User manual

VETTA Theory of Operation………………Line 6 confidential ……………………………. Page 4 of 18
While the main power is turned ON, the 3.3V supply the SRAM U29. When the main power is
OFF the SRAM supply is maintained (to avoid memory lost) by the battery BAT2 voltage. The
battery voltage should be above 2.7V. If it drops below the battery should be replaced. The
current draw on the battery, while the main power is OFF, should be less than 3.7 micro amps.
This will correspond to a maximum voltage of 100mV across R185. With this maximum
current, and a fresh battery, the battery life should be a minimum of six years.
On the U.I. PCBs:
After arriving on the U.I. Left PCB, the +5V and its ground (GND) are separated into two local
signal pairs +5V/ GND and +5VA/AGND. The separation between these pairs is only achieved
through the U.I. PCB layout. The +5VA/AGND drives the 10 potentiometers and the front
panel ADC U10. The +5V/ GND drives all other circuits on the front panel PCBs. This setup
improves the potentiometer jitters immunity.