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(R)
OPA 634
OPA634 OPA635
For most current data sheet and other product information, visit www.burr-brown.com
Wideband, Single Supply OPERATIONAL AMPLIFIERS
TM
FEATURES
q q q q q q q q q HIGH BANDWIDTH: 150MHz (G = +2) +3V AND +5V OPERATION ZERO POWER DISABLE (OPA635) INPUT RANGE INCLUDES GROUND 4.8V OUTPUT SWING ON +5V SUPPLY HIGH OUTPUT CURRENT: 80mA HIGH SLEW RATE: 250V/s LOW INPUT VOLTAGE NOISE: 5.6nV/HZ AVAILABLE IN SOT23 PACKAGES
APPLICATIONS
q q q q q SINGLE SUPPLY ADC INPUT BUFFER SINGLE SUPPLY VIDEO LINE DRIVER WIRELESS LAN IF AMPLIFIER CCD IMAGING CHANNELS LOW POWER ULTRASOUND
DESCRIPTION
The OPA634 and OPA635 are low power, voltagefeedback, high-speed amplifiers designed to operate on +3V or +5V single-supply voltages. Operation on 5V or +10V supplies is also supported. The input range extends below ground and to within 1.2V of the positive supply. Using complementary common-emitter outputs provides an output swing to within 30mV of ground and 140mV of positive supply. The high output drive current, low differential gain and phase errors make them ideal for single-supply composite video line driving. Low distortion operation is ensured by the high gain bandwidth (140MHz) and slew rate (250V/s). This makes the OPA634 and OPA635 ideal input buffer stages to 3V and 5V CMOS converters. Unlike other low power, single-supply operational amplifiers, distortion performance improves as the signal swing is decreased.
+3V 2.26k 374 VIN
OPA635
A low 5.6nV input voltage noise supports wide dynamic range operation. Multiplexing or system power reduction can be achieved using the high-speed disable line with the OPA635. Power dissipation can be reduced to zero by taking the disable line High. The OPA634 and OPA635 are available in an industry standard SO-8 package. The OPA634 is also available in an ultra-small SOT23-5 package, while the OPA635 is available in the SOT23-6. Where lower supply current and speed are required, consider the OPA631 and OPA632. RELATED PRODUCTS
SINGLES Medium Speed, No Disable With Disable High Speed, No Disable With Disable OPA631 OPA632 OPA634 OPA635 DUALS OPA2631 -- OPA2634 --
Disable
+3V Pwrdn ADS900 10-Bit 20Msps 22pF
DIS
100
562
750
International Airport Industrial Park * Mailing Address: PO Box 11400, Tucson, AZ 85734 * Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 * Tel: (520) 746-1111 Twx: 910-952-1111 * Internet: http://www.burr-brown.com/ * Cable: BBRCORP * Telex: 066-6491 * FAX: (520) 889-1510 * Immediate Product Info: (800) 548-6132
(c) 1999 Burr-Brown Corporation
PDS-1465A
Printed in U.S.A. June, 1999
SPECIFICATIONS: VS = +5V
At TA = 25C, G = +2, RF = 750, and RL = 150 to VS/2, unless otherwise noted (see Figure 1). OPA634U, N OPA635U, N TYP GUARANTEED 0C to 70C -40C to +85C MIN/ MAX TEST LEVEL(1)
PARAMETER AC PERFORMANCE (Figure 1) Small-Signal Bandwidth
CONDITIONS G = +2, VO 0.5Vp-p G = +5, VO 0.5Vp-p G = +10, VO 0.5Vp-p G +10 VO 0.5Vp-p G = +2, 2V Step 0.5V Step 0.5V Step G = +2, 1V Step VO = 2Vp-p, f = 5MHz f > 1MHz f > 1MHz
+25C
+25C
UNITS
Gain Bandwidth Product Peaking at a Gain of +1 Slew Rate Rise Time Fall Time Settling Time to 0.1% Spurious Free Dynamic Range Input Voltage Noise Input Current Noise NTSC Differential Gain NTSC Differential Phase DC PERFORMANCE Open-Loop Voltage Gain Input Offset Voltage Average Offset Voltage Drift Input Bias Current Input Offset Current Input Offset Current Drift INPUT Least Positive Input Voltage Most Positive Input Voltage Common-Mode Rejection (CMRR) Input Impedance Differential-Mode Common-Mode OUTPUT Least Positive Output Voltage Most Positive Output Voltage
150 36 16 140 5 250 2.4 2.4 15 63 5.6 2.8 0.10 0.16 66 3 -- 25 0.6 -- -0.24 3.8 78 10 || 2.1 400 || 1.2
100 24 11 100 -- 170 3.4 3.5 19 56 6.2 3.8 -- -- 63 7 -- 45 2 -- -0.1 3.5 75 -- -- 0.05 0.14 4.8 4.55 50 80 -- -- 1.0 4.1 110 -- 30 -- -- -- 2.7 10.5 12.5 11.3 52
84 20 10 82 -- 125 4.7 4.5 22 51 7.3 4.2 -- -- 60 8 -- 55 2.3 -- -0.05 3.45 73 -- -- 0.06 0.15 4.75 4.5 45 65 -- -- 1.0 4.2 120 -- 40 -- -- -- 2.7 10.5 13 9.75 50
78 18 8 75 -- 115 5.2 4.8 23 50 7.7 5 -- -- 53 10 4.6 80 4 15 -0.01 3.4 65 -- -- 0.07 0.22 4.7 4.4 20 20 -- -- 1.0 4.3 120 -- 50 -- -- -- 2.7 10.5 13.25 8.5 49
MHz MHz MHz MHz dB V/s ns ns ns dBc nV/Hz pA/Hz % degrees dB mV V/C A A nA/C V V dB k || pF k || pF V V V V mA mA mA V V A A A ns ns dB V V mA mA dB C C/W C/W
min min min min typ min max max max min max max typ typ min max max max max max max min min typ typ max max min min min min typ typ min max max typ max typ typ typ min max max min min typ typ typ
B B B B C B B B B B B B C C A A B B B B B A A C C B A B A A A C C A A A C A C C C A A A A A C C C
VCM = 2.0V VCM = 2.0V
Input Referred
RL = 1k to 2.5V R L = 150 to 2.5V RL = 1k to 2.5V R L = 150 to 2.5V
Current Output, Sourcing Current Output, Sinking Short-Circuit Current (output shorted to either supply) Closed-Loop Output Impedance G = +2, f 100kHz DISABLE (OPA635 only) On Voltage (device enabled Low) Off Voltage (device disabled High) On Disable Current (DIS pin) Off Disable Current (DIS pin) Disabled Quiescent Current Disable Time Enable Time Off Isolation POWER SUPPLY Minimum Operating Voltage Maximum Operating Voltage Maximum Quiescent Current Minimum Quiescent Current Power Supply Rejection Ratio (PSRR) THERMAL CHARACTERISTICS Specification: U, N Thermal Resistance U SO-8 N SOT23-5, SOT23-6
0.03 0.1 4.86 4.65 80 100 100 0.2 1.0 4.0 70 0 0 100 60 70 -- -- 12 12 55 -40 to +85 125 150
f = 5MHz, Input to Output
Input Referred
NOTE: (1) Test Levels: (A) 100% tested at 25C. Over temperature limits by characterization and simulation. (B) Limits set by characterization and simulation. (C) Typical value only for information.
