Features

• ±250 mV input voltage range optimized with parallel resistors

• Very low nonlinearity: 0.075% max at 5 V

• Low offset error: 1.5 mV max

• Low noise: 3.1 mVRMS typical

• Low and high side supply current: 8mA max at 5V

• Input bandwidth: 60 kHz min

• Fixed gain: 8 (0.5% accuracy)

• High CMRR: 108dB

• Low side operation: 3.3 V

• Certified Galvanic Isolation:

– Certified to UL1577 and IEC60747-5-2

– Isolation voltage: 4250 V peak – Operating voltage: 1200 V peak

– Transient immunity: 2.5kV/μs min

• Typical 10-year life at rated operating voltage (see application report SLLA197)

• Fully specified over extended industrial temperature range

application

• Parallel Resistor Current Sensing:

-Meter

– Green Energy – Power Measurement Application

illustrate

The AMC1100 is a precision isolation amplifier whose output is separated from the input circuit by a silicon dioxide (silicon dioxide) barrier that is highly resistant to magnetic interference. The barrier is certified to provide galvanic isolation up to 4250 VPEAK according to UL1577 and IEC60747-5-2. This unit is used with isolated power supplies to prevent noise currents on high common-mode voltage lines from entering the local ground, interfering with or damaging sensitive circuits.

The AMC1100 inputs are optimized for direct connection to shunt resistors or other low voltage level signal sources. The excellent performance of this device enables accurate current and voltage measurements in energy metering applications. The output signal common-mode voltage is automatically adjusted to a 3-V or 5-V low-side supply.

Fully specified over the extended industrial temperature range of -40°C to +105°C, the AMC1100 is available in SMD style, wide body SOIC-8 (DWV) and gull wing-8 (DUB) packages.

Typical features

At VDD1=VDD2=5 V, VINP=-250 mV to +250 mV and VINN=0 V, unless otherwise noted.

Detailed description

Overview

The AMC1100 includes a delta-sigma modulator input stage, including an internal reference and clock generator. The outputs of the modulator and clock signals are transmitted differentially through an integrated capacitive isolation barrier that separates the high and low voltage regions. The received bit stream and clock signal are synchronized and processed by a third-order analog filter with a nominal gain of 8 on the low side and displayed as the differential output of the device, as shown in this section of the functional block diagram.

Silicon dioxide based capacitive isolation barriers support a high level of magnetic field immunity as described in the application report SLLA181, ISO72x Magnetic Field Immunity for Digital Isolators.

Functional block diagram

Feature description

The differential analog input of the AMC1100 is a switched capacitor circuit based on a second-order modulator stage that digitizes the input signal into a 1-bit output stream. The device uses an internal capacitor that charges and discharges continuously at a typical frequency of 10 MHz to compare the differential input signal (VIN = VINP – VINN) to an internal reference voltage of 2.5 V. With the S1 switch closed, CIND charges the voltage difference between VINP and VINN. During the discharge phase, the two S1 switches are opened first, and then the two S2 switches are closed. During this phase, the cinder discharges to about GND1 + 0.8 V. Figure 31 shows a simplified equivalent input circuit.

The analog input range is customized to directly accommodate the voltage drop through the shunt resistor for current sensing. However, there are two restrictions on analog input signals: VINP and VINN. If the input voltage exceeds the range of GND1–0.5 V to VDD1+0.5 V, the input current must be limited to within 10 mA to protect the implemented input protection diodes from damage. In addition, the linearity and noise performance of the device are guaranteed only when the differential analog input voltage is maintained within ±250mV.

Device functional mode

When the power is turned on, the AMC1100 is powered up. The unit is operated from a nominal 5 volt supply on the high side. The potential of the ground reference GND1 can be floated, which is usually the case in shunt-based current measurement applications. TI recommends connecting one side of the shunt to the GND1 pin of the AMC1100 to maintain the device's operating common-mode range requirements.

The low side of the AMC1100 can be powered by a nominal 3.0V, 3.3V or 5.0V supply. When operating at 5V, the common-mode voltage of the output stage is set to a nominal 2.55V; in the other two cases, the common-mode voltage is automatically set to 1.29V.

While the AMC1100 is typically used in shunt-based current sensing circuits, it can also be used in isolated voltage measurement applications, as shown in a simplified manner in Figure 32. In this application, a resistor divider (R1 and R2 in Figure 32) is typically used to match the relatively small input voltage range of the AMC1100. R2 and the AMC1100 input resistance (RIN) also create a resistive divider, resulting in additional gain error. Assuming the values of R1 and RIN are much larger than R2, the resulting total gain error can be estimated using Equation 1:

Where: GERR = device gain error.

