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 sys-
tem microprocessor from starting to operate with insuffi-
cient voltage or prior to stabilization of the oscillator. When
Vcc 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 preset mini-
mum V
TRIP
. The RESET signal prevents the microproces-
sor 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 Vcc returns and
exceeds V
TRIP
for 200ms.
watchdog timer
The Watchdog Timer circuit monitors the microprocessor
activity by monitoring the WDI input. The microprocessor
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 watchdog 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 Vcc 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
below, and requires the application of a high voltage con-
trol signal.
Setting the V
TRIP
Voltage
This procedure is used to set the V
TRIP
to a higher volt-
age 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 cur-
rent 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 Vcc 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” volt-
age 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 something
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
Vcc pin and tie the W
PE
pin to the programming voltage
Vp. Then a V
TRIP
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 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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XICOR [ XICOR INC. ]
