LM359
SNOSBT4C –MAY 1999–REVISED MARCH 2013
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The nVBE biasing configuration is most useful for low noise applications where a reduced input impedance can
be accommodated (see Typical Applications section).
OPERATING CURRENT PROGRAMMABILITY (ISET
)
The input bias current, slew rate, gain bandwidth product, output drive capability and total device power
consumption of both amplifiers can be simultaneously controlled and optimized via the two programming pins
ISET(OUT) and ISET(IN)
.
ISET(OUT)
The output set current (ISET(OUT)) is equal to the amount of current sourced from pin 1 and establishes the class A
biasing current for the Darlington emitter follower output stage. Using a single resistor from pin 1 to ground, as
shown in Figure 28, this current is equal to:
Figure 28. Establishing the Output Set Current
The output set current can be adjusted to optimize the amount of current the output of the amplifier can sink to
drive load capacitance and for loads connected to V+. The maximum output sinking current is approximately 10
times ISET(OUT). This set current is best used to reduce the total device supply current if the amplifiers are not
required to drive small load impedances.
ISET(IN)
The input set current ISET(IN) is equal to the current flowing into pin 8. A resistor from pin 8 to V+ sets this current
to be:
Figure 29. Establishing the Input Set Current
ISET(IN) is most significant in controlling the AC characteristics of the LM359 as it directly sets the total input stage
current of the amplifiers which determines the maximum slew rate, the frequency of the open loop dominant pole,
the input resistance of the (−) input and the biasing current Ib(−). All of these parameters are significant in wide
band amplifier design. The input stage current is approximately 3 times ISET(IN) and by using this relationship the
following first order approximations for these AC parameters are:
10
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