AD AD8527ARM-REEL 7 mhz rail-to-rail low voltage operational amplifier Datasheet

a
7 MHz Rail-to-Rail
Low Voltage Operational Amplifiers
AD8517/AD8527
FEATURES
Single Supply Operation: 1.8 V to 6 V
Space-Saving SOT-23, ␮SOIC Packaging
Wide Bandwidth: 7 MHz @ 5 V
Low Offset Voltage: 3.5 mV Max
Rail-to-Rail Output Swing and Rail-to-Rail Input
8 V/␮s Slew Rate
Only 900 ␮A Supply Current @ 5 V
APPLICATIONS
Portable Communications
Portable Phones
Sensor Interface
Active Filters
PCMCIA Cards
ASIC Input Drivers
Wearable Computers
Battery-Powered Devices
New Generation Phones
Personal Digital Assistants
PIN CONFIGURATIONS
5-Lead SOT-23
(RT Suffix)
5 V+
V– 2
+IN A 3
4 –IN A
8-Lead SOIC
(R Suffix)
OUT A 1
8
–IN A 2
AD8527
+IN A 3
V– 4
V+
7 OUT B
6
–IN B
5
+IN B
8-Lead MSOP
(RM Suffix)
GENERAL DESCRIPTION
The AD8517 brings precision and bandwidth to the SOT-23-5
package even at single supply voltages as low as 1.8 V. The
small package makes it possible to place the AD8517 next to
sensors, reducing external noise pickup. The AD8527 dual
amplifier is offered in the space-saving MSOP package.
AD8517
OUT A 1
OUT A
–IN A
+IN A
V–
1
8
AD8527
4
5
V+
OUT B
–IN B
+IN B
The AD8517 and AD8527 are rail-to-rail input and output
bipolar amplifiers with a gain bandwidth of 7 MHz and typical
voltage offset of 1.3 mV from a 1.8 V supply. The low supply
current makes these parts ideal for battery-powered applications.
The 8 V/µs slew rate makes the AD8517/AD8527 a good match
for driving ASIC inputs, such as voice codecs.
The AD8517/AD8527 is specified over the extended industrial
(–40°C to +125°C) temperature range. The AD8517 single is
available in 5-lead SOT-23 surface-mount packages. The dual
AD8527 is available in 8-lead SOIC and MSOP packages.
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.
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., 2000
AD8517/AD8527–SPECIFICATIONS
ELECTRICAL CHARACTERISTICS (V = 5.0 V, V– = 0 V, V
S
Parameter
Symbol
INPUT CHARACTERISTICS
Offset Voltage
AD8517ART (SOT-23-5)
VOS
AD8527
VOS
Input Bias Current
IB
Input Offset Current
IOS
Input Voltage Range
Common-Mode Rejection Ratio
VCM
CMRR
Large Signal Voltage Gain
AVO
Offset Voltage Drift
Bias Current Drift
OUTPUT CHARACTERISTICS
Output Voltage Swing High
Output Voltage Swing Low
