SC410 SEMTECH [Semtech Corporation], SC410 Datasheet - Page 12

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

Applications Information
Synchronous Buck Converter
The SC410 is a step down synchronous buck DC-DC regu-
lator. The device is capable of 3A operation at very high
effi ciency in a tiny 3 x 3-10 pin package. The programma-
ble operating frequency range of 200kHz – 1MHz enables
the user to optimize the design for minimum board space
and optimum effi ciency.
The buck regulator employs pseudo-fixed frequency
adaptive on-time control. This control method allows fast
transient response thereby lowering the size of the power
components used in the system.
Input Voltage Range
The SC410 can operate with a wide input voltage ranging
from 5.5V to 24V. The internal LDO generates a fixed 5V
output that provides power for the bias of the SC410. The
LDO can also provide additional power to an external load.
Psuedo-fi xed Frequency Adaptive On-time Control
The PWM control method used by the SC410 is pseudo-
fi xed frequency, adaptive on-time, as shown in Figure 1.
The ripple voltage generated at the output capacitor ESR
is divided down by the feedback resistor network and
used as a PWM ramp signal. The ripple seen at the FB pin
is used to trigger the on-time of the controller.
The adaptive on-time is determined by an internal one-
shot timer. When the one-shot is triggered by the feed-
back ripple, the device sends a single on-time pulse to the
high-side MOSFET. The pulse period is determined by the
Q1
Q2
V
IN
Figure 1 — PWM Control Method, V
V
LX
C
IN
L
TON
V
+
ESR
FB
C
OUT
V
LX
OUT
FB Threshold
Ripple
FB
V
OUT
output voltage value and V
to output voltage and inversely proportional to input
voltage. The value of the output voltage is obtained by
fi ltering the voltage seen on the LX pin.
With this adaptive on-time design, the device automati-
cally anticipates the on-time needed to regulate V
the present V
The advantages of adaptive on-time control are:
One-Shot Timer and Operating Frequency
The one-shot timer operates as shown in Figure 2. The
feedback comparator output goes high when V
than the internal 750mV reference. This feeds into the
gate drive and turns on the high-side MOSFET, and also
starts the one-shot timer. The one-shot timer uses an
internal comparator, timing capacitor, and a low pass
fi lter (LPF) which regenerates V
tor input is connected to the fi ltered LX voltage, the other
input is connected to the capacitor. When the on-time
begins, the internal capacitor charges from zero volts
through a current which is proportional to V
capacitor voltage reaches V
and the high-side MOSFET turns off .
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•
•
•
•
Predictable operating frequency during CCM
compared to other variable frequency
methods.
Reduced component count by eliminating the
e r r o r a m p l i f i e r a n d c o m p e n s a t i o n
components.
Reduced component count by removing the
need to sense and control inductor current.
Fast transient response — the response time is
controlled by a fast comparator instead of a
typically slow error amplifi er.
Reduced output capacitance due to fast tran-
sient response
IN
condition and at the selected frequency.
IN
OUT
. The period is proportional
, the on-time is completed
OUT
from LX. One compara-
IN
SC410
. When the
FB
OUT
is less
for
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