X5163S8IZT1 Datasheet, PDF (5/22 Pages) Intersil Corporation – Selectable watchdog timer

X5163, X5165
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.
CS
V_P
SCK
V_P
SI
FIGURE 1. SET V_TRIP VOLTAGE
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.
CS
SCK
V_CC
V_P
SI
FIGURE 2. RESET V_TRIP VOLTAGE
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FN8128.4
August 13, 2015