PRINCIPLES OF OPERATION
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 VCC exceeds the device
VTRIP value for 200ms (nominal) the circuit releases
RESET/RESET, allowing the processor to begin exe-
Low Voltage Monitoring
During operation, the X5328/X5329 monitors the VCC
level and asserts RESET/RESET if supply voltage
falls below a preset minimum VTRIP. 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
VCC returns and exceeds VTRIP for 200ms.
VCC Threshold Reset Procedure
The X5328/X5329 has a standard VCC threshold
(VTRIP) voltage. This value will not change over normal
operating and storage conditions. However, in applica-
tions where the standard VTRIP is not exactly right, or
for higher precision in the VTRIP value, the
X5328/X5329 threshold may be adjusted.
Setting the VTRIP Voltage
This procedure sets the VTRIP to a higher voltage
value. For example, if the current VTRIP is 4.4V and
the new VTRIP 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 VTRIP voltage, apply the desired VTRIP
threshold to the VCC 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 VP to
both SCK and SI and pulse CS LOW then HIGH.
Remove VP and the sequence is complete.
Figure 1. Set VTRIP Voltage
Resetting the VTRIP Voltage
This procedure sets the VTRIP to a “native” voltage
level. For example, if the current VTRIP is 4.4V and the
VTRIP is reset, the new VTRIP is something less than
1.7V. This procedure must be used to set the voltage
to a lower value.
To reset the VTRIP voltage, apply a voltage between
2.7 and 5.5V to the VCC 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 VP to the SI pin ONLY and pulse CS
LOW then HIGH. Remove VP and the sequence is
Figure 2. Reset VTRIP Voltage
October 17, 2005