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Chapter 3
Signal Connections
Power Connections
Caution
Never connect the +5 V power pins (pins 49 and 99) directly to analog or digital
!
ground or to any other voltage source on your DAQPad device or any other device.
Doing so can damage your DAQPad device and the computer. National
Instruments is not liable for damages resulting from such a connection.
Connecting Power Sources to Digital I/O Lines
Caution
Always turn your DAQPad on before applying external power to the digital I/O
!
(DIO) lines. If your DAQPad is off and external power is applied to the DIO lines,
your DAQPad may be damaged. National Instruments is not liable for damage
caused by incorrect power sequencing.
DAQPad-6507/6508 User Manual
Two pins on the I/0 connector supply +5 V from your DAQPad
device's power supply through a self-resetting fuse. The fuse resets
automatically within a few seconds after the overcurrent condition is
removed. These two pins are referenced to DGND and can be used to
power external digital circuitry.The power rating is indicated below.
Power rating: +4.65 VDC to +5.25 VDC at 1 A combined total for both pins
Pins 49 and 99 of the I/O connector are connected to the +5 V supply of the
DAQPad-6507/6508 devices. You can power the DAQPad-6507 or
DAQPad-6508 from either USB power or an external source. The DAQPad
uses USB power when the external source is not plugged in. USB power
limits any device from using more than 0.5 A. If you are running from USB
power (that is, if your external power source is not plugged in), you have
only 150 mA to drive signals and supply power for your circuitry. If you
require more power than 150 mA, attach the external power source. Also,
your host computer might turn off power to your DAQPad device if no
activity is detected. This cuts the power to any external circuitry powered
by your DAQPad device if you are not using an external power source.
Refer to
Power
Considerations, in Chapter 2,
Configuration, of this manual.
When supplying power to DIO lines, we strongly recommend you use the
+5 V source from the DAQPad. If you must use an external power source,
it is important to sequence the power correctly—DAQPad first, then
external power—to prevent damage to the CMOS circuits. Because of a
trait common to all CMOS circuits, applying external power first may cause
current to flow incorrectly, damaging the circuit.
3-8
Installation and
© National Instruments Corporation
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