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INA190 in Practice: REF Pin Gotchas, Overload Limits, and Fixes

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Quick-Reference Card: INA190 at a Glance

Attribute Detail
Component Type Current Sense Amplifier (Bidirectional)
Manufacturer Texas Instruments
Key Spec 500 pA (Typ) Input Bias Current
Supply Voltage 1.7V to 5.5V
Package Options SC70-6 (DCK) and UQFN
Lifecycle Status Active
Best For Ultra-precise battery-powered devices and telecom equipment

INA190 product photo or IC package


1. What Is the INA190? (Definition + Architecture)

The INA190 is a bidirectional, zero-drift current-sense amplifier from Texas Instruments that features a picoamp input bias current and an enable function for ultra-precise, low-power measurements. Unlike traditional current sense amplifiers that draw significant current from the bus they are measuring, the INA190 is specifically engineered to minimize measurement error when paired with large input filter resistors or when measuring micro-amp level sleep currents.

1.1 Core Architecture & Design Philosophy

The standout architectural feature of the INA190 is its zero-drift topology combined with a capacitive-coupled input stage. This design decision drastically reduces the input bias current to a mere 500 pA (typical). For a hardware engineer, this means you can place large RC filters directly on the input pins to reject high-frequency PWM noise without inducing massive offset voltage errors—a common trap when using older architectures like the INA181 or INA219.

1.2 Where It Fits in the Signal Chain / Power Path

The INA190 sits at the very front of the power path, directly across a shunt resistor on either the high side or low side of the load. It translates a small differential voltage riding on a high common-mode voltage (up to 40V) into a ground-referenced, scaled analog voltage that directly drives a microcontroller's ADC.


2. Electrical Characteristics: The Numbers That Matter

2.1 Power Supply & Consumption Profile

The INA190 operates on a low supply voltage of 1.7V to 5.5V, making it natively compatible with both 1.8V and 3.3V logic domains without level shifting. For battery-powered applications, the critical spec is the shutdown current: 100 nA (maximum). When the enable pin is pulled low, the device practically disappears from the power budget, which is vital for IoT sleep states.

2.2 Performance Specs (Speed, Accuracy, or Efficiency)

  • Offset Voltage: ±15 μV (Max). Why it matters: This ultra-low offset allows designers to use much smaller shunt resistors (reducing I2R power losses and thermal dissipation) while still maintaining accuracy at low load currents.
  • Gain Options: Up to 500 V/V (A5 version). Why it matters: High gain amplifies tiny voltage drops, but it requires careful dynamic range planning to avoid railing the ADC.
  • Input Bias Current: 500 pA (Typ). Why it matters: Prevents the amplifier itself from draining the battery it is supposed to be monitoring.

2.3 Absolute Maximum Ratings — What Will Kill It

  • Common-Mode Voltage: -0.2V to 40V. Warning: The -0.2V lower limit is a frequent point of failure. Inductive kickback or negative transients on the load side that dip below -0.2V will forward-bias internal ESD diodes and destroy the IC. Always use Schottky clamping diodes if negative transients are expected.

3. Pinout & Package Guide

3.1 Pin-by-Pin Functional Groups

Pin Group Pins Function
Power VS, GND Supply voltage (1.7V - 5.5V) and Ground reference.
Signal Input IN+, IN- Differential inputs connected across the shunt resistor.
Signal Output OUT Analog voltage output proportional to shunt current.
Control/Config REF, EN Reference voltage for bidirectional offset; Enable pin (package dependent).

(Note: The Enable pin is typically available on specific package variants like the UQFN. Refer to the official datasheet for exact pinout mappings per package.)

3.2 Package Variants & Soldering Notes

Package Pitch Thermal Pad? Soldering Method
SC70-6 (DCK) 0.65 mm No Reflow / Fine-tip hand solder
UQFN (RSW) 0.40 mm Yes Reflow only (Stencil required)

The SC70-6 is highly popular for space-constrained designs but requires steady hands for rework. The UQFN variant offers the EN (Enable) pin but mandates a proper reflow profile due to the bottom thermal pad.

3.3 Part Number Decoder

When ordering, the part number (e.g., INA190A5DCKR) breaks down as: - INA190: Base part number. - A5: Gain variant (A1 = 25 V/V, A2 = 50 V/V, A3 = 100 V/V, A4 = 200 V/V, A5 = 500 V/V). - DCK: Package designator (SC70-6). - R: Tape and reel packaging.


4. Known Issues, Errata & Real-World Pain Points

Why this section exists: Community forums, application notes, and field reports reveal problems the datasheet glosses over. This section saves you hours of debugging.

Problem: Excess Supply Current on REF Pin - Root Cause: In bidirectional applications, engineers often bias the REF pin to VS/2 using a simple high-value resistor divider to save power. However, the REF pin has a dynamic input impedance. A simple unbuffered divider causes excess supply current (often ~120 μA) and skews the reference voltage. - Recommended Fix: Always account for the REF pin's input impedance. Drive the REF pin with a low-impedance voltage source, a dedicated voltage reference IC, or an op-amp buffer.

Problem: Input Differential Overload (Clipping) - Root Cause: When using the high-gain A5 version (500 V/V), even a tiny transient voltage across the shunt can cause the differential input to exceed the output swing limits, driving the OUT pin to the supply rail and causing a loss of measurement data during peaks. - Recommended Fix: Calculate your absolute maximum peak current. If it saturates the output, either reduce the shunt resistor value or select a lower-gain version (e.g., A1 to A4).

