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OPA684

Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of

Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.

SBOS219D – OCTOBER 2001 – REVISED JUNE 2009

Low-Power, Current Feedback

OPERATIONAL AMPLIFIER With Disable

FEATURES

● MINIMAL BANDWIDTH CHANGE VERSUS GAIN

● > 120MHz BANDWIDTH TO GAIN > +10

● LOW DISTORTION: < –78dBc at 5MHz

● HIGH OUTPUT CURRENT: 120mA

● SINGLE +5V TO +12V SUPPLY OPERATION

● DUAL ±2.5 TO ±6.0V SUPPLY OPERATION

● LOW SUPPLY CURRENT: 1.7mA

● LOW SHUTDOWN CURRENT: 100µA

V+

V–

ERR

(S)

ERR

Low-Power Amplifier

DESCRIPTION

The OPA684 provides a new level of performance in low-power,

wideband, current-feedback (CFB) amplifiers. This CFB

plus

ampli-

fier is the first to use an internally closed-loop input buffer stage that

enhances performance significantly over earlier low-power CFB

amplifiers. While retaining the benefits of very low power operation,

this new architecture provides many of the benefits of a more ideal

CFB amplifier. The closed-loop input stage buffer gives a very low

and linearized impedance path at the inverting input to sense the

feedback error current. This improved inverting input impedance

retains exceptional bandwidth to much higher gains and improves

harmonic distortion over earlier solutions limited by inverting input

linearity. Beyond simple high-gain applications, the OPA684 CFB

plus

amplifier permits the gain setting element to be set with consider-

able freedom from amplifier bandwidth interaction. This allows

frequency response peaking elements to be added, multiple input

inverting summing circuits to have greater bandwidth, and low-

APPLICATIONS

● LOW-POWER BROADCAST VIDEO DRIVERS

● EQUALIZING FILTERS

● SAW FILTER HIGH GAIN POST AMPLIFIERS

● MULTICHANNEL SUMMING AMPLIFIERS

● PROFESSIONAL CAMERAS

● ADC INPUT DRIVERS

power line drivers to meet the demanding requirements of studio

cameras and broadcast video.

The output capability of the OPA684 also sets a new mark in

performance for low-power current feedback amplifiers. Delivering

a full ±4V

swing on ±5V supplies, the OPA684 also has the

output current to support this swing into a 100Ω load. This minimal

output headroom requirement is complemented by a similar 1.2V

input stage headroom giving exceptional capability for single +5V

operation.

The OPA684’s low 1.7mA supply current is precisely trimmed at

25°C. This trim, along with low shift over temperature and supply

voltage, gives a very robust design over a wide range of operating

conditions. System power may be further reduced by using the

optional disable control pin. Leaving this disable pin open, or holding

it HIGH, gives normal operation. If pulled LOW, the OPA684 supply

current drops to less than 100µA while the I/O pins go to a high

impedance state.

–3

–6

–9

–12

–15

–18

–21

Normalized Gain

= 1kΩ

G = 100

G = 50

G = 20

G = 10

G = 5

G = 2

10 100 200

BW (MHz) vs GAIN

PRODUCTION DATA information is current as of publication date.

Products conform to specifications per the terms of Texas Instruments

standard warranty. Production processing does not necessarily include

testing of all parameters.

Patent Pending

All trademarks are the property of their respective owners.

www.ti.com

Summary of content (31 pages)

