LM7321MA - Texas Instruments High-Performance Analog

LM7321/LM7321Q Single/

LM7322/LM7322Q Dual Rail-

to-Rail Input/Output

January 5, 2012

±15V, High Output Current and Unlimited Capacitive Load

Operational Amplifier

General Description

The LM7321/LM7321Q/LM7322/LM7322Q are rail-to-rail in-

put and output amplifiers with wide operating voltages and

high output currents. The LM7321/LM7321Q/LM7322/

LM7322Q are efficient, achieving 18 V/µs slew rate and 20

MHz unity gain bandwidth while requiring only 1 mA of supply

current per op amp. The LM7321/LM7321Q/LM7322/

LM7322Q performance is fully specified for operation at 2.7V,

±5V and ±15V.

The LM7321/LM7321Q/LM7322/LM7322Q are designed to

drive unlimited capacitive loads without oscillations. All

LM7321/LM7321Q and LM7322/LM732Q parts are tested at

−40°C, 125°C, and 25°C, with modern automatic test equip-

ment. High performance from −40°C to 125°C, detailed spec-

ifications, and extensive testing makes them suitable for

industrial, automotive, and communications applications.

Greater than rail-to-rail input common mode voltage range

with 50 dB of common mode rejection across this wide voltage

range, allows both high side and low side sensing. Most de-

vice parameters are insensitive to power supply voltage, and

this makes the parts easier to use where supply voltage may

vary, such as automotive electrical systems and battery pow-

ered equipment. These amplifiers have true rail-to-rail output

and can supply a respectable amount of current (15 mA) with

minimal head- room from either rail (300 mV) at low distortion

(0.05% THD+Noise). There are several package options for

each part. Standard SOIC versions of both parts make up-

grading existing designs easy. LM7322LM7322Q are offered

in a space saving 8-Pin MSOP package. The LM7321/

LM7321Q are offered in small SOT23-5 package, which

makes it easy to place this part close to sensors for better

circuit performance.

Features

(VS = ±15, TA = 25°C, Typical values unless specified.)

■Wide supply voltage range 2.5V to 32V

■Output current +65 mA/−100 mA

■Gain bandwidth product 20 MHz

■Slew rate 18 V/µs

■Capacitive load tolerance Unlimited

■Input common mode voltage 0.3V beyond rails

■Input voltage noise 15 nV/√Hz

■Input current noise 1.3 pA/√Hz

■Supply current/channel 1.1 mA

■Distortion THD+Noise −86 dB

■Temperature range −40°C to 125°C

■Tested at −40°C, 25°C and 125°C at 2.7V, ±5V, ±15V.

■LM7321Q/LM7322Q are Automotive Grade products that

are AEC-Q100 Grade 1 qualified.

Applications

■Driving MOSFETs and power transistors

■Capacitive proximity sensors

■Driving analog optocouplers

■High side sensing

■Below ground current sensing

■Photodiode biasing

■Driving varactor diodes in PLLs

■Wide voltage range power supplies

■Automotive

■International power supplies

Typical Performance Characteristics

Output Swing vs. Sourcing Current

20205736

Large Signal Step Response

20205749

LM7321/LM7321Q Single/ LM7322/LM7322Q Dual Rail-to-Rail Input/Output, ±15V, High Output

Current and Unlimited Capacitive Load Operational Amplifier

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

please contact the Texas Instruments Sales Office/

Distributors for availability and specifications.

