R Maximum Peakto-Peak Output Noise (µV p-p), 100 kHz Frequency Bandwidth
Code
Zero-Scale
Half-Scale
Full-Scale
Maximum Peak-to-Peak Output Noise
AD5761R Internal
ADR4525
Reference
44.4 µV p-p, 0.15 LSB p-p 68.2 µV p-p, 0.22 LSB p-p
30.8 µV p-p, 0.10 LSB p-p 30.4 µV p-p. 0.10 LSB p-p
75.2 µV p-p, 0.25 LSB p-p 88.8 µV p-p, 0.29 LSB p-p
Table 9. ADP5070, LDOs, and AD5761R Maximum Peak-toPeak Output Noise (µV p-p), 100 kHz Frequency Bandwidth
Code
Zero-Scale
Half-Scale
Full-Scale
Maximum Peak-to-Peak Output Noise
AD5761R Internal
ADR4525
Reference
35.2 µV p-p, 0.12 LSB p-p 60.4 µV p-p, 0.20 LSB p-p
22.8 µV p-p, 0.07 LSB p-p 22.4 µV p-p, 0.07 LSB p-p
31.2 µV p-p, 0.10 LSB p-p 67.6 µV p-p, 0.22 LSB p-p
50
50
CODE = 0xFFFF
CODE = 0x7FFF
CODE = 0x0
40
30
30
AMPLITUDE (µV)
AMPLITUDE (µV)
20
10
0
–10
10
–10
–20
13102-027
CODE = 0xFFFF
CODE = 0x7FFF
CODE = 0x0
–40
–50
0
20
40
60
TIME (Seconds)
80
13102-029
–30
–30
–50
0
100
Figure 27. ADP5070, LC Filters, and AD5761R Peak-to-Peak Noise
(Voltage Output Noise), 100 kHz Bandwidth, Internal Reference
20
40
60
TIME (Seconds)
80
100
Figure 29. ADP5070, LDOs, and AD5761R Peak-to-Peak Noise
(Voltage Output Noise), 100 kHz Bandwidth, Internal Reference
50
50
CODE = 0xFFFF
CODE = 0x7FFF
CODE = 0x0
40
30
30
AMPLITUDE (µV)
10
0
–10
10
–10
–20
–40
CODE = 0xFFFF
–50
0
20
CODE = 0x7FFF
40
60
TIME (Seconds)
CODE = 0x0
80
13102-030
–30
–30
13102-028
AMPLITUDE (µV)
20
–50
100
0
Figure 28. ADP5070, LC Filters, AD5761R Peak-to-Peak Noise
(Voltage Output Noise), 100 kHz Bandwidth, External Reference
20
40
60
TIME (Seconds)
80
100
Figure 30. ADP5070, LDOs, and AD5761R Peak-to-Peak Noise
(Voltage Output Noise), 100 kHz Bandwidth, External Reference
Rev. A | Page 13 of 16
AN-1359
Application Note
Table 10. ADP5070, LC Filters, LDOs, and AD5761R
Maximum Peak-to-Peak Output Noise (µV p-p), 0.1 Hz to
10 Hz Frequency Bandwidth
Code
Zero-Scale
Half-Scale
Full-Scale
Maximum Peak-to-Peak Output Noise
AD5761R Internal
Reference
ADR4525
40.6 µV p-p, 0.13 LSB p-p 12.8 µV p-p, 0.04 LSB p-p
5.4 µV p-p, 0.018 LSB p-p 4.4 µV p-p, 0.014 LSB p-p
45.2 µV p-p, 0.15 LSB p-p 13.2 µV p-p, 0.04 LSB p-p
Table 11. ADP5070, LC Filters, LDOs, and AD5761R
Maximum Peak-to-Peak Output Noise (µV p-p), 100 kHz
Frequency Bandwidth
Code
Zero-Scale
Half-Scale
Full-Scale
Maximum Peak-to-Peak Output Noise
AD5761R Internal
Reference
ADR4525
36.8 µV p-p, 0.12 LSB p-p 60.4 µV p-p, 0.2 LSB p-p
23.8 µV p-p, 0.08 LSB p-p 22.6 µV p-p, 0.07 LSB p-p
33.6 µV p-p, 0.11 LSB p-p 60 µV p-p, 0.2 LSB p-p
50
50
CODE = 0xFFFF
CODE = 0x7FFF
CODE = 0x0
CODE = 0xFFFF
CODE = 0x7FFF
CODE = 0x0
30
AMPLITUDE (µV)
10
–10
–30
10
–10
13102-031
–30
–50
0
20
40
60
TIME (Seconds)
80
13102-033
AMPLITUDE (µV)
30
–50
100
0
Figure 31. ADP5070, LC Filters, LDOs, and AD5761R Peak-to-Peak Noise
(Voltage Output Noise), 0.1 Hz to 10 Hz Bandwidth, Internal Reference
20
40
60
TIME (Seconds)
100
Figure 33. ADP5070, LC Filters, LDOs, and AD5761R Peak-to-Peak Noise
(Voltage Output Noise), 100 kHz Bandwidth, Internal Reference
50
50
CODE = 0xFFFF
CODE = 0x7FFF
CODE = 0x0
CODE = 0xFFFF
CODE = 0x7FFF
CODE = 0x0
30
30
AMPLITUDE (µV)
10
–10