PAGE 1
OPA684 OPA 684 OPA68 4 SBOS219D – OCTOBER 2001 – REVISED JUNE 2009 Low-Power, Current Feedback OPERATIONAL AMPLIFIER With Disable FEATURES APPLICATIONS ● ● ● ● ● ● ● ● ● ● ● ● ● ● MINIMAL BANDWIDTH CHANGE VERSUS GAIN > 120MHz BANDWIDTH TO GAIN > +10 LOW DISTORTION: < –78dBc at 5MHz HIGH OUTPUT CURRENT: 120mA SINGLE +5V TO +12V SUPPLY OPERATION DUAL ±2.5 TO ±6.0V SUPPLY OPERATION LOW SUPPLY CURRENT: 1.
PAGE 2
ELECTROSTATIC DISCHARGE SENSITIVITY ABSOLUTE MAXIMUM RATINGS(1) Power Supply ............................................................................... ±6.5VDC Internal Power Dissipation ................................. See Thermal Information Differential Input Voltage .................................................................. ±1.2V Input Voltage Range ............................................................................ ±VS Storage Temperature Range: ID, IDBV ........................
PAGE 3
ELECTRICAL CHARACTERISTICS: VS = ±5V RF = 1kΩ, RL = 100Ω, and G = +2, (See Figure 1 for AC performance only), unless otherwise noted. OPA684ID, IDBV TYP PARAMETER AC PERFORMANCE (See Figure 1) Small-Signal Bandwidth (VO = 0.5VPP) Bandwidth for 0.
PAGE 4
ELECTRICAL CHARACTERISTICS: VS = +5V RF = 1.3kΩ, RL = 100Ω, and G = +2, (See Figure 3 for AC performance only), unless otherwise noted. OPA684ID, IDBV TYP PARAMETER AC PERFORMANCE (See Figure 3) Small-Signal Bandwidth (VO = 0.5VPP) Bandwidth for 0.
PAGE 5
TYPICAL CHARACTERISTICS: VS = ±5V At TA = +25°C, G = +2, RF = 1kΩ, RL = 100Ω, unless otherwise noted. NONINVERTING SMALL-SIGNAL FREQUENCY RESPONSE VO = 0.5Vp-p RF = 1kΩ Normalized Gain (3dB/div) 3 INVERTING SMALL-SIGNAL FREQUENCY RESPONSE +3 G = 50 G = 100 G=1 G=2 0 Normalized Gain (3dB/div) 6 –3 –6 –9 G=5 –12 VO = 0.
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TYPICAL CHARACTERISTICS: VS = ±5V (Cont.) At TA = +25°C, G = +2, RF = 1kΩ, RL = 100Ω, unless otherwise noted. HARMONIC DISTORTION vs LOAD RESISTANCE HARMONIC DISTORTION vs FREQUENCY –50 –50 VO = 2Vp-p f = 5MHz G = +2 –60 VO = 2Vp-p RL = 100Ω Harmonic Distortion (dBc) Harmonic Distortion (dBc) –55 –65 2nd-Harmonic –70 –75 3rd-Harmonic –80 –60 2nd-Harmonic –70 3rd-Harmonic –80 –85 See Figure 1 –90 See Figure 1 –90 100 0.
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TYPICAL CHARACTERISTICS: VS = ±5V (Cont.) At TA = +25°C, G = +2, RF = 1kΩ, RL = 100Ω, unless otherwise noted. 2-TONE, 3RD-ORDER INTERMODULATION DISTORTION INPUT VOLTAGE AND CURRENT NOISE DENSITY –50 100 20MHz 3rd-Order Spurious Level (dBc) Voltage Noise (nV/√Hz) Current Noise (pA/√Hz) Inverting Current Noise 17pA/√Hz Noninverting Current Noise 9.4pA/√Hz 10 Voltage Noise 3.
PAGE 8
TYPICAL CHARACTERISTICS: VS = ±5V (Cont.) At TA = +25°C, G = +2, RF = 1kΩ, RL = 100Ω, unless otherwise noted. OPEN-LOOP TRANSIMPEDANCE GAIN AND PHASE CMRR and PSRR vs FREQUENCY CMRR 60 50 +PSRR 40 –PSRR 30 20 10 0 102 103 104 105 106 Frequency (Hz) 107 120 0 20log (ZOL) 100 –30 80 –60 60 40 –120 20 –150 0 108 –180 102 103 0.07 2 dG 0.05 0Ω 3 VO (V) 108 109 = RL 50 Ω 1 0 –1 0.04 –2 0.03 dP –3 0.
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TYPICAL CHARACTERISTICS: VS = ±5V (Cont.) At TA = +25°C, G = +2, RF = 1kΩ, RL = 100Ω, unless otherwise noted. SETTLING TIME DISABLED SUPPLY CURRENT vs TEMPERATURE 0.05 120 Disabled Supply Current (µA) 2V Step See Figure 1 0.04 0.02 0.01 0 –0.01 –0.02 –0.03 110 100 90 80 70 –0.04 +VS Current –0.05 60 0 10 20 30 Time (ns) 40 50 60 –50 0 25 50 75 Ambient Temperature (°C) 125 INVERTING OVERDRIVE RECOVERY 8.0 8.0 3.2 6.4 6.4 6.4 2.4 4.8 4.8 4.8 1.6 3.2 0.8 1.
