INA12x-HT Precision, Low-Power Instrumentation Amplifiers
- SBOS501F January 2010 – February 2015 INA128-HT , INA129-HT
  
  PRODUCTION DATA.

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DATA SHEET

INA12x-HT Precision, Low-Power Instrumentation Amplifiers

1 Features

Low Offset Voltage: 25 uV Typical
Low Input Bias Current: 50 nA Typical ⁽¹⁾
High CMR: 95 dB Typical⁽¹⁾
Inputs Protected to ±40 V
Wide Supply Range: ±2.25 V to ±18 V
Low Quiescent Current: 2 mA Typical⁽¹⁾

(1) Typical values for 210°C application.

2 Applications

Bridge Amplifiers
Thermocouple Amplifiers
RTD Sensor Amplifiers
Medical Instrumentation
Data Acquisition
Supports Extreme Temperature Applications:
- Controlled Baseline
- One Assembly/Test Site
- One Fabrication Site
- Available in Extreme Temperature Ranges
  (–55°C to 210°C) ⁽¹⁾
- Extended Product Life Cycle
- Extended Product-Change Notification
- Product Traceability

(1) Custom temperature ranges available.

3 Description

The INA128-HT and INA129-HT are low-power, general-purpose instrumentation amplifiers offering excellent accuracy. The versatile three-operational-amplifier design and small size make them ideal for a wide range of applications. Current-feedback input circuitry provides wide bandwidth even at high gain. A single external resistor sets any gain from 1 to 10000. The INA128-HT provides an industry-standard gain equation; the INA129-HT gain equation is compatible with the AD620.

The INA128-HT and INA129-HT are laser trimmed for very low offset voltage (25 μV Typ) and high common-mode rejection (93 dB at G ≥ 100). These devices operate with power supplies as low as ±2.25 V, and quiescent current of 2 mA, typically. Internal input protection can withstand up to ±40 V without damage.

Texas Instruments' high-temperature products use highly optimized silicon (die) solutions with design and process enhancements to maximize performance over extended temperatures.

The INA129-HT is available in 8-pin ceramic DIP and 8-pin ceramic surface-mount packages, specified for the –55°C to 210°C temperature range. The INA128-HT is available in an 8-pin SOIC-8 surface-mount package, specified for the –55°C to 175°C temperature range.

Device Information⁽¹⁾

PART NUMBER	PACKAGE	BODY SIZE (NOM)
INA128-HT	SOIC (8)	4.90 mm × 3.91 mm
INA129-HT	CFP (8)	6.90 mm × 5.65 mm
INA129-HT	CDIP SB (8)	11.81 mm × 7.49 mm

For all available packages, see the orderable addendum at the end of the data sheet.

4 Simplified Schematic

5 Revision History

Changes from E Revision (July 2013) to F Revision

Added ESD Ratings table, Feature Description section, Device Functional Modes, Application and Implementation section, Power Supply Recommendations section, Layout section, Device and Documentation Support section, and Mechanical, Packaging, and Orderable Information section Go
Deleted Ordering Information table; for all available packages, see the package option addendum Go

6 Pin Configuration and Functions

D, HKJ, or JDJ Package

8-Pin SOIC, CFP, or CDIP SB

Top View

HKQ Package

8-Pin CFP

Top View

Pin Functions

PIN		I/O	DESCRIPTION
NAME	NO.	I/O	DESCRIPTION
Ref	5	I	Output voltage reference
RG	1, 8	O	Gain resistor connection
V+	7	Power	Positive power supply voltage from 2.25 V to 18 V
V–	4	Power	Negative power supply voltage from –2.25 V to –18 V
V+IN	3	I	Non-inverting input voltage
V–IN	2	I	Inverting input voltage
VO	6	O	Output voltage

Bare Die Information

DIE THICKNESS	BACKSIDE FINISH	BACKSIDE POTENTIAL	BOND PAD METALLIZATION COMPOSITION
15 mils	Silicon with backgrind	GND	Al-Si-Cu (0.5%)

