User`s manual
PK2100
Power Management s C-3
Do not forget the interaction between the watchdog timer and the power-
failure interrupt. If a brownout causes an extended stay in the power-
failure interrupt routine, the watchdog can time out and cause a system
restart.
A few milliseconds of computing time remain when the +5-volt supply
falls below 4.5 volts, even if power is abruptly cut off from the board.
The amount of time depends on the size of the capacitors in the power
supply. A standard wall transformer provides about 10 milliseconds. If
the power cable is abruptly removed from the PK2100 side, then only the
capacitors on the board are available, reducing the computing time to a
few hundred microseconds. These times can vary considerably, depend-
ing on the system configuration and loads on the 5- or 9-volt power
supplies.
The interval between the power-failure detection and entry to the power-
failure interrupt routine is approximately 100 microseconds, or less if
Dynamic C NMI communications is not in use.
Testing power-failure interrupt routines presents some problems. Nor-
mally, a power-failure interrupt routine disables interrupts. Probably the
best test method is to use battery-backed memory to leave messages that
track the execution of the power-failure routines. Use a variable trans-
former to simulate brownouts and other types of power-failure conditions.
The power-failure interrupt must be disabled if an external +5-volt power
supply is used.
Heat Sinking
The PK2100 has two power-supply regulators that are either heat-sinked
into the case or into the mounting rails for the PK2120/PK2130. The
+5-volt regulator dissipates the most heat and transfers heat to the case or
rails via two mounting pem nuts. The maximum heat dissipation by this
regulator is 10watts at an ambient temperature of 50°C. The regulator
will shut down protectively if an attempt is made to dissipate more heat
because of a combination of high input voltage or excessive current draw
on the +5-volt supply. The power dissipation is given by the formula:
P=(V
IN
5) × (I+0.15)
where
V
IN
=input voltage (1835V)
I = current, in amperes, drawn from +5-volt supply by external
accessories on bus or from VCC voltage terminal.
If the PK2100 is disassembled, take care to preserve or replace the silicon
grease in the heat-conductive paths. Heat dissipation can be improved by
bolting the PK2100 to a metal plate with a good heat transfer path near the
lower left corner of the PK2100.