Short Circuit Current
POWER SUPPLY
Power Supply Rejection Ratio
Supply Current/Amplifier
∆VOS/∆T
∆IB/∆T
VOH
VOL
ISC
PSRR
ISY
CM
= 2.5 V, TA = 25ⴗC unless otherwise noted)
Conditions
Min
Typ
Max
Unit
1.3
3.5
5
3.5
5
450
900
± 225
± 750
5
mV
mV
mV
mV
nA
nA
nA
nA
V
–40°C ≤ TA ≤ +125°C
1.3
–40°C ≤ TA ≤ +125°C
–40°C ≤ TA ≤ +125°C
–40°C ≤ TA ≤ +125°C
0
0 V ≤ VCM ≤ 5.0 V,
–40°C ≤ TA ≤ +125°C
RL = 2 kΩ, 0.5 V < VOUT < 4.5 V
RL = 10 kΩ, 0.5 V < VOUT < 4.5 V
RL = 10 kΩ, –40°C ≤ TA ≤ +125°C
60
50
30
70
20
100
dB
V/mV
V/mV
V/mV
µV/°C
pA/°C
2
500
IL = 250 µA,
–40°C ≤ TA ≤ +125°C
IL = 5 mA
IL = 250 µA,
–40°C ≤ TA ≤ +125°C
IL = 5 mA
Short to Ground, Instantaneous
4.965
4.70
V
V
35
200
± 10
mV
mV
mA
VS = 2.2 V to 6 V
–40°C ≤ TA ≤ +125°C
VOUT = 2.5 V
–40°C ≤ TA ≤ +125°C
90
65
900
8
7
400
50
V/µs
MHz
ns
Degrees
0.5
15
1.2
µV p-p
nV/√Hz
pA/√Hz
DYNAMIC PERFORMANCE
Slew Rate
Gain Bandwidth Product
Settling Time
Phase Margin
SR
GBP
TS
φm
1 V < VOUT < 4 V, RL = 10 kΩ
NOISE PERFORMANCE
Voltage Noise
Voltage Noise Density
Current Noise Density
en p-p
en
in
0.1 Hz to 10 Hz
f = 1 kHz
f = 1 kHz
4 V Step, 0.1%
1,200
1,400
dB
dB
µA
µA
Specifications subject to change without notice.
–2–
REV. B
AD8517/AD8527
ELECTRICAL CHARACTERISTICS (V = 2.2 V, V– = 0 V, V
S
Parameter
Symbol
INPUT CHARACTERISTICS
Offset Voltage
AD8517ART (SOT-23-5)
VOS
AD8527
VOS
Input Bias Current
Input Offset Current
Input Voltage Range
Common-Mode Rejection Ratio
IB
IOS
VCM
CMRR
Large Signal Voltage Gain
AVO
OUTPUT CHARACTERISTICS
Output Voltage Swing High
Output Voltage Swing Low
VOH
VOL
CM
= 1.1 V, TA = 25ⴗC unless otherwise noted)
Conditions
Min
Typ
Max
Unit
1.3
3.5
5
3.5
5
450
± 225
2.2
mV
mV
mV
mV
nA
nA
V
–40°C ≤ TA ≤ +125°C
1.3
–40°C ≤ TA ≤ +125°C
0
0 V ≤ VCM ≤ 2.2 V,
–40°C ≤ TA ≤ +125°C
RL = 2 kΩ, 0.5 V < VOUT < 1.7 V
RL = 10 kΩ
IL = 250 µA
IL = 2.5 mA
IL = 250 µA
IL = 2.5 mA
55
20
70
20
50
dB
V/mV
V/mV
2.165
1.9
35
200
V
V
mV
mV
1,100
1,300
µA
µA
POWER SUPPLY
Supply Current/Amplifier
ISY
VOUT = 1.1 V
–40°C ≤ TA ≤ +125°C
750
DYNAMIC PERFORMANCE
Slew Rate
Gain Bandwidth Product
Phase Margin
SR
GBP
φm
RL = 10 kΩ
8
7
50
V/µs
MHz
Degrees
NOISE PERFORMANCE
Voltage Noise Density
Current Noise Density
en
in
f = 1 kHz
f = 1 kHz
15
1.2
nV/√Hz
pA/√Hz
Specifications subject to change without notice.
