LM3905N National Semiconductor, LM3905N Datasheet - Page 7

• Manufacturer Part Number: LM3905N
• Description: IC TIMER PRECISION 8-DIP
• Manufacturer: National Semiconductor

Specifications of LM3905N

• Voltage - Supply: *
• Current - Supply: 2.5mA
• Operating Temperature: *
• Package / Case: *
• Frequency: *
• Count: *
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: *LM3905N; LM3905

Figure 1 is a basic timer using the collector output R
Figure 2 is again a basic timer but with the output taken
Figure 3 is an application where the LM122 is used to simu-
Pin Function Description
for instance cannot be held for more than 4 seconds
These levels are based on 40 C maximum initial chip tem-
perature When driving inductive loads always use a clamp
diode to protect the transistor from inductive kick-back
A boost pin is provided on the LM122 to increase the speed
of the internal comparator The comparator is normally op-
erated at low current levels for lowest possible input current
For timing periods less than 1 ms where low input current is
not needed comparator operating current can be increased
several orders of magnitude Shorting the boost terminal to
V
in the differential stage from 25 nA to 5 A This pin is not
available on the LM3905
With the timer in the unboosted state timing periods are
accurate down to about 1 ms In the boosted mode loss of
accuracy due to comparator speed is only about 800 ns so
timing periods of several microseconds can be used The
800 ns error is relatively insensitive to temperature so tem-
perature coefficient of pulse width is still good
The Logic pin is used to reverse the signal appearing at the
output transistor An open or ‘‘high’’ condition on the logic
pin programs the output transistor to be ‘‘off’’ during the
timing period and ‘‘on’’ all other times Grounding the logic
pin reverses the sequence to make the transistor ‘‘on’’ dur-
ing the timing period Threshold for the logic pin is typically
100 mV with 150 A flowing out of the terminal If an active
drive to the logic pin is desired a saturated transistor drive
is recommended either with a discrete transistor or the
open collector output of integrated logic A maximum V
of 25 mV at 200
voltages that may appear on the logic pin are 0 and
respectively
Typical Applications
Basic Timers
set the time interval with R
interval the output may be either high or low depending on
the connection of the logic pin Timing waveforms are
shown in the sketch along side Figure 1 Note that the trig-
ger pulse may be either shorter or longer than the output
pulse width
from the emitter of the output transistor As with the collec-
tor output either a high or low condition may be obtained
during the timing period
Simulating a Thermal Delay Relay
late a thermal delay relay which prevents power from being
applied to other circuitry until the supply has been on for
some time The relay remains de-energized for R
onds after V
until V
the relay is energized as soon as V
onds later the relay is de-energized and stays off until the
V
CC
a
increases the emitter current of the vertical PNP drivers
supply is recycled
CC
is turned off Figure 4 is a similar circuit except that
CC
is applied then closes and stays energized
A is required Minimum and maximum
L
as the load During the timing
CC
is applied R
(Continued)
t
t
t
C
C
and C
a
t
t
sec-
sec-
SAT
5 0
t
7
Figure 5 shows the timer interfacing 5V logic to a high volt-
age relay Although the V
in the IC or require extra wiring if the LM122 is on a logic
card In either case the threshold for the trigger is 1 6V
FIGURE 2 Basic Timer-Emitter Output and Timing Chart
a
a
(Relay Energized R
5V Supply Driving 28V Relay
28V supply this may be an unnecessary waste of power
FIGURE 3 Time Out on Power Up
FIGURE 1 Basic Timer-Collector
Output and Timing Chart
t
C
t
Seconds after V
a
terminal could be tied to the
CC
is Applied)
TL H 7768 – 11
TL H 7768 – 12
TL H 7768 – 13