lmv358-mda National Semiconductor Corporation, lmv358-mda Datasheet - Page 19

• Manufacturer Part Number: lmv358-mda
• Description: General Purpose, Low Voltage, Rail-to-rail Output Operational Amplifiers
• Manufacturer: National Semiconductor Corporation

When the output voltage V
pacitor C is charged toward V
across C rises exponentially with a time constant τ = R
this voltage is applied to the inverting input of the op amp.
Meanwhile, the voltage at the non-inverting input is set at the
positive threshold voltage (V
pacitor voltage continually increases until it reaches V
which point the output of the generator will switch to its low,
V
input is switched to the negative threshold voltage (V
the generator. The capacitor then starts to discharge toward
V
When the capacitor voltage reaches V
pulse generator switches to V
charge, and the cycle repeats itself.
As shown in the waveforms in Figure 17, the pulse width
(T
(T
to have different frequencies and pulse width by selecting dif-
ferent capacitor value and resistor values.
Figure 18 shows another pulse generator, with separate
charge and discharge paths. The capacitor is charged
through R
OL
OL
1
2
) is set by R
) is set by R
FIGURE 17. Waveforms of the Circuit in Figure 16
which 0V is in this case. The voltage at the non-inverting
exponentially through R
1
and is discharged through R
1
, C and V
2
, C and V
OL
. This pulse generator can be made
OH
O
1
, and the time between pulses
is first at its high, V
TH+
, with a time constant τ = R
OH
OH
) of the generator. The ca-
. The capacitor starts to
through R
TH−
2
.
, the output of the
2
. The voltage
OH
, the ca-
2
C, and
TH−
TH+
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) of
, at
1
C.
19
Figure 19 is a squarewave generator with the same path for
charging and discharging the capacitor.
CURRENT SOURCE AND SINK
The LMV321/LMV358/LMV324 can be used in feedback
loops which regulate the current in external PNP transistors
to provide current sources or in external NPN transistors to
provide current sinks.
Fixed Current Source
A multiple fixed current source is shown in Figure 20. A volt-
age (V
voltage divider (R
cause the voltage drop across R
controls the emitter current of transistor Q
the base current of Q
is available out of the collector of Q
Large input resistors can be used to reduce current loss and
a Darlington connection can be used to reduce errors due to
the β of Q
The resistor, R
Q
2
either above or below the 1 mA reference value.
REF
1
.
FIGURE 19. Squarewave Generator
= 2V) is established across resistor R
2
FIGURE 18. Pulse Generator
, can be used to scale the collector current of
3
and R
1
and Q
4
). Negative feedback is used to
2
, essentially this same current
1
to be equal to V
1
.
1
and if we neglect
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10006076
REF
3
10006077
by the
. This