lm26484sqx National Semiconductor Corporation, lm26484sqx Datasheet - Page 12

• Manufacturer Part Number: lm26484sqx
• Description: Power Management Unit
• Manufacturer: National Semiconductor Corporation

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SOFT START
The soft-start feature allows the power converter to gradually
reach the initial steady state operating point, thus reducing
start-up stresses and surges. The two LM26484 buck con-
verters have a soft-start circuit that limits in-rush current dur-
ing start-up or the one which ramps up output voltage linearly
over about 500 µs. During start-up the switch current limit is
ramped up (100 µs, typ.), depending on the kind of soft-start.
Soft start is activated only if EN goes from logic low to logic
high after V
LOW DROPOUT OPERATION
The LM26484 can operate at 100% duty cycle (no switching;
PMOS switch completely on) for low dropout support of the
IN
reaches 2.8V.
FIGURE 3. PFM vs PWM
12
output voltage. In this way the output voltage will be controlled
down to the lowest possible input voltage. When the device
operates near 100% duty cycle, output voltage ripple is ap-
proximately 25 mV. The minimum input voltage needed to
support the output voltage is
V
— I
— R
— R
IN,
MIN = I
LOAD
DSON, PFET
INDUCTOR
LOAD
* (R
Load current
Drain to source resistance of
Inductor resistance
DSON, PFET
PFET switch in the triode region
+ R
INDUCTOR
30066105
) + V
OUT