This is the compact version of a simple carrier for Allegro’s CT433-HSWF70MR TMR-based, electrically isolated current sensor that is optimized for high dV/dt applications and offers a high 1 MHz bandwidth with low noise. The typical primary current path resistance of the sensor IC is 1 mΩ.

Overview:

• CT432/CT433 sensors use Allegro’s patented XtremeSense™ TMR (tunneling magnetoresistance) technology for high accuracy, high bandwidth, electrically isolated current measurements.
• Sensor can be inserted anywhere along the current path and be used in applications that require electrical isolation.
• 1 mΩ primary current path resistance in the sensor IC, and the PCB is made with 2-layer (compact versions under 50A), 4-layer (compact versions 50A and up), or 6-layer (large versions) 2-oz copper, so very little power is lost in the module.
• TMR sensing rejects common-mode fields, so the orientation of the sensor relative to uniform external magnetic fields (e.g. the Earth’s magnetic field) has less effect on the measurement.
• Optimized for high dV/dt applications, allowing the sensor to be used in switching applications.
• High-bandwidth 1 MHz analog output voltage proportional to AC or DC currents.
• Typical 300 ns response time.
• Output is not ratiometric (i.e. the zero point and sensitivity are independent of the actual supply voltage), which provides immunity from noisy supplies.
• Optional overcurrent fault output indicates when the current magnitude exceeds 110% of the maximum linear sensing range.
• Operating temperature range of -40°C to 125°C.
• Carrier boards, available in compact and large sizes, offer a variety of ways to insert it into the current path along with 0.1″-pitch (breadboard-compatible) power, ground, and output pins.

• 3.3V (CT433) and 5V (CT432) versions available.

  

CT433           70MR       ±70 A       (bidirectional) 3.0 V to 3.6 V     14.3 mV/A     1.65 V            0.8″×1.1″  4

A larger carrier with a 6-layer PCB is also available for this sensor IC with room for larger connectors and thicker wires for the high-current path, offering different ways to use or evaluate this current sensor.

Using the sensor

This sensor has five required connections: the input current (IP+ and IP-), logic power (VCC and GND), and the sensor output (VOUT).

The sensor requires a supply voltage of 3.0 V to 3.6 V to be connected across the VCC and GND pads, which are labeled on the bottom silkscreen. The sensor outputs an analog voltage on VOUT that is centered at 1.65 V and changes by 14.3 mV per amp of input current, with positive current increasing the output voltage and negative current decreasing the output voltage:

VOUT=1.65V+0.0143VA⋅IP${\displaystyle {\mathrm{<span\; style="font-size:\; 14px;">V</span>}}_{\text{<span style="font-size: 14px;">OUT</span>}}<span\; style="font-size:\; 14px;">=</span>\mathrm{<span\; style="font-size:\; 14px;">1.65</span>}\text{<span style="font-size: 14px;">V</span>}<span\; style="font-size:\; 14px;">+</span>\mathrm{<span\; style="font-size:\; 14px;">0.0143</span>}\frac{\text{<span style="font-size: 14px;">V</span>}}{\text{<span style="font-size: 14px;">A</span>}}<span\; style="font-size:\; 14px;">\cdot </span>{\mathrm{<span\; style="font-size:\; 14px;">I</span>}}_{\text{<span style="font-size: 14px;">P</span>}}}$

IP=VOUT–1.65V0.0143VA=(VOUT–1.65V)⋅70AV

The output is not ratiometric, so the zero point and sensitivity are independent of the actual supply voltage.

The optional FLT pin is normally at VCC and is pulled low when the IP current magnitude exceeds 110% of the maximum sensing range. This pin only asserts while the fault condition is present (it is not latched).

Note: The datasheet warns that using the FLT (TEST) pin as a fault output rather than grounding it will reduce the sensor’s immunity to high dV/dt events. If you do not need the fault feature, you can externally connect this pin to ground. Alternatively, we have the ability to custom-assemble these boards with this pin grounded (which would also disable the fault feature).

Making connections to the board

You can insert the board into your current path in a variety of ways. For typical high-current applications, you can solder wires directly to the through-holes that best match your wires, or you can use solderless ring terminal connectors. The largest through-holes are big enough for 10 AWG wires or #6 or M3.5 screws, and the second-largest through-holes (and mounting holes) are sized for 14 AWG wires or #2 or M2 screws. Holes with 0.1″, 3.5 mm, and 5 mm spacing are also available as shown in the diagram above for connecting male header pins or terminal blocks, but please note that these connection options are generally not suitable for high currents and could limit the usable range of the sensor. Examples of different kinds of connections are shown in the pictures below.

           

The FLT, VOUT, VCC, and GND pins work with 0.1″-pitch header pins and are compatible with standard solderless breadboards

Warning: This product is intended for use below 30 V. Working with higher voltages can be extremely dangerous and should only be attempted by qualified individuals with appropriate equipment and experience.

Schematic and dimension diagrams:

The dimension diagram is available as a downloadable PDF (436k pdf).

Real-world power dissipation considerations

Depending on the version, the CT432 and CT433 can measure up to ±70 A. However, the sensor chip will typically overheat at lower currents. In our tests, we found that our 2-layer CT432/CT433 compact carrier board (cs07a) could conduct about 45 A continuously, and the 4-layer compact carrier board (cs07b) could conduct about 50 A continuously, without reaching the thermal limit for the IC. (Sensors with ranges under 45 A use the cs07a board while sensors with ranges over 45 A use the cs07b board.) Our tests were conducted at approximately 25°C ambient temperature with no forced air flow.

The actual current you can pass through the sensor will depend on how well you can keep it cool. The carrier’s printed circuit board is designed to help with this by drawing heat out of the sensor chip. Solid connections to the current path pins (such as with thick soldered wires or large, tightly-secured lugs) can also help reduce heat build-up in the sensor and carrier board.

Warning: Exceeding temperature or current limits can cause permanent damage to the sensor. If you are measuring an average continuous current greater than 30 A, we strongly recommend that you monitor the sensor’s temperature and look into additional cooling if necessary.

This product can get hot enough to burn you long before the chip overheats. Take care when handling this product and other components connected to it.

Package Includes:

• 1 x Pololu 5315 CT433-HSWF70MR TMR Current Sensor Compact Carrier -70A to +70A, 3.3V