Intersil – Power Density vs. Heat Dissipation: Power Modules No Longer Have to Choose

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Power modules are the way to go when it comes to leveraging the expertise of power experts, increasing power density and getting your design to market quickly. Their architectural choices can easily mitigate the seemingly divergent requirements of power density and power supply’s thermal performance.

System designers tasked with integrating more power in ever-shrinking form factors must overcome various obstacles, such as heat dissipation, adversely affecting the system’s electrical and thermal characteristics.

Fortunately, power module designers continue to innovate through various architectural design approaches that maximize performance from the smallest package. Yet, designers in need of the optimum power module should be careful in their solutions choice. Varied power module architectures can greatly affect the overall system performance such as heat dissipation, transient response, ripple voltage and even ease of use. It’s very much a case of ‘buyer beware’.

The Case for Modular Versus Discrete

There are many reasons to opt for a power module versus designing a power converter with discrete components. By integrating a controller, MOSFETs, inductors and passive components, modules only require input and output capacitors to operate. Designs can be finished relatively easily and quickly, with confidence that basic performance and space requirements have been met.

For example, Intersil’s ISL8205M power module with its extremely low 1.85mm profile package can easily be placed on either side of a printed circuit board (PCB) for greater density and placement flexibility, while delivering excellent electrical and thermal performance. Normally that knowledge would be sufficient, but how that module was designed can greatly affect more nuanced parameters, features and capabilities.

Small Module Package Offers Excellent Thermal Performance

The ISL8205M uses a QFN (quad-flat, no-leads) copper lead-frame package, where internal components are soldered directly to the copper lead frame, see Figure 1. Wire bonds followed by the molding compound complete the encapsulated package.

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Figure 1: ISL8205M internal structure

This structure allows the heat generated by the internal components to be dissipated directly by the copper in the lead frame, which has a thermal conductivity of ~385 W/mK. This is about 1000 times the thermal conductivity of the PCB and its typical thermal conductivity of ~0.343 W/mK. As a result, the copper-based lead frame can help the heat dissipate much more efficiently than a PCB-based module. Furthermore, thicker copper lead frame may spread the heat over a larger area, thus accelerating the effective heat transfer to the system board.

It’s important to note that the molding material in the structure can have a similar heat-spreading effect by increasing the effective heat transfer area from the internal components and providing an additional path to the lead frame.

This thermal performance is perfectly illustrated by Intersil’s ISL8203M. Mounted on a standard four-layer evaluation board (2oz/1oz copper layers), the module’s maximum temperature is only 66.8°C under a worst-case conversion scenario of 5VIN to 3.3VOUT/6A with no air ow and an ambient temperature of +25°C. See Figure 2.

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Figure 2: ISL8203M – 5VIN to 3.3VOUT at 6A conversion – no air flow

Intersil’s family of power modules comes in ultra-compact packages addressing the most drastic needs for power density. As a complete DC-DC power supply, this family has been optimized for low power, low voltage applications while meeting electrical and thermal performance requirements.

ISL8202MISL8203M (Single)ISL8205MISL8203M (Dual)
Regulated Output(s)1211
Output Current Per Channel3A3A5A6A
Input Voltage Range2.6V to 5.5V2.85V to 6.0V2.6V to 5.5V2.85V to 6.0V
Output Voltage Range0.6V to 5.2V0.8V to 5.0V0.6V to 5.2V0.8V to 5.0V
TopologyCurrent Mode PWM/PFMCurrent Mode PWMCurrent Mode PWM/PFMCurrent Mode PWM
Peak Efficiency95%95%95%95%
Light-Load Efficiency ModeYes - PFMNoYes - PFMNo
Current SharingNoYesNoYes
Package (mm x mm x mm)QFN 4.5 x 7.5 x 1.85QFN 6.5 x 9 x 1.83QFN 4.5 x 7.5 x 1.85QFN 6.5 x 9 x 1.83
Footprint33.75mm258.5mm233.75mm258.5mm2

When power density, time-to-market, reliability and design capabilities are all motivating factors, many designers choose power modules.

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