Datasheet

LM3488
LM3488-Q1
www.ti.com SNVS089M –JULY 2000–REVISED MARCH 2013
SHORT-CIRCUIT PROTECTION
When the voltage across the sense resistor (measured on I
SEN
Pin) exceeds 350mV, short-circuit current limit
gets activated. A comparator inside LM3488 reduces the switching frequency by a factor of 5 and maintains this
condition till the short is removed.
TYPICAL APPLICATIONS
The LM3488 may be operated in either continuous or discontinuous conduction mode. The following applications
are designed for continuous conduction operation. This mode of operation has higher efficiency and lower EMI
characteristics than the discontinuous mode.
BOOST CONVERTER
The most common topology for LM3488 is the boost or step-up topology. The boost converter converts a low
input voltage into a higher output voltage. The basic configuration for a boost regulator is shown in Figure 32. 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, MOSFET Q is turned on and energy is stored in the
inductor. During this cycle, diode D is reverse biased and load current is supplied by the output capacitor, C
OUT
.
In the second cycle, MOSFET Q is off 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:
(6)
(ignoring the drop across the MOSFET and the diode), or
where
• D is the duty cycle of the switch
• V
D
is the forward voltage drop of the diode
• V
Q
is the drop across the MOSFET when it is on (7)
The following sections describe selection of components for a boost converter.
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