Texas Instruments OPA2373AIDGS, OPA2373AIDRC, OPA2374AIDCN, OPA373AIDBV, OPA374AIDBV Schematic [ru]

OPA373, OPA2373

OPA374

OPA2374, OPA4374

SBOS279E − SEPTEMBER 2003 − REVISED MAY 2008

6.5MHz, 585 A, Rail-to-Rail I/O

CMOS Operational Amplifier

FEATURES

DESCRIPTION

D

LOW OFFSET: 5mV (max)

The OPA373 and OPA374 families of operational

D

LOW IB: 10pA (max)

amplifiers are low

power

and

low cost with

excellent

D

HIGH BANDWIDTH: 6.5MHz

bandwidth (6.5MHz) and slew rate (5V/ s). The input

D RAIL-TO-RAIL INPUT AND OUTPUT

range extends 200mV beyond the rails and the output

SINGLE SUPPLY: +2.3V to +5.5V

D

range is within 25mV of the rails. The speed/power ratio

D

SHUTDOWN: OPAx373

and small size make them ideal for portable and

D SPECIFIED UP TO +125°C

battery-powered applications.

D MicroSIZE PACKAGES: SOT23-5, SOT23-6,

The OPA373 family includes a shutdown mode. Under

SOT23-8 and DFN-10

logic control, the amplifiers can be switched from normal

APPLICATIONS

operation to a standby current that is less than 1 A.

D

PORTABLE EQUIPMENT

The OPA373 and OPA374 families of operational

D

BATTERY-POWERED DEVICES

amplifiers are specified for single or dual power supplies

D

ACTIVE FILTERS

of +2.7V to +5.5V, with operation from +2.3V to +5.5V. All

D

DRIVING A/D CONVERTERS

models are specified for −40 °C to +125°C.

OPA373

OPA374

OPA2373

Out

1

A75

6

V+

Out

1

5

V+

OUT A

1

10

V+

V−

2

5

Enable

V−

2

−IN A

2

9

OUT B

− IN

−IN

A

+IN

3

4

+IN

3

4

+IN A

3

B

8

− IN B

V−

SOT23−6(1)

SOT23−5

4

7

+IN B

OPA373

Enable A

5

6

Enable B

OPA2373

MSOP−10

OUT A

V+

NC(2)

1

8

Enable

Exposed

OPA4374

−IN A

OUT B

− IN

2

7

V+

thermal

die pad on

−IN B

+IN A

+IN

3

6

OUT

OUT A

1

14

OUT D

underside

V−

(Must be

+IN B

V−

NC(2)

connected to V−)

4

5

− IN A

2

13

− IN D

A

D

Enable A

Enable B

SO−8

+IN A

3

12

+IN D

DFN−10

V+

4

11

V−

OPA374

OPA2374

+IN B

5

10

+IN C

NC(2)

1

8

NC(2)

− IN B

6

B

C

9

− IN C

OUT A

1

8

V+

A

−IN

2

7

V+

−IN A

2

7

OUT B

OUT B

7

8

OUT C

B

+IN

3

6

OUT

+IN A

3

6

−IN B

V−

4

5

NC(2)

SO−14, TSSOP−14

V−

4

5

+IN B

SO−8

SO−8, SOT23−8

(1)Pin 1 of the SOT23-6 is determined by orienting the package marking as shown.

(2)NC indicates no internal connection.

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.

All trademarks are the property of their respective owners.

PRODUCTION DATA information is current as of publication date. Products	Copyright 2003-2008, Texas Instruments Incorporated
conform to specifications per the terms of Texas Instruments standard warranty.
Production processing does not necessarily include testing of all parameters.

