Datasheet

ManualsBrandsTEXAS INSTRUMENTS ManualsLinear ICsLinear IC - Op-amp Multi-purpose SOIC 8

IN+

IN-

~ 100 M:

Ion CHAMBER

LMP7721

HIGH VOLTAGE DC SUPPLY

a100 VDC

LMP7721

www.ti.com

SNOSAW6D –JANUARY 2008–REVISED MARCH 2013

LMP7721 3 Femtoampere Input Bias Current Precision Amplifier

Check for Samples: LMP7721

FEATURES

DESCRIPTION

The LMP7721 is the industry’s lowest specified input

• Unless Otherwise Noted, Typical Values at T

bias current precision amplifier. The ultra low input

= 25°C, V

= 5V.

bias current is 3 fA, with a specified limit of ±20 fA at

• Input Bias Current (V

= 1V)

25°C and ±900 fA at 85°C. This is achieved with the

– Max @ 25°C ±20 fA

latest patent pending technology of input bias current

cancellation amplifier circuitry. This technology also

– Max @ 85°C ±900 fA

maintains the ultra low input bias current over the

• Offset Voltage ±26 µV

entire input common mode voltage range of the

• Offset Voltage Drift −1.5 μV/°C

amplifier.

• DC Open Loop Gain 120 dB

Other outstanding features, such as low voltage noise

• DC CMRR 100 dB

(6.5 nV/√Hz), low DC offset voltage (±150 µV

maximum at 25°C) and low offset voltage

• Input Voltage Noise (at f = 1 kHz) 6.5 nV/√Hz

temperature coefficient (−1.5 µV/°C), improve system

• THD 0.0007%

sensitivity and accuracy in high precision

• Supply Current 1.3 mA

applications. With a supply voltage range of 1.8V to

5.5V, the LMP7721 is the ideal choice for battery

• GBW 17 MHz

operated portable applications. The LMP7721 is part

• Slew Rate (Falling Edge) 12.76 V/μs

of the LMP™ precision amplifier family.

• Supply Voltage 1.8V to 5.5V

As part of Texas Instruments' PowerWise™ products,

• Operating Temperature Range −40°C to 125°C

the LMP7721 provides the remarkably wide gain

• 8-Pin SOIC

bandwidth product (GBW) of 17 MHz while

consuming only 1.3 mA of current. This wide GBW

along with the high open loop gain of 120 dB enables

APPLICATIONS

accurate signal conditioning. With these

• Photodiode Amplifier

specifications, the LMP7721 has the performance to

• High Impedance Sensor Amplifier

excel in a wide variety of applications such as

electrochemical cell amplifiers and sensor interface

• Ion Chamber Amplifier

circuits.

• Electrometer Amplifier

The LMP7721 is offered in an 8-pin SOIC package

• pH Electrode Amplifier

with a special pinout that isolates the amplifier’s input

• Transimpedance Amplifier

from the power supply and output pins. With proper

board layout techniques, the unique pinout of the

LMP7721 will prevent PCB leakage current from

reaching the input pins. Thus system error will be

further reduced.

Block Diagram of a Typical Application

Figure 1. Ion Chamber: Current to Voltage Converter

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.

2LMP, PowerWise are trademarks of Texas Instruments.

3All other trademarks are the property of their respective owners.

PRODUCTION DATA information is current as of publication date.

Products conform to specifications per the terms of the Texas

Instruments standard warranty. Production processing does not

necessarily include testing of all parameters.

Summary of content (25 pages)