(R)
OPA634, OPA635
2
SPECIFICATIONS: VS = +3V
At TA = 25C, G = +2 and RL = 150 to VS/2, unless otherwise noted (see Figure 2). OPA634U, N OPA635U, N TYP GUARANTEED 0C to 70C -40C to +85C MIN/ TEST MAX LEVEL(1)
PARAMETER AC PERFORMANCE (Figure 2) Small-Signal Bandwidth
CONDITIONS G = +2, VO 0.5Vp-p G = +5, VO 0.5Vp-p G = +10, VO 0.5Vp-p G +10 VO 0.5Vp-p 1V Step 0.5V Step 0.5V Step 1V Step VO = 1Vp-p, f = 5MHz f > 1MHz f > 1MHz
+25C
+25C
UNITS
Gain Bandwidth Product Peaking at a Gain of +1 Slew Rate Rise Time Fall Time Settling Time to 0.1% Spurious Free Dynamic Range Input Voltage Noise Input Current Noise DC PERFORMANCE Open-Loop Voltage Gain Input Offset Voltage Average Offset Voltage Drift Input Bias Current Input Offset Current Input Offset Current Drift INPUT Least Positive Input Voltage Most Positive Input Voltage Common-Mode Rejection (CMRR) Input Impedance Differential-Mode Common-Mode OUTPUT Least Positive Output Voltage Most Positive Output Voltage
110 39 16 150 5 215 2.8 3.0 14 65 5.6 2.8 67 1.5 -- 25 0.6 -- -0.25 1.8 75 10 || 2.1 400 || 1.2
77 24 12 100 -- 160 4.3 4.4 30 56 6.2 3.7 64 4 -- 42 2 -- -0.1 1.6 67 -- -- 0.043 0.08 2.86 2.70 35 30 -- -- 0.5 1.9 100 -- 30 -- -- -- 2.7 10.5 11.1 10.1 49
65 20 10 85 -- 123 4.5 4.6 32 52 7.3 4.2 60 5 -- 55 2.3 -- -0.05 1.55 64 -- -- 0.045 0.09 2.85 2.69 30 27 -- -- 0.5 2.1 110 -- 40 -- -- -- 2.7 10.5 11.4 8.6 45
58 19 8 80 -- 82 6.3 6.0 38 47 7.7 4.4 56 6 46 60 4 40 -0.01 1.5 61 -- -- 0.06 0.13 2.45 2.65 12 10 -- -- 0.5 2.2 110 -- 50 -- -- -- 2.7 10.5 11.6 8.0 44
MHz MHz MHz MHz dB V/s ns ns ns dBc nV/Hz pA/Hz dB mV V/C A A nA/C V V dB k || p k || p V V V V mA mA mA V V A A A ns ns dB V V mA mA dB C C/W C/W
min min min min typ min max max max min max max min max max max max max max min min typ typ max max min min min min typ typ min max max typ max typ typ typ min max max min min typ typ typ
B B B B C B B B B B B B A A B B B B B A A C C A A A A A A C C A A A C A C C C A A A A A C C C
VCM = 1.0V VCM = 1.0V
Input Referred
RL = 1k to 1.5V RL = 150 to 1.5V RL = 1k to 1.5V RL = 150 to 1.5V
Current Output, Sourcing Current Output, Sinking Short Circuit Current (output shorted to either supply) Closed-Loop Output Impedance Figure 2, f < 100kHz DISABLE (OPA635 only) On Voltage (device enabled Low) Off Voltage (device disabled High) On Disable Current (DIS pin) Off Disable Current (DIS pin) Disabled Quiescent Current Disable Time Enable Time Off Isolation POWER SUPPLY Minimum Operating Voltage Maximum Operating Voltage Maximum Quiescent Current Minimum Quiescent Current Power Supply Rejection Ratio (PSRR) THERMAL CHARACTERISTICS Specification: U, N Thermal Resistance U SO-8 N SOT23-5, SOT23-6
0.035 0.06 2.9 2.8 45 65 100 0.2 1.0 1.8 66 0 0 100 60 70 -- -- 10.8 10.8 50 -40 to +85 125 150
f = 5MHz, Input to Output
Input Referred
NOTE: (1) Test Levels: (A) 100% tested at 25C. Over temperature limits by characterization and simulation. (B) Limits set by characterization and simulation. (C) Typical value only for information.
The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes no responsibility for the use of this information, and all use of such information shall be entirely at the user's own risk. Prices and specifications are subject to change without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant any BURR-BROWN product for use in life support devices and/or systems.
(R)
3
OPA634, OPA635
ABSOLUTE MAXIMUM RATINGS
Power Supply ................................................................................ +11VDC Internal Power Dissipation .................................... See Thermal Analysis Differential Input Voltage .................................................................. 1.2V Input Voltage Range ............................................................... -0.5 to +VS Storage Temperature Range: P, U, N ........................... -40C to +125C Lead Temperature (soldering, 10s) .............................................. +300C Junction Temperature (TJ ) ........................................................... +175C
ELECTROSTATIC DISCHARGE SENSITIVITY
Electrostatic discharge can cause damage ranging from performance degradation to complete device failure. Burr-Brown Corporation recommends that all integrated circuits be handled and stored using appropriate ESD protection methods. ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet published specifications.
