The OPA350 series of rail-to-rail CMOS operational amplifiers are optimized for low voltage, single-supply operation. Rail-to-rail input and output, low noise (5 nV/√Hz), and high speed operation (38 MHz, 22 V/μs) make the amplifiers ideal for driving sampling Analog-to-Digital (A/D) converters. They are also suited for cell phone PA control loops and video processing (75-Ω drive capability), as well as audio and general purpose applications. Single, dual, and quad versions have identical specifications for maximum design flexibility.
The OPA350 series operates on a single supply as low as 2.5 V, with an input common-mode voltage range that extends 300 mV below ground and 300 mV above the positive supply. Output voltage swing is to within 10 mV of the supply rails, with a 10-kΩ load. Dual and quad designs feature completely independent circuitry for lowest crosstalk and freedom from interaction.
The single (OPA350) and dual (OPA2350) come in the miniature MSOP-8 surface mount, SO-8 surface mount, and DIP-8 packages. The quad (OPA4350) packages are in the space-saving SSOP-16 surface mount and SO-14 surface mount. All are specified from −40°C to 85°C and operate from −55°C to 150°C.
PART NUMBER | PACKAGE | BODY SIZE (NOM) |
---|---|---|
OPA350 | MSOP (8) | 3.00 mm × 3.00 mm |
SOIC (8) | 3.91 mm × 4.90 mm | |
PDIP (8) | 6.35 mm × 9.81 mm | |
OPA2350 | MSOP (8) | 3.00 mm × 3.00 mm |
SOIC (8) | 3.91 mm × 4.90 mm | |
PDIP (8) | 6.35 mm × 9.81 mm | |
OPA4350 | SSOP (16) | 3.90 mm × 4.90 mm |
SOIC (14) | 3.91 mm × 8.65 mm |
Changes from C Revision (January 2005) to D Revision
PIN | I/O | DESCRIPTION | ||||
---|---|---|---|---|---|---|
NAME | OPA350 NO. |
OPA2350 NO. |
OPA4350 SO-14 NO. |
OPA4350 SSOP NO. |
||
NC | 1, 5, 8 | — | — | 8, 9 | — | No internal connection |
–In | 2 | — | — | — | I | Inverting input |
+In | 3 | — | — | — | I | Noninverting input |
V– | 4 | 4 | 11 | 13 | I | Negative power supply |
Output | 6 | — | — | — | O | Output |
V+ | 7 | 8 | 4 | 4 | I | Positive power supply |
Out A | — | 1 | 1 | 1 | O | Output channel A |
–In A | — | 2 | 2 | 2 | I | Inverting input channel A |
+In A | — | 3 | 3 | 3 | I | Noninverting input channel A |
+In B | — | 5 | 5 | 5 | I | Noninverting input channel B |
–In B | — | 6 | 6 | 6 | I | Inverting input channel B |
Out B | — | 7 | 7 | 7 | O | Output channel B |
Out C | — | — | 8 | 10 | O | Output channel C |
–In C | — | — | 9 | 11 | I | Inverting input channel C |
+In C | — | — | 10 | 12 | I | Noninverting input channel C |
+In D | — | — | 12 | 14 | I | Noninverting input channel D |
–In D | — | — | 13 | 15 | I | Inverting input channel D |
Out D | — | — | 14 | 16 | O | Output channel D |
MIN | MAX | UNIT | |||
---|---|---|---|---|---|
Supply voltage | 7 | V | |||
Signal input terminals(2) | Voltage | (V−) − 0.3 | (V+) + 0.3 | V | |
Current | 10 | mA | |||
Open short circuit current(3) | Continuous | ||||
Operating temperature | –55 | 150 | °C | ||
Lead temperature (soldering, 10 s) | 300 | °C | |||
Junction temperature | 150 | °C | |||
Tstg | Storage temperature | –55 | 150 | °C |
VALUE | UNIT | |||
---|---|---|---|---|
OPA350, OPA2350, OPA4350 (ALL PACKAGE TYPES) | ||||