REV. B
–3–
AD8517/AD8527–SPECIFICATIONS
ELECTRICAL CHARACTERISTICS (V = 1.8 V, V– = 0 V, V
S
Parameter
Symbol
INPUT CHARACTERISTICS
Offset Voltage
AD8517ART (SOT-23-5)
VOS
AD8527
VOS
Input Bias Current
Input Offset Current
Input Voltage Range
Common-Mode Rejection Ratio
IB
IOS
VCM
CMRR
Large Signal Voltage Gain
AVO
OUTPUT CHARACTERISTICS
Output Voltage Swing High
Output Voltage Swing Low
POWER SUPPLY
Power Supply Rejection Ratio
Supply Current/Amplifier
VOH
VOL
PSRR
ISY
CM
= 0.9 V, TA = 25ⴗC unless otherwise noted)
Conditions
Min
Typ
Max
Unit
1.3
3.5
5
3.5
5
450
± 225
1.8
mV
mV
mV
mV
nA
nA
V
0°C ≤ TA ≤ 125°C
1.3
0°C ≤ TA ≤ 125°C
0
0 V ≤ VCM ≤ 1.8 V,
0°C ≤ TA ≤ 125°C
RL = 2 kΩ, 0.5 V < VOUT < 1.3 V
RL = 10 kΩ
IL = 250 µA
IL = 2.5 mA
IL = 250 µA
IL = 2.5 mA
VS = 1.7 V to 2.2 V,
0°C ≤ TA ≤ 125°C
VOUT = 0.9 V
0°C ≤ TA ≤ 125°C
50
20
70
20
50
dB
V/mV
V/mV
1.765
1.5
50
65
650
35
200
V
V
mV
mV
1,100
1,300
dB
µA
µA
DYNAMIC PERFORMANCE
Slew Rate
Gain Bandwidth Product
Phase Margin
SR
GBP
φm
RL = 10 kΩ
7
7
50
V/µs
MHz
Degrees
NOISE PERFORMANCE
Voltage Noise Density
Current Noise Density
en
in
f = 1 kHz
f = 1 kHz
15
1.2
nV/√Hz
pA/√Hz
Specifications subject to change without notice.
–4–
REV. B
AD8517/AD8527
ABSOLUTE MAXIMUM RATINGS
1
NOTES
1
Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the
device at these or any other conditions above those listed in the operational
sections of this specification is not implied. Exposure to absolute maximum rating
conditions for extended periods may affect device reliability.
2
For supply voltages less than 6 V the input voltage is limited to less than or equal
to the supply voltage.
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 V
Input Voltage2 . . . . . . . . . . . . . . . . . . . . . . . . . . . GND to VS
Differential Input Voltage . . . . . . . . . . . . . . . . . . . . . . ± 0.6 V
Internal Power Dissipation
SOT-23 (RT) . . . . . . . . . . . . See Thermal Resistance Chart
SOIC (R) . . . . . . . . . . . . . . . See Thermal Resistance Chart
µSOIC (RM) . . . . . . . . . . . . See Thermal Resistance Chart
Output Short-Circuit Duration
. . . . . . . . . . . . . . . . . . . . . . . . Indefinite for TA < +40°C
Storage Temperature Range
R, RM and RT Packages . . . . . . . . . . . . . –65°C to +150°C
Operating Temperature Range
AD8517, AD8527 . . . . . . . . . . . . . . . . . . –40°C to +125°C
Junction Temperature Range
R, RM and RT Packages . . . . . . . . . . . . . –65°C to +150°C
Lead Temperature Range (Soldering, 60 sec) . . . . . . . 300°C
Package Type
␪JA1
␪JC
Unit
5-Lead SOT-23 (RT)
8-Lead SOIC (R)
8-Lead µSOIC (RM)
230
158
210
146
43
45
°C/W
°C/W
°C/W
NOTE
1
θJA is specified for worst-case conditions, i.e., θJA is specified for device soldered
in circuit board for SOT-23 and SOIC packages.
ORDERING GUIDE
Model
Temperature
Range
Package
Description
Package
Option
Branding
Information
AD8517ART-REEL
AD8527AR
AD8527ARM-REEL
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
5-Lead SOT-23
8-Lead SOIC
8-Lead µSOIC
RT-5
SO-8
RM-8
ADA
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 AD8517/AD8527 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high-energy electrostatic discharges. Therefore, proper
ESD precautions are recommended to avoid performance degradation or loss of functionality.
WARNING!
