Mindray Passport 5-Lead, Service Manual

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Passport 5-Lead, 5L, LT, XG Service Manual 0070-00-0420 2 - 39
Theory of Operation Block Diagrams
Any data written to the PM/NIM data port is accepted by the microcontroller on port B.
Data to be sent to the host is asserted on port A. Communications with the SpO2 Module
take place by a CMOS level asynchronous serial link in J23. The parameters are 8 data
bits, even parity, one start bit, one stop bit, with the data having “true” polarity. The baud
rate is selectable under U1 software control as 9600 baud.
SCTS* on port C bit 5 is used to enable the Flash Programming voltage on the Interface
board. To allow the in-system programming for the MS-1 SpO2 Module this signal should be
set High. SCTS* on port C bit 5 also allows U1 to suspend transmissions from the Nellcor
Module.
Power Supplies
The Power for the OEM SpO2 module and Interface board is derived from a combination of
the 5V and the Switch_Bulk_OUT supply. The isolated voltages for the OEM SpO2
board is derived from the Switch_Bulk_Out supply, this bypasses one DC/DC convertor and
its associated inefficiencies. The power consumption of the OEM SpO2 board and Interface
board should be similar to that of the Datascope SpO2 module.
The Masimo SpO2 module requires four isolated voltages: +5V, +/-15V, and +12V.
The Nellcor Module requires four isolated voltages; +5 volts, +/-15 volts and -6 to -15 volts.
The latter voltage is tied directly to the -15V supply on the PM/NIM by connecting J23 pin 6
and 7. This prevents the need for jumper JP4 on the Nellcor Module which would otherwise
accomplish the same task. Also, the additional power needed to drive this voltage with -15
volts versus -6 volts (if it were available) is negligible since the maximum current needed for it
is only 5.3mA.
The is5 voltage is generated and isolated by DC-DC converter, VC1. The +/-15V is
derived from the is5V convertor and is generated by a Boost Switching regulator. A
N-Channel Mosfet controls the +5V voltage level seen by the SpO2 board. The Gate of the
Mosfet is connected to the +15V Regulator and the +5V is connected to the Drain. This
allows the +/-15V source to always lead the +5V by at least +0.3V as required by the
Nellcor Module power supply sequencing requirements. An additional 5K ohm load was
added to the +15V to assure that the +/-15V switching regulator will stay in the continuous
mode when lightly loaded by the Nellcor module.
Additionally there is a +12V switched capacitor supply on board to supply the Flash
programming voltage and current required for in-system software updates for the Masimo
SpO2 module. The +12V supply derives its input from the is5V supply. The +12V
supply is controlled by the SCTS* output of the micro-controller. This voltage should normally
be turned off to give added protection against the flash memory being overwritten, and to
eliminate load and noise from this supply. In order to disable this supply voltage, the SCTS*
line must be taken to a logic level Low.