PIN CONFIGURATIONS
Top View--OPA634, OPA635 SO-8
NC Inverting Input Non-Inverting Input GND
1 2 3 4
8 7 6 5
DIS (OPA635 only) +VS Output NC
Top View--OPA634
SOT23-5
Top View--OPA635
SOT23-6
Output
1
6
+VS
Output
1
6
+VS
GND
2
GND
2
5
DIS
Non-Inverting Input
3
4
Inverting Input
Non-Inverting Input
3
4
Inverting Input
6
5
6
4
B34
1 2 3
A35
1 2
Pin Orientation/Package Marking
Pin Orientation/Package Marking
PACKAGE/ORDERING INFORMATION
PACKAGE DRAWING NUMBER(1) 182 SPECIFIED TEMPERATURE RANGE -40C to +85C PACKAGE MARKING OPA635U ORDERING NUMBER(2) OPA635U OPA635U/2K5 OPA635N/250 OPA635N/3K OPA634U OPA634U/2K5 OPA634N/250 OPA634N/3K TRANSPORT MEDIA Rails Tape and Reel Tape and Reel Tape and Reel Rails Tape and Reel Tape and Reel Tape and Reel
PRODUCT OPA635U
PACKAGE SO-8 Surface-Mount
"
OPA635N
"
6-Lead SOT23-6
"
332
"
-40C to +85C
"
A35
"
OPA634U
"
SO-8 Surface-Mount
"
182
"
-40C to +85C
"
OPA634U
"
OPA634N
"
5-Lead SOT23-5
"
331
"
-40C to +85C
"
B34
"
"
"
"
"
NOTES: (1) For detailed drawing and dimension table, please see end of data sheet, or Appendix C of Burr-Brown IC Data Book. (2) Models with a slash (/) are available only in Tape and Reel in the quantities indicated (e.g., /2K5 indicates 2500 devices per reel). Ordering 3000 pieces of "OPA635N/3K" will get a single 3000-piece Tape and Reel. For detailed Tape and Reel mechanical information, refer to Appendix B of Burr-Brown IC Data Book.
(R)
OPA634, OPA635
4
3
4
TYPICAL PERFORMANCE CURVES: VS = +5V
At TA = 25C, G = +2, RF = 750, and RL = 150 to VS/2, unless otherwise noted (see Figure 1).
SMALL-SIGNAL FREQUENCY RESPONSE 6 VO = 0.2Vp-p 3 G = +2 9 G = +5 6 12
LARGE-SIGNAL FREQUENCY RESPONSE VO = 0.2Vp-p
Normalized Gain (dB)
0
-6 -9 -12 -15 -18 1 10 Frequency (MHz) 100 300 G = +10
Gain (dB)
-3
3 0 VO = 1Vp-p -3 -6 VO = 4Vp-p -9 -12 1 10 Frequency (MHz) 100 300 VO = 2Vp-p
SMALL-SIGNAL PULSE RESPONSE
Input and Output Voltage (500mV/div) Input and Output Voltage (50mV/div)
LARGE-SIGNAL DISABLE/ENABLE RESPONSE VO = 2Vp-p VO
VO = 200mVp-p VO
VIN
VIN
Time (10ns/div)
Time (10ns/div)
LARGE-SIGNAL DISABLE/ENABLE RESPONSE VDIS
DISABLE FEEDTHROUGH vs FREQUENCY -35 -40 Output Voltage (250mV/div) -45
Feedthrough (dB)
OPA635 only VDIS = +5V
Disable Voltage (1V/div)
-50 -55 -60 -65 -70 -75 -80 -85 1 10 100 Frequency (MHz) 1000
VO
VIN = 0.5V OPA635 only Time (50ns/div)
(R)
5
OPA634, OPA635
TYPICAL PERFORMANCE CURVES: VS = +5V
At TA = 25C, G = +2, RF = 750, and RL = 150 to VS/2, unless otherwise noted (see Figure 1).
(CONT)
5MHz 2nd HARMONIC DISTORTION vs OUTPUT VOLTAGE -40 -45 -40 -45
5MHz 3rd HARMONIC DISTORTION vs OUTPUT VOLTAGE
2nd Harmonic Distortion (dBc)
-50 -55 -60 -65 -70 -75 -80 -85 -90 0.1 1 Output Voltage (Vp-p) RL = 150 RL = 250 RL = 500 4
3rd Harmonic Distortion (dBc)
-50 -55 -60 -65 -70 -75 -80 -85 -90 0.1
RL = 150
RL = 250 RL = 500
1 Output Voltage (Vp-p)
4
10MHz 2nd HARMONIC DISTORTION vs OUTPUT VOLTAGE -40 -45 -40 -45
10MHz 3rd HARMONIC DISTORTION vs OUTPUT VOLTAGE
2nd Harmonic Distortion (dBc)
-50 -55 -60 -65 -70 -75 -80 -85 -90 0.1 1 Output Voltage (Vp-p) 4 RL = 500 RL = 150 RL = 250
3rd Harmonic Distortion (dBc)
-50 -55 -60 -65 -70 -75 -80 -85 -90 0.1 RL = 150
RL = 500 RL = 250
1 Output Voltage (Vp-p)
4
20MHz 2nd HARMONIC DISTORTION vs OUTPUT VOLTAGE -40 -45
2nd Harmonic Distortion (dBc) 3rd Harmonic Distortion (dBc)
20MHz 3rd HARMONIC DISTORTION vs OUTPUT VOLTAGE -40 -45 -50 -55 -60 -65 -70 -75 -80 -85 -90 RL = 150 RL = 500 RL = 250
-50 -55 -60 -65 -70 -75 -80 -85 -90 0.1
RL = 250 RL = 150
RL = 500
1 Output Voltage (Vp-p)
4
0.1
1 Output Voltage (Vp-p)
4
(R)
OPA634, OPA635
6
TYPICAL PERFORMANCE CURVES: VS = +5V
At TA = 25C, G = +2, RF = 750, and RL = 150 to VS/2, unless otherwise noted (see Figure 1).