ESD Tolerance (Note 2)

Human Body Model 2 kV

Machine Model 200V

Charge-Device Model 1 kV

VIN Differential ±10V

Output Short Circuit Current (Note 3)

Supply Voltage (VS = V+ - V−)35V

Voltage at Input/Output pins V+ +0.8V, V− −0.8V

Storage Temperature Range −65°C to 150°C

Junction Temperature (Note 4) 150°C

Soldering Information:

Infrared or Convection (20 sec.) 235°C

Wave Soldering (10 sec.) 260°C

Operating Ratings

Supply Voltage (VS = V+ - V−)2.5V to 32V

Temperature Range (Note 4) −40°C to 125°C

Package Thermal Resistance, θJA,(Note 4)

5-Pin SOT-23 325°C/W

8-Pin MSOP 235°C/W

8-Pin SOIC 165°C/W

2.7V Electrical Characteristics (Note 5)

Unless otherwise specified, all limits guaranteed for TA = 25°C, V+ = 2.7V, V− = 0V, VCM = 0.5V, VOUT = 1.35V, and

RL > 1 MΩ to 1.35V. Boldface limits apply at the temperature extremes.

Symbol Parameter Condition Min

(Note 7)

Typ

(Note 6)

Max

(Note 7)Units

VOS Input Offset Voltage VCM = 0.5V & VCM = 2.2V −5

−6 ±0.7 +5

+6 mV

TC VOS Input Offset Voltage Temperature Drift VCM = 0.5V & VCM = 2.2V

(Note 8) ±2 µV/C

IBInput Bias Current

VCM = 0.5V

(Note 9)

−2.0

−2.5

−1.2

µA

VCM = 2.2V

(Note 9)

0.45 1.0

1.5

IOS Input Offset Current VCM = 0.5V and VCM = 2.2V 20 200

300 nA

CMRR Common Mode Rejection Ratio

0V ≤ VCM ≤ 1.0V 70

100

0V ≤ VCM ≤ 2.7V 55

PSRR Power Supply Rejection Ratio 2.7V ≤ VS ≤ 30V 78

104 dB

CMVR Common Mode Voltage Range CMRR > 50 dB

−0.3 −0.1

0.0 V

2.8

2.7

3.0

AVOL Open Loop Voltage Gain

0.5V ≤ VO ≤ 2.2V

RL = 10 kΩ to 1.35V

0.5V ≤ VO ≤ 2.2V

RL = 2 kΩ to 1.35V

VOUT

Output Voltage Swing

High

RL = 10 kΩ to 1.35V

VID = 100 mV

50 150

160

mV from

either rail

RL = 2 kΩ to 1.35V

VID = 100 mV

100 250

280

Output Voltage Swing

Low

RL = 10 kΩ to 1.35V

VID = −100 mV

20 120

150

RL = 2 kΩ to 1.35V

VID = −100 mV

40 120

150

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LM7321/LM7321Q/LM7322/LM7322Q

Symbol Parameter Condition Min

(Note 7)

Typ

(Note 6)

Max

(Note 7)Units

IOUT Output Current

Sourcing

VID = 200 mV, VOUT = 0V (Note 3)

Sinking

VID = −200 mV, VOUT = 2.7V (Note 3)

ISSupply Current

LM7321 0.95 1.3

1.9 mA

LM7322 2.0 2.5

3.8

SR Slew Rate (Note 10) AV = +1, VI = 2V Step 8.5 V/µs

fuUnity Gain Frequency RL = 2 kΩ, CL = 20 pF 7.5 MHz

GBW Gain Bandwidth f = 50 kHz 16 MHz

enInput Referred Voltage Noise Density f = 2 kHz 11.9 nV/

inInput Referred Current Noise Density f = 2 kHz 0.5 pA/

THD+N Total Harmonic Distortion + Noise

V+ = 1.9V, V− = −0.8V

f = 1 kHz, RL = 100 kΩ, AV = +2

VOUT = 210 mVPP

−77 dB

CT Rej. Crosstalk Rejection f = 100 kHz, Driver RL = 10 kΩ 60 dB

±5V Electrical Characteristics (Note 5)

Unless otherwise specified, all limited guaranteed for TA = 25°C, V+ = 5V, V− = −5V, VCM = 0V, VOUT = 0V, and

RL > 1 MΩ to 0V. Boldface limits apply at the temperature extremes.