V(ESD) | Electrostatic discharge | Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001(1) | ±1000 | V |
OPA350, OPA2350, OPA4350 (SOIC PACKAGES ONLY) | ||||
V(ESD) | Electrostatic discharge | Charged-device model (CDM), per JEDEC specification JESD22-C101(2) | ±1500 | V |
MIN | NOM | MAX | UNIT | ||
---|---|---|---|---|---|
Power supply voltage, (V+)-(V-) | 2.7 (±1.35) | 5 (±2.5) | 5.5 (±2.75) | V | |
Specified temperature | –40 | 25 | 85 | °C | |
Operating temperature | –55 | 25 | 150 | °C |
THERMAL METRIC(1) | OPA350, OPA2350 | UNIT | |||
---|---|---|---|---|---|
DGK (VSSOP) | P (PDIP) | D (SOIC) | |||
8 PINS | 8 PINS | 8 PINS | |||
RθJA | Junction-to-ambient thermal resistance | 169.2 | 53.1 | 140.1 | °C/W |
RθJC(top) | Junction-to-case (top) thermal resistance | 62.8 | 42.5 | 89.8 | °C/W |
RθJB | Junction-to-board thermal resistance | 89.8 | 30.3 | 80.6 | °C/W |
ψJT | Junction-to-top characterization parameter | 7.5 | 19.7 | 28.7 | °C/W |
ψJB | Junction-to-board characterization parameter | 88.2 | 30.2 | 80.1 | °C/W |
RθJC(bot) | Junction-to-case (bottom) thermal resistance | N/A | N/A | N/A | °C/W |
THERMAL METRIC(1) | OPA4350 | UNIT | ||
---|---|---|---|---|
D (SOIC) | DBQ (SSOP) | |||
14 PINS | 16 PINS | |||
RθJA | Junction-to-ambient thermal resistance | 83.8 | 115.8 | °C/W |
RθJC(top) | Junction-to-case (top) thermal resistance | 70.7 | 67 | °C/W |
RθJB | Junction-to-board thermal resistance | 59.5 | 58.3 | °C/W |
ψJT | Junction-to-top characterization parameter | 11.6 | 19.9 | °C/W |
ψJB | Junction-to-board characterization parameter | 37.7 | 57.9 | °C/W |
RθJC(bot) | Junction-to-case (bottom) thermal resistance | N/A | N/A | °C/W |
PARAMETER | TEST CONDITIONS | MIN | TYP(1) | MAX | UNIT | ||
---|---|---|---|---|---|---|---|
OFFSET VOLTAGE | |||||||
VOS | Input offset voltage | VS = 5 V | ±150 | ±500 | µV | ||
TA = −40°C to 85°C | ±1 | mV | |||||
vs Temperature | TA = –40°C to 85°C | ±4 | μV/°C | ||||
PSRR | vs Power-supply rejection ratio | VS = 2.7 V to 5.5 V, VCM = 0 V | 40 | 150 | µV/V | ||
175 | |||||||
Channel separation (dual, quad) | DC | 0.15 | µV/V | ||||
INPUT BIAS CURRENT | |||||||
IB | Input bias current | ±0.5 | ±10 | pA | |||
vs Temperature | See Typical Characteristics | ||||||
IOS | Input offset current | ±0.5 | ±10 | pA | |||
NOISE | |||||||
Input voltage noise, f = 100 Hz to 400 kHz | 4 | μVrms | |||||
en | Input voltage noise density, f = 10 kHz | 7 | nV/√Hz | ||||
Input current noise density, f = 100 kHz | 5 | nV/√Hz | |||||
in | Current noise density, f = 10 kHz | 4 | fA/√Hz | ||||
INPUT VOLTAGE RANGE | |||||||
VCM | Common-mode voltage range | TA = −40°C to 85°C | –0.1 | (V+) + 0.1 | V | ||
CMRR | Common-mode rejection ratio | VS = 2.7 V, −0.1 V < VCM < 2.8 V | 66 | 84 | dB | ||
VS = 5.5 V, −0.1 V < VCM < 5.6 V | 74 | 90 | |||||
TA = −40°C to 85°C, VS = 5.5 V, −0.1 V < VCM < 5.6 V |
74 | ||||||
INPUT IMPEDANCE | |||||||
Differential | 1013 || 2.5 | Ω || pF | |||||
Common-mode | 1013 || 6.5 | Ω || pF | |||||
OPEN-LOOP GAIN | |||||||
AOL | Open-loop voltage gain | RL = 10 kΩ, 50 mV < VO < (V+) –50 mV | 100 | 122 | dB | ||
