TMN103921-0182 3201966-007G Defibrillator Keypad Board LIFEPAK 20 LP20

Med-tronic Physio-Control LIFEPAK 20 LP20 Therapy Board and Pacing board 3202259 100-002-421F BMP006722-0067 21330-001560

► Brief Introduction

The Therapy PCB controls the pacing and defibrillation therapy features. The primary communication between the Therapy PCB and the remainder of the device is through the data bus. A microprocessor and digital memory make up the central processing unit (CPU) that manages communication with the System Control PCB.

► Major subsystems

Power Supplies — The Therapy PCB uses SW_VBatt (switched battery voltage) from the Power Module to originate five power supply voltages for use throughout the PCB as follows:

• +5 V logic power to drive the CPU microprocessor and memory
• ±15 V analog power for the pacing and therapy drive circuit
• Patient-isolated 5 V analog power for the pacing and therapy circuits
• Patient-isolated 15 V analog power for the pacing and therapy circuits
• Patient-isolated 30 V analog power for the pacing and therapy circuits

Power Switch — A power switch is a control circuit that detects the ON button selection from the User Interface PCB or a timer event from the System Control PCB to power up the device. This portion of the Therapy PCB is powered at all times, with very low quiescent current draw. When a power-on request is detected, this circuit switches VBatt (battery and/or ac converted dc power) provided by thePower Module to the remaining PCBs in the device. Low Battery (Battery Fail) is detected and a discrete signal is broadcast to other PCBs if battery voltage falls rapidly or reaches the point where normal operation is no longer feasible.

Cap Charger — The cap charger is a high-voltage, patient-isolated circuit that charges the Energy Capacitor to the correct voltage for biphasic defibrillation (2 to 360 joules). Control is provided by the CPU, and capacitor voltage is provided back to the CPU for feedback. The cap charger is designed to nominally provide maximum charge rates and to automatically scale back to slower charge rates when low battery voltage is detected.

Pacer Power Supply — The pacer power supply is a patient-isolated circuit that charges the Energy Capacitor up to the correct voltage for pacing. Control is provided by the CPU, and voltage regulation is maintained locally within the pacer supply. Capacitor voltage is provided back to the CPU for control through the cap charger circuitry

H-Bridge — The H-Bridge is a patient-isolated circuit that creates the biphasic defibrillation waveform. A combination of silicon controlled rectifiers (SCR) and insulated gate bipolar transistors (IGBT) are used to place a positive-oriented defibrillation pulse across the patient load, followed immediately by a negative-oriented defibrillation pulse. The defibrillation pulse is delivered through the relay and Therapy Connector assembly to the external therapy cable on the outside of the device.

Pacer — The pacer is a patient-isolated circuit that creates the pacing waveform. A portion of the H-Bridge circuitry is used to support the pacer by providing energy from the Defibrillation Capacitor. A current drive is used to control the amount of current provided to the patient during pacing.

Relay — The relay provides patient isolation from the pacing and defibrillation circuitry when not in use. The relay is closed when the pacing current is set above zero and stays closed until the pacing current is set back to zero.

► Specification

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