X5648 Datasheet, PDF (3/18 Pages) Intersil Corporation – CPU Supervisor with 64Kbit SPI EEPROM

X5648, X5649
PRINCIPLES OF OPERATION
Power-on Reset
Application of power to the X5648/X5649 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 exe-
cuting code.
Low Voltage Monitoring
During operation, the X5648/X5649 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 X5648/X5649 has a standard V_CC threshold
(V_TRIP) voltage. This value will not change over normal
operating and storage conditions. However, in applica-
tions where the standard V_TRIP is not exactly right, or
for higher precision in the V_TRIP value, the
X5648/X5649 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 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 V_P to
both SCK and SI and pulse CS LOW then HIGH.
Remove V_P and the sequence is complete.
Figure 1. Set V_TRIP Voltage
CS
V_P
SCK
V_P
SI
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 volt-
age V_P to the SI pin ONLY and pulse CS LOW then
HIGH. Remove V_P and the sequence is complete.
Figure 2. Reset V_TRIP Voltage
CS
SCK ^VCC
V_P
SI
3
FN8136.0
March 17, 2005