Brochure

The VCC and GND pins of the wireless transceiver are
connected to the HI and LO leads of the Series 2280S power
supply. To ensure the voltage level applied at the device is
accurate, the sense lead jumpers should be removed from the
connector on the rear of the instrument and a separate set of
sense leads should be run to the device’s VCC and GND pins.
This will allow the instrument to compensate for any voltage
drops in HI and LO leads that may occur due to the device’s
large current draw during transmission.
The Chip Select (CS), MISO, MOSI and SCLK lines of the
wireless transceiver module’s SPI interface are routed to the SPI
lines of the USB-to-SPI/I2C controller. The Reset, Interrupt and
Sleep/Transmit lines are routed to the USB-to-SPI/I2C controller’s
digital I/O port.
Note that the wireless transceiver module’s Sleep/Transmit
line and GND lines are routed not only to the USB-to-SPI/I2C
controller but also to the digital I/O port of the power supply.
Data transmission for this wireless transceiver can be controlled
by toggling this line, making it a perfect trigger source for
triggering a measurement on the power supply. However, this
line cannot be used directly to trigger it, and an in-line converter
is required. Refer to the next section for details on this converter.
The PC controls the entire test system using a custom
test program.
Converting the Digital I/O Signals
The wireless transceiver module and all of its digital signals
operate at 1.8V; the power supply’s digital I/O port requires at
least 3.4V. This 1.8V is not large enough to register as a signal
level high on the power supply’s digital I/O, so it can’t be used
directly to trigger the instrument. Furthermore, the signal that
starts the transmission on the wireless transceiver is a rising
edge, but a falling edge is required to trigger the power supply.
In order to use the Sleep/Transmit line of the wireless transceiver
as a trigger signal for the power supply, the line must first be
level-converted.
A couple of resistors and a small signal NPN BJT (Part No.
2N3904) are all that’s needed both to create a simple circuit that
will convert the signal from 1.8V to 5V and to invert its polarity,
creating a 5V falling edge trigger from the 1.8V rising edge
trigger.
Figure 2 illustrates the details of this circuit.
1
5
6
9
2kΩ
5kΩ
2N3904NPN
BJT
+5V
GND
Trigger In
Sleep Transmit
GND
Model 2280S
Digital I/O
9-Pin D-Sub
Figure 2. 1.8V to 5V trigger level converter circuit diagram
Configuring the Instrument
To measure current pulses as small as 140µs, a Series 2280S
Precision Measurement DC Power Supply must be configured for
fast, synchronized measurements by following these steps:
• Reset the instrument to Power On Defaults.
• Change the Measure Function to Current (default is
Concurrent, measuring both voltage and current).
• Turn the Averaging Filter off.
• Change the NPLC to 0.002, the fastest measurement time.
• Change the Measure Range to a fixed 1A or 10A range
depending on the current level drawn by your device.
– Note: 100mA and 10mA ranges can be used for pulses
lasting 2ms or longer.
• Turn off Auto-Zero
– Auto-zero will automatically measure an internal reference
to zero the instrument for each triggered measurement.
This will extend the length of the measurement interval and
result in the measurement missing the pulse. Turn auto-zero
off to ensure proper measurement timing.
• Configure the Trigger Layer Trigger Source as External.
• Configure the Source Delay to delay the start of the
measurement from the input trigger and place the
measurement at the flat top of the current pulse.
Using these settings, the instrument makes a fast current
measurement every time it receives a trigger on its digital I/O
port. Using the Sleep/Transmit line of the wireless transceiver
module as a trigger source, this measurement is aligned with the
top of the current pulse.
Automating the Pulse Current Measurement
The process of configuring the instrument for fast current
measurements and collecting the data can be automated by
sending the instrument the following SCPI commands:
*RST Reset the instrument to defaults.
:VOLT:PROT:LEV 3.3
:VOLT:L IM 2.2
:CURR:PROT:LEV 0.1
Configure the Over Voltage Protection, 3.3V,
Voltage Limit, 2.2V and Over Current Protection,
0.1A, to protect both the operator and
the device.
:SENS:FUNC “CURR” Change the measure function to Current only.
:SENS:CURR:AVER:STAT OFF Turn off the averaging filter.
:SENS:CURR:NPLC 0.002
Change the NPLC setting to 0.002 for a 33µs
measurement aperture.
:SENS:CURR:RANG 1
Set the current measurement range to a
fixed 1A range.
:SYST:AZER OFF Turn off auto-zero.
:INIT:CONT OFF
Turn off continuous initiation of the
trigger model.
:TR IG:SOUR EX T
Set the trigger source to External (Digital I/O
Trigger in).
:TRIG:SEQ:COUN 1
Set the trigger count to match the number of
pulses being measured in the test. Note: you
will need a Digital I/O Trigger in for each count.