5
FN8128.4
August 13, 2015
Submit Document Feedback
Principles Of Operation
Power-on Reset
Application of power to the X5163, X5165 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
/RESET, allowing the processor to
begin executing code.
Low Voltage Monitoring
During operation, the X5163, X5165 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.
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
/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 Status Register determine the watchdog timer period.
The microprocessor can change these watchdog bits, or
they may be “locked” by tying the WP
pin LOW and setting
the WPEN bit HIGH.
V
CC
Threshold Reset Procedure
The X5163, X5165 has a standard V
CC
threshold (V
TRIP
)
voltage. This value will not change over normal operating
and storage conditions. However, in applications where the
standard V
TRIP
is not exactly right, or for higher precision in
the V
TRIP
value, the X5163, X5165 threshold may 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/WDI pin and the WP
pin HIGH. RESET
and SO pins are left unconnected. Then
apply the programming voltage V
P
to both SCK and SI and
pulse CS
/WDI LOW then HIGH. Remove V
P
and the
sequence is complete.
Resetting the V
TRIP
Voltage
This procedure sets the V
TRIP
to a “native” voltage level. For
example, if the current 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/WDI pin, the WP pin, AND
THE SCK pin HIGH. RESET
and SO pins are left
unconnected. Then apply the programming voltage V
P
to the
SI pin ONLY and pulse CS
/WDI LOW then HIGH. Remove V
P
and the sequence is complete.
SCK
SI
V
P
V
P
CS
FIGURE 1. SET V
TRIP
VOLTAGE
SCK
SI
V
CC
V
P
CS
FIGURE 2. RESET V
TRIP
VOLTAGE
X5163, X5165