PAGE 1
LMP7721 www.ti.com SNOSAW6D – JANUARY 2008 – REVISED MARCH 2013 LMP7721 3 Femtoampere Input Bias Current Precision Amplifier Check for Samples: LMP7721 FEATURES DESCRIPTION • The LMP7721 is the industry’s lowest specified input bias current precision amplifier. The ultra low input bias current is 3 fA, with a specified limit of ±20 fA at 25°C and ±900 fA at 85°C. This is achieved with the latest patent pending technology of input bias current cancellation amplifier circuitry.
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LMP7721 SNOSAW6D – JANUARY 2008 – REVISED MARCH 2013 www.ti.com These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates. Absolute Maximum Ratings (1) (2) ESD Tolerance (3) Human Body Model 2000V Machine Model 200V VIN Differential ±0.3V Supply Voltage (VS = V+ – V−) (4) 6.0V Voltage on Input/Output Pins V+ +0.3V, V− −0.
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LMP7721 www.ti.com SNOSAW6D – JANUARY 2008 – REVISED MARCH 2013 2.5V Electrical Characteristics (continued) Unless otherwise specified, all limits are specified for TA = 25°C, V+ = 2.5V, V− = 0V, VCM = (V+ + V−)/2. Boldface limits apply at the temperature extremes. Symbol IBIAS Parameter Input Bias Current Conditions VCM = 1V Min (1) 25°C (4) (5) Typ (2) ±3 −40°C to 85°C −40°C to 125°C Input Offset Current VCM = 1V CMRR Common Mode Rejection Ratio 0V ≤ VCM ≤ 1.
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LMP7721 SNOSAW6D – JANUARY 2008 – REVISED MARCH 2013 www.ti.com 5V Electrical Characteristics Unless otherwise specified, all limits are specified for TA = 25°C, V+ = 5V, V− = 0V, VCM = (V+ + V−)/2. Boldface limits apply at the temperature extremes. Symbol Parameter Conditions Min (1) Typ Max Units (2) (1) VOS Input Offset Voltage ±26 ±150 ±450 μV TC VOS Input Offset Average Drift –1.
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LMP7721 www.ti.com SNOSAW6D – JANUARY 2008 – REVISED MARCH 2013 CONNECTION DIAGRAM IN+ N/C - V VOUT 1 8 2 7 3 6 4 5 IN- N/C V + N/C Figure 2.
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LMP7721 SNOSAW6D – JANUARY 2008 – REVISED MARCH 2013 www.ti.com Typical Performance Characteristics Unless otherwise specified: TA = 25°C, VCM = (V+ + V−)/2. Input Bias Current vs. VCM Input Bias Current vs. VCM 5 10 0 INPUT BIAS (fA) INPUT BIAS (fA) 0 -5 -10 -10 -20 -30 + + V = 5V V = 0V -15 V = 5V V = 0V -40 TA = 25°C -20 0 TA = 25°C 1 0.5 2 1.5 3 2.5 -50 3.5 0 1 2 VCM (V) Figure 3. Input Bias Current vs.
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LMP7721 www.ti.com SNOSAW6D – JANUARY 2008 – REVISED MARCH 2013 Typical Performance Characteristics (continued) Unless otherwise specified: TA = 25°C, VCM = (V+ + V−)/2. Offset Voltage Distribution 25 TCVOS Distribution 25 + V = 5.0V - V = 0V 20 PERCENTAGE (%) PERCENTAGE (%) 20 + V = 2.5V - 15 10 V = 0V 15 10 5 5 0 -200 -100 0 100 0 -4 200 -3 OFFSET VOLTAGE (PV) -2 Figure 9. Offset Voltage vs. VCM 400 + + V = 1.8V V- = 0V V = 5.
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LMP7721 SNOSAW6D – JANUARY 2008 – REVISED MARCH 2013 www.ti.com Typical Performance Characteristics (continued) Unless otherwise specified: TA = 25°C, VCM = (V+ + V−)/2. Offset Voltage vs. Supply Voltage Offset Voltage vs. Temperature 200 400 150 300 + OFFSET VOLTAGE (PV) 200 100 25°C 0 -100 -200 125°C V = +2.5V 100 - V = 0V 50 0 + V = +5V -50 - V = 0V -100 -300 -150 -400 1.5 2.5 3.5 4.5 5.5 -200 -40 -20 6 VS (V) 0 20 40 60 Figure 16. Supply Current vs.
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LMP7721 www.ti.com SNOSAW6D – JANUARY 2008 – REVISED MARCH 2013 Typical Performance Characteristics (continued) Unless otherwise specified: TA = 25°C, VCM = (V+ + V−)/2. Phase Margin vs. Capacitive Load CMRR vs. Frequency 45 100 VS = 5V 40 90 RL = 600: 30 RL = 10 k: 25 20 80 CMRR (dB) PHASE MARGIN (°) 35 RL = 10 M: 70 15 60 10 50 5 + V = +2.5V - 0 20 V = -2.5V 40 10 100 200 1k Figure 21. PSRR vs. Frequency 1M Input Referred Voltage Noise vs.
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LMP7721 SNOSAW6D – JANUARY 2008 – REVISED MARCH 2013 www.ti.com Typical Performance Characteristics (continued) Unless otherwise specified: TA = 25°C, VCM = (V+ + V−)/2. Small Signal Step Response Large Signal Step Response + + f = 1 MHz V = +2.5V V = -1.25V - AV = +1 V = -2.5V VIN = 20 mVPP CL = 10 pF V = +1.25V CL = 10 pF VIN = 1 VPP f = 200 kHz - RL = 1 M: AV = +1 10 mV/DIV 200 mV/DIV RL = 1 M: 1 Ps/DIV 200 ns/DIV Figure 27. Figure 28. Large Signal Step Response THD+N vs.