PAGE 10
TYPICAL CHARACTERISTICS: VS = +5V At TA = +25°C, VS = 5V, G = +2, RF = 1.3kΩ, RL = 100Ω, unless otherwise noted. NONINVERTING SMALL-SIGNAL FREQUENCY RESPONSE RF = 1.3kΩ Normalized Gain (3dB/div) 3 INVERTING SMALL-SIGNAL FREQUENCY RESPONSE +3 G = 50 RF = 1.
PAGE 11
TYPICAL CHARACTERISTICS: VS = +5V (Cont.) At TA = +25°C, VS = 5V, G = +2, RF = 1.3kΩ, RL = 100Ω, unless otherwise noted. HARMONIC DISTORTION vs FREQUENCY HARMONIC DISTORTION vs LOAD RESISTANCE –50 –50 Harmonic Distortion (dBc) Harmonic Distortion (dBc) VO = 2Vp-p RL = 100Ω VO = 2Vp-p f = 5MHz –55 –60 3rd-Harmonic –65 –70 –75 2nd-Harmonic –80 2nd-Harmonic –60 –70 3rd-Harmonic –80 –85 See Figure 3 100 0.
PAGE 12
APPLICATIONS INFORMATION LOW-POWER, CURRENT-FEEDBACK OPERATION The OPA684 gives a new level of performance in low-power, current-feedback op amps. Using a new input stage buffer architecture, the OPA684 CFBplus amplifier holds nearly constant AC performance over a wide gain range. This closed-loop internal buffer gives a very low and linearized impedance at the inverting node, isolating the amplifier’s AC performance from gain element variations.
PAGE 13
voltage bias. The input voltage can swing to within 1.25V of either supply pin, giving a 2.5VPP input signal range centered between the supply pins. The input impedance of Figure 3 is set to give a 50Ω input match. If the source does not require a 50Ω match, remove RM and drive directly into the blocking capacitor. The source will then see the 5kΩ load of the biasing network. The gain resistor (RG) is AC coupled, giving the circuit a DC gain of +1, which puts the non-inverting input DC bias voltage (2.
PAGE 14
INVERTING SUMMING APPLICATIONS SAW FILTER POST- AMPLIFIER The OPA684 provides one of the most robust summing operations available in a wideband op amp. Figure 6 shows a typical inverting summing application where, in this case, 4 sources are summed through 500Ω gain resistors while also including an 88.9Ω terminating impedance to present a 75Ω input impedance to each source. The gain for each channel is –2 to the output pin and –1 to the matched load.
PAGE 15
Figure 8 shows the small-signal frequency response for the amplifier portion of this circuit, from the non-inverting input to the output pin. This particular example is configured as a single-supply circuit that will operate over a supply range from +5V to +12V. Where higher frequencies or 3rd-order intercepts are required, consider the OPA685, a very high bandwidth (> 500MHz) current-feedback op amp.
PAGE 16
OPERATING SUGGESTIONS SETTING RESISTOR VALUES TO OPTIMIZE BANDWIDTH Any current-feedback op amp like the OPA684 can hold high bandwidth over signal-gain settings with the proper adjustment of the external resistor values. A low-power part like the OPA684 typically shows a larger change in bandwidth due to the significant contribution of the inverting input impedance to loop-gain changes as the signal gain is changed. Figure 10 shows a simplified analysis circuit for any current-feedback amplifier.
PAGE 17
detailed view of the OPA684’s output drive capabilities. Superimposing resistor load lines onto the plot shows the available output voltage and current for specific loads. BANDWIDTH AND RF OPTIMIZED vs GAIN 2000 200 Feedback Resistor (Ω) 1500 150 1250 RF Left Scale 1000 100 Bandwidth (MHz) Bandwidth Right Scale 1750 750 500 50 2 5 10 20 50 100 Voltage Gain (V/V) FIGURE 11. Bandwidth and RF Optimized vs Gain.
