SC9301 Datasheet, PDF (13/29 Pages) Semtech Corporation – 10A EcoSpeed® Integrated FET Regulator with 5V LDO and Hiccup Restart

SC9301
Applications Information
Synchronous Buck Converter
The SC9301 is a step down synchronous DC-DC buck con-
verter with integrated power MOSFETs and a 200mA
capable 5V LDO. The device is capable of 10A operation at
very high efficiency. A space saving 5x5 (mm) 32-pin
package is used. The programmable operating frequency
of up to 1MHz enables optimizing the configuration for
PCB area and efficiency.
The buck controller uses a pseudo-fixed frequency adap-
tive on-time control. This allows fast transient response
which permits the use of smaller output capacitors.
Input Voltage Requirements
The SC9301 requires two input supplies for normal opera-
tion: V and VDD. V operates over the wide range of 3V
IN
IN
to 28V. VDD requires a 3V to 5.5V supply which can be
from an external source or from the internal fixed 5V
LDO.
Power Up Sequence
When the SC9301 uses an external power source at the
VDD pin, the switching regulator initiates the start up
when V , VDD and EN are above their respective thresh-
IN
olds. When EN is at a logic high, VDD can be applied after
V rises. It is also recommended to use a10Ω resistor
IN
between an external power source and the VDD pin. To
start up using the EN pin when both VDD and V are above
IN
their respective thresholds, apply EN to enable the start-
up process. For SC9301 in self-biased mode, refer to the
LDO section for a full description.
Shutdown
The SC9301 can be shutdown by pulling either VDD or EN
below its threshold. When VDD is active and EN at low
logic, the output voltage discharges through an internal
FET.
Psuedo-fixed Frequency Adaptive On-time Control
The PWM control method used by the SC9301 is pseudo-
fixed frequency, adaptive on-time, as shown in Figure 1.
The ripple voltage generated at the output capacitor ESR
is used as a PWM ramp signal. This ripple is used to trigger
the on-time of the controller.
V_IN
Q1
V_LX
Q2
TON
V_LX
C_IN
V_FB
FB Threshold
L
ESR
+
C_OUT
V_OUT
FB
Figure 1 — PWM Control Method, V_OUT Ripple
The adaptive on-time is determined by an internal one-
shot timer. When the one-shot is triggered by the output
ripple, the device sends a single on-time pulse to the high-
side MOSFET. The pulse period is determined by V and
OUT
V . The period is proportional to output voltage and
IN
inversely proportional to input voltage. With this adaptive
on-time configuration, the device automatically antici-
pates the on-time needed to regulate V for the present
OUT
V condition and at the selected frequency.
IN
The advantages of adaptive on-time control are:
• Predictable operating frequency compared to
other variable frequency methods.
• Reduced component count by eliminating the
error amplifier and compensation 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 typi-
cally slow error amplifier.
• Reduced output capacitance due to fast tran-
sient response.
One-Shot Timer and Operating Frequency
One-shot timer operation is shown in Figure 2. The FB com-
parator output goes high when V is less than the internal
FB
600mV reference. This feeds into the DH gate drive and
turns on the high-side MOSFET, and also starts the one-shot
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