5V

1.8V

Master Power

Supply

SS/TRACK

LM2744

1 k:

150:

10 k:

5 k:

FB

LM2744

www.ti.com

SNVS292F – SEPTEMBER 2004 – REVISED MARCH 2013

Figure 21. 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)

should be set slightly higher than the reference voltage (say about 50mV higher as in the above equation). If the

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

diagram for the equal soft-start time case is shown in Figure 22.

Figure 22. 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 LM2744

always reaches regulation before the output voltage of the master supply. In this case, the tracking resistors can

be determined based on the following equation:

(5)

above equation to be 267

Ω. A timing diagram for the case of equal slew rates is shown in Figure 23.

Copyright © 2004–2013, Texas Instruments Incorporated

Submit Documentation Feedback

11

Product Folder Links: LM2744