SECTION 4 THEORY OF OPERATION
430-00587-008 (Rev. 2/05)
4 - 14
Plum XL Series
The AC (mains) amplifier circuitry (IC U8A) processes negative spikes that may signify an
occlusion on DISTPRES to a level manageable by the MCU PWA analog-to-digital (A/D)
converter. The AC amplifier blocks slow pressure changes and amplifies the spikes to the
required level. The AC amplifier also divides into the logarithmic compression circuit
(resistor R7 and diodes CR1 and CR3), the bias/high-pass circuit (capacitor C8 and
resistor R10), and the amplifier circuit (IC U8B, resistors R4 and R9, and capacitor C7).
The logarithmic compression circuit limits the amplitude of the negative spikes at high
back-pressure. The bias/high pass circuit blocks the slow pressure changes and biases
the AC (mains) amplifier to +2.5 VDC.
The voltage reference circuitry consists of ICs U1 and U6; transistor Q1; diodes CR2 and
CR5; resistors R17 through R20, R22, and R23; and capacitors C9, C11, and C12. R22,
C11, and C12 filter VMOT. R18 biases the reference U1. U6B buffers the +2.5 VDC REF.
The +2.5 VDC REF is boosted by Q1, U6A, and associated components to generate the
main +3.75 VDC reference 3V75REF. CR2 limits 3V75REF to VDIG level to protect the
MCU PWA micro controller, U6. CR5 protects the base-emitter junction of Q1.
When PSENSEN is active, transistors Q2 and Q3 drive all LEDs in ICs U2, U3, and U4
with a constant current of approximately 22 milliamperes (mA). Resistor R24 limits the
current.
The EEPROM circuitry (IC U5) communicates serially with the MCU PWA. U5 receives
commands and data through pin 3 as TXD. Stored data is transferred through pin 4 as
EE_DO. When EE_CS is active at pin 1 and EE_CLK (pin 2) is in synchronization with
TXD, U5 is enabled.
The bubble sensor PWA consists of the following circuitry: transmitter, receiver (which
includes two channels, proximal and distal), and pin detector flex
Figure 9-22, Pin Detector Flex Circuit Schematic)
Note:
Both proximal and distal sensors can transmit or receive.
Summary of Contents for LifeCare XL Series
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