Bond Pad Coordinates in Mils

DESCRIPTION	PAD NUMBER	a	b	c	d
NC	1	–57.4	–31.1	–53.3	–27
V-_IN	2	–9.85	–31.4	–5.75	–27.3
V+_IN	3	25.05	–31.4	29.15	–27.3
V-	4	56.2	–34.3	60.3	–30.2
Ref	5	53.75	–17.6	57.85	–11
V_O	6	50.35	27.8	56.95	31.9
V+	7	7.75	30.2	11.85	34.3
NC	8	–57.4	28.4	–53.3	32.5
R_G⁽¹⁾	9	–57.4	13.4	–53.3	20
R_G⁽¹⁾	10	–57.5	2.7	–53.4	9.3
R_G⁽¹⁾	11	–57.5	–7.9	–53.4	–1.3
R_G⁽¹⁾	12	–57.4	–18.6	–53.3	–12

(1) Pads 9 and 10 must both be bonded to a common point and correspond to package pin 8. Pads 11 and 12 must both be bonded to a common point and correspond to package pin 1.

7 Specifications

7.1 Absolute Maximum Ratings

over operating free-air temperature range (unless otherwise noted) ⁽¹⁾

		MIN	MAX	UNIT
Volttage	Supply		±18	V
Volttage	Analog input		±40	V
Current	Output short-circuit (to ground)	Continuous
Operating temperature	HKJ, HKQ, KGD and JD packages	–55	210	°C
Operating temperature	D package	–55	175	°C
Storage temperature, T_stg	HKJ, HKQ, KGD and JD packages	–55	210	°C
Storage temperature, T_stg	D package	–55	175	°C

(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.

7.2 ESD Ratings

			VALUE	UNIT
A. INA218-HT (D, HKJ, or JDJ Package)
V_(ESD)	Electrostatic discharge	Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001⁽¹⁾	±2000	V
V_(ESD)	Electrostatic discharge	Charged-device model (CDM), per JEDEC specification JESD22-C101⁽²⁾	±50	V
B. INA129-HT (HKQ Package)
V_(ESD)	Electrostatic discharge	Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001⁽¹⁾	±4000	V
V_(ESD)	Electrostatic discharge	Charged-device model (CDM), per JEDEC specification JESD22-C101⁽²⁾	±200	V

(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.

(2) JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.

7.3 Recommended Operating Conditions

over operating free-air temperature range (unless otherwise noted)

	MIN	NOM	MAX	UNIT
V power supply	±2.25	±15	±18	V
Input common-mode voltage range for V_O = 0	V - 2 V		V + –2 V
T_A operating temperature INA128-HT	–55		175	°C
T_A operating temperature INA129-HT	–55		210	°C

7.4 Thermal Information: INA128-HT

THERMAL METRIC⁽¹⁾		INA128-HT	UNIT
		D [SOIC]
		8 PINS
R_θJA	Junction-to-ambient thermal resistance	110	°C/W
R_θJC(top)	Junction-to-case (top) thermal resistance	57
R_θJB	Junction-to-board thermal resistance	54
ψ_JT	Junction-to-top characterization parameter	11
ψ_JB	Junction-to-board characterization parameter	53

(1) For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.

7.5 Electrical Characteristics: INA128-HT

over operating free-air temperature range (unless otherwise noted)

