Solution: Advanced DC/DC switching regulators
To assist design engineers address the challenges of electronic noise, heat and size in medical applications, Linear Technology offers a broad selection of over fifty different µModule® power products. Each of these products is a highly efficient, fully integrated DC/DC switching power management solution in a compact surface mount package (Figure 1
). These switch mode regulators were carefully designed to operate with low output ripple in both negative (inverting) output voltage and positive output voltage circuit configurations as shown in Figures 2 & 3
. A sub-group of µModule power products, the EN55022 class B certified µModule regulators, present an ideal solution to overcome the EMI challenges found in medical applications. These switching regulators were certified by independent laboratories such as TUV to meet the industry’s EN55022 class B (equivalent to CISPR11 / EN55011 Group 1 - Class B) standard for radiated EMI at output currents up to 8A. The test results using their respective standard demo boards are publicly available online. An excerpt is shown in Figure 4
. Selecting a known compliant fully integrated step-down solution such as a µModule regulator, reduces design time and risk associated with common switching regulators or controllers in meeting these requirements.
Figure 1: µModule power products are a complete DC/DC switching solution in a thermally enhanced LGA or BGA package, providing a convenient means to dissipate heat through the top & bottom of the package
Figure 2a & 2b: LTM8023 12VIN to -7VOUT @ 1A schematic operates with less than 30mVpp output ripple to minimize noise injection into the CMOS sensor & signal conditioning components, which require a negative voltage supply
Figure 3: LTM4613 has just 26mVpp output ripple (12VIN to 5VOUT @ 5A) to minimize noise injection into the CMOS sensor & signal conditioning components for a high quality image
Figure 4: LTM4613 meets EN55022 Class B (CISPR11 Group 1 Class B) requirements with more than 6dBµV/m margin (12VIN to 5VOUT at 8A)
The risk associated with high output ripple and radiated EMI should not be underestimated. These two factors impact a product’s ability to function properly the first time and meet strict government regulations. Recalling their impact on a X-ray flat panel’s operation, product designs with well controlled output ripple and EMI emissions deliver high signal to noise ratio for a high quality high resolution image, reliable first time right image capture to avoid delays in treatment and unnecessary repeat radiation exposure, reliable wireless communication and speed EMI compliance testing. For these reasons, Linear Technology took great care in ensuring these devices were certified by independent test laboratories such as TUV with the tests results made publicly available online. After overcoming noise and EMI concerns, the right power management solution needs to address the issues of efficiency, reliability and thermal dissipation.
µModule power products are highly efficient switching regulators offered in a surface mount LGA or BGA package constructed of thermally conductive plastic with a flat top. A single flat top covering a complete power management solution is conducive to heat sinking techniques to minimize the temperature rise at any particular point of the medical device’s exterior (Figure 5
). As mentioned previously, maintaining a cool operating temperature improves patient safety, signal to noise ratio and equipment operating lifetime. With the largest µModule power products measuring 15mm x 15mm x 5mm and the smallest measuring 6.25mm x 6.25mm x 2.3mm, space is freed up for more important features such as increased battery size for longer operating time between charging.
Figure 5: Without a heat sink under natural convection, the LTM4613 has a max case temperature of 41°C (12VIN to 5VOUT @ 5A). Once thermally connected to the metal case (a heat sink at no extra cost), the peak temperature would decrease further below 40°C.