A day in Maxim Integrated's product engineering lab opens your eyes to the different tasks they perform to make sure that your boards and systems are working as they should.
On this day, Manisha Potay, Member of Maxim's Technical Staff, was characterising digital temperature sensor ICs that cover the range of -55°C to 150°C. The sensors use internal diodes to detect temperature, then digitise and linearise the diode's forward voltage, producing a digital representation of temperature that's available over the SPI bus.
Figure 4: Manisha Potay explains the process for testing diode temperature sensors.
Testing temperature sensors requires a stable, controlled temperature, the kind you can't get with the diodes exposed to air. Thus, this test setup consists of a control board and a DUT board connected through a ribbon cable. Figure 5 shows a Fluke temperature bath—the kind you often see in calibration labs—with the control board on top. A board holding the DUTs is in the oil bath.
Figure 5: Temperature sensors under test are mounted to a DUT board immersed in an oil bath. The control board sits on top.
The control board provides power, control and readback to and from the DUTs. Because the temperature sensors communicate to other devices through the SPI bus, the control board uses that bus to send control signals to the DUTs. It also provides power. Data from the DUTs gets converted to USB for transfer to the host PC which lets engineers analyse the data. Figure 7 shows a DUT board.
Figure 6: The control board communicates with the host PC while providing power and control signals to the DUT board.
Figure 7: The DUT board holds the sensors under test while routing power to the devices. It also routes control and readback signals to and from each DUT.
ADCs have long been a staple of Maxim's product line. That tradition continues today. In Figure 8, Shyam Shankar, Associate Member of Technical staff was evaluating high-speed (about 1 Msample/s) 12-bit and 14-bit ADCs.
Figure 8: Shyam Shankar demonstrates a test setup used for evaluating ADCs.
The setup uses an Audio Precision SYS-2722 audio generator/analyser for generating the ADC's input signals. An Agilent Technologies (now Keysight) 3458A metrology-grade DMM makes voltage measurements through the test board (Figure 9). The ADC's digital output connects to a PXI digital I/O card, which provides SPI bus digital patterns to control the ADC and capture its output. The setup needs to be coherent and synchronized to perform dynamic measurements such as signal-to-noise ratio (SNR) and total-harmonic distortion (THD). Using the CLK_IN features of the test equipment lets the system synchronize the signal source, digital card, and DUT to an external clock source.
Figure 9: The ADC test board provides the DUT with access to stimulation signals from an audio generator/analyzer and it routes digital outputs to an I/O module.
On this day, Seema Venkatesh, Associate Member of Technical Staff was testing a nanoPower buck/boost converter.
Figure 10: Seema Venkatesh explains how she tests DC/DC converters.
The DC-DC converter test board contains an array of relays that route the input voltage from a power supply to the DUT and it routes the output voltage from the DUT to a 3458A DMM. An oscilloscope lets Venkatesh measure characteristics such as output ripple and noise. The underside of the board contains a series of mechanical relays because they eliminate leakage problems that could arise from using semiconductor switches.
Figure 11: Relays mounted on the underside of the test board route power to and from the DC/DC converters under test.
Maxim Integrated also manufactures LED drivers. Leo Apostol, Senior Member of Technical Staff, was testing a driver circuit targeted for 12 V MR16 LED and MR11 LED bulbs.
Figure 12: Leo Apostol explains the tests he performs on LED driver ICs.
The bench-test board does more than just provide power to the DUT. As part of the testing, the DUT must be trimmed to provide the right amount of current. As part of his evaluation, Apostol programmed the PC to perform the trims based on the trim algorithm and targets provided by the design engineer. In addition, he tested for parameters such as thresholds, lock-out voltages, bias currents, and dimming ratio (the ratio of the highest-to-lowest amount of current that the driver can produce). The drivers are tested with loads rather than LEDs themselves.
Figure 13: A test board for LED drivers has a "keep out" area to isolate the DUT from support circuits.
Note the ring in the center of the LED test board in Figure 13. The DUT is located at the center of the ring, with all support circuits outside. This "keep-out ring" provides thermal isolation between the LED driver and support circuits while the DUT undergoes thermal testing. A socket in the center of the ring holds the DUT. You can see the probes surrounding the LED driver under test.
When you design a reference device such as a voltage reference into a circuit, you know its voltage will drift over time, but by how much and for how long? That's where LTD testing comes in. LTD is a key parameter for precise reference ICs and it's an industry norm to publish LTD data for 1000 hours in the datasheet. For these lengthy tests, engineers at Maxim surely need an automated setup to record measurements so they can perform other tasks. Product engineers can program the equipment to change the frequency of measurements over the test period. For example, devices might drift more during a test's early hours than later. Thus, more measurements are often needed up front.
Because LTD measurements take many hours, engineers need to test many devices at once. Maxim's LTD test setup lets engineers insert several boards into a thermal chamber. Each board can contain a different flavor of a part while they share a power supply and DMM.
Figure 14: Multiple test board can be stacked and inserted into a temperature chamber for long-term drift measurements.
Product engineers at Maxim Integrated perform many tasks and this article is just a snapshot of what they were doing on this day. So, the next time you design a board or system, remember that it's the product engineers who verified that the part will perform as you expected.
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