PARAMETER			TEST CONDITIONS	T_A = –55°C to +125°C			T_A = 175°C⁽¹⁾			UNIT
PARAMETER			TEST CONDITIONS	MIN	TYP	MAX	MIN	TYP	MAX	UNIT
INPUT
OFFSET VOLTAGE, RTI
Initial			T_A = 25°C		±25 ±100/G	±125 ±1000/G				µV
	vs temperature		T_A = T_MIN to T_MAX		±0.2 ±5/G	±1 ±20/G			±3.5 ±80/G	µV/°C
	vs power supply		V_S = ±2.25 V to ±18 V			±2 ±200/G			±5 ±500/G	µV/V
Long-term stability					±1 ±3/G			±1 ±3/G		µV/mo
Impedance, differential					10¹⁰ \|\| 2			10¹⁰ \|\| 2		Ω \|\| pF
	Common mode				10¹¹\|\|9			10¹¹\|\|9		Ω \|\| pF
Common mode voltage range⁽²⁾			V_O = 0 V	(V+) − 2	(V+) − 1.4		(V+) − 2	(V+) − 1.4		V
				(V−) + 2	(V−) + 1.7		(V−) + 2	(V−) + 1.7		V
Safe input voltage						±40			±40	V
Common-mode rejection			V_CM = ±13 V, ΔR_S = 1 kΩ
			G = 1	58	86		58	75		dB
			G = 10	78	106		78	85
			G = 100	99	125		99	110
			G = 1000	113	130		113	120
CURRENT
Bias current					±2	±10			±45	nA
	vs temperature				±30			±550		pA/°C
Offset Current					±1	±10			±45	nA
	vs temperature				±30			±550		pA/°C
NOISE
Noise voltage, RTI			G = 1000, R_S = 0 Ω
	f = 10 Hz				10			10		nV/√Hz
	f = 100 Hz				8			8		nV/√Hz
	f = 1 kHz				8			8		nV/√Hz
	f_B = 0.1 Hz to 10 Hz				0.2			0.8		µV_PP
Noise current
	f = 10 Hz				0.9					pA/√Hz
	f = 1 kHz				0.3					pA/√Hz
	f_B = 0.1 Hz to 10 Hz				30					pA_PP
GAIN
Gain equation					1 + (50 kΩ/R_G)			1 + (50 kΩ/R_G)		V/V
Range of gain				1		10000	1		10000	V/V
Gain error			G = 1		±0.01	±0.1		±0.1%	±0.5%
			G = 10		±0.02	±0.5		±0.5%	±1%
			G = 100		±0.05	±0.7		±0.7%	±1.5%
			G = 1000		±0.5	±2.5		±2%	±4%
Gain vs temperature⁽³⁾			G = 1		±1	±10		±75		ppm/°C
	50-kΩ resistance⁽³⁾⁽⁴⁾				±25	±100		±75		ppm/°C
Nonlinearity			V_O = ±13.6 V, G = 1		±0.0001	±0.001			±0.008	% of FSR
			G = 10		±0.0003	±0.002			±0.01
			G = 100		±0.0005	±0.002			±0.01
			G = 1000		±0.001	See ⁽⁵⁾		±0.6	See ⁽⁵⁾
OUTPUT
Voltage		Positive	R_L = 10 kΩ	(V+) − 1.4	(V+) − 0.9		(V+) − 1.4	(V+) − 0.9		V
Voltage		Negative	R_L = 10 kΩ	(V−) + 1.4	(V−) + 0.8		(V−) + 1.4	(V−) + 0.8		V
Load capacitance stability					1000			1000		pF
Short-circuit current					+6/−15			+6/−15		mA
FREQUENCY RESPONSE
Bandwidth, −3 dB			G = 1		1300			1100		kHz
			G = 10		700			700
			G = 100		200			190
			G = 1000		20			17.5
Slew rate			V_O = ±10 V, G = 10		4			4		V/µs
Settling time, 0.01%			G = 1		7			7		µs
			G = 10		7			7
			G = 100		9			9
			G = 1000		80			80
Overload recovery			50% overdrive		4			4		µs
POWER SUPPLY
Voltage range				±2.25	±15	±18	±2.25	±15	±18	V
Current, total			V_IN = 0 V		±0.7	±1			±1	mA
TEMPERATURE RANGE
Specification				−55		+125			175	°C
Operating				−55		+125			175	°C

(1) Minimum and maximum parameters are characterized for operation at T_A = 175°C, but may not be production tested at that temperature. Production test limits with statistical guardbands are used to ensure high temperature performance.

(2) Input common-mode range varies with output voltage — see typical curves.

(3) Specified by wafer test.