Symbol Parameter Condition Min

(Note 7)

Typ

(Note 6)

Max

(Note 7)Units

VOS Input Offset Voltage VCM = −4.5V and VCM = 4.5V −5

−6

±0.7 +5

+6 mV

TC VOS Input Offset Voltage Temperature Drift VCM = −4.5V and VCM = 4.5V

(Note 8) ±2 µV/°C

IBInput Bias Current

VCM = −4.5V

(Note 9)

−2.0

−2.5

−1.2

µA

VCM = 4.5V

(Note 9)

0.45 1.0

1.5

IOS Input Offset Current VCM = −4.5V and VCM = 4.5V 20 200

300 nA

CMRR Common Mode Rejection Ratio

−5V ≤ VCM ≤ 3V 80

100

−5V ≤ VCM ≤ 5V 65

PSRR Power Supply Rejection Ratio 2.7V ≤ VS ≤ 30V, VCM = −4.5V 78

104 dB

CMVR Common Mode Voltage Range CMRR > 50 dB

−5.3 −5.1

−5.0 V

5.1

5.0

5.3

AVOL Open Loop Voltage Gain

−4V ≤ VO ≤ 4V

RL = 10 kΩ to 0V

−4V ≤ VO ≤ 4V

RL = 2 kΩ to 0V

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LM7321/LM7321Q/LM7322/LM7322Q

Symbol Parameter Condition Min

(Note 7)

Typ

(Note 6)

Max

(Note 7)Units

VOUT

Output Voltage Swing

High

RL = 10 kΩ to 0V

VID = 100 mV

100 250

280

mV from

either rail

RL = 2 kΩ to 0V

VID = 100 mV

160 350

450

Output Voltage Swing

Low

RL = 10 kΩ to 0V

VID = −100 mV

35 200

250

RL = 2 kΩ to 0V

VID = −100 mV

80 200

250

IOUT Output Current

Sourcing

VID = 200 mV, VOUT = −5V (Note 3)

Sinking

VID = −200 mV, VOUT = 5V (Note 3)

ISSupply Current VCM = −4.5V

LM7321 1.0 1.3

2mA

LM7322 2.3 2.8

3.8

SR Slew Rate (Note 10) AV = +1, VI = 8V Step 12.3 V/µs

fuUnity Gain Frequency RL = 2 kΩ, CL = 20 pF 9 MHz

GBW Gain Bandwidth f = 50 kHz 16 MHz

enInput Referred Voltage Noise Density f = 2 kHz 14.3 nV/

inInput Referred Current Noise Density f = 2 kHz 1.35 pA/

THD+N Total Harmonic Distortion + Noise f = 1 kHz, RL = 100 kΩ, AV = +2

VOUT = 8 VPP

−79 dB

CT Rej. Crosstalk Rejection f = 100 kHz, Driver RL = 10 kΩ 60 dB

±15V Electrical Characteristics (Note 5)

Unless otherwise specified, all limited guaranteed for TA = 25°C, V+ = 15V, V− = −15V, VCM = 0V, VOUT = 0V, and

RL > 1MΩ to 15V. Boldface limits apply at the temperature extremes.

Symbol Parameter Condition Min

(Note 7)

Typ

(Note 6)

Max

(Note 7)Units

VOS Input Offset Voltage VCM = −14.5V and VCM = 14.5V −6

−8

±0.7 +6

+8 mV

TC VOS Input Offset Voltage Temperature Drift VCM = −14.5V and VCM = 14.5V

(Note 8)

±2 µV/°C

IBInput Bias Current

VCM = −14.5V

(Note 9)

−2

−2.5

−1.1

µA

VCM = 14.5V

(Note 9)

0.45 1.0

1.5

IOS Input Offset Current VCM = −14.5V and VCM = 14.5V 30 300

500 nA

CMRR Common Mode Rejection Ratio

−15V ≤ VCM ≤ 12V 80

100

−15V ≤ VCM ≤ 15V 72

PSRR Power Supply Rejection Ratio 2.7V ≤ VS ≤ 30V, VCM = −14.5V 78

100 dB

CMVR Common Mode Voltage Range CMRR > 50 dB

−15.3 −15.1

−15 V

15.1

15.3

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LM7321/LM7321Q/LM7322/LM7322Q

