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PDF LM122 Data sheet ( Hoja de datos )

Número de pieza LM122
Descripción Precision Timers
Fabricantes National Semiconductor 
Logotipo National Semiconductor Logotipo



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No Preview Available ! LM122 Hoja de datos, Descripción, Manual

February 1995
LM122 LM322 LM3905 Precision Timers
General Description
The LM122 series are precision timers that offer great ver-
satility with high accuracy They operate with unregulated
supplies from 4 5V to 40V while maintaining constant timing
periods from microseconds to hours Internal logic and reg-
ulator circuits complement the basic timing function
enabling the LM122 series to operate in many different ap-
plications with a minimum of external components
The output of the timer is a floating transistor with built in
current limiting It can drive either ground referred or supply
referred loads up to 40V and 50 mA The floating nature of
this output makes it ideal for interfacing lamp or relay driv-
ing and signal conditioning where an open collector or emit-
ter is required A ‘‘logic reverse’’ circuit can be programmed
by the user to make the output transistor either ‘‘on’’ or
‘‘off’’ during the timing period
The trigger input to the LM122 series has a threshold of
1 6V independent of supply voltage but it is fully protected
against inputs as high as g40V even when using a 5V
supply The circuitry reacts only to the rising edge of the
trigger signal and is immune to any trigger voltage during
the timing periods
An internal 3 15V regulator is included in the timer to reject
supply voltage changes and to provide the user with a con-
venient reference for applications other than a basic timer
External loads up to 5 mA can be driven by the regulator An
internal 2V divider between the reference and ground sets
the timing period to 1 RC The timing period can be voltage
controlled by driving this divider with an external source
through the VADJ pin Timing ratios of 50 1 can be easily
achieved
The comparator used in the LM122 utilizes high gain PNP
input transistors to achieve 300 pA typical input bias current
over a common mode range of 0V to 3V A boost terminal
allows the user to increase comparator operating current for
timing periods less than 1 ms This lets the timer operate
over a 3 ms to multi-hour timing range with excellent repeat-
ability
The LM122 operates over a temperature range of b55 C to
a125 C An electrically identical LM322 is specified from
0 C to a70 C The LM3905 is identical to the LM122 series
except that the boost and VADJ pin options are not avail-
able limiting minimum timing period to 1 ms
Features
Y Immune to changes in trigger voltage during timing
interval
Y Timing periods from microseconds to hours
Y Internal logic reversal
Y Immune to power supply ripple during the timing
interval
Y Operates from 4 5V to 40V supplies
Y Input protected to g40V
Y Floating transistor output with internal current limiting
Y Internal regulated reference
Y Timing period can be voltage controlled
Y TTL compatible input and output
Connection Diagrams
Metal Can Package
Dual-In-Line Package
Dual-In-Line Package
TL H 7768–6
Top View
Order Number LM122H
See NS Package Number H10C
TL H 7768 – 7
Top View
Order Number LM322N
See NS Package Number N14A
TL H 7768 – 8
Top View
Order Number LM3905N
See NS Package Number N08E
C1995 National Semiconductor Corporation TL H 7768
RRD-B30M115 Printed in U S A

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LM122 pdf
Functional Diagram
Timing Diagram
TL H 7768 – 9
Pin Function Description
One of the main features of the LM122 is its great versatility
Since this device is unique a description of the functions
and limitations of each pin is in order This will make it much
easier to follow the discussion of the various applications
presented in this note
Va is the positive supply terminal of the LM122 When us-
ing a single supply this terminal may be driven by any volt-
age between 4 5V and 40V The effect of supply variations
on timing period is less than 0 005% V so supplies with
high ripple content may be used without causing pulse width
changes Supply bypassing on Va is not generally needed
but may be necessary when driving highly reactive loads
TL H 7768 – 10
Quiescent current drawn from the Va terminal is typically
2 5 mA independent of the supply voltage Of course addi-
tional current will be drawn if the reference is externally
loaded
The VREF pin is the output of a 3 15V series regulator refer-
enced to the ground pin Up to 5 0 mA can be drawn from
this pin for driving external networks In most applications
the timing resistor is tied to VREF but it need not be in
situations where a more linear charging current is required
The regulated voltage is very useful in applications where
the LM122 is not used as a timer such as switching regula-
tors variable reference comparators and temperature con-
5

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LM122 arduino
Application Hints (Continued)
‘‘high’’ is 2 5V R2 may be calculated from the divider equa-
tion with R1 to give these levels
Timer Protected
Against Damage
for up to 50V
TL H 7768 – 26
FIGURE 15 Comparator with 0V to 3V Threshold
Eliminating Timing Cycle Upon Initial
Application of Power
The LM122 will normally start a timing cycle (with no trigger
input) when Va is first turned on If this characteristic is
undesirable it can be defeated by tying the timing capacitor
to VREF instead of ground as shown in Figure 16 This con-
nection does not affect operation of the timer in any other
way If an electrolytic timing capacitor is used be sure the
negative end is tied to the R C pin and the positive end to
VREF A 1 0 kX resistor should be included in series with the
timing capacitor to limit the surge current load on VREF
when the capacitor is discharged
TL H 7768 – 28
Select for Proper Level Shift
Emitter Terminal or Emitter Load must be Tied to GND Pin of Timer
FIGURE 17 Operating Off Dual Supplies
Linearizing the Charging Sweep
In some applications (such as a linear pulse width modula-
tor) it may be desirable to have the timing capacitor charge
from a constant current source A simple way to accomplish
this is shown in Figure 18
TL H 7768 – 27
FIGURE 16 Eliminating Initial Timing Cycle
Using Dual Supplies
The LM122 can be operated off dual supplies as shown in
Figure 17 The only limitation is that the emitter terminal
cannot be tied to ground it must either drive a load referred
to Vb or be actually tied to Vb as shown Although capaci-
tive coupling is shown for the trigger input (to allow 5V trig-
gering) a resistor can be substituted for C1 R2 must be
chosen to give proper level shifting between the trigger sig-
nal and the trigger pin of the timer Worst case ‘‘lo’’ on the
trigger pin (with respect to Vb) is 0 8V and worst case
TL H 7768 – 29
FIGURE 18 Temperature Compensated
Linear Charging Sweep
Q1 converts the current through R1 to a current source in-
dependent of the voltage across Ct R2 R3 D1 and D2 are
added to make the current through R1 independent of sup-
ply variations and temperature changes (D2 is a low TC
type) D2 and R3 can be omitted if the Va supply is stable
and D1 and R2 can be omitted also if temperature stability is
not critical With D1 D2 R2 and R3 omitted the current
through R1 will change about 0 015% C with a 15V supply
and 0 1% C with a 5 0V supply
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