(4) Temperature coefficient of the 50-kΩ term in the gain equation.

(5) Nonlinearity measurements in G = 1000 are dominated by noise. Typical nonlinearity is ±0.001%.

7.6 Electrical Characteristics: INA129-HT

over operating free-air temperature range (unless otherwise noted)

PARAMETER			TEST CONDITIONS	T_A = –55°C to +125°C			T_A = 210°C⁽¹⁾			UNIT
PARAMETER			TEST CONDITIONS	MIN	TYP	MAX	MIN	TYP	MAX	UNIT
INPUT
OFFSET VOLTAGE, RTI
Initial			T_A = 25°C		±25 ±100/G	±125 ±1000/G				µV
	vs temperature		T_A = T_MIN to T_MAX		±0.2 ±5/G	±1 ±20/G		±1 ±850/G		µV/°C
	vs power supply		V_S = ±2.25 V to ±18 V		±0.2 ±20/G	±2 ±200/G		±20 ±1000/G		µV/V
Long-term stability					±1 ±3/G			±1 ±3/G		µV/mo
Impedance, differential					10¹⁰ \|\| 2			10¹⁰ \|\| 2		Ω \|\| pF
	Common mode				10¹¹\|\|9			10¹¹\|\|9		Ω \|\| pF
Common mode voltage range⁽²⁾			V_O = 0 V	(V+) − 2	(V+) − 1.4		(V+) − 2	(V+) − 1.4		V
				(V−) + 2	(V−) + 1.7		(V−) + 2	(V−) + 1.7		V
Safe input voltage						±40			±40	V
Common-mode rejection			V_CM = ±13 V, ΔR_S = 1 kΩ
			G = 1	58	86			53		dB
			G = 10	78	106			69
			G = 100	99	125			89
			G = 1000	113	130			95
CURRENT
Bias current					±2	±10		±50		nA
	vs temperature				±30			±600		pA/°C
Offset Current					±1	±10		±50		nA
	vs temperature				±30			±600		pA/°C
NOISE
Noise voltage, RTI			G = 1000, R_S = 0 Ω
	f = 10 Hz				10			25		nV/√Hz
	f = 100 Hz				8			20		nV/√Hz
	f = 1 kHz				8			20		nV/√Hz
	f_B = 0.1 Hz to 10 Hz				0.2			2		µV_PP
Noise current
	f = 10 Hz				0.9					pA/√Hz
	f = 1 kHz				0.3					pA/√Hz
	f_B = 0.1 Hz to 10 Hz				30					pA_PP
GAIN
Gain equation					1 + (49.4 kΩ/R_G)			1 + (49.4 kΩ/R_G)		V/V
Range of gain				1		10000	1		10000	V/V
Gain error			G = 1		±0.01%	±0.1%		±1.1%
			G = 10		±0.02%	±0.5%		±2.6%
			G = 100		±0.05%	±0.7%		±13.5%
			G = 1000		±0.5%	±2.5%		±65.5%
Gain vs temperature⁽³⁾			G = 1		±1	±10		±100		ppm/°C
	49.4-kΩ resistance⁽³⁾⁽⁴⁾				±25	±100		±100		ppm/°C
Nonlinearity			V_O = ±13.6 V, G = 1		±0.0001	±0.001		±0.1		% of FSR
			G = 10		±0.0003	±0.002		±0.2
			G = 100		±0.0005	±0.002		±0.7
			G = 1000		±0.001	See ⁽⁵⁾		±2.4	See ⁽⁵⁾
OUTPUT
Voltage		Positive	R_L = 10kΩ	(V+) − 1.4	(V+) − 0.9		(V+) − 1.4	(V+) − 0.9		V
Voltage		Negative	R_L = 10kΩ	(V−) + 1.4	(V−) + 0.8		(V−) + 1.4	(V−) + 0.8		V
Load capacitance stability					1000			1000		pF
Short-curcuit current					+6/−15			+12/−5		mA
FREQUENCY RESPONSE
Bandwidth, −3 dB			G = 1		1300			850		kHz
			G = 10		700			400
			G = 100		200			50
			G = 1000		20			7.5
Slew rate			V_O = ±10 V, G = 10		4			4		V/µs
Settling time, 0.01%			G = 1		7			10		µs
			G = 10		7			10
			G = 100		9			30
			G = 1000		80			150
Overload recovery			50% overdrive		4			4		µs
POWER SUPPLY
Voltage range				±2.25	±15	±18	±2.25	±15	±18	V
Current, total			V_IN = 0 V		±0.7	±1		±2		mA
TEMPERATURE RANGE
Specification				−55		+125			210	°C
Operating				−55		+125			210	°C

