Figure 5-1. Equivalent Diagrams for UVLO and Hysteresis

5.6

Setting the Voltage Divider for Output Rails

Generically, the equation is stated as:

resistor connected to lower rail (usually IC ground). However, with so many topologies, in effect the following three

cases in all the typical schematics presented so far are present.

• Isolated topologies with divider to another reference (such as TL431 with an internal reference of 2.5V). For this,

• Non-isolated topologies with a differential divider connected to differential voltage amplifier of the LX7309. The

differential amplifier 7). Two identical dividers are required.

5.7

Selecting the Sense Resistor

headroom for proper transient response at maximum load must also be included. As the peak voltage on the sense

resistor is 0.2V, to leave headroom, it must be planned in such a way that the switch current peak stays at around

0.18V at the most, at maximum load. This means the following:

An adjust resistor must be placed in parallel (for example, the 22Ω placeholder).

divided by number of secondary-side turns). The sense resistance must also be lowered further (by means of the

adjust resistor), to account for the magnetization current component on the switch side.

PD70211

Applications Information

Datasheet

DS00003672A-page 26