X4003/X4005
PRINCIPLES OF OPERATION
Power On Reset
signal remains active until the voltage drops below 1V.
It also remains active until V returns and exceeds
CC
V
for 200ms.
TRIP
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.
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 pre-
vent a RESET/RESET signal. The state of two nonvol-
atile control bits in the control register determine the
watchdog timer period. The microprocessor can
change these watchdog bits, or they may be “locked”
by tying the WP pin HIGH.
– 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
exceeds the device V
threshold value
CC
TRIP
for 200ms (nominal) the circuit releases RESET/
RESET, allowing the system to begin operation.
Figure 1. Watchdog Restart
Low Voltage Monitoring
.6µs
.6µs
During operation, the X4003/X4005 monitors the V
CC
SCL
SDA
level and asserts RESET/RESET if supply voltage falls
below a preset minimum V . The RESET/RESET
signal prevents the microprocessor from operating in a
power fail or brownout condition. The RESET/RESET
TRIP
Start
Condition
Stop
Condition
Restart
Set V
Level Sequence (V = desired V
value)
TRIP
CC
TRIP
V
= 15-18V
P
WP
0
1
2
3 4 5 6 7
0
1
2
4 5 6 7
3
0
1
2
3
4
5
6
7
SCL
SDA
A0h
01h
00h
V
THRESHOLD RESET PROCEDURE
Setting the V
Voltage
CC
TRIP
This procedure is used to set the V
voltage value. For example, if the current V
to a higher
TRIP
The X4003/X4005 is shipped with a standard V
CC
is 4.4V
TRIP
threshold (V
) voltage. This value will not change
TRIP
and the new V
is 4.6V, this procedure will directly
TRIP
over normal operating and storage conditions. How-
ever, in applications where the standard V is not
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.
TRIP
exactly right, or if higher precision is needed in the
value, the X4003/X4005 threshold may be
V
TRIP
adjusted. The procedure is described below, and uses
the application of a nonvolatile control signal.
Characteristics subject to change without notice. 3 of 18
REV 1.1.3 4/30/02
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XICOR [ XICOR INC. ]