(CONT)
2nd HARMONIC DISTORTION vs FREQUENCY -40 -40 -45 -50 -55 -60 -65 -70 -75 -80 -85 -90 1 Frequency (MHz) 10 20 G = +10 G = +5 G = +2 VO = 2Vp-p RL = 100 -45
3rd HARMONIC DISTORTION vs FREQUENCY VO = 2Vp-p RL = 100
2nd Harmonic Distortion (dBc)
3rd Harmonic Distortion (dBc)
-50 -55 -60 -65 -70 -75 -80 -85 -90 1 Frequency (MHz) 10 20 G = +10 G = +2 G = +5
HARMONIC DISTORTION vs LOAD RESISTANCE -40
3rd-Order Spurious Level (dBc)
-40
TWO-TONE, 3rd-ORDER INTERMODULATION SPURIOUS -45 -50 -55 -60 -65 -70 -75 -80 -85 -90 -16 -14 -12 -10 -8 fO = 5MHz Load Power at Matched 50 Load -6 -4 -2 0 fO = 20MHz fO = 10MHz
-45
Harmonic Distortion (dBc)
-50 -55 -60 -65 -70 -75 -80 -85 -90 100
VO = 2Vp-p fO = 5MHz 3rd Harmonic Distortion
2nd Harmonic Distortion 200 RL () 300 400 500
Single-Tone Load Power (dBm)
CMRR AND PSRR vs FREQUENCY 80
Rejection Ratio, Input Referred (dB)
INPUT NOISE DENSITY vs FREQUENCY 100
75 70 65 60 55 50 45 40 35 30 100 1k
CMRR
Voltage Noise (nV/Hz) Current Noise (pA/Hz)
PSRR
10 Voltage Noise, eni = 5.6nV/Hz
Current Noise, ini = 2.8pA/Hz 1 10k 100k 1M 10M 100 1k 10k 100k 1M 10M Frequency (Hz) Frequency (Hz)
(R)
7
OPA634, OPA635
TYPICAL PERFORMANCE CURVES: VS = +5V
At TA = 25C, G = +2, RF = 750, and RL = 150 to VS/2, unless otherwise noted (see Figure 1).
(CONT)
1000
RS vs CAPACITIVE LOAD 2 1 0
Normalized Gain (dB)
FREQUENCY RESPONSE vs CAPACITIVE LOAD VO = 0.2Vp-p CL = 1000pF CL = 10pF
100
RS ()
-1 -2 -3 -4 -5 -6 -7
OPA63x CL 1k +VS/2 RS VO
CL = 100pF
10
1 1 10 100 1000 Capacitive Load (pF)
-8 1 10 Frequency (MHz) 100 300
OPEN-LOOP GAIN AND PHASE 100 90 80 70 60 50 40 30 20 10 0 -10 -20 0 -30 -60 -90 -120 -150 -180 -210 -240 -270 -300 -330 -360 1G
CLOSED-LOOP OUTPUT IMPEDANCE vs FREQUENCY 100 G = +1 RF = 25
Open-Loop Phase Open-Loop Gain
Output Impedance ()
Open-Loop Gain (dB)
Open-Loop Phase ()
10
1
0.1 1k 10k 100k 1M 10M 100M Frequency (Hz)
1k
10k
100k
1M
10M
100M
Frequency (Hz)
INPUT DC ERRORS vs TEMPERATURE 5.0 4.5 Input Offset Voltage 50 45 16 14
Power Supply Current (mA)
SUPPLY AND OUTPUT CURRENT vs TEMPERATURE 160 Sinking Output Current Quiescent Supply Current 10 8 6 4 2 0 -40 -20 0 20 40 60 80 100 Temperature (C) 100 80 60 40 20 0
Output Current (mA)
Input Offset Voltage (mV)
Input Bias Current (A)
4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 -40 -20 0
40 35 30
10X Input Offset Current (A)
140 120
12 Sourcing Output Current
Input Bias Current
25 20 15
10X Input Offset Current
10 5 0
20
40
60
80
100
Temperature (C)
(R)
OPA634, OPA635
8
TYPICAL PERFORMANCE CURVES: VS = +3V
At TA = 25C, G = +2, RF = 750, and RL = 150 to VS/2, unless otherwise noted (see Figure 2).
SMALL-SIGNAL FREQUENCY RESPONSE 6 VO = 0.2Vp-p 3 G = +2 9 6 G = +5 12
LARGE-SIGNAL FREQUENCY RESPONSE VO = 0.2Vp-p
Normalized Gain (dB)
0
Gain (dB)
-3 -6 -9 -12 -15 -18 1 10 Frequency (MHz) 100 300 G = +10
3 0 -3 -6 -9 -12 1 10 Frequency (MHz) 100 300 VO = 1Vp-p VO = 2Vp-p
2nd HARMONIC DISTORTION vs FREQUENCY -40 -45 -40 VO = 1Vp-p RL = 100 -45
3rd HARMONIC DISTORTION vs FREQUENCY VO = 1Vp-p RL = 100
2nd Harmonic Distortion (dBc)
-50 -55 -60 -65 -70 -75 -80 -85 -90 1
3rd Harmonic Distortion (dBc)
-50 -55 -60 -65 -70 -75 -80 -85 -90
G = +2 G = +5 G = +10
G = +2 G = +5 G = +10 10 Frequency (MHz) 20
1 Frequency (MHz)
10
20
HARMONIC DISTORTION vs LOAD RESISTANCE -40 -40 -45
Harmonic Distortion (dBc)
TWO-TONE, 3rd-ORDER INTERMODULATION SPURIOUS -45 -50 -55 -60 -65 -70 -75 -80 -85 -90 -16 fO = 5MHz -14 -12 -10 Load Power at Matched 50 Load -8 -6 -4 fO = 10MHz fO = 20MHz
-50 -55 -60 -65 -70 -75 -80 -85 -90 100
3rd Harmonic Distortion
2nd Harmonic Distortion 200 RL () 300 400 500
3rd-Order Spurious Level (dBc)
VO = 1Vp-p fO = 5MHz
Single-Tone Load Power (dBm)
(R)
9
OPA634, OPA635
TYPICAL PERFORMANCE CURVES: VS = +3V
At TA = 25C, G = +2, RF = 750, and RL = 150 to VS/2, unless otherwise noted (see Figure 2).
