LM359
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SNOSBT4C –MAY 1999–REVISED MARCH 2013
(1)
where Ccomp is the total capacitance from the compensation pin (pin 3 or pin 13) to ground, AVOL is the low
frequency open loop voltage gain in V/V and an ambient temperature of 25°C is assumed (KT/q = 26 mV and
βtyp = 150). ISET(IN) also controls the DC input bias current by the expression:
(2)
which is important for DC biasing considerations.
The total device supply current (for both amplifiers) is also a direct function of the set currents and can be
approximated by:
Isupply ≃ 27 × ISET(OUT) + 11 × ISET(IN)
(3)
with each set current programmed by individual resistors.
PROGRAMMING WITH A SINGLE RESISTOR
Operating current programming may also be accomplished using only one resistor by letting ISET(IN) equal
ISET(OUT). The programming current is now referred to as ISET and it is created by connecting a resistor from pin 1
to pin 8 (Figure 30).
(4)
ISET(IN) = ISET(OUT) = ISET
Figure 30. Single Resistor Programming of ISET
This configuration does not affect any of the internal set current dependent parameters differently than previously
discussed except the total supply current which is now equal to:
Isupply ≃ 37 × ISET
(5)
Care must be taken when using resistors to program the set current to prevent significantly increasing the supply
voltage above the value used to determine the set current. This would cause an increase in total supply current
due to the resulting increase in set current and the maximum device power dissipation could be exceeded. The
set resistor value(s) should be adjusted for the new supply voltage.
One method to avoid this is to use an adjustable current source which has voltage compliance to generate the
set current as shown in Figure 31.
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