SC410 SEMTECH [Semtech Corporation], SC410 Datasheet - Page 21

• Manufacturer Part Number: SC410
• Description: 3A EcoSpeed TM Step-Down Regulator with LDO and Ultrasonic Power Save
• Manufacturer: SEMTECH [Semtech Corporation]

SC410
Applications Information (continued)
The output inductor value may change with current. This
will change the output ripple and therefore will have a
minor eff ect on the DC output voltage. The output ESR
also aff ects the output ripple and thus has a minor eff ect
on the DC output voltage.
Switching Frequency Variation
The switching frequency will vary depending on line and
load conditions. The line variations are a result of fi xed
propagation delays in the on-time one-shot, as well as
unavoidable delays in the power FET switching. As V
IN
increases, these factors make the actual DH on-time
slightly longer than the ideal on-time. The net eff ect is
that frequency tends to fall slightly with increasing input
voltage.
The switching frequency also varies with load current as a
result of the power losses in the MOSFETs and the induc-
tor. For a conventional PWM constant-frequency con-
verter, as load increases the duty cycle also increases
slightly to compensate for IR and switching losses in the
MOSFETs and inductor. A adaptive on-time converter
must also compensate for the same losses by increasing
the effective duty cycle (more time is spent drawing
energy from V
as losses increase). The on-time is essen-
IN
tially constant for a given V
and V
combination, to
OUT
IN
off set the losses the off -time will tend to reduce slightly as
load increases. The net eff ect is that switching frequency
increases slightly with increasing load.
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