X5001_06 Datasheet, PDF (5/20 Pages) Intersil Corporation – CPU Supervisor

X5001
PRINCIPLES OF OPERATION
Power-on Reset
Application of power to the X5001 activates a power-
on reset circuit. This circuit goes active at 1V and pulls
the RESET/RESET pin active. This signal prevents
the system microprocessor from starting to operate
with insufficient voltage or prior to stabilization of the
oscillator. When V_CC exceeds the device V_TRIP value
for 200ms (nominal) the circuit releases RESET,
allowing the processor to begin executing code.
Low Voltage Monitoring
During operation, the X5001 monitors the V_CC level
and asserts RESET if supply voltage falls below a pre-
set minimum V_TRIP. The RESET signal prevents the
microprocessor from operating in a power fail or
brownout condition. The RESET signal remains active
until the voltage drops below 1V. It also remains active
until V_CC returns and exceeds V_TRIP for 200ms.
Watchdog Timer
The watchdog timer circuit monitors the microprocessor
activity by monitoring the WDI input. The microproces-
sor must toggle the CS/WDI pin periodically to prevent
a RESET signal. The CS/WDI pin must be toggled
from HIGH to LOW prior to the expiration of the watch-
dog time out period. The state of two nonvolatile control
bits in the watchdog register determine the watchdog
timer period.
Vcc Threshold Reset Procedure
The X5001 is shipped with a standard V_CC threshold
(V_TRIP) voltage. This value will not change over normal
operating and storage conditions. However, in applica-
tions where the standard V_TRIP is not exactly right, or if
higher precision is needed in the V_TRIP value, the
X5001 threshold may be adjusted. The procedure is
described in the following sections, and requires the
application of a high voltage control signal.
Setting the V_TRIP Voltage
This procedure is used to set the V_TRIP to a higher
voltage value. For example, if the current V_TRIP is 4.4V
and the new V_TRIP is 4.6V, this procedure will directly
make the change. If the new setting is to be lower than
the current setting, then it is necessary to reset the trip
point before setting the new value.
To set the new V_TRIP voltage, apply the desired V_TRIP
threshold voltage to the V_CC pin and tie the W_PE pin to
the programming voltage V_P. Then a V_TRIP programming
command sequence is sent to the device over the SPI
interface. This V_TRIP programming sequence consists of
pulling CS LOW, then clocking in data 03h, 00h and 01h.
This is followed by bringing CS HIGH then LOW and
clocking in data 02h, 00h, and 01h (in order) and bringing
CS HIGH. This initiates the V_TRIP programming
sequence. V_P is brought LOW to end the operation.
Resetting the V_TRIP Voltage
This procedure is used to set the V_TRIP to a “native”
voltage level. For example, if the current V_TRIP is 4.4V
and the new V_TRIP must be 4.0V, then the V_TRIP must
be reset. When V_TRIP is reset, the new V_TRIP is some-
thing less than 1.7V. This procedure must be used to
set the voltage to a lower value.
To reset the V_TRIP voltage, apply greater than 3V to
the V_CC pin and tie the W_PE pin to the programming
voltage V_P. Then a V_TRIP command sequence is sent
to the device over the SPI interface. This V_TRIP pro-
gramming sequence consists of pulling CS LOW, then
clocking in data 03h, 00h and 01h. This is followed by
bringing CS HIGH then LOW and clocking in data 02h,
00h, and 03h (in order) and bringing CS HIGH. This
initiates the V_TRIP programming sequence. V_P is
brought LOW to end the operation.
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FN8125.1
May 30, 2006