SC410 SEMTECH [Semtech Corporation], SC410 Datasheet - Page 14

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

Applications Information (continued)
Ultrasonic Power Save Operation
The SC410 provides ultrasonic power save operation at
light loads, with the minimum operating frequency fi xed
at 22kHz. This is accomplished using an internal timer that
monitors the time between consecutive high-side gate
pulses. If the time exceeds 40μs, DL drives high to turn the
low-side MOSFET on. This draws current from V
the inductor, forcing both V
drops to the 750mV threshold, the next DH on-time is trig-
gered. After the on-time is completed the high-side
MOSFET is turned off and the low-side MOSFET turns on.
The low-side MOSFET remains on until the inductor
current ramps down to zero, at which point the low-side
MOSFET is turned off .
Because the on-times are forced to occur at intervals no
greater than 40μs, the frequency will not fall below
~22kHz. Figure 5 shows ultrasonic power save operation.
DH
Voltage (V
DL
Inductor
Current
FB Ripple
Figure 4 — Continuous Mode Operation
DL remains high until V
FB
)
DL drives high when on-time is completed.
On-time
(T
ON
)
V
DH on-time is triggered when
OUT
FB
FB
reaches the FB Threshold.
and V
falls to the FB threshold.
FB
to fall. When V
DC Load Current
FB threshold
OUT
(750mV)
through
FB
Smart Power Save Protection
Active loads may leak current from a higher voltage into
the switcher output. Under light load conditions with
power save enabled, this can force V
reach the over-voltage threshold, resulting in a hard shut-
down. Smart power save prevents this condition. When
the FB voltage exceeds 10% above nominal (exceeds
825mV), the device immediately disables power-save,
and DL drives high to turn on the low-side MOSFET. This
draws current from V
V
a normal T
vents a hard OVP shutdown and also cycles energy from
V
smart power save feature.
Inductor
Current
FB Ripple
OUT
OUT
DH
DL
Voltage
(V
After the 40μsec time-out, DL drives high if V
back to V
to fall. When V
FB
Figure 5 — Ultrasonic Power Save Operation
)
has not reached the FB threshold.
ON
40μsec time-out
IN
switching cycle begins. This method pre-
Minimum f
. Figure 6 shows typical waveforms for the
On-time
(T
FB
ON
OUT
drops back to the 750mV trip point,
)
SW
through the inductor and causes
~ 25kHz
DH On-Time is triggered when
V
FB
reaches the FB Threshold
OUT
to slowly rise and
FB
FB threshold
SC410
(750mV)
(0A)
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