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LMP7721 www.ti.com SNOSAW6D – JANUARY 2008 – REVISED MARCH 2013 Typical Performance Characteristics (continued) Unless otherwise specified: TA = 25°C, VCM = (V+ + V−)/2. THD+N vs. Frequency 0.008 Sourcing Current vs. Supply Voltage 80 + V = +2.5V 0.007 V- = -2.5V 70 125°C 60 ISOURCE (mA) THD+N (%) 0.006 VO = 4 VPP AV = +2 0.005 0.004 0.003 50 25°C 40 -40°C 30 RL = 600: 0.002 20 0.001 10 RL = 100 k: 0 10 100 1k 0 1.5 100k 10k 2.5 3.5 FREQUENCY (Hz) 4.5 5.5 VS (V) Figure 33.
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LMP7721 SNOSAW6D – JANUARY 2008 – REVISED MARCH 2013 www.ti.com Typical Performance Characteristics (continued) Unless otherwise specified: TA = 25°C, VCM = (V+ + V−)/2. Sinking Current vs. Output Voltage Output Swing High vs. Supply Voltage 35 50 + RL = 10 k: V = +5V - V = 0V 125°C VOUT FROM RAIL (mV) 30 ISINK (mA) 25 20 15 25°C -40°C 10 40 125°C 30 25°C 20 10 -40°C 5 0 0 1 2 3 4 0 1.5 5 2.5 3.5 VOUT (V) Figure 40. Output Swing Low vs. Supply Voltage Output Swing High vs.
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LMP7721 www.ti.com SNOSAW6D – JANUARY 2008 – REVISED MARCH 2013 Typical Performance Characteristics (continued) Unless otherwise specified: TA = 25°C, VCM = (V+ + V−)/2. Output Swing Low vs. Supply Voltage 140 RL = 600: VOUT FROM RAIL (mV) 120 25°C 100 125°C 80 60 -40°C 40 20 0 1.5 2.5 3.5 4.5 5.
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LMP7721 SNOSAW6D – JANUARY 2008 – REVISED MARCH 2013 www.ti.com APPLICATION INFORMATION ADVANTAGES OF THE LMP7721 Ultra Low Input Bias Current The LMP7721 has the industry’s lowest specified input bias current. The ultra low input bias current is typically 3 fA, with a specified limit of ±20 fA at 25°C, ±900 fA at 85°C and ±5 pA at 125°C when VCM = 1V with a 5V or a 2.5V power supply.
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LMP7721 www.ti.com SNOSAW6D – JANUARY 2008 – REVISED MARCH 2013 OUTER SHIELD/GROUND GUARD 1 SIGNAL CONDUCTOR Figure 46. The Structure of a Triax The signal conductor and the guard of the triax should be kept at the same potential; therefore, the leakage current between them is practically zero. Since triax has an extra layer of insulation and a second conducting sheath, it offers greater rejection of interference than coaxial cable/connector.
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LMP7721 SNOSAW6D – JANUARY 2008 – REVISED MARCH 2013 www.ti.com (4) regardless of whether the amplifier is being used in inverting or non-inverting mode. Note that a feedback capacitor is more likely to be needed when the noise gain is low and/or the feedback resistor is large.
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LMP7721 www.ti.com SNOSAW6D – JANUARY 2008 – REVISED MARCH 2013 Using the smaller capacitors will give much higher bandwidth with little degradation of transient response.
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LMP7721 SNOSAW6D – JANUARY 2008 – REVISED MARCH 2013 www.ti.com CF RF + V 0.1 µF TRIAX LMP7721 + VREF LIGHT Vout 10 k: 0.1 µF - 10 k: V 0.1 µF 100: + LMP7715 - 0.1 µF Figure 49. LMP7721 as Transimpedance Amplifier The current generated by the photodiode is fed to the signal conductor of the triax and then sent to the inverting input of the LMP7721. The LMP7721’s non-inverting input is biased at VREF/2 for level shifting purposes.
PAGE 19
LMP7721 www.ti.com SNOSAW6D – JANUARY 2008 – REVISED MARCH 2013 RF + V 0.1 µF RG LMP7721 Vout + TRIAX 0.1 µF - V 0.1 µF 100: + LMP7715 0.1 µF pH ELECTRODE Figure 51. LMP7721 as pH Electrode Amplifier The output voltage from the pH electrode is fed to the signal conductor of the triax and then sent to the noninverting input of the LMP7721. In this application, the inverting input is a low impedance node and hence is used to drive the LMP7715 which acts as a guard driver.
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LMP7721 SNOSAW6D – JANUARY 2008 – REVISED MARCH 2013 www.ti.com REVISION HISTORY Changes from Revision C (March 2013) to Revision D • 20 Page Changed layout of National Data Sheet to TI format ..........................................................................................................
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PACKAGE OPTION ADDENDUM www.ti.
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PACKAGE MATERIALS INFORMATION www.ti.com 8-Apr-2013 TAPE AND REEL INFORMATION *All dimensions are nominal Device LMP7721MAX/NOPB Package Package Pins Type Drawing SOIC D 8 SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) 2500 330.0 12.4 Pack Materials-Page 1 6.5 B0 (mm) K0 (mm) P1 (mm) 5.4 2.0 8.0 W Pin1 (mm) Quadrant 12.
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PACKAGE MATERIALS INFORMATION www.ti.com 8-Apr-2013 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) LMP7721MAX/NOPB SOIC D 8 2500 367.0 367.0 35.
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IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and complete.