ESD SENSITIVE DEVICE
950
120
VS = 5V
VCM = 2.5V
TA = 25ⴗC
COUNT = 935 OP AMPS
900
90
SUPPLY CURRENT – ␮A
QUANTITY OF AMPLIFIERS
AFA
60
30
850
800
750
700
650
0
ⴚ4
ⴚ3
ⴚ2
ⴚ1
0
1
2
INPUT OFFSET VOLTAGE – mV
3
600
4
2
3
4
SUPPLY VOLTAGE – V
5
6
Figure 2. Supply Current per Amplifier vs. Supply Voltage
Figure 1. Input Offset Voltage Distribution
REV. B
1
–5–
AD8517/AD8527–Typical Characteristics
60
1,200
VS = 5V
1,000
900
800
700
GAIN
30
20
90
PHASE
10
45
0
0
ⴚ10
ⴚ45
ⴚ20
ⴚ90
PHASE SHIFT – Degrees
40
OPEN-LOOP GAIN – dB
SUPPLY CURRENT – ␮A
VS = 5V
TA = 25ⴗC
50
1,100
ⴚ30
600
ⴚ50
ⴚ25
0
25
50
75
TEMPERATURE – ⴗC
100
125
ⴚ40
100k
150
Figure 3. Supply Current per Amplifier vs. Temperature
10M
1M
FREQUENCY – Hz
100M
Figure 6. Open-Loop Gain vs. Frequency
600
60
VS = ⴞ2.5V
TA = 25ⴗC
VS = 5V
TA = 25ⴗC
CL ⱕ 10pF
40
CLOSED-LOOP GAIN – dB
INPUT BIAS CURRENT – nA
400
200
0
ⴚ200
0
ⴚ20
ⴚ400
ⴚ600
ⴚ3
20
ⴚ2
0
ⴚ1
1
COMMON-MODE VOLTAGE – V
ⴚ40
3
2
Figure 4. Input Bias Current vs. Common-Mode Voltage
10
100
1k
10k
100k
FREQUENCY – Hz
1M
10M
100M
Figure 7. Closed-Loop Gain vs. Frequency
0
140
TA = 25ⴗC
VS = ⴞ2.5V
TA = 25ⴗC
120
SINKⴚ
CMRR – dB
OUTPUT VOLTAGE – mV
20
100
80
60
40
60
SOURCE+
40
80
20
0
10
100
1k
100
LOAD CURRENT – ␮A
10k
Figure 5. Output Voltage to Supply Rail vs. Load Current
10
100
1k
10k
100k
FREQUENCY – Hz
1M
10M
Figure 8. CMRR vs. Frequency
–6–
REV. B
AD8517/AD8527
100
0
VS = ⴞ2.5V
TA = 25ⴗC
20
80
OUTPUT IMPEDANCE – ⍀
ⴚPSRR
40
PSRR – dB
VS = 5V
TA = 25ⴗC
90
60
ⴙPSRR
80
70
60
50
40
30
AVCC = 1
20
100
10
120
0
100
10
10k
100k
1k
FREQUENCY – Hz
1M
10M
Figure 9. PSRR vs. Frequency
1k
10k
100k
FREQUENCY – Hz
1M
10M
100M
40
VS = 5V
TA = 25ⴗC
Hz
VS = 5V
VCM = 2.5V
R L = 10k⍀
TA = 25ⴗC
VIN = ⴞ50mV
AV = 1
VOLTAGE NOISE DENSITY – nV/
OVERSHOOT – %
100
50
50
ⴚOS
30
20
+OS
10
0
10
100
CAPACITANCE – pF
40
30
20
10
0
10
1k
100
1k
FREQUENCY – Hz
10k
Figure 13. Voltage Noise Density vs. Frequency
Figure 10. Overshoot vs. Capacitance Load
12
6
4
3
2
1
0
10k
100k
1M
FREQUENCY – Hz
VS = 5V
TA = 25ⴗC
Hz
5
VS = 5V
A V = +1
R L = 10k⍀
TA = 25ⴗC
CL = 15pF
CURRENT NOISE DENSITY – pA/
DISTORTION = 3%
MAXIMUM OUTPUT SWING – V p-p
10
Figure 12. Output Impedance vs. Frequency
60
8
4
0
10
10M
100
1k
FREQUENCY – Hz
10k
Figure 14. Current Noise Density vs. Frequency
Figure 11. Output Swing vs. Frequency
REV. B
AVCC = 10
–7–
AD8517/AD8527
VOLTAGE – 20mV/Div
VOLTAGE – 20mV/Div
VS = ⴞ2.5V
AV = 120k
TA = 25ⴗC
VS = ⴞ2.5V
AV = 1
TA = 25ⴗC
CL = 100pF
R L = 10k⍀
TIME – 500ns/Div
TIME – 1s/Div
Figure 17. Small Signal Transient Response
Figure 15. 0.1 Hz to 10 Hz Noise
0
VOLTAGE – 1V/Div
0
VS = ⴞ2.5V
AV = 1
RL = 10k⍀
TA = 25ⴗC
VOLTAGE – 500mV/Div
VS = ⴞ2.5V
AV = + 1
VIN = SINEWAVE
TA = 25ⴗC
0
0
0
0
0
0
TIME – 200ns/Div
TIME – 200␮s/Div
Figure 16. No Phase Reversal
Figure 18. Large Signal Transient Response
configuration. The output swing when sinking or sourcing 250 µA
is 35 mV from each rail.
