Pmod OD1 Reference Manual

The Digilent Pmod OD1 (Revision A) uses open-drain MOSFETs to drive high current applications.

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  • Two dual power N-FETs
  • Comfortable drives 3.0 A of continuous current
  • 4.1 A peak output current (t < 5 s)
  • 20V maximum output voltage
  • Four output clamp diodes
  • 6-pin Pmod connector with GPIO interface

Functional Description

The Pmod OD1 utilizes two NTHD4508 dual power N-FETs. Each channel can comfortably drive 3.0 A of continuous current at 25°C and up to 4.1 A of current for under 5 seconds, making this Pmod ideal for high current applications that require a simple on/off switch mechanism.

Interfacing with the Pmod

The Pmod OD1 communicates with the host board via the GPIO protocol. A logic high signal “turns on” a particular MOSFET after passing through a Schmitt Trigger Buffer (NL27WZ17) and a logic low signal turns off the MOSFET. Pmod OD1 Block Diagram

Pinout Description Table

Pin Signal Description
1 G1 Output 1
2 G2 Output 2
3 G3 Output 3
4 G4 Output 4
5 GND Power Supply Ground
6 VCC Positive Power Supply (3.3/5V)

Each output provides a clamp diode to prevent damage due to flyback voltages generated by inductive loads. Each output transistor functions independently of the others, so they can be used individually or simultaneously.

Output Circuit with a Load Connection

As illustrated in the above figure, a load is connected so that current from an external voltage source conducts through the load to ground when the output transistor is turned on. In order to complete the circuit, the GND pin on J4 must be connected to the ground for the external voltage supply. Additionally, the external voltage source must be connected to the VL pin on J4 to complete the circuit for the output clamp diode.

Any external power applied to pin 6 (Vcc) of the Pmod OD1 must be within 2.7V and 5.25V to stay within power supply limitations of the integrated Schmitt Trigger. If using an external power source, be sure to disconnect the JP1 jumper, disconnecting the external power from the host system board through Vcc.

Physical Dimensions

The pins on the pin header are spaced 100 mil apart. The PCB is 1.15 inches long on the sides parallel to the pins on the pin header and 0.8 inches long on the sides perpendicular to the pin header.

Additional Information

The schematics of the Pmod OD1 are available here. Additional information about the MOSFET including specific timings of the chip can be found by checking out its datasheet here.

Example code demonstrating how to get information from the Pmod OD1 can be found here.

If you have any questions or comments about the Pmod OD1, feel free to post them under the appropriate section (“Add-on Boards”) of the Digilent Forum.