Principles Of Operation
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 VCC
exceeds the device VTRIP 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 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.
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.
VCC Threshold Reset Procedure
The X5163, X5165 has a standard VCC threshold (VTRIP)
voltage. This value will not change over normal operating
and storage conditions. However, in applications where the
standard VTRIP is not exactly right, or for higher precision in
the VTRIP value, the X5163, X5165 threshold may be
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/WDI pin and the WP
pin HIGH. RESET and SO pins are left unconnected. Then
apply the programming voltage VP to both SCK and SI and
pulse CS/WDI 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/WDI pin, the WP pin, AND
THE SCK pin HIGH. RESET and SO pins are left
unconnected. Then apply the programming voltage VP to the
SI pin ONLY and pulse CS/WDI LOW then HIGH. Remove VP
and the sequence is complete.
FIGURE 2. RESET VTRIP VOLTAGE
June 1, 2006