Symbol Parameter Condition Min

(Note 7)

Typ

(Note 6)

Max

(Note 7)Units

AVOL Open Loop Voltage Gain

−13V ≤ VO ≤ 13V

RL = 10 kΩ to 0V

−13V ≤ VO ≤ 13V

RL = 2 kΩ to 0V

VOUT

Output Voltage Swing

High

RL = 10 kΩ to 0V

VID = 100 mV

150 300

350

mV from

either rail

RL = 2 kΩ to 0V

VID = 100 mV

250 550

650

Output Voltage Swing

Low

RL = 10 kΩ to 0V

VID = −100 mV

60 200

250

RL = 2 kΩ to 0V

VID = −100 mV

130 300

400

IOUT Output Current

Sourcing

VID = 200 mV, VOUT = −15V (Note 3)

40 65

Sinking

VID = −200 mV, VOUT = 15V (Note 3)

60 100

ISSupply Current VCM = −14.5V

LM7321 1.1 1.7

2.4 mA

LM7322 2.5 4

5.6

SR Slew Rate

(Note 10)

AV = +1, VI = 20V Step 18 V/µs

fuUnity Gain Frequency RL = 2 kΩ, CL = 20 pF 11.3 MHz

GBW Gain Bandwidth f = 50 kHz 20 MHz

enInput Referred Voltage Noise Density f = 2 kHz 15 nV/

inInput Referred Current Noise Density f = 2 kHz 1.3 pA/

THD+N Total Harmonic Distortion +Noise f = 1 kHz, RL 100 kΩ,

AV = +2, VOUT = 23 VPP

−86 dB

CT Rej. Crosstalk Rejection f = 100 kHz, Driver RL = 10 kΩ 60 dB

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Rating indicate conditions for which the device is

intended to be functional, but specific performance is not guaranteed. For guaranteed specifications and the test conditions, see the Electrical Characteristics.

Note 2: Human Body Model, applicable std. MIL-STD-883, Method 3015.7. Machine Model, applicable std. JESD22-A115-A (ESD MM std. of JEDEC)

Field-Induced Charge-Device Model, applicable std. JESD22-C101-C (ESD FICDM std. of JEDEC).

Note 3: Applies to both single-supply and split-supply operation. Continuous short circuit operation at elevated ambient temperature can result in exceeding the

maximum allowed junction temperature of 150°C. Short circuit test is a momentary test. Output short circuit duration is infinite for VS ≤ 6V at room temperature

and below. For VS > 6V, allowable short circuit duration is 1.5 ms.

Note 4: The maximum power dissipation is a function of TJ(MAX), θJA. The maximum allowable power dissipation at any ambient temperature is

PD = (TJ(MAX)) - TA)/ θJA. All numbers apply for packages soldered directly onto a PC board.

Note 5: Electrical Table values apply only for factory testing conditions at the temperature indicated. Factory testing conditions result in very limited self-heating

of the device such that TJ = TA. No guarantee of parametric performance is indicated in the electrical tables under conditions of internal self-heating where TJ >

TA.

Note 6: Typical values represent the most likely parametric norm as determined at the time of characterization. Actual typical values may vary over time and will

also depend on the application and configuration. The typical values are not tested and are not guaranteed on shipped production material.

Note 7: All limits are guaranteed by testing or statistical analysis.

Note 8: Offset voltage temperature drift determined by dividing the change in VOS at temperature extremes into the total temperature change.

Note 9: Positive current corresponds to current flowing into the device.

Note 10: Slew rate is the slower of the rising and falling slew rates. Connected as a Voltage Follower.