(1) Minimum and maximum parameters are characterized for operation at T_A = 210°C, but may not be production tested at that temperature. Production test limits with statistical guardbands are used to ensure high temperature performance.

(2) Input common-mode range varies with output voltage — see typical curves.

(3) Specified by wafer test.

(4) Temperature coefficient of the 49.4-kΩ term in the gain equation.

(5) Nonlinearity measurements in G = 1000 are dominated by noise. Typical nonlinearity is ±0.001%.

1. See the data sheet for absolute maximum and minimum recommended operating conditions.

2. The predicted operating lifetime vs. junction temperature is based on reliability modeling using electromigration as the dominant failure mechanism affecting device wearout for the specific device process and design characterisitics.

3. Wirebond lifetime is only applicable for D package.

Figure 1. INA128HD, INA129SKGD1, and INA129SKGD2 Operating Life Derating Chart

7.7 Typical Characteristics

At T_A = 25°C, V_S = ±15 V, unless otherwise noted.

INA128-HT INA129-HT gain-freq_bos501.gif

Figure 2. Gain vs Frequency

INA128-HT INA129-HT pwrsupp-freq_bos501.gif

Figure 4. Positive Power-Supply Rejection vs Frequency

V_S = ±15 V

Figure 6. Input Common-Mode Range vs Output Voltage

INA128-HT INA129-HT inrefvn-freq_bos501.gif

Figure 8. Input-Referred Noise vs Frequency

Figure 10. Quiescent Current and Slew Rate vs Temperature

INA128-HT INA129-HT invoff_time_bos501.gif

Figure 12. Input Offset Voltage Warm-Up

INA128-HT INA129-HT vswing_io_bos501.gif

Figure 14. Output Voltage Swing vs Output Current

INA128-HT INA129-HT isc_temp1_bos501.gif

Figure 16. Short-Circuit Output Current vs Temperature

Figure 18. Total Harmonic Distortion + Noise vs Frequency

INA128-HT INA129-HT moderej-freq_bos501.gif

Figure 3. Common-Mode Rejection vs Frequency

INA128-HT INA129-HT negpwrsupp-freq_bos501.gif

Figure 5. Negative Power-Supply Rejection vs Frequency

V_S = ±5 V, ±2.5 V

Figure 7. Input Common-Mode Range vs Output Voltage

INA128-HT INA129-HT tset_gain_bos501.gif

Figure 9. Settling Time vs Gain

Figure 11. Input Overvoltage Voltage-to-Current Characteristics

INA128-HT INA129-HT inib_temp1_bos501.gif

Figure 13. Input Bias Current vs Temperature

INA128-HT INA129-HT vswing_vsupp_bos501.gif

Figure 15. Output Voltage Swing vs Power Supply Voltage

INA128-HT INA129-HT maxvo_freq_bos501.gif

Figure 17. Maximum Output Voltage vs Frequency

8 Detailed Description

8.1 Overview

The INA12x instrumentation amplifier is a type of differential amplifier that has been outfitted with input protection circuit and input buffer amplifiers, which eliminate the need for input impedance matching and make the amplifier particularly suitable for use in measurement and test equipment. Additional characteristics of the INA12x include a very low DC offset, low drift, low noise, very high open-loop gain, very high common-mode rejection ratio, and very high input impedances. The INA12x is used where great accuracy and stability of the circuit both short and long term are required.

