Novametrix Medical Systems 515 Service Manual page 19

Service Manual: Model 515 Theory of Operation :Analog Board #2
Resistors R66 and R67 along with C34 and C35 form low pass filters to
ter out any noise that may falsely trigger the comparators.
1.4.2 Power Supplies
Three separate voltages are run to the 2288 analog board. A digita
5VDC (VDD) and dual 12 volt analog supplies (+VA, -VA). The dij
ground (DGND) and the analog ground (AGND) are connected at only
point which is at ICl 1 pins 8 and 28. The dual analog supplies (+VAF, -V.
are filtered by L2, L3, C90, and C91, these supply most of the analog circu
on the board with the following exceptions.
Voltage regulator IC19 develops +5 volts (+5VA) from the +VAF sup
this is for IC12 which drives the inputs of ICll, this is done in order to pre^
over voltage damage to the inputs of ICll.Voltage regulator IC24 develops
volts VLED and VOPP from +VA. The VOPP voltage is taken directly fi
the output of IC24 and powers 1C23 (LM393 dual comparator). The VLEE
used as the power supply for the RED and IR LEDs. Fuse FI protects aga
short circuits or excessive power consumption by the LEDs, LI and C38 ft
the output from high frequency noise created from the fast switching of
LEDs. The dual analog supplies 4-VAF and -VAF are further filtered by R
C96 for +VA21, and R75, C97 for -VA21 to power IC21 which handles the c
ical front end circuitry.
1.4.3 Reference Voltages
There are two reference voltages on the 2288 analog board. A -1.23 V
potential is created by D5 and R24, it appears on pin 5 of ICl5. This
amplified by ICl5 pin 7 with a gain of 3.42 created by R25 and R28, ;
appears as -4.2 VDC (VREF-). Capacitors C17 and Cl8 help stabilize
reference voltage, C21 is used to filter noise from the output of IC15 pin 7. "
negative reference voltage (VREF-) is applied to ICl5 pin 2 which
configured as an inverting unity gain amplifier (R26 and R27 set the gain to
therefore +4.2 VDC appears at pin 1 of ICl5 (VREF+).
1.4.4 E^PROM
The electrically erasable programmable read only memory (E^PRO
ICIO is used to store offset values for the Ir and Red channels obtained dur
a factory front end calibration. It also stores factory programmed battery mo
toring voltage values. This device can store 64 separate 16 bit values, it is p
grammed serially through pins D1 (Data In), CS (Chip Select), SK (Sei
Clock), and DO (Data Out).
The device is selected by bringing the CS line high, then the first three I
on the DI line indicate the function required (read, write, or erase). Once
function is determined the next six bits indicate the address of the operati