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LM7321/LM7321Q/LM7322/LM7322Q

Connection Diagrams

5-Pin SOT-23

20205705

Top View

8-Pin SOIC

20205703

Top View

8-Pin MSOP/SOIC

20205706

Top View

Ordering Information

Package Part Number Package

Marking Media Transport NSC Drawing

5-Pin SOT-23

LM7321MF

AU4A

1k Units Tape and Reel

MF05A

LM7321MFE 250 Units Tape and Reel

LM7321MFX 3k Units Tape and Reel

LM7321QMF

AR8A

1k Units Tape and Reel

LM7321QMFE 250 Units Tape and Reel

LM7321QMFX 3k Units Tape and Reel

8-Pin MSOP

LM7322MM

AZ4A

1k Units Tape and Reel

MUA08ALM7322MME 250 Units Tape and Reel

LM7322MMX 3.5k Units Tape and Reel

8-Pin SOIC

LM7321MA LM7321MA 95 Units/Rail

M08A

LM7321MAX 2.5k Units Tape and Reel

LM7322MA LM7322MA 95 Units/Rail

LM7322MAX 2.5k Units Tape and Reel

LM7322QMA LM7322QMA 95 Units/Rail

LM7322QMAX 2.5k Units Tape and Reel

Automotive Grade (Q) product incorporates enhanced manufacturing and support processes for the automotive market, including

defect detection methodologies. Reliability qualification is compliant with the requirements and temperature grades defined in the

AEC-Q100 standard. Automotive Grade products are identified with the letter Q. PPAP (Production Part Approval Process) doc-

umentation of the device technology, process and qualification is available from Texas Instruments upon request.

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LM7321/LM7321Q/LM7322/LM7322Q

Typical Performance Characteristics Unless otherwise specified: TA = 25°C.

Output Swing vs. Sourcing Current

20205734

Output Swing vs. Sinking Current

20205731

Output Swing vs. Sourcing Current

20205735

Output Swing vs. Sinking Current

20205732

Output Swing vs. Sourcing Current

20205736

Output Swing vs. Sinking Current

20205733

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LM7321/LM7321Q/LM7322/LM7322Q

VOS Distribution

20205730

VOS vs. VCM (Unit 1)

20205707

VOS vs. VCM (Unit 2)

20205708

VOS vs. VCM (Unit 3)

20205709

VOS vs. VCM (Unit 1)

20205710

VOS vs. VCM (Unit 2)

20205711

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LM7321/LM7321Q/LM7322/LM7322Q

VOS vs. VCM (Unit 2)

20205712

VOS vs. VCM (Unit 1)

20205713

VOS vs. VCM (Unit 2)

20205714

VOS vs. VCM (Unit 3)

20205715

VOS vs. VS (Unit 1)

20205750

VOS vs. VS (Unit 2)

20205751

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LM7321/LM7321Q/LM7322/LM7322Q

VOS vs. VS (Unit 3)

20205752

VOS vs. VS (Unit 1)

20205753

VOS vs. VS (Unit 2)

20205754

VOS vs. VS (Unit 3)

20205755

IBIAS vs. VCM

20205723

IBIAS vs. VCM

20205724

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LM7321/LM7321Q/LM7322/LM7322Q

IBIAS vs. VCM

20205725

IBIAS vs. VS

20205722

IBIAS vs. VS

20205721

IS vs. VCM (LM7321)

20205718

IS vs. VCM (LM7322)

20205775

IS vs. VCM (LM7321)

20205719

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LM7321/LM7321Q/LM7322/LM7322Q

IS vs. VCM (LM7322)

20205776

IS vs. VCM (LM7321)

20205720

IS vs. VCM (LM7322)

20205777

IS vs. VS (LM7321)

20205717

IS vs. VS (LM7322)

20205779

IS vs. VS (LM7321)

20205716

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LM7321/LM7321Q/LM7322/LM7322Q

IS vs. VS (LM7322)