(CONT)
1000
RS vs CAPACITIVE LOAD
FREQUENCY RESPONSE vs CAPACITIVE LOAD 2 1 0
Normalized Gain (dB)
VO = 0.2Vp-p
CL = 1000pF
CL = 10pF
100
RS ()
-1 -2 -3 -4 -5 -6 -7
OPA63x CL 1k +VS/2 RS VO
CL = 100pF
10
1 1 10 100 1000 Capacitive Load (pF)
-8 1 10 Frequency (MHz) 100 300
OUTPUT SWING vs LOAD RESISTANCE 3.0 2.9 Maximum VO 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 Minimum VO 0.2 0.1 50 100 RL () 0.0 1000
Maximum Output Voltage (V)
2.8 2.7 2.6 2.5 2.4 2.3 2.2 2.1 2.0
(R)
OPA634, OPA635
10
Minimum Output Voltage (V)
APPLICATIONS INFORMATION
WIDEBAND VOLTAGE FEEDBACK OPERATION The OPA634 and OPA635 are unity-gain stable, very high speed voltage feedback op amps designed for single supply operation (+3V to +5V). The input stage supports input voltages below ground, and within 1.2V of the positive supply. The complementary common-emitter output stage provides an output swing to within 30mV of ground and 140mV of the positive supply. They are compensated to provide stable operation with a wide range of resistive loads. The OPA635's internal disable circuitry is designed to minimize supply current when disabled. Figure 1 shows the AC-coupled, gain of +2 configuration used for the +5V Specifications and Typical Performance Curves. For test purposes, the input impedance is set to 50 with a resistor to ground. Voltage swings reported in the Specifications are taken directly at the input and output pins. For the circuit of Figure 1, the total effective load on the output at high frequencies is 150 || 1500. The disable pin needs to be driven by a low impedance source, such as a CMOS inverter. The 1.50k resistors at the non-inverting input provide the common-mode bias voltage. Their parallel combination equals the DC resistance at the inverting input, minimizing the DC offset.
+VS = 3V 6.8F + 2.26k 374 VIN 57.6 DIS (OPA635 only) 0.1F +
OPA63x
RL 150
VOUT
562
750
+VS 2
FIGURE 2. DC-Coupled Signal--Resistive Load to Supply Midpoint. SINGLE SUPPLY ADC CONVERTER INTERFACE The front page shows a DC-coupled, single supply ADC driver circuit. Many systems are now requiring +3V supply capability of both the ADC and its driver. The OPA635 provides excellent performance in this demanding application. Its large input and output voltage ranges, and low distortion, support converters such as the ADS900 shown in this figure. The input level-shifting circuitry was designed so that VIN can be between 0V and 0.5V, while delivering an output voltage of 1V to 2V for the ADS900. Both the OPA635 and ADS900 have power reduction pins with the same polarity for those systems that need to conserve power. DC LEVEL SHIFTING
+VS = 5V 6.8F + 1.50k 0.1F VIN 53.6 1.50k DIS (OPA635 only) 0.1F +
OPA63x
RL 150
VOUT
0.1F
750
750
+VS 2
FIGURE 1. AC-Coupled Signal--Resistive Load to Supply Midpoint. Figure 2 shows the DC-coupled, gain of +2 configuration used for the +3V Specifications and Typical Performance Curves. For test purposes, the input impedance is set to 50 with a resistor to ground. Though not strictly a "rail-to-rail" design, these parts come very close, while maintaining excellent performance. They will deliver 2.8Vp-p on a single +3V supply with 110MHz bandwidth. The 374 and 2.26k resistors at the input level-shift VIN so that VOUT is within the allowed output voltage range when VIN = 0. See the Typical Performance Curves for information on driving capacitive loads.
Figure 3 shows a DC-coupled non-inverting amplifier that level-shifts the input up to accommodate the desired output voltage range. Given the desired signal gain (G), and the amount VOUT needs to be shifted up (VOUT) when VIN is at the center of its range, the following equations give the resistor values that produce the best DC offset. NG = G + VOUT/VS R1 = R4/G R2 = R4/(NG - G) R3 = R4/(NG -1) where: NG = 1 + R4/R3 VOUT = (G)VIN + (NG - G)VS Make sure that VIN and VOUT stay within the specified input and output voltage ranges.
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+VS R2 R1 VIN
A unity gain buffer can be designed by selecting RT = RF = 20.0 and RC = 40.2 (do not use RG ). This gives a Noise Gain of 2, so its response will be similar to the Characteristics Plots with G = +2. Decreasing RC to 20.0 will increase the Noise Gain to 3, which typically gives a flat frequency response, but with less bandwidth.
VOUT
OPA63x
The circuit in Figure 1 can be redesigned to have less peaking by increasing the noise gain to 3. This is accomplished by adding RC = 2.55k between the op amps inputs.
R3
R4
DESIGN-IN TOOLS
DEMONSTRATION BOARDS Two PC boards are available to assist in the initial evaluation of circuit performance using the OPA634 and OPA635 in their three package styles. These are available free as an unpopulated PC board delivered with descriptive documentation. The summary information for these boards is shown below:
BOARD PART NUMBER DEM-OPA68xU DEM-OPA6xxN LITERATURE REQUEST NUMBER MKT-351 MKT-348
FIGURE 3. DC Level-Shifting Circuit. The front page circuit is a good example of this type of application. It was designed to take VIN between 0V and 0.5V, and produce VOUT between 1V and 2V, when using a +3V supply. This means G = 2.00, and VOUT = 1.50V - G * 0.25V = 1.00V. Plugging into the above equations gives: NG = 2.33, R1 = 375, R2 = 2.25k, and R3 = 563. The resistors were changed to the nearest standard values. NON-INVERTING AMPLIFIER WITH REDUCED PEAKING Figure 4 shows a non-inverting amplifier that reduces peaking at low gains. The resistor RC compensates the OPA634 or OPA635 to have higher Noise Gain (NG), which reduces the AC response peaking (typically 5dB at G = +1 without RC) without changing the DC gain. VIN needs to be a low impedance source, such as an op amp. The resistor values are low to reduce noise. Using both RT and RF helps minimize the impact of parasitic impedances.
PRODUCT OPA63xU OPA63xN
PACKAGE 8-Pin SO-8 5-Pin SOT23-5 6-Pin SOT23-6
Contact the Burr-Brown Applications support line to request any of these boards.
