CAT1027 CATALYST [Catalyst Semiconductor], CAT1027 Datasheet - Page 7

• Manufacturer Part Number: CAT1027
• Description: Dual Voltage Supervisory Circuits with I2C Serial 2k-bit CMOS EEPROM
• Manufacturer: CATALYST [Catalyst Semiconductor]

DEVICE OPERATION
Reset Controller Description
The CAT1026 and CAT1027 precision RESET
controllers ensure correct system operation during
brownout and power up/down conditions. They are
configured with open drain RESET outputs.
During power-up, the RESET outputs remain active
until V
driving the outputs for approximately 200 ms (t
after reaching V
device will cease to drive the reset outputs. At this point
the reset outputs will be pulled up or down by their
respective pull up/down resistors.
During power-down, the RESET outputs will be active
when V
valid so long as V
designed to ignore the fast negative going V
pulses (glitches).
Reset output timing is shown in Figure 1.
Manual Reset Capability
The RESET pin can operate as reset output and manual
reset input. The input is edge triggered; that is, the
RESET input will initiate a reset timeout after detecting
a high to low transition.
When RESET I/O is driven to the active state, the 200
msec timer will begin to time the reset interval. If external
reset is shorter than 200 ms, Reset outputs will remain
active at least 200 ms.
Monitoring Two Voltages
The CAT1026 and CAT1027 feature a second voltage
sensor, V
output low whenever the input voltage is below 1.25 V.
The auxiliary voltage monitor timing is shown in Figure
2.
By using an external resistor divider the sense circuitry
can be set to monitor a second supply in the system.
The circuit shown in Figure 3 provides an externally
adjustable threshold voltage, V
auxiliary voltage. The low leakage current at V
allows the use of large value resistors, to reduce the
system power consumption. The V
externally connected to the RESET output to generate
a reset condition when either of the supplies is invalid.
In other applications, V
interrupt the system controller for an impending power
failure notification.
CC
CC
reaches the V
SENSE
falls below V
TH
, which drives the open drain V
CC
. After the t
is >1.0 V (V
TH
TH
LOW
. The RESET output will be
threshold and will continue
PURST
signal can be used to
TH_ADJ
RVALID
timeout interval, the
LOW
). The device is
to monitor the
output can be
CC
transient
PURST
SENSE
LOW
)
7
The CAT1026 and CAT1027 devices have been designed
to solve many of the data corruption issues that have long
been associated with serial EEPROMs. Data corruption
occurs when incorrect data is stored in a memory location
which is assumed to hold correct data.
Whenever the device is in a Reset condition, the embedded
EEPROM is disabled for all operations, including write
operations. If the Reset output(s) are active, in progress
communications to the EEPROM are aborted and no new
communications are allowed. In this condition an internal
write cycle to the memory can not be started, but an in
progress internal non-volatile memory write cycle can not
be aborted. An internal write cycle initiated before the
Reset condition can be successfully finished if there is
enough time (5ms) before VCC reaches the minimum
value of 2 V.
In addition, to avoid data corruption due to the loss of
power supply voltage during the memory internal write
operation, the system controller should monitor the
unregulated DC power. Using the second voltage sensor,
V
CAT1026 and CAT1027 signals an impending power
failure by setting V
Watchdog Timer
The Watchdog Timer provides an independent protection
for microcontrollers. During a system failure, the CAT1027
device will provide a reset signal after a time-out interval
of 1.6 seconds for a lack of activity. CAT1027 is designed
with the Watchdog timer feature on the WDI pin. If WDI
does not toggle within 1.6 second intervals, the reset
condition will be generated on reset output. The watchdog
timer is cleared by any transition on monitored line.
As long as reset signal is asserted, the watchdog timer
will not count and will stay cleared.
Data Protection
SENSE
, to monitor an unregulated power supply, the
LOW
low.
CAT1026, CAT1027
Doc No. 3010, Rev. K