MINIATURIZATION OF LEFT VENTRICULAR ASSIST DEVICE ELECTRONICS PACKAGE

P11021Andrew Hoag (CE), Juan Jackson (EE), Zachery Shivers (EE), Smiha Sayal (IE), Nicole Varble (ME), Jason Walzer (ME)

Customer: Dr. Steven Day and Dr. Shanbao ChengFaculty Guide: Edward Hanzlik

Sponsors: NIH and The Utah Heart Institute

Process: The LVAD electronics package consists of three main sub-systems. The electronics sub-system comprises of a PCB board that was equipped with A/D converters and RC filters to convert the signals received from the hall effect sensors of the pump, PWM amplifiers that provided amplified signal outputs, H-bridges that were responsible for controlling the AMBs, and the power supply that kept the system running. The software sub-system constituted an MSP 430 microcontroller that was programmed to control the electronics of the pump and the user interface. The external enclosure for the package was created by rapid prototyping of ABS plastic and was made waterproof to prevent damage against splashing

Acknowledgements:P11021 would like to thank the following:

Ed Hanzlik, Dr. Day, Dr. Chang and Aaron Burger of the LVAD labTexas Instruments, RIT Brinkman Lab

PCB:A 4-layer PCB was selected for this design with the two internal layers dedicated to power routing and ground plane. A ground plane acts to remedy many noise and current loop issues, and is recommended whenever possible for PCB designs. Top and bottom layers are used for signal routing.

Amplifiers:The DRV8412 provides two H-bridges per chip with 3A continuous and 6A peak currents. It features high power efficiency, PWM frequencies up to 500 kHz, and integrated self protection circuits. This IC contains the power MOSFETs, biasing, and monitoring circuitry required.

Microcontroller and Software:• Pump hall-effect sensors were sampled 5000 times per second using the MSP430 analog-to-digital converter. • Pulse width modulated signals were generated to control both pump motor rotation and active magnetic bearings.• A proportional-integral-derivative control feedback loop was implemented in software to achieve and maintain pump impeller levitation.• System status was displayed on a 100x32 monochrome display• System debug data was transferred to PC at 115200 baud over USB• The use of a dedicated microcontroller allowed for simple, yet powerful control of the LVAD.

Motivation:A Left Ventricular Assist Device (LVAD) is a mechanical device that helps pump blood from the heart to the rest of the body. The current RIT- LVAD system is centered on a custom, levitating impeller blood pump with the ability magnetically levitate the impeller within the pump's housing, drastically reducing friction losses and increasing pump lifetime. It uses a custom printed circuit board and discreet components as intermediate electronics between the pump and National Instruments DAQ boards that help control the pump. Even though the system in its current state is fully functional, the external package that houses the electronics is too large. Therefore, the goal of this project is to miniaturize this enclosure such that portability and robustness are achieved while sustaining the functionality of the pump.

Microcontroller Specs:

Texas Instruments MSP43F5438A• 100 LQFP package• 256KB Flash• 16KB RAM• 12-bit SAR ADC• Max frequency 25MHz

External Enclosure:• A 180x82x103 mm ABS plastic box was created to house the electronics. • Maximum heat dissipation was analytically calculated to be 79°C which was

under the maximum critical operating temperature of electronics. • The box was tested for robustness by performing drop test from operating

height. The results from the test ensured enclosure toughness.• All UI elements are rated to IP67• Enclosure was made waterproof by spraying a rubberized coating .• Water ingress tests were performed to verify waterproofing.

Previous system TI MSP430F5438A on custom PCB