www.ti.com

	OPA373, OPA2373
	OPA374
	OPA2374, OPA4374						www.ti.com
	SBOS279E − SEPTEMBER 2003 − REVISED MAY 2008
	PACKAGE/ORDERING INFORMATION(1)
			PACKAGE	SPECIFIED	PACKAGE	ORDERING	TRANSPORT
	PRODUCT	PACKAGE-LEAD		TEMPERATURE
			DESIGNATOR		MARKING	NUMBER	MEDIA, QUANTITY
				RANGE
	Shutdown
	OPA373	SOT23-6	DBV	−40 °C to +125°C	A75	OPA373AIDBVT	Tape and Reel, 250
	″	″	″	″	″	OPA373AIDBVR	Tape and Reel, 3000
	OPA373	SO-8	D	−40 °C to +125°C	OPA373A	OPA373AID	Rails, 100
	″	″	″	″	″	OPA373AIDR	Tape and Reel, 2500
	OPA2373	MSOP-10	DGS	−40 °C to +125°C	AYO	OPA2373AIDGST	Tape and Reel, 250
	″	″	″	″	″	OPA2373AIDGSR	Tape and Reel, 2500
	OPA2373	DFN-10	DRC	−40 °C to +125°C	OCEQ	OPA2373AIDRCT	Tape and Reel, 250
	″	″	″	″	″	OPA2373AIDRCR	Tape and Reel, 3000
	Non-Shutdown
	OPA374	SOT23-5	DBV	−40 °C to +125°C	A76	OPA374AIDBVT	Tape and Reel, 250
	″	″	″	″	″	OPA374AIDBVR	Tape and Reel, 3000
	OPA374	SO-8	D	−40 °C to +125°C	OPA274A	OPA374AID	Rails, 100
	″	″	″	″	″	OPA374AIDR	Tape and Reel, 2500
	OPA2374	SOT23-8	DCN	−40 °C to +125°C	ATP	OPA2374AIDCNT	Tape and Reel, 250
	″	″	″	″	″	OPA2374AIDCNR	Tape and Reel, 3000
	OPA2374	SO-8	D	−40 °C to +125°C	OPA2374A	OPA2374AID	Rails, 100
	″	″	″	″	″	OPA2374AIDR	Tape and Reel, 2500
	OPA4374	SO-14	D	−40 °C to +125°C	OPA4374A	OPA4374AID	Rails, 58
	″	″	″	″	″	OPA4374AIDR	Tape and Reel, 2500
	OPA4374	TSSOP-14	PW	−40 °C to +125°C	OPA4374A	OPA4374AIPWT	Tape and Reel, 250
	″	″	″	″	″	OPA4374AIPWR	Tape and Reel, 2500

(1) For the most current package and ordering information, see the Package Option Addendum located at the end of this datasheet.

ABSOLUTE MAXIMUM RATINGS(1)

. . . . . . . . . . . . . . . . . . . . . . . . .Supply Voltage	. . . . . . . . . . . . +7.0V
Signal Input Terminals, Voltage(2) . . . . . . . . .	−0.5V to (V+) + 0.5V
Current(2) . . . . . . . .	. . . . . . . . . . . ±10mA
Output Short-Circuit(3) . . . . . . . . . . . . . . . . . .	. . . . . . . Continuous
Operating Temperature . . . . . . . . . . . . . . . . . .	. . . −55 °C to +150°C
Storage Temperature . . . . . . . . . . . . . . . . . . . .	. . . −65 °C to +150°C
Junction Temperature . . . . . . . . . . . . . . . . . . . .	. . . . . . . . . . . +150°C
Lead Temperature (soldering, 10s) . . . . . . . . .	. . . . . . . . . . . +300°C

(1)Stresses above these ratings may cause permanent damage.

Exposure to absolute maximum conditions for extended periods may degrade device reliability. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those specified is not implied.

(2)Input terminals are diode-clamped to the power-supply rails.

Input signals that can swing more than 0.5V beyond the supply rails should be current-limited to 10mA or less.

(3)Short-circuit to ground, one amplifier per package.

This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with appropriate precautions. Failure to observe

proper handling and installation procedures can cause damage.

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 its published specifications.

2

	OPA373, OPA2373
	OPA374
www.ti.com	OPA2374, OPA4374

SBOS279E − SEPTEMBER 2003 − REVISED MAY 2008

ELECTRICAL CHARACTERISTICS: VS = +2.7V to +5.5V

Boldface limits apply over the specified temperature range, TA = −40 °C to +125°C.

At TA = +25°C, RL = 10kΩ connected to VS/2, and VOUT = VS/2, unless otherwise noted.

