5
FN8130.2
June 15, 2006
Principles of Operation
Power-on Reset
Application of power to the X5168, X5169 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 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 X5168, X5169 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 X5168, X5169 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 X5168, X5169 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 pin and the WP pin
HIGH. RESET
/RESET and SO pins are left unconnected.
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.
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 pin, the WP pin, and the SCK
pin HIGH. RESET
/RESET and SO pins are left unconnected.
Then apply the programming voltage V
P
to the SI pin ONLY
and pulse CS
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
X5168, X5169