TA = –40°C to 85°C | RL = 10 kΩ, 50 mV < VO < (V+) –50 mV | 100 | |||||
RL = 1 kΩ, 200 mV < VO < (V+) –200 mV | 100 | 120 | |||||
RL = 1 kΩ, 200 mV < VO < (V+) –200 mV | 100 | ||||||
FREQUENCY RESPONSE (CL = 100 pF) | |||||||
GBW | Gain-bandwidth product | G = 1 | 38 | MHz | |||
SR | Slew rate | G = 1 | 22 | V/µs | |||
Settling time | 0.1% | G = ±1, 2-V Step | 0.22 | µs | |||
0.01% | 0.5 | ||||||
Overload recovery time | VIN × G = VS | 0.1 | µs | ||||
THD+N | Total harmonic distortion + noise | RL = 600 Ω, VO = 2.5 VPP(2), G = 1, f = 1 kHz | 0.0006% | ||||
Differential gain error | G = 2, RL = 600 Ω, VO = 1.4 V(3) | 0.17% | |||||
Differential phase error | G = 2, RL = 600 Ω, VO = 1.4 V(3) | 0.17 | ° | ||||
OUTPUT | |||||||
VOUT | Voltage output swing from rail(4) | RL = 10 kΩ, AOL ≥ 100 dB | 10 | 50 | mV | ||
TA = –40°C to 85°C | RL = 10 kΩ, AOL ≥ 100 dB | 50 | |||||
RL = 1 kΩ, AOL ≥ 100 dB | 25 | 200 | |||||
IOUT | Output current | ±40(5) | mA | ||||
ISC | short circuit current | ±80 | mA | ||||
CLOAD | Capacitive load drive | See Typical Characteristics | |||||
POWER SUPPLY | |||||||
VS | Operating voltage range | TA = −40°C to 85°C | 2.7 | 5.5 | V | ||
Minimum operating voltage | 2.5 | V | |||||
IQ | Quiescent current (per amplifier) | IO = 0 | 5.2 | 7.5 | mA | ||
TA = –40°C to 85°C | 8.5 | ||||||
TEMPERATURE RANGE | |||||||
Specified range | –40 | 85 | °C | ||||
Operating range | –55 | 150 | °C |
The OPA350 series rail-to-rail CMOS operational amplifiers are optimized for low voltage, single-supply operation. Rail-to-rail input and output, low noise (5 nV/√Hz), and high speed operation (38 MHz, 22 V/μs) make the amplifiers ideal for driving sampling Analog-to-Digital (A/D) converters. They are also suited for cell phone PA control loops and video processing (75-Ω drive capability), as well as audio and general purpose applications. Single, dual, and quad versions have identical specifications for maximum design flexibility.
The OPA350 series of operational amplifiers (op amps) are fabricated on a state-of-the-art 0.6 micron CMOS process. They are unity-gain stable and suitable for a wide range of general purpose applications. Rail-to-rail input and output make them ideal for driving sampling A/D converters. They are also suited for controlling the output power in cell phones. These applications often require high speed and low noise. In addition, the OPA350 series offers a low-cost solution for general-purpose and consumer video applications (75-Ω drive capability).
Excellent AC performance makes the OPA350 series suited for audio applications. Their bandwidth, slew rate, low noise (5 nV/√Hz), low THD (0.0006%), and small package options are ideal for these applications. The class AB output stage is capable of driving 600-Ω loads connected to any point between V+ and ground.
Rail-to-rail input and output swing significantly increases dynamic range, especially in low voltage supply applications. Figure 25 shows the input and output waveforms for the OPA350 in unity-gain configuration. Operation is from a single 5-V supply with a 1-kΩ load connected to VS/2. The input is a 5 VPP sinusoid. Output voltage swing is approximately 4.95 VPP.
