LM359M datasheet(11/34 Pages) TI1

11 / 34 page

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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