LMC6953CM/NOPB National Semiconductor, LMC6953CM/NOPB Datasheet - Page 8

• Manufacturer Part Number: LMC6953CM/NOPB
• Description: IC POWER SUP PCI LOCAL BUS 8SOIC
• Manufacturer: National Semiconductor
• Type: Multi-Voltage Supervisorr

Specifications of LMC6953CM/NOPB

• Number Of Voltages Monitored: 2
• Output: Open Drain or Open Collector
• Reset: Active Low
• Reset Timeout: 100 ms Minimum
• Voltage - Threshold: 3.3V, 5V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: *LMC6953CM; *LMC6953CM/NOPB; LMC6953CM

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Truth Table
X = Don’t Care
Pin Description
Application Note
HOW THE LMC6953 FUNCTIONS
The LMC6953 is a power supply supervisor with its perfor-
mance specifications compliant to PCI Specifications Revi-
sion 2.1. The chip monitors power-up, power-down, brown-
out, power failure and manual reset interrupt situations.
During power-up, the LMC6953 holds RESET low for 100
ms after both 5V and 3.3V are within specified windows. It
asserts reset in 490 ns when a brown-out is detected.
Brown-out occurs when 5V supply is above 5.75V over-
voltage or below 4.25V under-voltage or when 3.3V supply is
above 4.1V over-voltage or 2.5V under-voltage. In case of
power failure where the 5V supply falls under 3.3V supply by
300 mV maximum, reset is asserted in 90 ns. RESET also
can be asserted by sending a 5V CMOS logic low to the
manual reset pin.
Each time RESET is asserted, it holds low for 100 ms after a
fault condition is recovered. The 100 ms reset delay is
generated by the 0.01 µF C
justed by changing the value of C
It is highly recommended to place lands on printed circuit
boards for 120 pF capacitors between pin 2 and ground and
also between pin 3 and ground. As power supplies may
change abruptly, there can be very high frequency noise
present and the capacitors can minimize the noise,
Pin
1
2
3
4
5
6
7
8
Failure
Power
Fail
OK
X
X
X
X
X
PWR__GND
RESET
Name
GND
C
3.3V
V
MR
5V
EXT
DD
Over-Voltage
Fail
OK
5V
X
X
X
X
X
EXT
capacitor, and can be ad-
EXT
5V input supply voltage. This pin supplies power to the internal comparators. It can be
connected to a capacitor acting as a back-up battery. Otherwise, it should be shorted to
the 5V pin.
5V input supply voltage. This pin is not connected to the positive power supply of the
internal comparators. It provides input signal to the 5V window comparators as well as
the power failure comparator.
3.3V input supply voltage. This pin provides input signal to the 3.3V window
comparators and the power failure comparator.
Manual reset input pin. It takes 5V CMOS logic low and triggers RESET . If not used,
this pin should be connected to V
Ground.
This pin should be grounded at all times.
Active low reset output. RESET holds low for 100 ms after both 5V and 3.3V powers
recover, or after manual reset signal returns to high state.
External capacitor pin. The value of C
.
Under-Voltage
Fail
OK
5V
X
X
X
X
X
8
Over-Voltage
MINIMUM SUPPLY VOLTAGE FOR RESET ASSERTION
The LMC6953 guarantees V
supply voltage to achieve consistent RESET assertion. This
ensures system stability in initialization state.
Figure 1 is measured by shorting pins 1, 2 and 3 together
when supply voltage is from 0V to 3.3V. Then pin 3 is
3.3V
DD
Fail
OK
X
X
X
X
X
.
FIGURE 1. Output Voltage vs Supply Voltage
EXT
Function
sets the reset delay.
Under-Voltage
3.3V
Fail
OK
X
X
X
X
X
DD
= 1.55V as the minimum
High
High
High
High
High
High
Low
MR
01284612
RESET
High
Low
Low
Low
Low
Low
Low