3
FN8111.0
March 28, 2005
PRINCIPLES OF OPERATION
Power On Reset
Application of power to the X40010/11/14/15 activates a
Power On Reset Circuit that pulls the RESET/RESET
pins 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 stabili-
zation of the oscillator.
– It allows time for an FPGA to download its configura-
tion prior to initialization of the circuit.
– It prevents communication to the EEPROM, greatly
reducing the likelihood of data corruption on power up.
When V
CC
exceeds the device V
TRIP1
threshold value for
t
PURST
(selectable) the circuit releases the RESET
(X40011) and RESET (X40010) pin allowing the system
to begin operation.
Low Voltage V
CC
(V1 Monitoring)
During operation, the X40010/11/14/15 monitors the
V
CC
level and asserts RESET/RESET if supply voltage
falls below a preset minimum V
TRIP1
. The
RESET/RESET
signal prevents the microprocessor
from operating in a power fail or brownout condition.
The V1FAIL
signal remains active until the voltage
drops below 1V. It also remains active until V
CC
returns
and exceeds V
TRIP1
for t
PURST
.
Low Voltage V2 Monitoring
The X40010/11/14/15 also monitors a second voltage
level and asserts V2FAIL
if the voltage falls below a
preset minimum V
TRIP2
. The V2FAIL signal is either
ORed with RESET to prevent the microprocessor from
operating in a power fail or brownout condition or used to
interrupt the microprocessor with notification of an
impending power failure. For the X40010/11 the V2FAIL
signal remains active until the V
CC
drops below 1V (V
CC
falling). It also remains active until V2MON returns and
exceeds V
TRIP2
by 0.2V. This voltage sense circuitry
monitors the power supply connected to the V2MON pin.
If V
CC
= 0, V2MON can still be monitored.
For the X40014/15 devices, the V2FAIL
signal remains
actice until V
CC
drops below 1Vx and remains active
until V2MON returns and exceeds V
TRIP2
. This sense
circuitry is powered by V
CC
. If V
CC
= 0, V2MON cannot
be monitored.
Figure 1. Two Uses of Multiple Voltage Monitoring
68SCLSerial Clock. The Serial Clock controls the serial bus timing for data input and output.
71WDO
WDO Output. WDO is an active LOW, open drain output which goes active whenever the watch-
dog timer goes active.
82V
CC
Supply Voltage
PIN DESCRIPTION (Continued)
Pin
Name FunctionSOIC TSSOP
6–10V
V
CC
5V
Reg
V2MON
X40011-A
Resistors selected so 3V appears on V2MON when unregulated
supply reaches 6V.
Unreg.
Supply
V
CC
X40014-C
RESET
V2FAIL
System
V
CC
Reset
RESET
V2FAIL
V
CC
System
Reset
Notice: No external components required to monitor two voltages.
1M
1M
V2MON
3.3V
Reg
1.2V
Reg
V2MON
(2.9V)
X40010, X40011, X40014, X40015
