Physio Control LIFEPAK 9 - Page 29

Energy Monitor
Serial Data Interface
Analog Voltage
Evaluation
© August 1993 Physio—Control
Description 1
The Energy Monitor circuit confirms the level of energy that is discharged
into the internal test load. When an energy transfer is performed as a test,
this circuit senses the energy delivered to the test load and informs the
System microprocessor. The System microprocessor then displays the
information (e.g., 200J DELIVERED).
The value of the defibrillation pulse is acquired by monitoring the delivered
energy with a current transformer, T3. A proportional current is generated in
the secondary with each transfer pulse. A rectifier bridge, CR8 through
CR10, delivers the secondary current to C10. The voltage is indexed in the
System microprocessor to a specific delivered energy.
Capacitor C10 must start each transfer cycle with OV for accurate evaluation
of the delivery. FET O8 is in parallel with C10 and resets C10 before each
charge energy pulse. The gate of O8 is driven by the inverted Charge Inhibit
signal. The FET O8 shorts C10 when the charge is enabled which makes
sure that each time the instrument is ready to deliver energy, the Energy
Monitor circuit determines the correct energy level. Op amp UIA functions
as a noninverting buffer, providing high-impedance isolation from the rest of
the signal processing circuitry.
The Serial Data Interface consists of four lines; Converter Data In and
Converter Data Out allow communication while Converter Function Select
and I/O Clock control data flow. The Analog Voltage Evaluation circuit and
the D/A converter U18, used with the Capacitor Charge Control circuit, share
this common set of serial lines for communication with the System
microprocessor.
A low on the Converter Function Select line at connector P14 pin 7A enables
the Analog Voltage Evaluation circuit for data transfer. The data flow rate is
set by I/O Clock at P14 pin 6A. A high on the Converter Function Select line
at P14 enables 8-bit shift registers U19 and U20, allowing VO Clock access
to the register clock inputs. Information on the Converter Data Out line is
stored in the low-order location, and all other bits are advanced one position
during the positive-going transitions of YO Clock. At the same time, U12A
through U12C route the output data on the Converter Data In line. A logic
high at U11C pin 8 following a byte transfer indicates a communication
failure.
The Analog Voltage Evaluation circuit monitors operating voltages on the
Power Conversion PCB. An A/D converter, U9, converts these voltages to
digital code for evaluation for correct tolerances by the System
microprocessor.
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