Measurement Specialties PMD-1024HLS manual Power terminals, Output sink current limits

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PMD-1024HLS User's Guide

Functional Details

Port A0

+GND

+5 V

Figure 3-4. Schematic showing switch detection by digital channel Port A0

For more information on digital signal connections

For more information on digital signal connections and digital I/O techniques, refer to the Guide to Signal Connections (available on our web site at www.mccdaq.com/signals/signals.pdf).

Power terminals

The USB +5 V connection (pin 30) is on the bottom screw terminal of the PMD-1024HLS. Refer to the pinout diagram on page 3-2for the location of this terminal. This terminal draws power from the USB connector. The +5 volt screw terminal is a +5 volt output that is supplied by the connected computer.

Caution! The USB +5 V terminal is an output. Do not connect to an external power supply or you may damage the PMD-1024HLS and possibly the computer.

Just connecting the PMD-1024HLS to your computer draws 60 mA of current from the USB +5 V supply. Once you start running applications with the PMD-1024HLS, each DIO bit can draw up to

15 mA. The maximum amount of +5 V current available for external use, over and above that required by the PMD-1024HLS, is the difference between the total current requirement of the PMD-1024HLS (based on the application), and the allowed current draw of the computer platform.

The following power limits depend on whether you are sourcing current out of the PMD-1024HLS, or you are sinking current into the PMD-1024HLS.

Output (source) current limits: desktop computers and self-powered hubs

The maximum allowed current draw for a typical desktop computer and self-powered hub is 500 mA. For an application running on a PC or self-powered hub, this value yields a maximum user current of 500 mA

60 mA = 440 mA. Since each DIO line can output 15 mA maximum, 24 DIO × 15 mA = 360 mA (maximum rating for the chips).

Output (source) current limits: notebook computers and bus-powered hubs

The maximum allowed current draw for a typical notebook computer and bus-powered hub is 100 mA.

Because the PMD-1024HLS needs 60 mA from the USB +5 V supply, this leaves you with only 40 mA. If you want to use 15 mA per DIO line, you can only do so with two DIO lines. To overcome this limitation, an external self-powered hub can be used to supply the proper current level required for full output capability as noted above.

Output (sink) current limits

Each PMD-1024HLS DIO output can sink up to 64 mA. For an individual line, this is not a problem. But if you were to apply this maximum load to all 24 DIO lines, you would damage the PMD-1024HLS because the total amount of current is well over the 440 mA maximum (24 DIO × 64 mA = 1536 mA ≈ 1.54 A).

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Contents Page PMD-1024HLS Management committed to your satisfaction Trademark and Copyright Information Table of Contents Where to find more information About this Users GuideWhat you will learn from this users guide Conventions in this users guideIntroducing the PMD-1024HLS ChapterPMD-1024HLS block diagram Software featuresConnecting a PMD-1024HLS to your computer is easy Installing the PMD-1024HLS What comes with your PMD-1024HLS shipment?Hardware SoftwareInstalling the software Installing the hardware Be sure you are using the latest system softwareUnpacking the PMD-1024HLS DocumentationIf the LED turns off Functional Details USB connectorExternal components Main connector and pin out Screw terminal wiringScrew terminal pins False For more information on digital signal connections Power terminalsOutput sink current limits Counter terminal Ground terminalsPull-up/pull-down terminals Pull-down connection for Port a Specifications Digital input/outputPower Counter sectionMain connector and pin out GeneralEnvironmental MechanicalDeclaration of Conformity USAMailinfo@mccdaq.com