OPERATING SUGGESTIONS
OPTIMIZING RESISTOR VALUES Since the OPA634 and OPA635 are voltage feedback op amps, a wide range of resistor values may be used for the feedback and gain setting resistors. The primary limits on these values are set by dynamic range (noise and distortion) and parasitic capacitance considerations. For a non-inverting unity gain follower application, the feedback connection should be made with a 25 resistor, not a direct short (see Figure 4). This will isolate the inverting input capacitance from the output pin and improve the frequency response flatness. Usually, for G > 1 application, the feedback resistor value should be between 200 and 1.5k. Below 200, the feedback network will present additional output loading which can degrade the harmonic distortion performance. Above 1.5k, the typical parasitic capacitance (approximately 0.2pF) across the feedback resistor may cause unintentional band-limiting in the amplifier response. A good rule of thumb is to target the parallel combination of RF and RG (Figure 1) to be less than approximately 400. The combined impedance RF || RG interacts with the inverting input capacitance, placing an additional pole in the feedback network and thus, a zero in the forward response. Assuming a 3pF total parasitic on the inverting node, holding RF || RG <400 will keep this pole above 130MHz. By
RT VIN RC
OPA63x
VOUT
RG
RF
FIGURE 4. Compensated Non-Inverting Amplifier. The Noise Gain can be calculated as follows:
G1 = 1 + G2 = 1 +
RF RG R T + R F / G1 RC
NG = G1G 2
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itself, this constraint implies that the feedback resistor RF can increase to several k at high gains. This is acceptable as long as the pole formed by RF and any parasitic capacitance appearing in parallel is kept out of the frequency range of interest. BANDWIDTH VS GAIN: NON-INVERTING OPERATION Voltage feedback op amps exhibit decreasing closed-loop bandwidth as the signal gain is increased. In theory, this relationship is described by the Gain Bandwidth Product (GBP) shown in the specifications. Ideally, dividing GBP by the non-inverting signal gain (also called the Noise Gain, or NG) will predict the closed-loop bandwidth. In practice, this only holds true when the phase margin approaches 90, as it does in high gain configurations. At low gains (increased feedback factors), most amplifiers will exhibit a more complex response with lower phase margin. The OPA634 and OPA635 are compensated to give a slightly peaked response in a non-inverting gain of 2 (Figure 1). This results in a typical gain of +2 bandwidth of 150MHz, far exceeding that predicted by dividing the 140MHz GBP by 2. Increasing the gain will cause the phase margin to approach 90 and the bandwidth to more closely approach the predicted value of (GBP/NG). At a gain of +10, the 16MHz bandwidth shown in the Typical Specifications is close to that predicted using the simple formula and the typical GBP. The OPA634 and OPA635 exhibit minimal bandwidth reduction going to +3V single supply operation as compared with +5V supply. This is because the internal bias control circuitry retains nearly constant quiescent current as the total supply voltage between the supply pins is changed. INVERTING AMPLIFIER OPERATION Since the OPA634 and OPA635 are general purpose, wideband voltage feedback op amps, all of the familiar op amp application circuits are available to the designer. Figure 5 shows a typical inverting configuration where the I/O impedances and signal gain from Figure 1 are retained in an inverting circuit configuration. Inverting operation is one of the more common requirements and offers several performance benefits. The inverting configuration shows improved slew rate and distortion. It also allows the input to be biased at VS/2 without any headroom issues. The output voltage can be independently moved to be within the output voltage range with coupling capacitors, or bias adjustment resistors. In the inverting configuration, three key design consideration must be noted. The first is that the gain resistor (RG) becomes part of the signal channel input impedance. If input impedance matching is desired (which is beneficial whenever the signal is coupled through a cable, twisted pair, long PC board trace or other transmission line conductor), RG may be set equal to the required termination value and RF adjusted to give the desired gain. This is the simplest approach and results in optimum bandwidth and noise performance. However, at low inverting gains, the resultant feedback resistor value can present a significant load to the amplifier output. For an inverting gain of 2, setting RG to 13
+5V
+ 0.1F 6.8F
2RT 523
DIS
RO 50 50 Load
0.1F
2RT 523
OPA63x
50 Source
RG 374
RF 750
RM 57.6
FIGURE 5. Gain of -2 Example Circuit. 50 for input matching eliminates the need for RM but requires a 100 feedback resistor. This has the interesting advantage that the noise gain becomes equal to 2 for a 50 source impedance--the same as the non-inverting circuits considered above. However, the amplifier output will now see the 100 feedback resistor in parallel with the external load. In general, the feedback resistor should be limited to the 200 to 1.5k range. In this case, it is preferable to increase both the RF and RG values as shown in Figure 5, and then achieve the input matching impedance with a third resistor (RM) to ground. The total input impedance becomes the parallel combination of RG and RM. The second major consideration, touched on in the previous paragraph, is that the signal source impedance becomes part of the noise gain equation and hence influences the bandwidth. For the example in Figure 5, the RM value combines in parallel with the external 50 source impedance, yielding an effective driving impedance of 50 || 576 = 26.8. This impedance is added in series with RG for calculating the noise gain. The resultant is 2.87 for Figure 5, as opposed to only 2 if RM could be eliminated as discussed above. The bandwidth will therefore be lower for the gain of -2 circuit of Figure 5 (NG = +3) than for the gain of +2 circuit of Figure 1. The third important consideration in inverting amplifier design is setting the bias current cancellation resistors on the non-inverting input (a parallel combination of RT = 263). If this resistor is set equal to the total DC resistance looking out of the inverting node, the output DC error, due to the input bias currents, will be reduced to (Input Offset Current) * RF. If the 50 source impedance is DC-coupled in Figure 5, the total resistance to ground between the inverting input and the source will be 401. Combining this in parallel with the feedback resistor gives the RT = 263 used in this
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example. To reduce the additional high frequency noise introduced by this resistor, and power supply feedthrough, RT is bypassed with a capacitor. As long as RT < 400, its noise contribution will be minimal. As a minimum, the OPA634 and OPA635 require an RT value of 50 to damp out parasitic-induced peaking--a direct short to ground on the non-inverting input runs the risk of a very high frequency instability in the input stage. OUTPUT CURRENT AND VOLTAGE The OPA634 and OPA635 provide outstanding output voltage capability. Under no-load conditions at +25C, the output voltage typically swings closer than 140mV to either supply rail; the guaranteed swing limit is within 450mV of either rail (VS = +5V). The minimum specified output voltage and current specifications over temperature are set by worst-case simulations at the cold temperature extreme. Only at cold start-up will the output current and voltage decrease to the numbers shown in the guaranteed tables. As the output transistors deliver power, their junction temperatures will increase, decreasing their VBE's (increasing the available output voltage swing) and increasing their current gains (increasing the available output current). In steady-state operation, the available output voltage and current will always be greater than that shown in the over-temperature specifications since the output stage junction temperatures will be higher than the minimum specified operating ambient. To maintain maximum output stage linearity, no output short-circuit protection is provided. This will not normally be a problem since most applications include a series matching resistor at the output that will limit the internal power dissipation if the output side of this resistor is shorted to ground. However, shorting the output pin directly to the adjacent positive power supply pin (8-pin packages) will, in most cases, destroy the amplifier. If additional short-circuit protection is required, consider a small series resistor in the power supply leads. This will, under heavy output loads, reduce the available output voltage swing. DRIVING CAPACITIVE LOADS One of the most demanding and yet very common load conditions for an op amp is capacitive loading. Often, the capacitive load is the input of an A/D converter--including additional external capacitance which may be recommended to improve A/D linearity. A high speed, high open-loop gain amplifier like the OPA634 and OPA635 can be very susceptible to decreased stability and closed-loop response peaking when a capacitive load is placed directly on the output pin. When the primary considerations are frequency response flatness, pulse response fidelity and/or distortion, the simplest and most effective solution is to isolate the capacitive load from the feedback loop by inserting a series isolation resistor between the amplifier output and the capacitive load.