Application and Implementation

Notice

The information in the application section below is not part of the TI component specification and TI does not warrant its accuracy or completeness. TI's customers are responsible for determining the suitability of parts for their purpose. Customers should verify and test their design implementation to confirm system functionality.

Application Information

The AMC1100 features unique linearity, high input common mode rejection, and low DC error and drift. These features make the AMC1100 a robust, high-performance isolation amplifier for industrial applications where users and subsystems must be protected from high voltages.

typical application

AMC1100 in inverter

Typical operation of the AMC1100 is isolated current and voltage measurements in inverter applications such as industrial motor drives, photovoltaic inverters, or uninterruptible power supplies, as shown in Figure 33. Depending on the end application, only two-phase or three-phase currents are sensed.

Design requirements

The current measurement through the motor power line phases is done through the parallel resistor RSHUNT (in a double-ended shunt); see Figure 34. For better performance, the differential signal is filtered using an RC filter (components R2, R3 and C2). Optionally, C3 and C4 can be used to reduce dumping from inputs. In this case, care must be taken when choosing the quality of these capacitors; mismatches in the values of these capacitors can cause common-mode errors at the modulator input. If necessary, NP0 capacitors are recommended.

Isolation voltage measurements can be made as described in this section. Device functional mode

Detailed design procedure

The floating ground reference (GND1) comes from the end of a parallel resistor connected to the negative input of the AMC1100 (VINN). If using a four-terminal shunt, the input of the AMC1100 is connected to the internal lead and GND1 is connected to one of the external shunt leads. The differential inputs of the AMC1100 ensure accurate operation even in noisy environments.

The differential output of the AMC1100 can directly drive the analog-to-digital converter (ADC) input, or it can be further filtered before being processed by the ADC.

Apply Curve

In frequency converter applications, the power switch must be protected against overcurrent conditions. In order to power down the system quickly, the low latency caused by the isolation amplifier is required. Figure 35 shows the typical full-scale step response of the AMC1100.

AMC1100 in Energy Metering

Due to its immunity to magnetic fields, the AMC1100 can be used for shunt-based current sensing in smart meter (e-meter) designs, as shown in Figure 36. Three AMC1100 devices are used for isolated current sensing. For voltage sensing, a resistive divider is typically used to reduce the common-mode voltage to a level that allows non-isolated measurements.

Design requirements

For best performance, an RC low pass filter can be used in front of the AMC1100. Further improvements can be achieved by filtering the output signal of the device. In both cases, the values of the resistors and capacitors must be adjusted according to the bandwidth requirements of the system.

The analog output of the device is converted to the digital domain using the on-chip analog-to-digital converter (ADC) of an appropriate metering microcontroller. The architecture of the MSP430F47177 X7 family of ultra-low-power microcontrollers is tailored for this type of application. The MSP430F471x7 provides up to seven ADCs for simultaneous sampling: six for three-phase current and voltage, while the seventh channel can be used for additional voltage sensing of the neutral in applications requiring tamper-proof measures.

Detailed design procedure

The high side power supply for the AMC1100 can be obtained by using the phase voltage of the capacitor drop power supply (capacitance drop) as shown in Figure 37 and performed in the application report SLAA552, AMC1100: Replacing the Input Main Sensing Transformer in the Inverter with an Isolation Amplifier explained.

Alternatively, as demonstrated by TI reference design TIPD121, Isolated Current Sensing Reference Design Solution 5A, 2kV, the high-side power supply for each AMC1100 can also be derived from the low-side power supply using the SN6501 to drive the transformer.

Apply Curve

The noise performance of the energy meter is one of the key parameters of the energy meter, which is mainly affected by the performance of the ADC and current sensor. When using a shunt-based approach, the sensor front end consists of an actual shunt resistor and an isolation amplifier. Figure 38 shows the typical output noise density of the AMC1100 as a basis for the overall performance evaluation.

Power Recommendations

In a typical inverter application, the high-side power supply for the AMC1100 (VDD1) comes from the system power supply, as shown in Figure 39. To reduce cost, a Zener diode can be used to limit the voltage to 5V±10%. A 0.1µF decoupling capacitor is recommended to filter this power path. Place this capacitor (C1) as close as possible to the VDD1 pin for best performance. Additional 1-10-fi capacitors can be used if better filtering is required.

For higher power efficiency and better performance, a buck converter can be used; an example of this approach is based on the LM5017 . A reference design including performance test results and layout files is available for download at the PMP9480, an isolated bias supply + isolation amplifier combination for line voltage or current measurements.

layout

Layout Guidelines

The layout recommendations shown in Figure 40 show critical placement of the decoupling capacitors as close to the AMC1100 as possible while maintaining differential routing of the input signal.