20205778

Positive Output Swing vs. Supply Voltage

20205727

Positive Output Swing vs. Supply Voltage

20205726

Negative Output Swing vs. Supply Voltage

20205728

Negative Output Swing vs. Supply Voltage

20205729

Open Loop Frequency Response with Various Capacitive

Load

20205782

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LM7321/LM7321Q/LM7322/LM7322Q

Open Loop Frequency Response with Various Resistive

Load

20205783

Open Loop Frequency Response with Various Supply

Voltage

20205784

Phase Margin vs. Capacitive Load

20205738

CMRR vs. Frequency

20205739

+PSRR vs. Frequency

20205740

−PSRR vs. Frequency

20205741

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LM7321/LM7321Q/LM7322/LM7322Q

Small Signal Step Response

20205737

Large Signal Step Response

20205749

Input Referred Noise Density vs. Frequency

20205742

Input Referred Noise Density vs. Frequency

20205743

Input Referred Noise Density vs. Frequency

20205744

THD+N vs. Frequency

20205745

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LM7321/LM7321Q/LM7322/LM7322Q

THD+N vs. Output Amplitude

20205746

THD+N vs. Output Amplitude

20205747

THD+N vs. Output Amplitude

20205748

Crosstalk Rejection vs. Frequency

20205768

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LM7321/LM7321Q/LM7322/LM7322Q

Application Information

DRIVING CAPACITIVE LOADS

The LM7321/LM7321Q/LM7322/LM7322Q are specifically

designed to drive unlimited capacitive loads without oscilla-

tions as shown in Figure 1.

20205769

FIGURE 1. ±5% Settling Time vs. Capacitive Load

In addition, the output current handling capability of the device

allows for good slewing characteristics even with large ca-

pacitive loads as shown in Figure 2 and Figure 3.

20205770

FIGURE 2. +SR vs. Capacitive Load

20205771

FIGURE 3. −SR vs. Capacitive Load

The combination of these features is ideal for applications

such as TFT flat panel buffers, A/D converter input amplifiers,

etc.

However, as in most op amps, addition of a series isolation

resistor between the op amp and the capacitive load improves

the settling and overshoot performance.

Output current drive is an important parameter when driving

capacitive loads. This parameter will determine how fast the

output voltage can change. Referring to the Slew Rate vs.

Capacitive Load Plots (typical performance characteristics

section), two distinct regions can be identified. Below about

10,000 pF, the output Slew Rate is solely determined by the

op amp’s compensation capacitor value and available current

into that capacitor. Beyond 10 nF, the Slew Rate is deter-

mined by the op amp’s available output current. Note that

because of the lower output sourcing current compared to the

sinking one, the Slew Rate limit under heavy capacitive load-

ing is determined by the positive transitions. An estimate of

positive and negative slew rates for loads larger than 100 nF

can be made by dividing the short circuit current value by the

capacitor.

For the LM7321/LM7321Q/LM7322/LM7322Q, the available

output current increases with the input overdrive. Referring to

Figure 4 and Figure 5, Output Short Circuit Current vs. Input

Overdrive, it can be seen that both sourcing and sinking short

circuit current increase as input overdrive increases. In a

closed loop amplifier configuration, during transient condi-

tions while the fed back output has not quite caught up with

the input, there will be an overdrive imposed on the input al-

lowing more output current than would normally be available

under steady state condition. Because of this feature, the op

amp’s output stage quiescent current can be kept to a mini-

mum, thereby reducing power consumption, while enabling

the device to deliver large output current when the need arises

(such as during transients).

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LM7321/LM7321Q/LM7322/LM7322Q

20205772

FIGURE 4. Output Short Circuit Sourcing Current vs.

Input Overdrive

20205773

FIGURE 5. Output Short Circuit Sinking Current vs. Input

Overdrive

Figure 6 shows the output voltage, output current, and the

resulting input overdrive with the device set for AV = +1 and

the input tied to a 1 VPP step function driving a 47 nF capacitor.