8.2 Functional Block Diagram

8.3 Feature Description

The INA128-HT and INA129-HT are low power, general-purpose instrumentation amplifiers offering excellent accuracy. The versatile three-operational-amplifier design and small size make the amplifiers ideal for a wide range of applications. Current-feedback input circuitry provides wide bandwidth, even at high gain. A single external resistor sets any gain from 1 to 10,000. The INA128-HT and INA129-HT are laser trimmed for very low offset voltage (25 μV typical) and high common-mode rejection (93 dB at G ≥ 100). These devices operate with power supplies as low as ±2.25 V, and quiescent current of 2 mA, typically. The internal input protection can withstand up to ±40 V without damage.

8.4 Device Functional Modes

8.4.1 Noise Performance

The INA128-HT and INA129-HT provide very low noise in most applications. Low-frequency noise is approximately 2 μVPP measured from 0.1 Hz to 10 Hz (G ≥ 100). This provides dramatically improved noise when compared to state-of-the-art, chopper-stabilized amplifiers.

G ≥ 100

Figure 19. 0.1-Hz to 10-Hz Input-Referred Voltage Noise

8.4.2 Input Common-Mode Range

The linear input voltage ranges of the input circuitry of the INA128-HT and INA129-HT are from approximately 1.4 V below the positive supply voltage to 1.7 V above the negative supply. As a differential input voltage causes the output voltage increase, however, the linear input range will be limited by the output voltage swing of amplifiers A1 and A2. So the linear common-mode input range is related to the output voltage of the complete amplifier. This behavior also depends on supply voltage (see Figure 6 and Figure 7).

Input-overload can produce an output voltage that appears normal. For example, if an input overload condition drives both input amplifiers to their positive output swing limit, the difference voltage measured by the output amplifier will be near zero. The output of A3 will be near 0 V even though both inputs are overloaded.

9 Application and Implementation

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.

9.1 Application Information

The INA12x measures small differential voltage with high common-mode voltage developed between the non-inverting and inverting input. The high-input voltage protection circuit in conjunction with high input impedance make the INA12x suitable for a wide range of applications. The ability to set the reference pin to adjust the functionality of the output signal offers additional flexibility that is practical for multiple configurations.

9.2 Typical Application

Figure 20 shows the basic connections required for operation of the INA128-HT and INA129-HT. Applications with noisy or high impedance power supplies may require decoupling capacitors close to the device pins as shown.

The output is referred to the output reference (Ref) pin that is normally grounded. This must be a low-impedance connection to assure good common-mode rejection. A resistance of 8 Ω in series with the Ref pin will cause a typical device to degrade.

INA128-HT INA129-HT basic_conn1_bos501.gif

Figure 20. Basic Connections

9.2.1 Design Requirements

The device can be configured to monitor the input differential voltage when the gain of the input signal is set by the external resistor R_G. The output signal references to the Ref pin. The most common application is where the output is referenced to ground when no input signal is present by connecting the Ref pin to ground, as Figure 20 shows. When the input signal increases, the output voltage at the OUT pin increases, too.

9.2.2 Detailed Design Procedure

9.2.2.1 Setting the Gain

Gain is set by connecting a single external resistor, R_G, between pins 1 and 8.

INA128-HT:

Equation 1. INA128-HT INA129-HT eq1a_bos501.gif

INA129-HT:

Equation 2. INA128-HT INA129-HT eq1_bos501.gif

Commonly used gains and resistor values are shown in Figure 20.

The 50-kΩ term in Equation 1 (49.4-kΩ in Equation 2) comes from the sum of the two internal feedback resistors of A1 and A2. These on-chip metal film resistors are laser trimmed to accurate absolute values. The accuracy and temperature coefficient of these internal resistors are included in the gain accuracy and drift specifications of the INA128-HT and INA129-HT.