THEORY OF OPERATION
The AD85x7 is a rail-to-rail operational amplifier that can operate at
supply voltages as low as 1.8 V. This family is fabricated using Analog
Devices’ high-speed complementary bipolar process, also called
XFCB. The process trench isolates each transistor to minimize
parasitic capacitance thereby allowing high-speed performance.
Figure 19 shows a simplified schematic of the AD85x7 family.
The input bias current characteristics depend on the commonmode voltage, see Figure 4. As the input voltage reaches about
1 V below VCC, the PNP pair (Q3 and Q4) turns off.
The 1 kΩ input resistor R1 and R2, together with the diodes D7
and D8, protect the input pairs against avalanche damage.
The input stage consists of two parallel complementary differential pair: one NPN pair (Q1 and Q2) and one PNP pair (Q3 and
Q4). The voltage drops across R7. R8, R9, and R10 are kept low
for rail-to-rail operation. The major gain stage of the op amp is a
double-folded cascode consisting of transistors Q5, Q6, Q8, and
Q9. The output stage, which also operates rail-to-rail, is driven by
Q14. The transistors Q13 and Q10 act as level-shifters to give
more headroom during 1.8 V operation.
The AD85x7 family exhibits no phase reversal as the input
signal exceeds the supply by more than 0.6 V. Excessive current
can flow through the input pins via the ESD diodes D1–D2 or
D3–D4, in the event their ~0.6 V thresholds are exceeded. Such
fault currents must be limited to 5 mA or less by the use of
external series resistance(s).
LOW VOLTAGE OPERATION
Battery Voltage Discharge
As the voltage at the base of Q13 increases, Q18 starts to sink
current. When the voltage at the base of Q13 decreases, I8 flows
through D16 and Q15 increasing the VBE of Q17, then Q20
sources current.
The AD8517 operates at supply voltages as low as 1.8 V. This
amplifier is ideal for battery-powered applications since it can
operate at the end of discharge voltage of most popular batteries.
Table I lists the Nominal and End of Discharge Voltages of several
typical batteries.
The output stage also furnishes gain, which depends on the load
resistance, since the output transistors are in common emitter
–8–
REV. B
AD8517/AD8527
VCC
VCC
R8
R7
R14
I8
I7
Q6
D1
D3
ESD
I1
ESD
ⴚIN
Q3
R1
Q1
Q4
R2
Q14
D9
C4
C2
Q10
R6
D8
Q18
C1
Q8
D4
ESD
ESD
R11
Q9
Q17
Q15
R9
I2
VOUT
C3
Q13
Q11
ⴙIN
D7
R5
D2
Q2
Q20
Q7
I3
R4
R3
Q19
Q5
R10
I6
I5
I4
D6
D16
R12
R13
VEE
VEE
Figure 19. Simplified Schematic
Table I. Typical Battery Life Voltage Range
Battery
Nominal
Voltage (V)
End of Voltage
Discharge (V)
Lead-Acid
Lithium
NiMH
NiCd
Carbon-Zinc
2
2.6-3.6
1.2
1.2
1.5
1.8
1.7-2.4
1
1
1.1
INPUT BIAS CONSIDERATION
The input bias current (IB) is a nonideal, real-life parameter that
affects all op amps. IB can generate a somewhat significant offset
voltage. This offset voltage is created by IB when flowing through
the negative feedback resistor RF. If IB is 500 nA (worst case),
and RF is 100 kΩ, the corresponding generated offset voltage is
50 mV (VOS = IB ⫻ RF).
