X4003 Datasheet, PDF (3/17 Pages) Xicor Inc. – CPU Supervisor

X4003, X4005
PRINCIPLES OF OPERATION
Power-on Reset
Application of power to the X4003/X4005 activates a
power-on reset circuit that pulls the RESET/RESET
pin active. This signal provides several benefits.
– It prevents the system microprocessor from starting
to operate with insufficient voltage.
– It prevents the processor from operating prior to
stabilization of the oscillator.
– It allows time for an FPGA to download its configura-
tion prior to initialization of the circuit.
When V_CC exceeds the device V_TRIP threshold value for
200ms (nominal) the circuit releases RESET/RESET,
allowing the system to begin operation.
Low Voltage Monitoring
During operation, the X4003/X4005 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
Set V_TRIP Level Sequence (V_CC = desired V_TRIP value)
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 microproces-
sor activity by monitoring the SDA and SCL pins. The
microprocessor must toggle the SDA pin HIGH to
LOW periodically, while SCL also toggles from HIGH
to LOW (this is a start bit) followed by a stop condition
prior to the expiration of the watchdog time out period
to prevent a RESET/RESET signal. The state of two
nonvolatile control bits in the control register deter-
mine the watchdog timer period. The microprocessor
can change these watchdog bits, or they may be
“locked” by tying the WP pin HIGH.
Figure 1. Watchdog Restart
.6µs
.6µs
SCL
SDA
Start
Condition
Restart
Stop
Condition
WP
V_P = 15-18V
0 1 2 34 56 7
0 1 23 4 56 7
0 1 23 4 56 7
SCL
SDA
A0h
01h
00h
V_CC THRESHOLD RESET PROCEDURE
The X4003/X4005 is shipped with a standard V_CC
threshold (V_TRIP) voltage. This value will not change
over normal operating and storage conditions. How-
ever, in applications where the standard V_TRIP is not
exactly right, or if higher precision is needed in the
V_TRIP value, the X4003/X4005 threshold may be
adjusted. The procedure is described below, and uses
the application of a nonvolatile control signal.
Setting the V_TRIP Voltage
This procedure is used to set 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 will directly
make the change. If the new setting is to be lower than
the current setting, then it is necessary to reset the trip
point before setting the new value.
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FN8113.0
March 15, 2005