The stability and temperature drift of the external gain setting resistor, R_G, also affects gain. The R_G contribution to gain accuracy and drift can be directly inferred from Equation 2. Low resistor values required for high gain can make wiring resistance important. Sockets add to the wiring resistance which will contribute additional gain error (possibly an unstable gain error) in gains of approximately 100 or greater.

9.2.2.2 Dynamic Performance

Figure 2 shows that, despite its low quiescent current, the INA128-HT and INA129-HT achieve wide bandwidth, even at high gain. This is due to the current-feedback topology of the input stage circuitry. Settling time also remains excellent at high gain.

9.2.2.3 Offset Trimming

The INA128-HT and INA129-HT are laser trimmed for low offset voltage and offset voltage drift. Most applications require no external offset adjustment. Figure 21 shows an optional circuit for trimming the output offset voltage. The voltage applied to Ref terminal is summed with the output. The operational amplifier buffer provides low impedance at the Ref terminal to preserve good common-mode rejection.

1. OPA177 and REF200 are not tested or characterized at 210°C.

Figure 21. Optional Trimming of Output Offset Voltage

9.2.2.4 Input Bias Current Return Path

The input impedances of the INA128-HT and INA129-HT are extremely high (approximately 10¹⁰ Ω). However, a path must be provided for the input bias current of both inputs. This input bias current is approximately ±50 nA. High input impedance means that this input bias current changes very little with varying input voltage.

Input circuitry must provide a path for this input bias current for proper operation. Figure 22 shows various provisions for an input bias current path. Without a bias current path, the inputs will float to a potential which exceeds the common-mode range, and the input amplifiers will saturate.

If the differential source resistance is low, the bias current return path can be connected to one input (see the thermocouple example in Figure 22). With higher source impedance, using two equal resistors provides a balanced input with possible advantages of lower input offset voltage due to bias current and better high-frequency common-mode rejection.

Figure 22. Providing an Input Common-Mode Current Path

9.2.3 Application Curves

INA128-HT INA129-HT smallsig_g1_bos501.gif

G = 1, 10

Figure 23. Small Signal

INA128-HT INA129-HT lrgesig_g1_bos501.gif

G = 1, 10

Figure 25. Large Signal

INA128-HT INA129-HT smallsig_g100_bos501.gif

G = 100, 1000

Figure 24. Small Signal

INA128-HT INA129-HT lrgesig_g100_bos501.gif

G = 100, 1000

Figure 26. Large Signal

10 Power Supply Recommendations

The minimum power supply voltage for INA12x is ±2.25 V and the maximum power supply voltage is ±18 V. This minimum and maximum range covers a wide range of power supplies; but for optimum performance, ±15 V is recommended. TI recommends adding a bypass capacitor at the input to compensate for the layout and power supply source impedance.

10.1 Low Voltage Operation

The INA128-HT and INA129-HT can be operated on power supplies as low as ±2.25 V. Performance remains excellent with power supplies ranging from ±2.25 V to ±18 V. Most parameters vary only slightly throughout this supply voltage range.

Operation at very low supply voltage requires careful attention to assure that the input voltages remain within their linear range. Voltage swing requirements of internal nodes limit the input common-mode range with low power supply voltage. Figure 6 and Figure 7 show the range of linear operation for ±15 V, ±5 V, and ±2.5 V supplies.

INA128-HT INA129-HT bridgeamp_bos501.gif

Figure 27. Bridge Amplifier

1. OPA130 is not tested or characterized at 210°C.

Figure 28. AC-Coupled Instrumentation Amplifier

INA128-HT INA129-HT thermoamp_bos501.gif

1. REF102 is not tested or characterized at 210°C.

Figure 29. Thermocouple Amplifier With RTD Cold-Junction Compensation

INA128-HT INA129-HT diffv_converter_bos501.gif

1. OPA177, OPA131, OPA602, and OPA128 are not tested or characterized at 210°C.

Figure 30. Differential Voltage-to-Current Converter

1. OPA2131 is not tested or characterized at 210°C.

Figure 31. ECG Amplifier With Right-Leg Drive