Datasheet

t (s)
t (s)
L
i'
I
L_AVG
I
D_AVG
=I
OUT_AVG
D*Ts Ts
D*Ts Ts
I
L
(A)
I
D
(A)
L
V
IN
L
VV
OUTIN

L
VV
OUTIN

(a)
(b)
LM2622
SNVS068E –MAY 2000–REVISED MARCH 2013 www.ti.com
INTRODUCTION TO COMPENSATION
(a) Inductor current
(b) Diode current
Figure 18.
The LM2622 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 10µH inductor is recommended for most 600 kHz applications, while a 4.7µH 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 LM2622 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 the typical application
circuit. For any given application, there exists a unique combination of R
C
and C
C
that will optimize the
performance of the LM2622 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:
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