Maker Pro

Texas Instruments ISO121x Digital Input Receivers for Industrial Applications

March 13, 2020 by Abdulwaliy Oyekunle

The ISO121x series digital input receivers from Texas Instruments enable a host of applications in data acquisition for industrial applications.

The ISO1211 and the ISO1212 are packaged in small outline integrated circuits (SOIC) and shrink small-outline package (SSOP) respectively. The digital input receiver is applicable in programmable logic controllers (PLCs), binary input modules, and more.


Overview of the ISO121x Digital Input Receivers

Texas Instruments’ ISO121x digital input receiver is an isolated 24V to 60V type. It is IEC 61131-2 type 1, 2 and 3 characteristics compliant. It has a high transient immunity of ±70-kV/μs and operates optimally in ambient temperatures ranging from –40°C to +125°C. The device does not support field-side power supplies, and its maximum data rate is 4Mbps.


ISO121x digital signal receivers.

A product image of the ISO121x digital input receiver. Image Credit: Texas Instruments.


Electrical Characteristics

The ISO121x digital input receiver operates on an input voltage supply ranging from 2.25V to 5.5V. The voltage on its sense pin varies from −60V to 60V. It is power-efficient, as its maximum low-level output current is 2mA when an input voltage supply of 2.5V is supplied via the supply pin. The ISO121x also has a high-input voltage range of ±80V, with reverse polarity protection.

The maximum power dissipation for the ISO1212 is 900mW when the input voltage is 5.5V. The device enters powered up mode when the input voltage supply is higher than 2.25V and powers down when the input voltage supply falls below 1.7V. 


How the Device Works

The isolated digital input receiver device receives digital input voltage signals ranging from 24V to 60V. An external sense resistor connected between the field-side current input pin and field-side voltage sense pin limits the current drawn from the field input based on an eternal feedback loop.

The limit of the current drawn can be anywhere from 2.2mA to 2.47mA and is adjustable up to 6.5mA. Internal comparators determine the input-voltage transition thresholds. The device sends out an isolated digital output using a buffer activated by the output enable pin.


Packaging and Pin Configuration

The ISO1211 comes in a single-channel, small outline integrated circuit (SOIC) package. It has eight pins, which includes a power supply pin, a ground pin, an output enable pin, a channel output pin, a field-side current input pin, and so on.

On the other hand, the ISO1212 comes in a dual-channel SSOP package. It has sixteen pins, which includes a power supply pin, two ground pins, one output-enable pin, two-channel outputs, two field-side voltage sense pins, and so on.


Safety Certifications

The ISO121x digital input receiver’s insulation specifications comply with several safety regulations. For example, it has a maximum transient isolation voltage of 3600VPK, a maximum repetitive peak isolation voltage of 566VPK and a maximum surge isolation voltage of 4000VPK. 

These specifications make the device compliant with DIN V VDE 0884-10. It also has CSA certification and is certified according to IEC 60950-1 and IEC 62368-1. Other safety-related certifications include UL, care quality commission (aka CQC) and TUV certifications.



With its robust features, the ISO121x from Texas Instruments is suitable for various applications in data acquisition. It supports 9 V to 300 VDC as well as AC digital input modules in a programmable logic controller (aka PLC). Control engineers can utilise the device for substation automation and position feedback.

Related Content


You May Also Like