OPA373, OPA2373, OPA374,

OPA2374, OPA4374

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNIT

OFFSET VOLTAGE

Input Offset Voltage

VOS

VS = 5V

1

5

mV

over Temperature

6.5

mV

Drift

dVOS/dT

3

µV/°C

vs Power Supply

PSRR

VS = 2.7V to 5.5V, VCM < (V+) − 2V

25

100

µV/V

over Temperature

VS = 2.7V to 5.5V, VCM < (V+) − 2V

150

µV/V

Channel Separation, DC

0.4

µV/V

f = 1kHz

128

dB

INPUT VOLTAGE RANGE

Common-Mode Voltage Range

VCM

(V−) − 0.2

(V+) + 0.2

V

Common-Mode Rejection Ratio

CMRR

(V−) − 0.2V < V

CM < (V+) − 2V

80

90

dB

over Temperature

(V−) − 0.2V < V

CM < (V+) − 2V

70

dB

VS = 5.5V, (V−) − 0.2V < V

CM < (V+) + 0.2V

66

dB

over Temperature

VS = 5.5V, (V−) − 0.2V < V

CM < (V+) + 0.2V

60

dB

INPUT BIAS CURRENT

Input Bias Current

IB

±0.5

±10

pA

Input Offset Current

IOS

±0.5

±10

pA

INPUT IMPEDANCE

Differential

1013 3

Ω pF

Common-Mode

1013 6

Ω pF

NOISE

VCM < (V+) − 2V

Input Voltage Noise, f = 0.1Hz to 10Hz

10

µVPP

Input Voltage Noise Density, f = 10kHz

en

15

nV/√

Hz

Input Current Noise Density, f = 10kHz

in

4

fA/√

Hz

OPEN-LOOP GAIN

Open-Loop Voltage Gain

AOL

VS = 5V, RL = 100kΩ, 0.025V < VO < 4.975V

94

110

dB

over Temperature

VS = 5V, RL = 100kΩ, 0.025V < VO < 4.975V

80

dB

VS = 5V, RL = 5kΩ, 0.125V < VO < 4.875V

94

106

dB

over Temperature

VS = 5V, RL = 5kΩ, 0.125V < VO < 4.875V

80

dB

OUTPUT

Voltage Output Swing from Rail

RL = 100kΩ

18

25

mV

over Temperature

RL = 100kΩ

25

mV

RL = 5kΩ

100

125

mV

over Temperature

RL = 5kΩ

125

mV

Short-Circuit Current

ISC

See Typical Characteristics

Capacitive Load Drive

CLOAD

See Typical Characteristics

Open-Loop Output Impedance

f = 1MHz, IO = 0

220

Ω

FREQUENCY RESPONSE

CL = 100pF

Gain-Bandwidth Product

GBW

6.5

MHz

Slew Rate

SR

G = +1

5

V/µs

Settling Time, 0.1%

tS

VS = 5V, 2V Step, G = +1

1

µs

0.01%

VS = 5V, 2V Step, G = +1

1.5

µs

Overload Recovery Time

VIN • Gain > VS

0.3

µs

Total Harmonic Distortion + Noise

THD+N

VS = 5V, VO = 3VPP, G = +1, f = 1kHz

0.0013

%

ENABLE/SHUTDOWN

tOFF

3

µs

tON

12

µs

VL (shutdown)

V−

(V−) + 0.8

V

VH (amplifier is active)

(V−) + 2

V+

V

Input Bias Current of Enable Pin

0.2

µA

IQSD (per amplifier)

< 0.5

1

µA

3

OPA373, OPA2373
OPA374
OPA2374, OPA4374					www.ti.com
SBOS279E − SEPTEMBER 2003 − REVISED MAY 2008
ELECTRICAL CHARACTERISTICS: VS = +2.7V to +5.5V (continued)
Boldface limits apply over the specified temperature range, TA = −40 °C to +125°C.
At TA = +25°C, RL = 10kΩ connected to VS/2, and VOUT = VS/2, unless otherwise noted.
			OPA373, OPA2373, OPA374,
			OPA2374, OPA4374
PARAMETER		CONDITIONS	MIN	TYP	MAX	UNIT
POWER SUPPLY
Specified Voltage Range	VS		2.7		5.5	V
Operating Voltage Range				2.3 to 5.5		V
Quiescent Current (per amplifier)	IQ	IO = 0		585	750	A
over Temperature					800	A
TEMPERATURE RANGE
Specified Range			−40		+125	°C
Operating Range			−55		+150	°C
Storage Range			−65		+150	°C
Thermal Resistance	qJA					°C/W
SOT23-5, SOT23-6, SOT23-8				200		°C/W
MSOP-10, SO-8				150		°C/W
SO-14, TSSOP-14				100		°C/W
DFN-10		JEDEC High-K Board		56		°C/W

4

	OPA373, OPA2373
	OPA374
www.ti.com	OPA2374, OPA4374
	SBOS279E − SEPTEMBER 2003 − REVISED MAY 2008

TYPICAL CHARACTERISTICS

At TA = +25°C, RL = 10kΩ connected to VS/2, and VOUT = VS/2, unless otherwise noted.