Obviously the lower RF the lower the generated voltage offset.
Using a compensation resistor, RB, as shown in Figure 21, can
significantly minimize this effect. With the input bias current minimized, we still need to be aware of the input offset current (IOS)
which will generate a slight offset error. Figure 21 shows three
different configurations to minimize IB-induced offset errors.
RAIL-TO-RAIL INPUT AND OUTPUT
The AD8517 features an extraordinary rail-to-rail input and
output with supply voltages as low as 1.8 V. With the amplifier’s
supply range set to 1.8 V, the input can be set to 1.8 V p-p,
allowing the output to swing to both rails without clipping. Figure
20 shows a scope picture of both input and output taken at unity
gain, with a frequency of 1 kHz, at VS = 1.8 V and VIN = 1.8 V p-p.
RF
RI
VI
ⱍⱍ
RB = RI RF
VS = ⴞ0.9V
VIN = 1.8 V p-p
AD8517
VOUT
INVERTING CONFIGURATION
RF
RI
ⱍⱍ
RB = RI RF
VIN
VI
AD8517
VOUT
NONINVERTING CONFIGURATION
RF = RS
VOUT
RS
VI
AD8517
VOUT
UNITY GAIN BUFFER
Figure 21. Input Bias Cancellation Circuits
TIME – 200␮s/Div
Figure 20. Rail-to-Rail Input Output
The rail-to-rail feature of the AD8517 can be observed over the
supply voltage range, 1.8 V to 5 V. Traces are shown offset for
clarity.
REV. B
–9–
AD8517/AD8527
DRIVING CAPACITIVE LOAD
Gain vs. Capacitive Load
F = 250kHz
AV = +1
C = 680pF
VOLTAGE – 200mV/Div
Most amplifiers have difficulty driving capacitance due to degradation
of phase caused by additional phase lag from the capacitive load.
Higher capacitance at the output can increase the amount of overshoot and ringing in the amplifier’s step response and could even
affect the stability of the device. The value of capacitance load an
amplifier can drive before oscillation varies with gain, supply voltage, input signal, temperature, and frequency, among others. Unity
gain is the most challenging configuration for driving capacitance
load. However, the AD8517 offers good capacitance driving ability.
Table II shows the AD8517’s ability to capacitance load at different gains before instability occurs. This table is good for all VSY.
TIME – 1␮s/Div
Table II. Gain and Capacitance Load
Figure 23. Photo of a Ringing Square Wave
Gain
Max Capacitance
1
2
2.5
3
400 pF
1.5 nF
8 nF
Unconditionally Stable
By connecting a series R–C from the output of the device to
ground, known as the “snubber” network, this ringing and overshoot can be significantly reduced. Figure 24 shows the network
setup, and Figure 25 shows the improvement of the output
response with the “snubber” network added.
In-the-Loop Compensation Technique for Driving
Capacitive Loads
5V
When driving capacitive loads in unity configuration, the in-theloop compensation technique is recommended to avoid oscillation
as is illustrated in Figure 22.
AD8517
VIN
RF
VOUT
RX
CL
CX
RG
VIN
CF
Figure 24. Snubber Network Compensation for Capacitive
Loads
RX
AD8517
VOUT
F = 250kHz
AV = +1
C = 680pF
CL
RO RG
RF
WHERE RO = OPEN-LOOP OUTPUT RESISTANCE
CF =
1+
冉
1
ACL
冊冉
RF + RG
RF
冊
VOLTAGE – 200mV/Div
RX =
CLRO
Figure 22. In-the-Loop Compensation Technique for
Driving Capacitive Loads
Snubber Network Compensation for Driving Capacitive Loads
As load capacitance increases, the overshoot and settling time
will increase and the unity gain bandwidth of the device will
decrease. Figure 23 shows an example of the AD8517 configured for unity gain and driving a 10 kΩ resistor and a 680 pF
capacitor placed in parallel, with a square wave input set to a
frequency of 250 kHz and unity gain.