The Typical Performance Curves show the recommended RS versus capacitive load and the resulting frequency response at the load. Parasitic capacitive loads greater than 2pF can begin to degrade the performance of the OPA634 and OPA635. Long PC board traces, unmatched cables, and connections to multiple devices can easily exceed this value. Always consider this effect carefully, and add the recommended series resistor as close as possible to the output pin (see Board Layout Guidelines). The criterion for setting this RS resistor is a maximum bandwidth, flat frequency response at the load. For a gain of +2, the frequency response at the output pin is already slightly peaked without the capacitive load, requiring relatively high values of RS to flatten the response at the load. Increasing the noise gain will also reduce the peaking (see Figure 4). DISTORTION PERFORMANCE The OPA634 and OPA635 provide good distortion performance into a 150 load. Relative to alternative solutions, it provides exceptional performance into lighter loads and/or operating on a single +3V supply. Generally, until the fundamental signal reaches very high frequency or power levels, the 2nd harmonic will dominate the distortion with a negligible 3rd harmonic component. Focusing then on the 2nd harmonic, increasing the load impedance improves distortion directly. Remember that the total load includes the feedback network; in the non-inverting configuration (Figure 1) this is sum of RF + RG, while in the inverting configuration, it is just RF. NOISE PERFORMANCE High slew rate, unity gain stable, voltage feedback op amps usually achieve their slew rate at the expense of a higher input noise voltage. The 5.6nV/Hz input voltage noise for the OPA634 and OPA635 is, however, much lower than comparable amplifiers. The input-referred voltage noise, and the two input-referred current noise terms (2.8pA/Hz), combine to give low output noise under a wide variety of operating conditions. Figure 6 shows the op amp noise analysis model with all the noise terms included. In this
ENI
RS
OPA63x IBN
EO
ERS 4kTRS RF 4kTRF 4kT = 1.6E -20J at 290K
4kT RG
RG
IBI
FIGURE 6. Noise Analysis Model.
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model, all noise terms are taken to be noise voltage or current density terms in either nV/Hz or pA/Hz. The total output spot noise voltage can be computed as the square root of the sum of all squared output noise voltage contributors. Equation 1 shows the general form for the output noise voltage using the terms shown in Figure 6. Equation 1:
EO =
(E
NI
2
+ ( I BN R S ) + 4kTR S NG 2 + ( I BI R F ) + 4kTR F NG
2 2
)
Dividing this expression by the noise gain (NG = (1+RF /RG)) will give the equivalent input-referred spot noise voltage at the non-inverting input, as shown in Equation 2. Equation 2:
I R 2 4kTR F 2 E N = E NI 2 + ( I BN R S ) + 4kTR S + BI F + NG NG
current through the feedback resistor. In selecting an offset trim method, one key consideration is the impact on the desired signal path frequency response. If the signal path is intended to be non-inverting, the offset control is best applied as an inverting summing signal to avoid interaction with the signal source. If the signal path is intended to be inverting, applying the offset control to the non-inverting input may be considered. Bring the DC offsetting current into the inverting input node through resistor values that are much larger than the signal path resistors. This will insure that the adjustment circuit has minimal effect on the loop gain and hence the frequency response. DISABLE OPERATION The OPA635 provides an optional disable feature that may be used either to reduce system power or to implement a simple channel multiplexing operation. To disable, the control pin must be asserted HIGH. Figure 7 shows a simplified internal circuit for the disable control feature. In normal operation, base current to Q1 is provided through the 50k resistor.
Evaluating these two equations for the circuit and component values shown in Figure 1 will give a total output spot noise voltage of 12.5nV/Hz and a total equivalent input spot noise voltage of 6.3nV/Hz. This is including the noise added by the resistors. This total input-referred spot noise voltage is not much higher than the 5.6nV/Hz specification for the op amp voltage noise alone. This will be the case as long as the impedances appearing at each op amp input are limited to the previously recommend maximum value of 400, and the input attenuation is low. Since the resistorinduced noise is relatively negligible, additional capacitive decoupling across the bias current cancellation resistor (RT) for the inverting op amp configuration of Figure 5 is not required. DC ACCURACY AND OFFSET CONTROL The balanced input stage of a wideband voltage feedback op amp allows good output DC accuracy in a wide variety of applications. The power supply current trim for the OPA634 and OPA635 gives even tighter control than comparable products. Although the high speed input stage does require relatively high input bias current (typically 25A out of each input terminal), the close matching between them may be used to reduce the output DC error caused by this current. This is done by matching the DC source resistances appearing at the two inputs. Evaluating the configuration of Figure 1 (which has matched DC input resistances), using worstcase +25C input offset voltage and current specifications, gives a worst-case output offset voltage equal to: (NG = noninverting signal gain at DC) (NG * VOS(MAX)) (RF * IOS(MAX)) = (1 * 7.0mV) (750 * 2.0A) = 8.5mV A fine scale output offset null, or DC operating point adjustment, is often required. Numerous techniques are available for introducing DC offset control into an op amp circuit. Most of these techniques are based on adding a DC
+VS
Q1
50k
IS Control
VDIS
FIGURE 7. Simplified Disable Control Circuit (OPA635). One key parameter in disable operation is the output glitch when switching in and out of the disabled mode. The transition edge rate (dv/dt) of the DIS control line will influence this glitch. Adding a simple RC filter into the DIS pin from a higher speed logic line will reduce the glitch. If extremely fast transition logic is used, a 1k series resistor will provide adequate bandlimiting using just the parasitic input capacitance on the DIS pin while still ensuring adequate logic level swing. THERMAL ANALYSIS Maximum desired junction temperature will set the maximum allowed internal power dissipation as described below. In no case should the maximum junction temperature be allowed to exceed 175C.