To maintain the isolation barrier and Common Mode Transient Immunity (CMTI) of the equipment, maximize the distance between the high-side ground (GND1) and the low-side ground (GND2); that is, the entire area under the equipment must not contain any conductive material.

layout example

Device and Documentation Support

equipment stand

Device naming

Quarantine Glossary

Creepage distance: The shortest path between two conductive input to output leads measured along an insulating surface. The shortest distance path is at the end of the inclusion.

Clearance: The shortest distance between two conductive input to output leads measured through air (line of sight).

Input-Output Barrier Capacitance: The total capacitance between all input terminals connected together and all output terminals connected together.

Input-Output Barrier Resistance: The total resistance between all input terminals connected together and all output terminals connected together.

Primary circuit: An internal circuit directly connected to an external power source or other equivalent power source to supply power to the main circuit.

Secondary Circuit: A circuit that has no direct connection to the mains power source and is powered from a separate isolated power source.

Comparative Tracking Index (CTI): CTI is an indicator of electrical insulating materials. It is defined as the voltage value that causes a failure by tracking during standard testing. Tracking is the process of creating locally degraded partially conductive paths on or through the surface of an insulating material due to the action of electrical discharge at or near the surface of the insulating material. The higher the CTI value of the insulating material, the smaller the minimum creepage distance.

Typically, dielectric breakdown occurs at the surface of the material or between the two. Surface failures can be caused by flashovers or by gradual degradation of insulating surfaces caused by small localized sparks. This spark is caused by rupture of the surface film of conductive contaminants on the insulating layer. The resulting leakage current interruption creates an overvoltage at the discontinuity and sparks. These sparks often cause carbonization of the insulating material and lead to carbon traces between different potential points. This process is called tracking.

Insulation: Operational Insulation - Insulation required for proper operation of equipment.

Basic Insulation - Provides basic protection against electric shock.

Supplementary Insulation - In addition to basic insulation, separate insulation is used to ensure protection against electric shock in the event of basic insulation failure.

Double Insulation - Insulation includes basic insulation and auxiliary insulation.

Reinforced Insulation - A single insulation system that provides a level of protection against electric shock equivalent to double insulation.

Contamination level:

Pollution Degree 1 - No pollution, or only dry, non-conductive pollution. Contamination has no effect on device performance.

Pollution Degree 2 - Normally, only non-conductive pollution occurs. However, temporary conductivity caused by condensation is to be expected.

Pollution Degree 3 - Conductive pollution occurs, or dry non-conductive pollution that becomes conductive due to condensation. Condensation is expected.

Pollution Degree 4 - Continued conductivity due to conductive dust, rain or other wet conditions.

Installation category:

Overvoltage categories - This section aims to achieve insulation coordination by identifying transient overvoltages that may occur and assigning four different levels as specified in IEC 60664.

1. Signal level: special equipment or parts of equipment.

2. Local level: portable equipment, etc.

3. Power distribution level: fixed installation.

4. Main supply level: overhead lines, cable systems.

Each class should be less affected by transients than the previous class.

file support

Related documents

High Voltage Life of Series Digital Isolators, Type SLLA197

Digital Isolator Magnetic Field Immunity, Type SLLA181

AMC1100: Replacing the Input Main Sensing Transformer in the Inverter with an Isolation Amplifier, Slav 552

Isolated Current Sensing Reference Design, 5A, 2kV, TIPD121#

Isolated Bias Supply + Isolation Amplifier Combination for Line Voltage or Current Measurement, Model PMP9480

TPS62120 product introduction, SLVSAD5

MSP430F471x product introduction, SLAS626

SN6501 product introduction, SLLSEA0

LM5017 product introduction, SNVS783

trademark

All trademarks are the property of their respective owners.

Electrostatic discharge precautions

This integrated circuit may be damaged by electrostatic discharge. Texas Instruments recommends taking proper precautions when handling all integrated circuits. Failure to follow proper operation and installation procedures may result in damage.

ESD damage can range from minor performance degradation to complete device failure. Precision integrated circuits can be more susceptible to damage because very small parameter changes can cause the device to not meet its published specifications.

Glossary

SLYZ022-TI Glossary.

This glossary lists and explains terms, acronyms and definitions.

Mechanical, Packaging and Ordering Information

The following pages include mechanical, packaging, and orderable information. This information is the latest data available for the specified device. This information is subject to change without notice or modification. See the left navigation for a browser-based version of this data sheet.