TIME – 1␮s/Div
Figure 25. Photo of a Square Wave with the Snubber
Network Compensation
The network operates in parallel with the load capacitor, CL,
and provides compensation for the added phase lag. The actual
values of the network resistor and capacitor have to be empirically determined. Table III shows some values of snubber network
for large capacitance load.
–10–
REV. B
AD8517/AD8527
Table III. Snubber Network Values for Large Capacitive Loads
MICROPHONE PREAMPLIFIER
CLOAD
Rx
Cx
The AD8517 is ideal to use as a microphone preamplifier.
Figure 28 shows this implementation.
680 pF
1 nF
10 nF
300 Ω
100 Ω
400 Ω
3 nF
10 nF
30 nF
R3
220k⍀
VCC
R1
2.2k⍀
VCC
C1
R2
0.1␮F 22k⍀
VIN
TOTAL HARMONIC DISTORTION + NOISE
The AD85x7 family offers a low total harmonic distortion, which
makes this amplifier ideal for audio applications. Figure 26 shows a
graph of THD + N, for a VS > 3 V the THD + N is about 0.001%
and 0.03% for VS ≥ 1.8 V in a noninverting configuration with a
gain of 1. In an inverting configuration, the noise is 0.003% for
all VSY.
1
AV = +2
AD8517
ELECTRET
MIC
VOUT
| AV | =
VREF
R3
R2
Figure 28. A Microphone Preamplifier
R1 is used to bias an electret microphone and C1 blocks dc
voltage from the amplifier. The magnitude of the gain of the
amplifier is approximately R3/R2 when R2 ≥ 10 × R1. VREF
should be equal to 1/2 1.8 V for maximum voltage swing.
Direct Access Arrangement for Telephone Line Interface
0.1
Figure 28 illustrates a 1.8 V transmit/receive telephone line
interface for 600 Ω transmission systems. It allows full duplex
transmission of signals on a transformer-coupled 600 Ω line in a
differential manner. Amplifier A1 provides gain that can be adjusted to meet the modem output drive requirements. Both A1
and A2 are configured to apply the largest possible signal on a
single supply to the transformer. Amplifier A3 is configured as a
difference amplifier for two reasons: (1) It prevents the transmit
signal from interfering with the receive signal and (2) it extracts
the receive signal from the transmission line for amplification by
A4. A4’s gain can be adjusted in the same manner as A1’s to
meet the modem’s input signal requirements. Standard resistor
values permit the use of SIP (Single In-line Package) format
resistor arrays. Couple this with the AD8517/AD8527’s 5-lead
SOT-23, 8-lead MSOP, and 8-lead SOIC footprint and this
circuit offers a compact solution.
THD + N – %
VS = 1.8V
0.01
VS > 3V TO 5V
0.001
0.0001
10
100
10k 20k
1k
FREQUENCY – Hz
Figure 26. THD + N vs. Frequency Graph
A MICROPOWER REFERENCE VOLTAGE GENERATOR
Many single supply circuits are configured with the circuit-biased
to one-half of the supply voltage. In these cases, a false-ground
reference can be created by using a voltage divider buffered by an
amplifier. Figure 27 shows the schematic for such a circuit.
P1
Tx GAIN
ADJUST
The two 1 MΩ resistors generate the reference voltages while
drawing only 0.9 µA of current from a 1.8 V supply. A capacitor
connected from the inverting terminal to the output of the op
amp provides compensation to allow for a bypass capacitor to be
connected at the reference output. This bypass capacitor helps
establish an ac ground for the reference output.
