Datasheet

V
OUT
=
V
IN
1-D
V
IN
C
OUT
PWM
L
R
LOAD
V
IN
L
C
OUT
R
LOAD
X
V
I
N
L
C
OUT
R
LOAD
Cycle
1
Cycle
2
(a)
(b)
+
V
OU
T
-
+
V
OUT
-
D
LM2698
SNVS153E –MAY 2001–REVISED APRIL 2013 www.ti.com
Operation
Continuous Conduction Mode
Figure 14. Simplified Boost Converter Diagram
(a) First Cycle of Operation (b) Second Cycle Of Operation
The LM2698 is a current-mode, PWM boost regulator. A boost regulator steps the input voltage up to a higher
output voltage. In continuous conduction mode (when the inductor current never reaches zero at steady state),
the boost regulator operates in two cycles.
In the first cycle of operation, shown in Figure 14 (a), the transistor is closed and the diode is reverse biased.
Energy is collected in the inductor and the load current is supplied by C
OUT
.
The second cycle is shown in Figure 14 (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 as:
(1)
where D is the duty cycle of the switch.
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