User Manual Part 1

CIRCUIT ANALYSIS
MM101271V1 R2A 29
for about 0.4 sec. U40-3 is inverted by U41. During the high part of the cycle, the
resulting low at U41-4 holds the HSC ON pin low keeping the HSC OFF.
When U40-3 switches low, U37-2, the HSC ON pin is allowed to go high through D35,
pulled up by resistor R157. The HSC turns ON, but if the fault is still present, it turns
OFF within 40µs and the cycle continues. If the fault is gone, the 555 is held reset and the
Controller Board resumes normal functioning.
Capacitor C119 and resistor R191 act as a slugging filter on the FB input to prevent fast
transients on the 5V from causing the HSC to generate a reset. Likewise, capacitor C118
and resistor R190 prevent large transients on the input 5V, i.e. when the RMIC is hot
swapped, from causing the HSC to generate a reset due to a transient on the ON pin.
7.3.2.5 3.3V Regulator
The controller board is provided with 5 Volts and ±12 Volts from the Interconnect Board.
Linear regulator U25 is used to provide 3.3 volts to be used by the majority of digital
logic on the Controller Board and the Board.
The Hot Swap Controller (HSC) is used to ramp up the 5V-power rail at a controlled
rate. This, in addition to other considerations, will allow the Controller Board to be hot
swappable. The 5V output from this circuit will also power the 3.3-Volt regulator, thus
causing the 3.3 V power rail to also ramp up at a controlled rate. As mentioned above, the
HSC has a built-in electronic circuit breaker.
7.3.2.6 3.3V Power Monitor
The 3.3V Power Monitor (U31) uses a precision temperature-compensated reference and
comparator circuit to monitor the status of the 3.3V supply. If a loss of power is detected
an internal power-fail signal forces reset to the active state, which is low. When the 3.3V
supply returns to a normal state, the reset signal is kept active for approximately 150 ms
to allow the power supply and microprocessor to stabilize. This 3.3V Power Monitor
circuit also monitors Reset Pushbutton S1 on the reset output, U31, Pin 1. If the reset is
pulled low, by pressing S1, a reset signal is generated upon release. The output of U31 is
held in reset output (low) for approximately 150 ms.
7.3.2.7 Test Points
Test Points TP1 thru TP10 are provided on the Controller Board as follows:
• TP1 thru TP3, TP7, TP8 and TP10 are ground connections
• TP4 is +12V
• TP5 is +3.3V
• TP6 is +5.0V
• TP9 is WALSHCLK
7.3.2.8 Programming Serial Port J8
This port (J8) is located at the front of the Controller Board just behind the hinged door.
It is provided so that a programmer can easily program the microprocessor from the front
of the SitePro Controller without removing it from the cabinet.