				120			OPEN−LOOP GAIN AND PHASE vs FREQUENCY																																												30
				100																																															0
			(dB)													Gain																																				−30
				80																																																	)(
			GainOpen−Loop																																																		MarginPhase
				60																																																−60
				40																																																−90
																	Phase
				20																																																−120
				0																																																−150
				−20																																																−180
				10			100										1k									10k							100k										1M						10M
																					Frequency (Hz)
																INPUT VOLTAGE NOISE
			1000								SPECTRAL DENSITY vs FREQUENCY
		(nV/√Hz)
		NoiseVoltage		100
				10
				10							100															1k													10k										100k
																					Frequency (Hz)
								OPEN−LOOP GAIN AND POWER−SUPPLY
				130							REJECTION RATIO vs TEMPERATURE
									RL = 100kΩ
		(dB)		120
				110
		PSRR,
																														RL		= 5kΩ
		OL		100
		A
																													PSRR
				90
				80
				−50			− 25				0					25										50						75 100											125					150

Temperature (_C)

POWER−SUPPLY AND COMMON−MODE

REJECTION RATIO vs FREQUENCY

	120
(dB)	100
	80																							CMRR
CMRR
	60											PSRR
and
PSRR	40
	20
	0
	100									1k											10k											100k												1M										10M
																					Frequency (Hz)
							TOTAL HARMONIC DISTORTION+NOISE
	0.100																		vs FREQUENCY
(%)				RL = 5kΩ
HarmonicTotalDistortion+Noise
																																										G = 1V/V
																																						G = 10V/V
	0.010
	0.001
	10									100																	1k													10k												100k
																				Frequency (Hz)
	120			COMMON−MODE REJECTION RATIO vs TEMPERATURE
	110			VS = 5.5V
	100										VCM = − 0.2V to 3.5V
(dB)
	90
CMRR
	80
	70																												VCM = − 0.2V to 5.7V
	60
	50
	40
	−50 −25									0									25		50											75						100 125														150

Temperature (_C)

5

OPA373, OPA2373
OPA374
OPA2374, OPA4374	www.ti.com
SBOS279E − SEPTEMBER 2003 − REVISED MAY 2008

TYPICAL CHARACTERISTICS (continued)

At TA = +25°C, RL = 10kΩ connected to VS/2, and VOUT = VS/2, unless otherwise noted.

	800
( A)	700
Current	600
Quiescent	500
	400
	300

−50

		16
	(mA)	14
		12
	Current
		10
	Short−Circuit	8
		6
		4

2

0

−50

QUIESCENT CURRENT vs TEMPERATURE

Quiescent Current ( A)

−25	0	25	50	75	100	125	150
		Temperature (_C)

SHORT−CIRCUIT CURRENT vs TEMPERATURE

+ISC

−ISC

− 25	0	25	50	75	100	125
		Temperature (_C)

QUIESCENT CURRENT vs SUPPLY VOLTAGE

800

VOUT = 1/2[(V+) − (V−)]

700

600

500

400

300

	2.0		2.5		3.0		3.5		4.0		4.5		5.0		5.5
							Supply Voltage (V)
			CONTINUOUS SHORT−CIRCUIT CURRENT vs
					POWER−SUPPLY VOLTAGE
	12
								+ISC
(mA)	10
	8
Current
								−ISC
Short−Circuit	6
	4
	2
	0
	2.0		2.5		3.0		3.5		4.0		4.5		5.0		5.5
					Power−Supply Voltage (V)

Input Bias Current (pA)

INPUT BIAS CURRENT vs TEMPERATURE

OUTPUT VOLTAGE SWING vs OUTPUT CURRENT

10k									3
1k									2
								(V)	1
								Voltage
100
								Output	0
10									−1
1									−2									− 55_C
																		25_C
									−3									150_C
0.1
− 50	−25	0	25	50	75	100	125		0	2	4	6	8	10	12	14	16	18	20
			Temperature (_C)										Output Current (mA)

6

	OPA373, OPA2373
	OPA374
www.ti.com	OPA2374, OPA4374
	SBOS279E − SEPTEMBER 2003 − REVISED MAY 2008

TYPICAL CHARACTERISTICS (continued)

At TA = +25°C, RL = 10kΩ connected to VS/2, and VOUT = VS/2, unless otherwise noted.