Power supply pins should be bypassed with 0.01-μF ceramic capacitors.
OPA350 series operational amplifiers are fully specified from 2.7 V to 5.5 V. Supply voltage may range from 2.5 V to 5.5 V. Parameters are tested over the specified supply range: a feature of the OPA350 series. In addition, many specifications apply from −40°C to 85°C. Most behavior remains virtually unchanged throughout the full operating voltage range. Parameters that vary significantly with operating voltage or temperature are shown in Typical Characteristics.
The tested input common-mode voltage range of the OPA350 series extends 100 mV beyond the supply rails. This is achieved with a complementary input stage: an N-channel input-differential pair in parallel with a P-channel differential pair, as shown in Figure 26. The N-channel pair is active for input voltages close to the positive rail, typically (V+) – 1.8 V to 100 mV above the positive supply, while the P-channel pair is on for inputs from 100 mV below the negative supply to approximately (V+) – 1.8 V. There is a small transition region, typically (V+) – 2 V to (V+) – 1.6 V, in which both pairs are on. This 400-mV transition region can vary ±400 mV with process variation. Thus, the transition region (both input stages on) can range from (V+) – 2.4 V to (V+) – 2 V on the low end, up to (V+) – 1.6 V to (V+) – 1.2 V on the high end.
OPA350 series operational amplifiers are laser-trimmed to reduce offset voltage difference between the N-channel and P-channel input stages, resulting in improved common-mode rejection and a smooth transition between the N-channel pair and the P-channel pair. However, within the 400-mV transition region PSRR, CMRR, offset voltage, offset drift, and THD may be degraded compared to operation outside this region.
A double-folded cascode adds the signal from the two input pairs and presents a differential signal to the class AB output stage. Normally, input bias current is approximately 500 fA. However, large inputs (greater than 300 mV beyond the supply rails) can turn on the input protection diodes, causing excessive current to flow in or out of the input pins. Momentary voltages greater than 300 mV beyond the power supply can be tolerated if the current on the input pins is limited to 10 mA. This is easily accomplished with an input resistor, as shown in Figure 27. Many input signals are inherently current-limited to less than 10 mA; therefore, a limiting resistor is not required.
A class AB output stage with common-source transistors achieves rail-to-rail output. For light resistive loads (>10 kΩ), the output voltage swing is typically ten millivolts from the supply rails. With heavier resistive loads (600 Ω to 10 kΩ), the output can swing to within a few tens of millivolts from the supply rails and maintain high open-loop gain. See Figure 17 and Figure 18 for more information.
OPA350 series operational amplifiers can drive a wide range of capacitive loads. However, all operational amplifiers under certain conditions may become unstable. operational amplifier configuration, gain, and load value are just a few of the factors to consider when determining stability. An operational amplifier in unity-gain configuration is the most susceptible to the effects of capacitive load. The capacitive load reacts with the output impedance of the operational amplifier, along with any additional load resistance, to create a pole in the small-signal response that degrades the phase margin.
In unity gain, OPA350 series operational amplifiers perform well with large capacitive loads. Increasing gain enhances the ability of the amplifier to drive more capacitance. Figure 21 shows performance with a 1-kΩ resistive load. Increasing load resistance improves capacitive load drive capability.
OPA350 series operational amplifiers are optimized for driving medium speed (up to 500 kHz) sampling A/D converters, and also offer excellent performance for higher speed converters. The OPA350 series provides an effective means of buffering the input capacitance of the A/D and resulting charge injection while providing signal gain.
Figure 28 shows the OPA350 driving an ADS7861. The ADS7861 is a dual, 500 kHz, 12-bit sampling converter in the tiny SSOP-24 package. When used with the miniature package options of the OPA350 series, the combination is ideal for space-limited applications. For further information, consult the ADS7861 data sheet, Dual, 500kSPS, 12-Bit, 2 + 2 Channel, Simultaneous Sampling ANALOG-TO-DIGITAL CONVERTER (SBAS110).