10
–10
–30
13102-032
–30
–50
0
20
40
60
TIME (Seconds)
80
13102-034
AMPLITUDE (µV)
80
–50
0
100
Figure 32. ADP5070, LC Filters, LDOs, and AD5761R Peak-to-Peak Noise
(Voltage Output Noise), 0.1 Hz to 10 Hz Bandwidth, External Reference
20
40
60
TIME (Seconds)
80
100
Figure 34. ADP5070, LC Filters, LDOs, and AD5761R Peak-to-Peak Noise
(Voltage Output Noise), 100 kHz Bandwidth, External Reference
Rev. A | Page 14 of 16
Application Note
AN-1359
AC PERFORMANCE
40
This section presents the signal-to-noise ratio (SNR), total
harmonic distortion (THD), signal-to-noise-and-distortion
(SINAD), and spurious-free dynamic range (SFDR) parameters
for the supply configurations using the ADR4525 as the voltage
reference. Table 12 summarizes the ac performance obtained for
the three supply configurations shown in Figure 35 to Figure 37,
for which a continuous 1 kHz sine wave was generated.
20
0
LEVEL (dBV)
–20
–80
–100
40
13102-036
–120
20
–140
0
–160
–20
LEVEL (dBV)
–40
–60
0
2
4
6
–40
8
10
12
14
FREQUENCY (kHz)
16
18
20
Figure 36. ADP5070, LC Filters, and AD5761R Digitally Generated Sine Wave,
1 kHz Tone at 17 dBV (7.07 V RMS)
–60
–80
40
–100
20
–120
–160
0
2
4
6
10
12
14
8
FREQUENCY (kHz)
16
18
20
Figure 35. External Supply and AD5761R Digitally Generated Sine Wave,
1 kHz Tone at 17 dBV (7.07 V RMS)
–20
LEVEL (dBV)
13102-035
0
–140
–40
–60
–80
–100
13102-037
–120
–140
–160
0
2
4
6
8
10
12
14
FREQUENCY (kHz)
16
18
20
Figure 37. ADP5070, LC Filters, LDOs, and AD5761R Digitally Generated Sine
Wave, 1 kHz Tone at 17 dBV (7.07 V RMS)
Table 12. AC Performance
Parameter
SNR
THD
SINAD
SFDR
External Supply and
AD5761R (dB)
95.05
−86.38
85.82
89.42
ADP5070, LC Filters, and
AD5761R (dB)
95.19
−86.30
85.77
89.35
Rev. A | Page 15 of 16
ADP5070, LC Filters, LDOs, and
AD5761R (dB)
95.24
−86.52
85.98
89.45
AN-1359
Application Note
CONCLUSION
The AD5761R is a 16-bit bipolar DAC with an integrated
output amplifier, reference buffer, and reference; the high
integration within the chip provides a complete solution. This
application note introduces a flexible power solution for the
AD5761R from a single supply rail using the ADP5070 dc-to-dc
switching regulator.
The configurations and results presented show the AD5761R
performing within specification. To obtain a DAC output low
noise response in a 0.1 Hz to 10 Hz frequency bandwidth, the
recommended power solution includes the ADP5070, LC filters,
and the AD5761R. However, if a DAC output low noise response
is required at a higher frequency bandwidth, the optimal power
solution includes the ADP5070, LC filters, LDO regulators, and
the AD5761R. The performance is also comparable when the LC
filters are removed from the power configuration, sufficiently
reducing the switching spurs from the ADP5070 down to the
target LSB threshold.
There is little variation in the ac performance across the
different power configurations, which is comparable to the
baseline measurement result using an external supply.
©2015–2016 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
AN13102-0-3/16(A)
Rev. A | Page 16 of 16
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