Datasheet

:
R
FB1
= R
FB2
x
V
OUT
- 1.259
1.259
V
OUT
=
V
IN
1-D
, D' = (1-D) =
V
IN
V
OUT
LM5000
www.ti.com SNVS176D –MAY 2004–REVISED MARCH 2007
The second cycle is shown in Figure 21 (b). During this cycle, the transistor is open and the diode is forward
biased. The energy stored in the inductor is transferred to the load and output capacitor.
The ratio of these two cycles determines the output voltage. The output voltage is defined approximately as:
where
• D is the duty cycle of the switch
• D and D′ will be required for design calculations (1)
SETTING THE OUTPUT VOLTAGE
The output voltage is set using the feedback pin and a resistor divider connected to the output as shown in
Figure 19. The feedback pin is always at 1.259V, so the ratio of the feedback resistors sets the output voltage.
(2)
INTRODUCTION TO COMPENSATION
Figure 22. (a) Inductor current. (b) Diode current.
The LM5000 is a current mode PWM regulator. The signal flow of this control scheme has two feedback loops,
one that senses switch current and one that senses output voltage.
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