Datasheet

Hz
1
2S(R
C
+ R
O
)C
C
f
PC
=
Hz
1
f
ZC
=
2SR
C
C
C
LM2700
SNVS152C –MAY 2001–REVISED MARCH 2013 www.ti.com
INTRODUCTION TO COMPENSATION
Figure 18. (a) Inductor current. (b) Diode current.
The LM2700 is a current mode PWM boost converter. The signal flow of this control scheme has two feedback
loops, one that senses switch current and one that senses output voltage.
To keep a current programmed control converter stable above duty cycles of 50%, the inductor must meet
certain criteria. The inductor, along with input and output voltage, will determine the slope of the current through
the inductor (see Figure 18(a)). If the slope of the inductor current is too great, the circuit will be unstable above
duty cycles of 50%. A 4.7µH inductor is recommended for most 600 kHz applications, while a 2.2µH inductor
may be used for most 1.25 MHz applications. If the duty cycle is approaching the maximum of 85%, it may be
necessary to increase the inductance by as much as 2X. See Inductor and Diode Selection for more detailed
inductor sizing.
The LM2700 provides a compensation pin (V
C
) to customize the voltage loop feedback. It is recommended that a
series combination of R
C
and C
C
be used for the compensation network, as shown in Figure 19. For any given
application, there exists a unique combination of R
C
and C
C
that will optimize the performance of the LM2700
circuit in terms of its transient response. The series combination of R
C
and C
C
introduces a pole-zero pair
according to the following equations:
(3)
(4)
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