5V

1.8V

Master Power

Supply

SS/TRACK

LM2743

1 k:

150:

10 k:

5 k:

FB

LM2743

www.ti.com

SNVS276F – MAY 2004 – REVISED JANUARY 2012

Figure 3. Tracking Circuit

One way to use the tracking feature is to design the tracking resistor divider so that the master supply’s output

explicitly showing the power components) both rise together and reach their target values at the same time. For

(4)

pin should be set higher than the feedback voltage of 0.6V (say about 0.65V as in the above equation). If the

needed to give the two supplies identical soft-start times would be 150

Ω. A timing diagram for the equal soft-start

time case is shown in Figure 4.

Figure 4. Tracking with Equal Soft-Start Time

TRACKING A VOLTAGE SLEW RATE

The tracking feature can alternatively be used not to make both rails reach regulation at the same time but rather

to have similar rise rates (in terms of output dV/dt). This method ensures that the output voltage of the LM2743

always reaches regulation before the output voltage of the master supply. Because the output of the master

supply is divided down, in order to track properly the output voltage of the LM2743 must be lower than the

voltage of the master supply. In this case, the tracking resistors can be determined based on the following

equation:

(5)

Copyright © 2004–2012, Texas Instruments Incorporated

Submit Documentation Feedback

11

Product Folder Links: LM2743