Master Power

Supply

SS/TRACK

LM2743

1 k:

150:

10 k:

5 k:

FB

10

7

+ 0.24

10

12

2

+

LM2743

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SNVS276H – APRIL 2004 – REVISED OCTOBER 2015

Feature Description (continued)

•

(1)

During soft start the Power Good flag is forced low and it is released when the FB pin voltage reaches 70% of

0.6V. At this point the chip enters normal operation mode, and the output overvoltage and undervoltage

monitoring starts.

7.3.2 Normal Operation

While in normal operation mode, the LM2743 regulates the output voltage by controlling the duty cycle of the

high side and low side MOSFETs (see Typical Application Diagram). The equation governing output voltage is:

(2)

the FREQ pin and ground. The resistance needed for a desired frequency is approximately:

(3)

7.3.3 Tracking a Voltage Level

The LM2743 can track the output of a master power supply during soft-start by connecting a resistor divider to

the SS/TRACK pin. In this way, the output voltage slew rate of the LM2743 will be controlled by the master

supply for loads that require precise sequencing. When the tracking function is used no soft-start capacitor

and ground should be used.

Figure 19. 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)

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Product Folder Links: LM2743