How to Test Power-supplySequencing with PicoScopes


Derek Hu  Pico Technology

1About power-supply sequencing

Power-supply sequencing is always essential in high-performance processing devices like DSP, CPU, FPGA, in order to achieve reliable operation, enhance efficiency and overall system health. Figure 1 is a schematic diagram of a power-supply sequencing. The high-performance processing device in the diagram has four power-supplyinputs named VCC1, VCC2, VCC3, VCC4 respectively, which are used to power different modules in the device. Four DC/DC LDO modules monitored and controlled by a voltage supervisor are used to provide the power-supplies for the four power inputs. In this example, the power-sequencing is VIN, VCC4, VCC3, VCC2, VCC1


Figure 1 A schematic diagram of a power-supply sequencing

In practice, the power-sequencing is always following the sequence of core supply, block RAM supply, auxiliary supply, I/O supplies. Figure 2 below shows thetiming ofthe power-supplies of a high-performance processor and figure 3 shows its timing specifications of each power-supply.


Figure 2 Power-supply sequencing of a high-performance processor


Figure 3 Power-supply sequencing specifications of a high-performance processor

In addition to the power-supply sequencing, the high-performance processors also require stable power-supplies. Figure 4 below shows the power supply specification of a high-performance processor. The ripple requirement of the core voltage is+/- 2% or +/- 20mV.


Figure 4Power supply specifications of a high-performance processor

2Test power-supply sequencing with PicoScopes

The test of power-supply sequencing can be done in PicoScope 7 software or under SDK.

PicoScope 7 isthe next generation user interface for any real-time PicoScope as standard.  It has all the analysis tools you need to get answers quickly, whether carrying out a simple test, or debugging a complex design. Delay/Phase measurementis one of dozens of automatic measurements in PicoScope 7. It can be used to test power-supply sequencing.Figure 5 shows the acquisition of four waveform in PicoScope 7 and the subsequent delay measurement between each pair of them.


Figure 5 Delay measurement in PicoScope 7

In addition to PicoScope 7 software, a great manyusers choose to develop their own testing platform with PicoScopesand SDK (Software Development Kits). They integrate PicoScopes into their ATE(AutomaticTesting Equipment) for verifying power-supply sequencing and power ripple. 8-channel PicoScopesarepopularly used for such application. Figure 6 below shows thewaveforms of power-supplies tested with a customized ATE which has PicoScope 4824A integrated for power-supply sequencing testing. The customer develops their own application software in LabView.


Figure 6 An ATE with PicoScope 4824A integrated for power-supply sequencing testing

3 Why PicoScopes?

PicoScope 4824A is a popular choice for the testing of power-supply sequencing. It is a well market-positioned product especially for powermeasurements with high cost-efficiency—right bandwidth (20MHz), multiple channels (8 channels), high ADC resolution (12 bits), powerful SDK etc.If you need a high channel-count oscilloscopes with high bandwidthto cover more frequency components forthe measurement of power noise, Pico Technology does have PicoScope 6824E model with 500MHz bandwidth, 8 analog channels, 8~12bits flexible ADC resolution.


Figure 7 PicoScopemodels with 8 channelsand high resolution

The main reasons that people like to integrate PicoScopes into their automated testing systems for power measurement are the unique advantages and powerful capabilities of PicoScopes.

  • High reliability

Established in 1991, Pico Technology has been focusing on the development and manufacture of PC-based test instrument and data acquisitionequipment.Decades of product iteration and stringent quality controls make PicoScopeshighly reliable.

  • Cost-efficiency

Different from benchtop instruments, the fact that PicoScopes don’t have PC in the box gives them more unique hardware advantages due to the simple structure, including high bandwidth/sampling rate, deep memory, high/flexible ADC resolution, multiple analog and digital inputs, fast speed, etc. The use of full capability of an external PC allows PicoScopes more software capabilities, including 30+ serial decoders, advanced math functions (FFT, filters, measurements plotting, etc). Moreover,dozens of PicoScope models make the customers easier to pick one affordable and suitable for their applications.

  • High/Flexible ADC resolution

PicoScopes offer a wide range of vertical resolution options from 8 to 16 bits. The higher the resolution, the greater the vertical accuracy and the dynamic range. The flexible resolution feature in PicoScopes is based on Pico’s breakthrough ADC technology which allows users to switch from 8 to 16 bits in one unit.

  • Fast and powerful SDK

PicoScopes provide a level of interconnectivity and customization that is not usually available on most benchtop oscilloscopes. The SDK(Software Development Kit) allows users to create custom applications for their particular projects. That makes PicoScopesgo beyond just being a regular oscilloscope. PicoScopes running under SDK have much better performance. For example, it can acquire and transmit data continuously to PC with the speed up to 312 MS/s; The memory can be segmented up to 2 million; The users can set the advanced triggers and generate waveforms programmatically. Programming with SDK is simple and easy. Professional technical support is always ready and lots of code examplescan be found in github.com/picotech.

All Pico products including PicoScopes come with a free-of-charge SDK. The SDK includes drivers for Windows, macOS, Linux and Raspberry Pi (ARM7). It allows users to write their own software to control the instruments with popular languages such as C, C#, C++, Python, MATLAB, LabVIEW and Microsoft Excel.

  • Compact and portable units

Unlike traditional benchtop instruments, PicoScopes are compact, light and portable. When used with a laptop computer, a PicoScope allows you to carry a complete electronics toolset in one bag with your PC. And small size also makesPicoScopes easier to be integrated into the systems with almost no increasein weight or size.

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