7
FN8114.2
August 25, 2008
Principles of Operation
Power-on Reset
Applying power to the X40030, X40031, X40034, X40035
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
stabilization of the oscillator.
• It allows time for an FPGA to download its configuration
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 (X40031,
X40035) and RESET (X40030, X40034) pin allowing the
system to begin operation.
FIGURE 1. CONNECTING A MANUAL RESET PUSH-BUTTON
Manual Reset
By connecting a push-button directly from MR to ground, the
designer adds manual system reset capability. The MR
pin is
LOW while the push-button is closed and RESET/RESET
pin remains HIGH/LOW until the push-button is released and
for t
PURST
thereafter.
Low Voltage V
CC
(V1 Monitoring)
During operation, the X40030, X40031, X40034, X40035
monitors the V
CC
level and asserts RESET/RESET if the
supply voltage falls below a preset minimum V
TRIP1
. The
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
TRIP1
for
t
PURST
.
Low Voltage V2 Monitoring
The X40030 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 X40030 and X40031 the V2FAIL
signal remains
active until the V2MON drops below 1V (V2MON falling). It
also remains active until V2MON returns and exceeds
V
TRIP2
.This voltage sense circuitry monitors the power
supply connected to V2MON pin. If V
CC
= 0, V2MON can still
be monitored.
For the X40034 and X40035, the V2FAIL
signal remains
active until V
CC
drops below 1V 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.
Low Voltage V3 Monitoring
The X40030, X40031, X40034, X40035 also monitors a third
voltage level and asserts V3FAIL
if the voltage falls below a
preset minimum V
TRIP3
. The V3FAIL 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. The V3FAIL
signal remains active until the V3MON
drops below 1V (V3MON falling). It also remains active until
V3MON returns and exceeds V
TRIP3
.
This voltage sense circuitry monitors the power supply
connected to V3MON pin. If V
CC
= 0, V3MON can still be
monitored.
Early Low V
CC
Detection (LOWLINE)
This CMOS output goes LOW earlier than RESET/RESET
whenever V
CC
falls below the V
TRIP1
voltage and returns
high when V
CC
exceeds the V
TRIP1
voltage. There is no
power-up delay circuitry (t
PURST
) on this pin.
FIGURE 2. TWO USES OF MULTIPLE VOLTAGE MONITORING
V
CC
MR
SYSTEM
RESET
MANUAL
RESET
X40030, X40034
RESET
6V TO 10V
V
CC
5V
V2MON
X40031-A
UNREG.
SUPPLY
V
CC
X40031-B
RESET
V2FAIL
SYSTEM
V
CC
RESET
RESET
V2FAIL
SYSTEM
RESET
NOTICE: NO EXTERNAL COMPONENTS REQUIRED TO MONITOR
THREE VOLTAGES.
1M
390k
V3MON
V3FAIL
V2MON
5V
REG
3.0V
REG
1.8V
REG
3.3V
V3FAIL
V3MON
(1.7V)
POWER
FAIL
INTERRUPT
V
CC
X40030, X40031, X40034, X40035