The low-frequency open-loop output impedance of the common-source output stage of the OPA350 is approximately 1 kΩ. When the operational amplifier is connected with feedback, this value is reduced significantly by the loop gain of the operational amplifier. For example, with 122 dB of open-loop gain, the output impedance is reduced in unity-gain to less than 0.001 Ω. For each decade rise in the closed-loop gain, the loop gain is reduced by the same amount which results in a ten-fold increase in effective output impedance (see Figure 15).
At higher frequencies, the output impedance rises as the open-loop gain of the operational amplifier drops. However, at these frequencies the output also becomes capacitive due to parasitic capacitance. This prevents the output impedance from becoming too high, which can cause stability problems when driving capacitive loads. The OPA350 has excellent capacitive load drive capability for an operational amplifier with its bandwidth.
The OPAx350 has a single functional mode and is operational when the power-supply voltage is greater than
2.7 V (±1.35 V). The maximum power supply voltage for the OPAx350 is 5.5V (±2.75 V).
NOTE
Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.
Low pass filters are commonly employed in signal processing applications to reduce noise and prevent aliasing. The OPAx350 are ideally suited to construct high speed, high precision active filters. Figure 29 illustrates a second order low pass filter commonly encountered in signal processing applications.
Use the following parameters for this design example:
The infinite-gain multiple-feedback circuit for a low-pass network function is shown in Equation 1. Use Equation 2 to calculate the voltage transfer function.
This circuit produces a signal inversion. For this circuit the gain at DC and the low pass cutoff frequency can be calculated using Equation 2.
Software tools are readily available to simplify filter design. WEBENCH® Filter Designer is a simple, powerful, and easy-to-use active filter design program. The WEBENCH Filter Designer lets you create optimized filter designs using a selection of TI operational amplifiers and passive components from TI's vendor partners. Available as a web based tool from the WEBENCH® Design Center, WEBENCH® Filter Designer allows you to design, optimize, and simulate complete multi-stage active filter solutions within minutes.
Figure 31 shows a circuit for a single supply, G = 2 composite video line driver. The synchronized outputs of a composite video line driver extend below ground. As shown, the input to the operational amplifier should be AC-coupled and shifted positively to provide adequate signal swing to account for these negative signals in a single-supply configuration.
The input is terminated with a 75-Ω resistor and AC-coupled with a 47-μF capacitor to a voltage divider that provides the DC bias point to the input. In Figure 31, this point is approximately (V−) + 1.7 V. Setting the optimal bias point requires some understanding of the nature of composite video signals. For best performance, avoid the distortion caused by the transition region of the complementary input stage of the OPA350. See the discussion of rail-to-rail input in Rail-to-Rail Input.
For optimum settling time and stability with high-impedance feedback networks, it may be necessary to add a feedback capacitor across the feedback resistor, RF, as shown in Figure 32. This capacitor compensates for the zero created by the feedback network impedance and the input capacitance of the OPA350 (and any parasitic layout capacitance). The effect becomes more significant with higher impedance networks.
A variable capacitor can be used for the feedback capacitor, because input capacitance may vary between operational amplifiers and layout capacitance is difficult to determine. For the circuit shown in Figure 32, the value of the variable feedback capacitor should be chosen so that the input resistance times the input capacitance of the OPA350 (typically 9 pF) plus the estimated parasitic layout capacitance equals the feedback capacitor times the feedback resistor:
where
The capacitor can be varied until optimum performance is obtained.
The OPAx350 is well suited for high input impedance applications such as an instrumentation amplifier. The two amplifier configuration shown in Figure 33 rejects any common mode signals and senses the small differential input voltage developed by the resistive bridge. The voltage reference sets the output to 2.5 V when the differential signal developed by the bridge is zero. The high common mode rejection versus frequency response of the OPAx350, rejects and common mode noise that may be coupled into the bridge circuit from the bridge excitation source. The gain of the circuit is determined by RG according to the equation shown in Figure 33.
High-pass filters are used to reject DC signals and low-frequency time varying signals such as drift versus temperature. Figure 34 illustrates a high-pass filter with a 10 kHz low-frequency cutoff frequency.