As can be seen, during the output transition, the input over-

drive reaches 1V peak and is more than enough to cause the

output current to increase to its maximum value (see Figure

4 and Figure 5 plots). Note that because of the larger output

sinking current compared to the sourcing one, the output neg-

ative transition is faster than the positive one.

20205774

FIGURE 6. Buffer Amplifier Scope Photo

ESTIMATING THE OUTPUT VOLTAGE SWING

It is important to keep in mind that the steady state output

current will be less than the current available when there is

an input overdrive present. For steady state conditions, the

Output Voltage vs. Output Current plot (Typical Performance

Characteristics section) can be used to predict the output

swing. Figure 7 and Figure 8 show this performance along

with several load lines corresponding to loads tied between

the output and ground. In each cases, the intersection of the

device plot at the appropriate temperature with the load line

would be the typical output swing possible for that load. For

example, a 1 kΩ load can accommodate an output swing to

within 250 mV of V− and to 330 mV of V+ (VS = ±15V) corre-

sponding to a typical 29.3 VPP unclipped swing.

20205756

FIGURE 7. Output Sourcing Characteristics with Load

Lines

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LM7321/LM7321Q/LM7322/LM7322Q

20205757

FIGURE 8. Output Sinking Characteristics with Load

Lines

SETTLING TIME WITH LARGE CAPACITIVE LOADS

Figure 9 below shows a typical application where the LM7321/

LM7321Q/LM7322/LM7322Q is used as a buffer amplifier for

the VCOM signal employed in a TFT LCD flat panel:

20205758

FIGURE 9. VCOM Driver Application Schematic

Figure 10 shows the time domain response of the amplifier

when used as a VCOM buffer/driver with VREF at ground. In this

application, the op amp loop will try and maintain its output

voltage based on the voltage on its non-inverting input

(VREF) despite the current injected into the TFT simulated

load. As long as this load current is within the range tolerable

by the LM7321/LM7321Q/LM7322/LM7322Q (45 mA sourc-

ing and 65 mA sinking for ±5V supplies), the output will settle

to its final value within less than 2 μs.

20205759

FIGURE 10. VCOM Driver Performance Scope Photo

OUTPUT SHORT CIRCUIT CURRENT AND DISSIPATION

ISSUES

The LM7321/LM7321Q/LM7322/LM7322Q output stage is

designed for maximum output current capability. Even though

momentary output shorts to ground and either supply can be

tolerated at all operating voltages, longer lasting short condi-

tions can cause the junction temperature to rise beyond the

absolute maximum rating of the device, especially at higher

supply voltage conditions. Below supply voltage of 6V, the

output short circuit condition can be tolerated indefinitely.

With the op amp tied to a load, the device power dissipation

consists of the quiescent power due to the supply current flow

into the device, in addition to power dissipation due to the load

current. The load portion of the power itself could include an

average value (due to a DC load current) and an AC compo-

nent. DC load current would flow if there is an output voltage

offset, or the output AC average current is non-zero, or if the

op amp operates in a single supply application where the out-

put is maintained somewhere in the range of linear operation.

Therefore:

PTOTAL = PQ + PDC + PAC

PQ = IS · VSOp Amp Quiescent Power

Dissipation

PDC = IO · (Vr - Vo) DC Load Power

PAC = See Table 1 below AC Load Power

where:

IS: Supply Current

VS: Total Supply Voltage (V+ − V−)

VO: Average Output Voltage

Vr: V+ for sourcing and V− for sinking current

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LM7321/LM7321Q/LM7322/LM7322Q

Table 1 below shows the maximum AC component of the load

power dissipated by the op amp for standard Sinusoidal, Tri-

angular, and Square Waveforms:

TABLE 1. Normalized AC Power Dissipated in the Output

Stage for Standard Waveforms

PAC (W.Ω/V2)

Sinusoidal Triangular Square

50.7 x 10−3 46.9 x 10−3 62.5 x 10−3

The table entries are normalized to VS2/RL. To figure out the

AC load current component of power dissipation, simply mul-

tiply the table entry corresponding to the output waveform by

the factor VS2/RL. For example, with ±12V supplies, a 600Ω

load, and triangular waveform power dissipation in the output

stage is calculated as:

PAC = (46.9 x 10−3) · (242/600) = 45.0 mW

The maximum power dissipation allowed at a certain temper-

ature is a function of maximum die junction temperature (TJ

(MAX)) allowed, ambient temperature TA, and package thermal

resistance from junction to ambient, θJA.