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Operating junction temperature (TJ) is given by TA + PD*JA. The total internal power dissipation (PD) is the sum of quiescent power (PDQ) and additional power dissipated in the output stage (PDL) to deliver load power. Quiescent power is simply the specified no-load supply current times the total supply voltage across the part. PDL will depend on the required output signal and load but would, for resistive load connected to mid-supply (VS/2), be at a maximum when the output is fixed at a voltage equal to VS/4 or 3VS/4. Under this condition, PDL = VS2/(16 * RL), where RL includes feedback network loading. Note that it is the power in the output stage and not into the load that determines internal power dissipation. As a worst-case example, compute the maximum TJ using an OPA635 (SOT23-6 package) in the circuit of Figure 1 operating at the maximum specified ambient temperature of +85C and driving a 150 load at mid-supply. PD = 10V * 13.25mA + 52/(16 * (150 || 1500)) = 144mW Maximum TJ = +85C + (0.14W * 150C/W) = 107C. Although this is still well below the specified maximum junction temperature, system reliability considerations may require lower guaranteed junction temperatures. The highest possible internal dissipation will occur if the load requires current to be forced into the output at high output voltages or sourced from the output at low output voltages. This puts a high current through a large internal voltage drop in the output transistors.
placed somewhat farther from the device and may be shared among several devices in the same area of the PC board. c) Careful selection and placement of external components will preserve the high frequency performance. Resistors should be a very low reactance type. Surfacemount resistors work best and allow a tighter overall layout. Metal film or carbon composition axially-leaded resistors can also provide good high frequency performance. Again, keep their leads and PC board traces as short as possible. Never use wirewound type resistors in a high frequency application. Since the output pin and inverting input pin are the most sensitive to parasitic capacitance, always position the feedback and series output resistor, if any, as close as possible to the output pin. Other network components, such as non-inverting input termination resistors, should also be placed close to the package. Where double-side component mounting is allowed, place the feedback resistor directly under the package on the other side of the board between the output and inverting input pins. Even with a low parasitic capacitance shunting the external resistors, excessively high resistor values can create significant time constants that can degrade performance. Good axial metal film or surfacemount resistors have approximately 0.2pF in shunt with the resistor. For resistor values >1.5k, this parasitic capacitance can add a pole and/or zero below 500MHz that can effect circuit operation. Keep resistor values as low as possible consistent with load driving considerations. The 750 feedback used in the typical performance specifications is a good starting point for design. See Figure 4 for the unity gain follower application. d) Connections to other wideband devices on the board may be made with short direct traces or through on-board transmission lines. For short connections, consider the trace and the input to the next device as a lumped capacitive load. Relatively wide traces (50mils to 100mils) should be used, preferably with ground and power planes opened up around them. Estimate the total capacitive load and set RS from the plot of Recommended RS vs Capacitive Load. Low parasitic capacitive loads (<5pF) may not need an RS since the OPA634 and OPA635 are nominally compensated to operate with a 2pF parasitic load. Higher parasitic capacitive loads without an RS are allowed as the signal gain increases (increasing the unloaded phase margin) If a long trace is required, and the 6dB signal loss intrinsic to a doubly terminated transmission line is acceptable, implement a matched impedance transmission line using microstrip or stripline techniques (consult an ECL design handbook for microstrip and stripline layout techniques). A 50 environment is normally not necessary on board, and in fact, a higher impedance environment will improve distortion as shown in the distortion versus load plots. With a characteristic board trace impedance defined (based on board material and trace dimensions), a matching series resistor into the trace from the output of the OPA634 and OPA635 is used as well as a terminating shunt resistor at the input of the destination device. Remember also that the terminating impedance will be the parallel combination of the shunt resistor and the input impedance of the destination device;
BOARD LAYOUT GUIDELINES
Achieving optimum performance with a high frequency amplifier like the OPA634 and OPA635 requires careful attention to board layout parasitics and external component types. Recommendations that will optimize performance include: a) Minimize parasitic capacitance to any AC ground for all of the signal I/O pins. Parasitic capacitance on the output and inverting input pins can cause instability: on the noninverting input, it can react with the source impedance to cause unintentional bandlimiting. To reduce unwanted capacitance, a window around the signal I/O pins should be opened in all of the ground and power planes around those pins. Otherwise, ground and power planes should be unbroken elsewhere on the board. b) Minimize the distance (<0.25") from the power supply pins to high frequency 0.1F decoupling capacitors. At the device pins, the ground and power plane layout should not be in close proximity to the signal I/O pins. Avoid narrow power and ground traces to minimize inductance between the pins and the decoupling capacitors. The power supply connections should always be decoupled with these capacitors. An optional supply decoupling capacitor (0.1F) across the two power supplies (for bipolar operation) will improve 2nd harmonic distortion performance. Larger (2.2F to 6.8F) decoupling capacitors, effective at lower frequency, should also be used on the main supply pins. These may be
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this total effective impedance should be set to match the trace impedance. If the 6dB attenuation of a doubly terminated transmission line is unacceptable, a long trace can be series-terminated at the source end only. Treat the trace as a capacitive load in this case and set the series resistor value as shown in the plot of Recommended RS vs Capacitive Load. This will not preserve signal integrity as well as a doubly terminated line. If the input impedance of the destination device is low, there will be some signal attenuation due to the voltage divider formed by the series output into the terminating impedance. e) Socketing a high speed part is not recommended. The additional lead length and pin-to-pin capacitance introduced by the socket can create an extremely troublesome parasitic network which can make it almost impossible to achieve a smooth, stable frequency response. Best results are obtained by soldering the OPA634 and OPA635 onto the board. If socketing for the DIP package is desired, high frequency flush mount pins (e.g., McKenzie Technology #710C) can give good results.
INPUT AND ESD PROTECTION The OPA634 and OPA635 are is built using a very high speed complementary bipolar process. The internal junction breakdown voltages are relatively low for these very small geometry devices. These breakdowns are reflected in the Absolute Maximum Ratings table. All device pins are protected with internal ESD protection diodes to the power supplies as shown in Figure 8. These diodes provide moderate protection to input overdrive voltages above the supplies as well. The protection diodes can typically support 30mA continuous current. Where higher currents are possible (e.g., in systems with 15V supply parts driving into the OPA634 and OPA635), current-limiting series resistors should be added into the two inputs. Keep these resistor values as low as possible since high values degrade both noise performance and frequency response.
+V CC
External Pin
Internal Circuitry
-V CC
FIGURE 8. Internal ESD Protection.
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