5
FN8132.1
October 17, 2005
PRINCIPLES OF OPERATION
Power-On Reset
Application of power to the X5328/X5329 activates a
Power-on Reset Circuit. This circuit goes active at
about 1V and pulls the RESET
/RESET pin active. This
signal prevents the system microprocessor from start-
ing to operate with insufficient voltage or prior to stabi-
lization of the oscillator. When V
CC
exceeds the device
V
TRIP
value for 200ms (nominal) the circuit releases
RESET
/RESET, allowing the processor to begin exe-
cuting code.
Low Voltage Monitoring
During operation, the X5328/X5329 monitors the V
CC
level and asserts RESET/RESET if supply voltage
falls below a preset minimum V
TRIP
. The
RESET
/RESET signal prevents the microprocessor
from operating in a power fail or brownout condition.
The RESET
/RESET signal remains active until the
voltage drops below 1V. It also remains active until
V
CC
returns and exceeds V
TRIP
for 200ms.
V
CC
Threshold Reset Procedure
The X5328/X5329 has 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
for higher precision in the V
TRIP
value, the
X5328/X5329 threshold ma y be adjusted.
Setting the V
TRIP
Voltage
This procedure sets 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 directly makes
the change. If the new setting is 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 to the V
CC
pin and tie the CS pin and the WP
pin HIGH. RESET/RESET and SO pins are left uncon-
nected. Then apply the programming voltage V
P
to
both SCK and SI and pulse CS
LOW then HIGH.
Remove V
P
and the sequence is complete.
Figure 1. Set V
TRIP
Voltage
Resetting the V
TRIP
Voltage
This procedure sets the V
TRIP
to a “native” voltage
level. For exam p le, if the cu rr en t V
TRIP
is 4.4V and the
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 a voltage between
2.7 and 5.5V to the V
CC
pin. Tie the CS pin, the WP
pin, and the SCK pin HIGH. RESET/RESET and SO
pins are left unconnected. Then apply the program-
ming voltage V
P
to the SI pin ONLY and pulse CS
LOW then HIGH. Remove V
P
and the sequence is
complete.
Figure 2. Reset V
TRIP
Voltage
SCK
SI
V
P
V
P
CS
SCK
SI
V
CC
V
P
CS
X5328, X5329
