“Device Power Supply ICs Must Consider Range Switching Glitches”

Glitch when switching to low current range, possible damage to DUT
MAX32010, Glitch-Free Range Switching Possible, Test Reliability ↑

This article discusses two important considerations when selecting a device power supply IC: range change glitch and power supply efficiency, and how to design a DPS system to meet the requirements of a specific application.

In automated test equipment (ATE), device power supply (DPS) ICs can flexibly supply force voltage (FV) and force current (FI) according to test requirements.

The DPS IC operates as a voltage source when the load current is between two preset current limits, and seamlessly switches to a precision current source/sink when the preset current limit is reached.

▲Figure 1. MAX32010 Diagram

Figure 1 shows the architecture of the MAX32010, a next-generation device power supply IC from Analog Devices.

The FIMODE, FVMODE, and FISLAVE MODE switches select FV, FI, and FI Slave modes, and the HIZF and HIZM switches select MV (measure voltage) and MI (measure current) modes, respectively.

RANGE MUX works with external sense resistors to enable different current ranges (RA (1.2A), RB (20mA), RC (2mA), RD (200mA)).

A specific current range can be set by changing the detection resistor value according to the formula R _SENSE = 1V/I _OUT . Voltage and current clamps can be set using the CLEN switch and the ICLMP and VCLMP DACs.

■ Range switching glitch

Looking at the first consideration, the range switching glitch, there are times when the ATE is testing a DUT and the system needs to change the current range to switch to another test.

IDDQ, or quiescent current, measurements typically require a very low current range to measure small values of current.

Switching to extremely low current ranges at this time can cause voltage spikes or glitches that can not only affect measurements but also damage the DUT.

Glitch-free range switching can protect the DUT and increase test reliability.

Figure 2 shows that ADI's DPS IC switches very smoothly without any glitches when tested using a 270pF load capacitor.

When no load capacitor is used (0 pF), this transition occurs over 20 ms with a ramp rate of 25 mV/20 ms.

This is much smaller than the glitches seen in competing products.

Competitive products exhibit glitches of 159 mV for several microseconds.

Therefore, we can see that ADI's DPS IC performance is 536% better than the range switching performance of the competitor's product, and does not cause any damage to the DUT.

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▲ Figure 2. Comparison of range transition glitches between Analog Devices products and competitor products

■ Device power supply efficiency

Another important consideration when selecting a DPS IC is the device power supply efficiency.

This efficiency directly impacts cost savings and system reliability.

Higher efficiency means greater cost savings, better reliability, and longer system life.

As DPS efficiency decreases, it generates more heat, and more heat means faster wear on components and more frequent failures.

DPS efficiency can be calculated as 'Efficiency = Output power / Input power'.

As shown in Table 1, ADI products provide higher current (1.2 A) with higher efficiency (58.33%) than competitive products.

ADI's DPS efficiency is 11% better than Competitor 2's DPS IC and 155% better than Competitor 1.

▲Table 1. Comparison of device power supply efficiency

■ How to design a DPS to meet specific load current requirements

In this article, we will explore some considerations when designing a DPS system to meet the requirements of a specific application.

▲Figure 3. Selecting a specific load current using a detection resistor

Each ATE has specific load current requirements depending on the device under test (DUT).

The MAX32010 allows you to select a specific range by changing just one sense resistor value.

The MAX32010's RANGE MUX selects one of the following current ranges: RA (1.2A), RB (20mA), RC (2mA), or RD (200mA).

The detection resistance value can be selected according to the formula R _SENSE = 1V/I _OUT .

If the required load current is 5mA, 5mA falls into range B.

If you want to choose an appropriate R _SENSE , R _SENSE = RB = 1V/5mA = 200Ω. ADI's Application Note 7068 provides more detailed information regarding sense resistor selection.

■ How to achieve higher output current

▲Figure 4. Achieving higher output current with parallel DPS configuration

DUTs often require higher current than the DPS can provide.

As shown in Figure 4, multiple DPS devices can be connected in parallel to provide currents greater than 1.2 A. To double the current, set both devices to FI mode.

For example, connecting two 7V 1.2A devices in parallel will achieve an output current of up to 2.4A at 7V.

▲Figure 5. 50% Duty Cycle Pulse Test Output of MAX32010

Another way to increase the output drive current of a DPS is to pulse the output.

When current is required only for a short duration, testing using pulses is possible, as shown in Figure 5.

An example of such a test is the IV characteristic analysis of a DUT. For pulsed testing, the duty cycle of the FI On time must be adjusted.

In this example, the DPS mode is set to FI mode 50% of the time and 'high impedance' mode the other 50% of the time.

The duty cycle can be adjusted based on the current demand of the DUT. When this test was performed with the MAX32010 IC, the result was the maximum output current = 1.436A at maximum 50% duty cycle.

■ How to select a heat sink suitable for your DPS system

To achieve a reliable and stable system, choosing the right heatsink is also important.

The following example provides a step-by-step guide to selecting a suitable heatsink using the MAX32010 as an example.

Step 1: Determine package specifications. Package thermal analysis is useful for selecting a suitable heat sink. It is important to know the exposed pad area for heat dissipation.

Step 2: Determine the PCB thermal characteristics and calculate the boundary conditions of JA. Calculate power losses and consider all media for heat dissipation (conduction, convection, radiation).

Step 3: Two important variables to consider when calculating the package temperature distribution are the heatsink base area and the airflow rate of the heatsink fan. The junction temperature of the IC must be kept below its thermal shutdown temperature. Analysis using still air shows that the MAX32010 requires a heatsink with a base area of 30.48mm x 30.48mm, a thickness of 5mm, and fin length of 15mm to keep the junction temperature below 140°C (Figure 6).

▲Figure 6. Temperature distribution of the MAX32010 package when using a heat sink.

Step 4: Airflow and heatsink material also play an important role in maintaining the junction temperature of the IC below 140C. Our analysis results show that adding 1 m/s of airflow to the copper heatsink can significantly improve the temperature performance.

▲Figure 7. Thermal Analysis of MAX32010

■ Conclusion

This article discusses the selection of device power supply (DPS) ICs for automated test equipment (ATE) systems, along with the system-level architecture to meet the output current and thermal requirements of the ATE system.

The considerations presented in this article can help you select the DPS IC that best suits your specific ATE system needs.

※ About the author
Madhura Tapse joined Maxim Integrated (now Analog Devices) in 2016 as a member of technical staff and has worked on a variety of product lines including supervisory ICs, power monitoring ICs, interface ICs, and ATE ICs. Prior to that, he was an applications engineer at Cypress Semiconductors. He holds a B.S. in Electrical Engineering from the University of Pune, India, and an M.S. in Biomedical Engineering from the Indian Institute of Technology – Bombay.