6

MAXIMUM OUTPUT VOLTAGE vs FREQUENCY

VS = 5.5V

5

)

VS = 5V

PP

(V

4

Voltage

3

VS =

2.5V

Output

2

1

0

10k

100k

1M

10M

Frequency (Hz)

OFFSET VOLTAGE DRIFT MAGNITUDE

PRODUCTION DISTRIBUTION

								Typical production distribution
									of packaged units.
Population
1	2	3	4	5	6	7	8	9	10 11 12	13 14 15 16
				Offset Voltage Drift (µV/_C)

OFFSET VOLTAGE PRODUCTION DISTRIBUTION

Population
− 5	− 4	−3	− 2	− 1	0	1	2	3	4	5	5.5
				Offset Voltage (mV)

SMALL−SIGNAL STEP RESPONSE

CL = 100pF

50mV/div

200ns/div

Small−Signal Overshoot (%)

SMALL−SIGNAL OVERSHOOT vs LOAD CAPACITANCE

LARGE −SIGNAL STEP RESPONSE

60

Refer to the Capacitive Load

CL = 100pF

50

and Stability section for tips

on improving performance.

40				1V/div
30	G = +1V/V
20
			G = ±10V/V
10			RFB = 10kΩ
0				400ns/div
10	100	1k	10k
	Load Capacitance (pF)

7

OPA373, OPA2373
OPA374
OPA2374, OPA4374	www.ti.com
SBOS279E − SEPTEMBER 2003 − REVISED MAY 2008

TYPICAL CHARACTERISTICS (continued)

At TA = +25°C, RL = 10kΩ connected to VS/2, and VOUT = VS/2, unless otherwise noted.

Settling Time ( s)

100

10

1

0.1

1

SETTLING TIME vs CLOSED−LOOP GAIN

0.01%

0.1%

10 100

Closed−Loop Gain (V/V)

Channel Separation (dB)

CHANNEL SEPARATION vs FREQUENCY

140 G = +1V/V, All Channels

120 RL = 5kΩ

100

80

60

40

20

0

10

100

1K

10K

100K

1M

10M

100M

Frequency (Hz)

8

www.ti.com

APPLICATIONS

The OPA373 and OPA374 series op amps 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 Analog-to-Digital Converters (ADCs). Excellent ac performance makes them well-suited for audio applications. The class AB output stage is capable of driving 100kΩ loads connected to any point between V+ and ground.

The input common-mode voltage range includes both rails, allowing the OPA373 and OPA374 series op amps to be used in virtually any single-supply application up to a supply voltage of +5.5V.

Rail-to-rail input and output swing significantly increases dynamic range, especially in low-supply applications.

Power-supply pins should be bypassed with 0.01µF ceramic capacitors.

OPERATING VOLTAGE

The OPA373 and OPA374 op amps are specified and tested over a power-supply range of +2.7V to +5.5V (±1.35V to ±2.75V). However, the supply voltage may range from +2.3V to +5.5V (±1.15V to ±2.75V). Supply voltages higher than 7.0V (absolute maximum) can permanently damage the amplifier. Parameters that vary over supply voltage or temperature are shown in the Typical Characteristics section of this data sheet.

COMMON-MODE VOLTAGE RANGE

The input common-mode voltage range of the OPA373 and OPA374 series extends 200mV beyond the supply rails. This is achieved with a complementary input stage—an N-channel input dif ferential pair in parallel with a P-channel differential pair. The N-channel pair is active for input voltages close to the positive rail, typically (V+) − 1.65V to 200mV above the positive supply, while the P-channel pair is on for inputs from 200mV below the negative supply to approximately (V+) − 1.65V . There is a 500mV transition region, typically (V+) − 1.9V to (V+) − 1.4V, in which both pairs are on. This 500mV transition region, shown in Figure 1, can vary ±300mV with process variation. Thus, the transition region (both stages on) can range from (V+) − 2.2V to (V+) − 1.7V on the low end, up to (V+) − 1.6V to (V+) − 1.1V on the high end. Within the 500mV transition region PSRR, CMRR, offset voltage, offset drift, and THD may be degraded compared to operation outside this region.