PAGE 18
The Typical Characteristics show the recommended RS vs CLOAD and the resulting frequency response at the load. To reduce the required value of RS, those curves show a slight increase in the feedback resistor value and an added load of 250Ω to ground. The 1kΩ resistor shown in parallel with the load capacitor is a measurement path and may be omitted. Parasitic capacitive loads greater than 5pF can begin to degrade the performance of the OPA684.
PAGE 19
The total output spot noise voltage can be computed as the square root of the sum of all squared output noise voltage contributors. Equation 3 shows the general form for the output noise voltage using the terms shown in Figure 13. (3) 2 2 EO =  ENI2 + (IBNR S ) + 4kTRS  GN2 + (IBIRF ) + 4kTRF GN Dividing this expression by the noise gain (GN = (1 + RF/RG)) will give the equivalent input referred spot noise voltage at the non-inverting input, as shown in Equation 4.
PAGE 20
The OPA684 provides very high power gain on low quiescent current levels. When disabled, internal high impedance nodes discharge slowly that, with the exceptional power gain provided, give a self-powering characteristic that leads to a slow turn-off characteristic. Typical turn-off times to rated 100µA disabled supply current are 4ms. Turn-on times are very fast—less than 40ns. b) Minimize the distance (< 0.25") from the power-supply pins to high-frequency 0.1µF decoupling capacitors.
PAGE 21
nominally compensated to operate with a 2pF parasitic load. 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).
PAGE 22
Revision History DATE 6/09 7/08 REVISION D C PAGE SECTION DESCRIPTION 2 Related Products 4 Electrical Characteristics Replaced OPA685 (obsolete) with OPA695 family. 8 Typical Characteristics Changed Open-Loop Transimpedance Gain and Phase plot to fix typo. 9 Typical Characteristics Changed Closed-Loop Output Impedance vs Frequency plot to fix typo. 2 Abs Max Ratings 3, 4 Electrical Characteristics Added missing value (0.006) to Closed-Loop Output Impedance parameter.
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PACKAGE OPTION ADDENDUM www.ti.
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PACKAGE OPTION ADDENDUM www.ti.com 11-Apr-2013 (4) Multiple Top-Side Markings will be inside parentheses. Only one Top-Side Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation of the previous line and the two combined represent the entire Top-Side Marking for that device. Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided.
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PACKAGE MATERIALS INFORMATION www.ti.com 26-Jan-2013 TAPE AND REEL INFORMATION *All dimensions are nominal Device Package Package Pins Type Drawing SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) OPA684IDBVR SOT-23 DBV 6 3000 180.0 OPA684IDBVT SOT-23 DBV 6 250 OPA684IDR SOIC D 8 2500 B0 (mm) K0 (mm) P1 (mm) 8.4 3.2 3.1 1.39 4.0 180.0 8.4 3.2 3.1 1.39 330.0 12.4 6.4 5.2 2.1 Pack Materials-Page 1 W Pin1 (mm) Quadrant 8.0 Q3 4.0 8.0 Q3 8.0 12.
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PACKAGE MATERIALS INFORMATION www.ti.com 26-Jan-2013 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) OPA684IDBVR SOT-23 DBV 6 3000 210.0 185.0 35.0 OPA684IDBVT SOT-23 DBV 6 250 210.0 185.0 35.0 OPA684IDR SOIC D 8 2500 367.0 367.0 35.
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