Problem: Unexpected Leakage or Negative Offsets - Root Cause: Designers sometimes observe unexpected current paths between IN- and GND, or negative offset readings in unidirectional setups. This is almost always caused by ground loops or the common-mode voltage dipping below the strict -0.2V limit during switching events. - Recommended Fix: Ensure strict adherence to the -0.2V to 40V common-mode range. Use a star-grounding topology to ensure the INA190 GND and the shunt ground reference are at the exact same potential.


5. Application Circuits & Integration Examples

5.1 Typical Application: Battery-Powered Device Monitoring

In a typical notebook or cell phone battery monitor, the INA190 is placed on the high side (between the battery positive terminal and the system load). A 10 mΩ shunt resistor is used. With the A3 (100 V/V) variant, a 1A load produces a 10 mV drop, which the INA190 amplifies to 1.0V at the OUT pin.

Because of the 500 pA input bias current, designers can place 1 kΩ resistors and a 0.1 μF capacitor at the IN+ and IN- pins to create a robust low-pass filter without introducing the massive offset errors that would occur with older amplifiers.

INA190 typical application circuit schematic

5.2 Interface Example: Connecting to a Microcontroller

The INA190 outputs a purely analog signal. To read this with an MCU (like an STM32 or Arduino), connect the OUT pin directly to an ADC channel. If using bidirectional sensing, the REF pin must be tied to a buffered reference voltage (e.g., 1.65V for a 3.3V ADC).

// Pseudocode for reading INA190 bidirectional current via ADC
#define ADC_MAX 4095.0
#define V_REF 3.3
#define SHUNT_RESISTOR 0.01 // 10 milliohms
#define INA190_GAIN 100.0
#define BIAS_OFFSET 1.65 // REF pin driven to 1.65V

float read_current() {
    uint16_t raw_adc = analogRead(PIN_INA190_OUT);
    float v_out = (raw_adc / ADC_MAX) * V_REF;

    // Subtract reference offset, divide by gain and shunt value
    float current_amps = (v_out - BIAS_OFFSET) / (INA190_GAIN * SHUNT_RESISTOR);
    return current_amps;
}

6. Alternatives, Replacements & Cross-Reference

6.1 Pin-Compatible Drop-In Replacements

Part Number Manufacturer Key Difference Compatible?
SGM8194 SGMICRO Similar specs, alternative supply chain ? (Check exact package)

6.2 Upgrade Path (Better Performance)

If your design has outgrown purely analog outputs and requires digital precision without the hassle of MCU-side ADC calibration, look to the INA228 or INA229. These are digital alternatives from Texas Instruments that integrate a high-resolution 20-bit ADC and communicate via I2C or SPI. If high-voltage isolation is required (e.g., motor drives), the AMC3301 isolated amplifier is the next step up.

6.3 Cost-Down Alternatives

If you are only using the INA190 for overcurrent protection and do not need continuous analog monitoring, consider the INA300. It is a current-sense comparator that simply flags an overcurrent event, significantly reducing BOM cost and MCU overhead.


7. Procurement & Supply Chain Intelligence

  • Lifecycle Status: Active. The INA190 is a modern, core TI part with no EOL (End of Life) or NRND (Not Recommended for New Designs) warnings.
  • Typical MOQ & Lead Time: Standard reels typically require MOQs of 3,000 units. Lead times have stabilized post-shortage, but TI parts are prone to allocation during automotive/industrial surges.
  • BOM Risk Factors: Single-sourcing is a slight risk, though parts like the SGM8194 provide an emergency second source. Battery management ICs are in high demand globally.
  • Recommended Safety Stock: Maintain 3-6 months of safety stock if designing into high-volume consumer electronics (e.g., cell phones, notebooks).
  • Authorized Distributors: Purchase strictly through authorized channels (Digi-Key, Mouser, TI Direct) to avoid counterfeit analog ICs which often fail offset and bias current specifications.

8. Frequently Asked Questions

Q: What is the INA190 used for? The INA190 is primarily used for precision current measurement in battery-powered devices, notebooks, telecom equipment, and battery chargers where low power consumption and high accuracy are critical.

Q: What are the best alternatives to the INA190? The SGM8194 is an analog alternative, while the INA228 and INA229 are excellent upgrades if you require a digital (I2C/SPI) output with a built-in ADC. For simple overcurrent detection, the INA300 is a cost-effective comparator alternative.

Q: Is the INA190 still in production? Yes, the INA190 is fully active and in production by Texas Instruments, making it safe for new designs.

Q: Can the INA190 work with 3.3V logic? Yes, the INA190 supports a supply voltage range of 1.7V to 5.5V, allowing its analog output to seamlessly interface with 1.8V, 3.3V, and 5V microcontrollers without level shifting.

Q: Where can I find the INA190 datasheet and evaluation board? The official datasheet and the INA190EVM evaluation module can be found directly on the Texas Instruments product page or through authorized distributors like Mouser and Digi-Key.


9. Resources & Tools

  • Official Datasheet: [Texas Instruments INA190 Product Page]
  • Evaluation / Development Kit: INA190EVM (Evaluation Module)
  • Reference Designs: TI Application Notes on "Filter Design for Current Sense Amplifiers"
  • Community Libraries: Search generic analog current sense libraries for Arduino / STM32CubeMX (requires standard ADC polling)
  • SPICE / LTspice Model: PSpice models are available directly from the TI product page under the "Design & development" tab.

INA190A5IDCKR PCB Symbol, Footprint & 3D Model

Texas Instruments INA190A5IDCKR

Texas Instruments

Precision Current-Sense Amplifier Bi-Directional 1-Channel 500V/V 1.7V to 5.5V 6-Pin SC-70 T/R

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