Powering Healthcare

Author:
Edmund Suckow, Field Applications Engineer, Fairchild Semiconductor

Date
09/23/2010

Categories:
Battery Charging & Management, DC-DC Converters, MOSFETs & Power MOSFETs, Power Supplies, Sensors

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Portable medical electronic trends make it possible to reduce health care costs. Non-invasive battery-powered sensors are mobile and, when coupled with on-board memory, can capture a complete data pattern for a given symptom. Due to the continuous advances in ICs, these units are getting smaller, lasting longer, and therefore are more easily deployed in the field. Compact battery technology has remained relatively unchanged over the last five years. Extending the life of these sensors has been a direct result of power supply design discipline and IC advances. Leveraging cell phone standards, these advances include: charging over USB, high efficiency DC/DC regulators, adoption of I/O standards (I2C, SPI, SDIO, etc), and display improvements. Project design cycles have been historically long, often several years. A key electronic trend is improving time to market while mitigating risk. All applications require some form of power, typically a primary battery or a rechargeable battery for portable designs. The power from this battery must be regulated due the complex sensors used downstream. This practice extends the life of the battery and allows feature sets to be isolated from it. DC/DC module integration One such IC is Fairchild Semiconductor's FAN4603 uModule. The basic controller with integrated FETs is co-packaged into a single module with input and output capacitors as well as the switching inductor required in DC/DC buck topologies. The upfront advantages are obvious such as reduced size, only one part to inventory, and reduced design time. However, there are technical advantages as well. With such close proximity of all active parts in a single module, high current and high frequency paths are physically smaller, resulting in a power supply with lower EMI, crucial to the medical industry with complex sensors and human body interfaces. Increasing the switching frequency of the buck topology to 6 MHz for this module allows the integration of a chip-scale inductor. As the switching frequency increases, inductor size decreases and since these passive components - inductor and capacitors - were selected by the actual PWM and FET designers, everything is tuned to perfect interoperability and efficiency for the recommended load range. Downstream smart FET technology To better distribute and control the power module's energy into downstream sensors, processors, and LCDs, a point of load power switch is gaining in popularity. This FET is surrounded by diodes and transistors for added features such as load discharge, in-rush current limit, and reverse current blocking (RCB). Intuitively obvious is the migration to an actual smart FET, which integrates these features into one IC. The IntellimaxTM line from Fairchild is one of many smart FET families available to designers, integrating over voltage protection (OVP), over current protection (OCP), RCB, slew rate control, and an error flag to notify the processor in the event of a fault trip. Signal path technology advances There have been advances in general small signal technology that bring value to medical applications. Products now include improved on-resistance and flatness, power-off protection, higher data rates, and much lower consumption. Newer Ron flatness specifications guarantee a range of Ron for a given condition set. This allows uses in calibration and sensor multiplexing routines within medical devices requiring sub 400mohm Ron levels, much improved over previous 8 ohm levels. Complementing sensors is the recent power-off protection feature, allowing input signals to be present while Vcc = 0V. Actual operating current is now very low, measured in uA even if the control voltage line is lower than the Vcc with input to output leakage measured in nA (nano amps), further adding to battery life. Impact on healthcare As ICs advance, feature sets are more easily integrated into medical designs. With the dramatic size reductions in ICs, the integration possibilities are unlimited. Similar systems will monitor heart rate, blood oxygen, glucose, and temperature all in one sensor module. It could be wireless or plugged into a USB port once a day to show a complete data trend and offers a much more accurate prognosis than the single data point collected upon hospital admittance. www.fairchildsemi.com

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