								OPA373, OPA2373
												OPA374
								OPA2374, OPA4374
			SBOS279E − SEPTEMBER 2003 − REVISED MAY 2008
	2.0
	1.5
(mV)	1.0
	0.5
Voltage
	0
Offset	− 0.5
	− 1.0
	− 1.5		V−
	− 2.0													V+
	− 0.5	0	0.5	1.0	1.5	2.0	2.5	3.0	3.5	4.0	4.5	5.0	5.5	6.0
					Common−Mode Voltage (V)

Figure 1. Behavior of Typical Transition Region at

Room Temperature

RAIL-TO-RAIL INPUT

The input common-mode range extends from (V−) − 0.2V to (V+) + 0.2V. For normal operation, inputs should be limited to this range. The absolute maximum input voltage is 500mV beyond the supplies. Inputs greater than the input common-mode range but less than the maximum input voltage, while not valid, will not cause any damage to the op amp. Unlike some other op amps, if input current is limited, the inputs may go beyond the supplies without phase inversion, as shown in Figure 2.

G = +1V/V, VS = 5V

VIN

5V

VOUT

1V/div

0V

1µs/div

Figure 2. OPA373: No Phase Inversion with Inputs Greater Than the Power-Supply Voltage

Normally, input bias current is approximately 500fA; however, input voltages exceeding the power supplies by more than 500mV can cause excessive current to flow in or out of the input pins. Momentary voltages greater than 500mV beyond the power supply can be tolerated if the current on the input pins is limited to 10mA. This is easily accomplished with an input resistor; see Figure 3. (Many input signals are inherently current-limited to less than 10mA, therefore, a limiting resistor is not required.)

9

OPA373, OPA2373
OPA374
OPA2374, OPA4374	www.ti.com
SBOS279E − SEPTEMBER 2003 − REVISED MAY 2008

V+

IOVERLOAD

10mA max

R

OPA373

VOUT

VIN

Figure 3. Input Current Protection for Voltages Exceeding the Supply Voltage

RAIL-TO-RAIL OUTPUT

A class AB output stage with common-source transistors is used to achieve rail-to-rail output. For light resistive loads ( > 100kΩ), the output voltage can typically swing to within 18mV from the supply rails. With moderate resistive loads (5kΩ to 50kΩ), the output can typically swing to within 100mV from the supply rails and maintain high open-loop gain. See the Typical Characteristic curve,

Output Voltage Swing vs Output Current, for more information.

CAPACITIVE LOAD AND STABILITY

OPA373 series op amps can drive a wide range of capacitive loads. However, under certain conditions, all op amps may become unstable. Op amp configuration, gain, and load value are just a few of the factors to consider when determining stability. An op amp in unity-gain configuration is the most susceptible to the effects of capacitive load. The capacitive load reacts with the op amp output resistance, along with any additional load resistance, to create a pole in the small-signal response that degrades the phase margin. The OPA373 series op amps perform well in unity-gain configuration, with a pure capacitive load up to approximately 250pF. Increased gains allow the amplifier to drive more capacitance. See the Typical Characteristics curve, Small-Signal Overshoot vs Capacitive Load, for further details.

One method of improving capacitive load drive in the unity-gain configuration is to insert a small (10Ω to 20Ω) resistor, RS, in series with the output, as shown in Figure 4. This significantly reduces ringing while maintaining dc performance for purely capacitive loads. When there is a resistive load in parallel with the capacitive load, RS must be placed within the feedback loop as shown to allow the feedback loop to compensate for the voltage divider created by RS and RL.

In unity-gain inverter configuration, phase margin can be reduced by the reaction between the capacitance at the op amp input and the gain setting resistors, thus degrading capacitive load drive. Best performance is achieved by using small valued resistors. However, when large valued resistors cannot be avoided, a small (4pF to 6pF)

capacitor, CFB, can be inserted in the feedback, as shown in Figure 5. This significantly reduces overshoot by compensating the effect of capacitance, CIN, which includes the amplifier input capacitance and printed circuit board (PCP) parasitic capacitance.

