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Making Pulse Current Measurements

with the Series 2280S Precision

Measurement DC Power Supplies

Introduction

More and more integrated circuits and electronic sub-assemblies

today are being designed for use in mobile applications, which

means this circuitry will operate on battery power and will

have a finite supply of power available to them. To maximize

the battery life of the end products into which these circuits

are built, it is imperative for device designers to minimize their

power consumption. This requires characterizing the power

consumption of a device in all states in order to understand

where to focus their efforts.

One of the biggest challenges associated with characterizing

the power consumption of mobile devices is that their current

draw varies greatly depending on the state in which the device is

operating. It is common for mobile devices to spend a majority

of their time in sleep mode, drawing only microamps of current

or less, waking up only periodically to perform a function.

While performing these functions, current draw can increase

dramatically, jumping to tens, hundreds, or even thousands

of milliamps. In many cases, this lasts for as little as a few

hundred microseconds, making measuring the device’s current

consumption during these operations difficult.

Typical power supplies are incapable of

measuring the sudden current pulses drawn by

a device while it is awake, requiring additional

instrumentation to make the measurement. This

not only adds to the cost of testing these devices

but increases the complexity of the test system.

Precision measurement DC power supplies like

the Keithley Series 2280S are capable of measuring

pulse currents as narrow as 140µs and include the

triggering features required to synchronize the

measurement with the current pulse.

This application note demonstrates how to use

the Keithley Series 2280S Precision Measurement

DC Power Supplies to measure the pulse of load

current drawn by a wireless transceiver module

during its transmission state.

Test Equipment

This application involves measuring the load

current drawn by an 802.15.4 Wireless Transceiver

Module when it is in its data transmission state.

The equipment used includes:

• Keithley Series 2280S Precision Measurement

DC Power Supply

• USB-to-SPI/I2C controller with digital I/O

• PC with custom test program

• Digital I/O converter

The wireless transceiver module is commonly used with the

ZigBee network stack for creating products designed for building

automation and remote sensor monitoring. This transceiver

includes an SPI digital interface for configuration and operation,

which allows it to be controlled easily by a microcontroller.

However, for device testing purposes, a USB-based SPI/I2C

controller with a digital I/O port is used to configure and operate

the device from test code running on a PC. This test code also

configures and controls the Keithley Series 2280S Precision

Power Supply to supply power to the device and make the pulsed

current measurement.

A Tektronix MDO4104B Mixed Domain Oscilloscope provides

verification and visual representation of the measurement.

Making Connections

Figure 1

illustrates the connections required for this test.

Number 3277

Application Note

Se ries

Model 2280S Rear PanelPC with Test Program

USB SPI/I2C

Controller

with

Digital I/O

GND

SHI

DIO 0

DIO 1

DIO 2

DIO 4

- -

DIO 7

MISO

MOSI

SCLK

SLO

Digital I/O

Converter

802.15.4

Wireless

Transceiver

Module

VCC

GND

RESET

IRQ

SLEEP TRANSMIT

MISO

MOSI

SCLK

GPIB, USB,

or Ethernet

USB

Figure 1. 802.15.4 wireless tranceiver test system connections

Summary of content (4 pages)

PAGE 1
Number 3277 Application Note Series Making Pulse Current Measurements with the Series 2280S Precision Measurement DC Power Supplies Introduction More and more integrated circuits and electronic sub-assemblies today are being designed for use in mobile applications, which means this circuitry will operate on battery power and will have a finite supply of power available to them.
PAGE 2
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.
PAGE 3
:TRIG:SAMP:COUN 1 :DEL:STAT ON :DELay 60e-6 :DATA:CLEAR :VOLT 1.8 :CURR 0.1 :OUTP ON :INIT *OPC? :TRAC:DATA? “READ” Set the sample count to 1 to take a single measurement during the pulse. If the pulse being measured is long enough, you can set this to a larger number to take more measurements per pulse. Turn the source delay on and set the delay value long enough to place the measurement at the top of the current pulse. For this DUT, the delay is set to 60µs. Clear the buffer.
PAGE 4
Specifications are subject to change without notice. All Keithley trademarks and trade names are the property of Keithley Instruments, Inc. All other trademarks and trade names are the property of their respective companies. A Greater Measure of Confidence KEITHLEY INSTRUMENTS, INC. ■ 28775 AURORA RD. ■ CLEVELAND, OH 44139-1891 ■ 440-248-0400 ■ Fax: 440-248-6168 ■ 1-888-KEITHLEY ■ www.keithley.com BENELUX +31-40-267-5506 www.keithley.nl FRANCE +33-01-69-86-83-60 www.keithley.