For the LM7321/LM7321Q/LM7322/LM7322Q, the maximum

junction temperature allowed is 150°C at which no power dis-

sipation is allowed. The power capability at 25°C is given by

the following calculations:

For MSOP package:

For SOIC package:

Similarly, the power capability at 125°C is given by:

For MSOP package:

For SOIC package:

Figure 11 shows the power capability vs. temperature for

MSOP and SOIC packages. The area under the maximum

thermal capability line is the operating area for the device.

When the device works in the operating area where PTOTAL is

less than PD(MAX), the device junction temperature will remain

below 150°C. If the intersection of ambient temperature and

package power is above the maximum thermal capability line,

the junction temperature will exceed 150°C and this should

be strictly prohibited.

20205765

FIGURE 11. Power Capability vs. Temperature

When high power is required and ambient temperature can't

be reduced, providing air flow is an effective approach to re-

duce thermal resistance therefore to improve power capabil-

ity.

Other Application Hints

The use of supply decoupling is mandatory in most applica-

tions. As with most relatively high speed/high output current

Op Amps, best results are achieved when each supply line is

decoupled with two capacitors; a small value ceramic capac-

itor (∼0.01 μF) placed very close to the supply lead in addition

to a large value Tantalum or Aluminum (> 4.7 μF). The large

capacitor can be shared by more than one device if neces-

sary. The small ceramic capacitor maintains low supply

impedance at high frequencies while the large capacitor will

act as the charge "bucket" for fast load current spikes at the

op amp output. The combination of these capacitors will pro-

vide supply decoupling and will help keep the op amp oscil-

lation free under any load.

SIMILAR HIGH OUTPUT DEVICES

The LM7332 is a dual rail-to-rail amplifier with a slightly lower

GBW capable of sinking and sourcing 100 mA. It is available

in SOIC and MSOP packages.

The LM4562 is dual op amp with very low noise and 0.7 mV

voltage offset.

The LME49870 and LME49860 are single and dual low noise

amplifiers that can work from ±22 volt supplies.

OTHER HIGH PERFORMANCE SOT-23 AMPLIERS

The LM7341 is a 4 MHz rail-to-rail input and output part that

requires only 0.6 mA to operate, and can drive unlimited ca-

pacitive load. It has a voltage gain of 97 dB, a CMRR of 93

dB, and a PSRR of 104 dB.

The LM6211 is a 20 MHz part with CMOS input, which runs

on ±12 volt or 24 volt single supplies. It has rail-to-rail output

and low noise.

The LM7121 has a gain bandwidth of 235 MHz.

Detailed information on these parts can be found at

www.national.com.

www.ti.com 20

LM7321/LM7321Q/LM7322/LM7322Q

Physical Dimensions inches (millimeters) unless otherwise noted

5-Pin SOT-23

NS Package Number MF05A

8-Pin MSOP

NS Package Number MUA08A

21 www.ti.com

LM7321/LM7321Q/LM7322/LM7322Q

8-Pin SOIC

NS Package Number M08A

www.ti.com 22

LM7321/LM7321Q/LM7322/LM7322Q

Notes

23 www.ti.com

LM7321/LM7321Q/LM7322/LM7322Q

Notes

LM7321/LM7321Q Single/ LM7322/LM7322Q Dual Rail-to-Rail Input/Output, ±15V, High Output

Current and Unlimited Capacitive Load Operational Amplifier

www.ti.com

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