1.8V TO 5V
TO
TELEPHONE
LINE
1:1
6.2V
R5
10k⍀
T1
MIDCOM
671-8005
7
R11
10k⍀
2
3
100⍀
1␮F
R12
10k⍀
VREF
0.9V TO 2.5V
1␮F
TRANSMIT
TxA
+1.8V DC
A3
A2
1
1/2
AD8527
R7
10k⍀
5
10␮F
R8
10k⍀
P2
Rx GAIN
R13
R14 ADJUST
10k⍀ 14.3k⍀
2k⍀
6
5
A4
7
C2
0.1␮F
RECEIVE
RxA
1/2
AD8527
Figure 29. A Single-Supply Direct Access Arrangement
for Modems
Figure 27. A Micropower Reference Voltage Generator
REV. B
R6
10k⍀
1/2
AD8517
R10
10k⍀
0.022␮F
AD8517
A1 3
6
10k⍀
1M⍀
1
C1
0.1␮F
R1
10k⍀
2
1/2
AD8517
6.2V
R9
10k⍀
1M⍀
2k⍀
R3
360⍀
ZO
600⍀
R2
9.09k⍀
–11–
identical to the actual AD8517 performance, which is a critical
feature with a rail-to-rail amplifier model. The model also accurately simulates many ac effects, such as gain-bandwidth product,
phase margin, input voltage noise, CMRR and PSRR versus
frequency, and transient response. Its high degree of model
accuracy makes the AD8517 macro-model one of the most
reliable and true-to-life models available for any amplifier.
SPICE Model
The SPICE model for the AD8517 amplifier is available and
can be downloaded from the Analog Devices’ web site at
http://www.analog.com. The macro-model accurately simulates
a number of AD8517 parameters, including offset voltage, input
common-mode range, and rail-to-rail output swing. The output
voltage versus output current characteristics of the macro-model is
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
8-Lead Narrow Body SOIC
(SO-8)
8-Lead MSOP
(RM-8)
0.1968 (5.00)
0.1890 (4.80)
8
5
1
4
0.2440 (6.20)
0.2284 (5.80)
8
5
0.199 (5.05)
0.187 (4.75)
0.122 (3.10)
0.114 (2.90)
1
PIN 1
0.0098 (0.25)
0.0040 (0.10)
0.0688 (1.75)
0.0532 (1.35)
0.0196 (0.50)
ⴛ 45ⴗ
0.0099 (0.25)
0.0500 0.0192 (0.49)
SEATING (1.27)
0.0098 (0.25)
PLANE BSC 0.0138 (0.35) 0.0075 (0.19)
4
PIN 1
0.0256 (0.65) BSC
0.120 (3.05)
0.112 (2.84)
8ⴗ
0ⴗ 0.0500 (1.27)
0.0160 (0.41)
0.120 (3.05)
0.112 (2.84)
0.043 (1.09)
0.037 (0.94)
0.006 (0.15)
0.002 (0.05)
0.018 (0.46)
SEATING 0.008 (0.20)
PLANE
0.011 (0.28)
0.003 (0.08)
33ⴗ
27ⴗ
0.028 (0.71)
0.016 (0.41)
5-Lead SOT-23
(RT-5)
0.1181 (3.00)
0.1102 (2.80)
0.0669 (1.70)
0.0590 (1.50)
5
1
4
2
0.1181 (3.00)
0.1024 (2.60)
3
PIN 1
0.0374 (0.95) BSC
0.0748 (1.90)
BSC
0.0512 (1.30)
0.0354 (0.90)
0.0059 (0.15)
0.0019 (0.05)
0.0079 (0.20)
0.0031 (0.08)
0.0571 (1.45)
0.0374 (0.95)
0.0197 (0.50)
0.0138 (0.35)
SEATING
PLANE
–12–
10ⴗ
0ⴗ
PRINTED IN U.S.A.
0.1574 (4.00)
0.1497 (3.80)
0.122 (3.10)
0.114 (2.90)
C3736b–2.5–7/00 (rev. B) 01020
AD8517/AD8527
0.0217 (0.55)
0.0138 (0.35)
REV. B