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)
LM3224
www.ti.com SNVS277C –DECEMBER 2004–REVISED MARCH 2013
SOFT-START CAPACITOR
The LM3224 has a soft-start pin that can be used to limit the inductor inrush current on start-up. The external SS
pin is used to tailor the soft-start for a specific application but is not required for all applications and can be left
open when not needed. When used, a current source charges the external soft-start capacitor, Css. The soft-
start time can be estimated as:
Tss = Css*1.24V/Iss (3)
THERMAL SHUTDOWN
The LM3224 includes thermal shutdown protection. If the die temperature exceeds 140°C the regulator will shut
off the power switch, significantly reducing power dissipation in the device. The switch will remain off until the die
temperature is reduced to approximately 120°C. If the cause of the excess heating is not removed (excessive
ambient temperature, excessive power dissipation, or both) the device will continue to cycle on and off in this
manner to protect from damage.
INTRODUCTION TO COMPENSATION
Figure 22. (a) Inductor current. (b) Diode current.
The LM3224 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.
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