V+

RS 10Ω to 20Ω

OPA373

VOUT

VIN

RL CL

Figure 4. Series Resistor in Unity-Gain Configuration Improves Capacitive Load Drive

CFB
RF
V+
RI
VIN
OPA373	VOUT
CIN	CL

Figure 5. Improving Capacitive Load Drive

For example, when driving a 100pF load in unity-gain inverter configuration, adding a 6pF capacitor in parallel with the 10kΩ feedback resistor decreases overshoot from 57% to 12%, as shown in Figure 6.

	60
		G = − 1V/V
	50	RFB = 10kΩ
(%)	40
Overshoot	30
	20
	10
			CFB = 6pF
	0
	10	100	1k	10k

Load Capacitance (pF)

Figure 6. Improving Capacitive Load Drive

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	OPA373, OPA2373
	OPA374
www.ti.com	OPA2374, OPA4374
	SBOS279E − SEPTEMBER 2003 − REVISED MAY 2008

DRIVING ADCs

The OPA373 and OPA374 series op amps are optimized for driving medium-speed sampling ADCs. The OPA373 and OPA374 op amps buffer the ADC input capacitance and resulting charge injection, while providing signal gain.

The OPA373 is shown driving the ADS7816 in a basic noninverting configuration, as shown in Figure 7. The ADS7816 is a 12-bit, MicroPower sampling converter in the MSOP-8 package. When used with the low-power, miniature packages of the OPA373, the combination is ideal for space-limited, low-power applications. In this configuration, an RC network at the ADC input can be used to provide anti-aliasing filtering.

Figure 8 shows the OPA373 driving the ADS7816 in a speech band-pass filtered data acquisition system. This small, low-cost solution provides the necessary amplification and signal conditioning to interface directly with an electret microphone. This circuit will operate with VS = 2.7V to 5V.

The OPA373 is shown in the inverting configuration described in Figure 9. In this configuration, filtering may be accomplished with the capacitor across the feedback resistor.

ENABLE/SHUTDOWN

OPA373 and OPA374 series op amps typically require 585 A quiescent current. The enable/shutdown feature of the OPA373 allows the op amp to be shut off in order to reduce this current to less than 1 A.

VIN

VIN = 0V to 5V for 0V to 5V output.

		+5V
			0.1µF		0.1µF
		8	V+	1	VREF
					7
500Ω	+In			DCLOCK
			ADS7816		6	Serial
OPA373
	2	12−Bit ADC			DOUT	Interface
					5
		− In
				CS/SHDN

3300pF

3

GND

4

fSAMPLE = 100kHz

RC network filters high frequency noise.

NOTE: ADC Input = 0 to VREF

Figure 7. The OPA373 in Noninverting Configuration Driving the ADS7816

V+ = +2.7V to +5V

Passband 300Hz to 3kHz

R9

510kΩ

R1

R2

R4

1.5kΩ

1MΩ

20kΩ

C3

C1

33pF

1000pF

R7

R8

VREF

1

8

V+

51kΩ

150kΩ

1/2

7

DCLOCK

OPA2373

Electret

R3

1/2

+IN

ADS7816

6

DOUT

Serial

Microphone(1)

1MΩ

R

C2

OPA2373

2

12−Bit ADC

5

CS/SHDN

Interface

6

1000pF

− IN

100kΩ

3

4

GND

NOTE: (1) Electret microphone

G = 100

powered by R1.

R5

20kΩ

Figure 8. The OPA2373 as a Speech Bypass Filtered Data Acquisition System

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OPA373, OPA2373
OPA374
OPA2374, OPA4374	www.ti.com
SBOS279E − SEPTEMBER 2003 − REVISED MAY 2008

		+5V
	330pF		0.1µF		0.1µF
5kΩ	5kΩ
VIN		8	V+	1	VREF
					7
	500kΩ	+IN		DCLOCK
			ADS7816		6	Serial

OPA373	2		12−Bit ADC	DOUT	Interface
VS		−IN		CS/SHDN	5
2
3300pF		3	GND	4
				NOTE: ADC Input = 0 to VREF

Figure 9. The OPA373 in Inverting Configuration Driving the ADS7816

			C3
			330pF
		R2	R3
R1	1/2	2.72kΩ	21.4kΩ
11.7kΩ	OPA373		1/2
			OPA373

C1						C2
680pF						330pF

NOTE: FilterPro is a low-pass filter design program available for download at no cost from TI’s web site (www.ti.com). The program can be used to determine component values for other cutoff frequencies or filter types.

Figure 10. Three-Pole Sallen-Key Butterworth Low-Pass Filter

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