LM3489

LM3489-Q1

SNVS443B – MAY 2006 – REVISED FEBRUARY 2013

www.ti.com

The LM3489 operates in discontinuous conduction mode at light load current or continuous conduction mode at

heavy load current. In discontinuous conduction mode, current through the inductor starts at zero and ramps up

to the peak, then ramps down to zero. The next cycle starts when the FB voltage reaches the reference voltage.

Until then, the inductor current remains zero and the output capacitor supplies the load. The operating frequency

is lower and switching losses reduced. In continuous conduction mode, current always flows through the inductor

and never ramps down to zero.

(1)

Figure 24. Hysteretic Window

(2)

(3)

(Equivalent Series Resistance) of output capacitor, and the delay. It can be approximately calculated using the

formula:

(4)

where:

α: (R1 + R2) / R2

delay: It includes the LM3489 propagation delay time and the PFET delay time. The propagation delay is 90ns

typically (see Figure 25).

10

Submit Documentation Feedback

Copyright © 2006–2013, Texas Instruments Incorporated

Product Folder Links: LM3489 LM3489-Q1