t (s)

t (s)

L

i

'

D*Ts

Ts

D*Ts

Ts

L

V

IN

L

V

V

OUT

IN

L

V

V

OUT

IN

(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.

Copyright © 2004–2013, Texas Instruments Incorporated

Submit Documentation Feedback

11

Product Folder Links: LM3224