XC9511A1434 TOREX [Torex Semiconductor], XC9511A1434 Datasheet - Page 8

• Manufacturer Part Number: XC9511A1434
• Description: Synchronous Step-Down DC/DC Converter with built-in LDO Regulator in parallel plus Voltage Detector
• Manufacturer: TOREX [Torex Semiconductor]

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■TYPICAL APPLICATION CIRCUIT
■OPERATIONAL EXPLANATION
●DC/DC Converter
The XC9511 series consists of a synchronous step-down DC/DC converter, a high speed LDO voltage regulator, and a
voltage detector.
XC9511
SD *1: XB0ASB03A1BR (TOREX)
*1 The DC/DC converter of the XC9511 series automatically switches between synchronous / non-synchronous. The Schottky
*2 Please pay much attention when external components are selected as recommended value of C
The series consists of a reference voltage source, ramp wave circuit, error amplifier, PWM comparator, phase
compensation circuit, output voltage adjustment resistors, driver transistor, synchronous switch, current limiter circuit,
U.V.L.O. circuit and others. The series ICs compare, using the error amplifier, the voltage of the internal voltage
reference source with the feedback voltage from the V
performed on the resulting error amplifier output, to input a signal to the PWM comparator to determine the turn-on time
during PWM operation. The PWM comparator compares, in terms of voltage level, the signal from the error amplifier
with the ramp wave from the ramp wave circuit, and delivers the resulting output to the buffer driver circuit to cause the
Lx pin to output a switching duty cycle. This process is continuously performed to ensure stable output voltage. The
current feedback circuit monitors the P-channel MOS driver transistor current for each switching operation, and
modulates the error amplifier output signal to provide multiple feedback signals. This enables a stable feedback loop
even when a low ESR capacitor, such as a ceramic capacitor, is used, ensuring stable output voltage.
<Reference Voltage Source>
The reference voltage source provides the reference voltage to ensure stable output voltage of the DC/DC converter.
<Ramp Wave Circuit>
The ramp wave circuit determines switching frequency. The frequency is fixed internally and can be selected from
300kHz, 600 kHz and 1.2 MHz. Clock pulses generated in this circuit are used to produce ramp waveforms needed for
PWM operation, and to synchronize all the internal circuits.
<PWM/PFM>
The XC9511A to C series are PWM control, while the XC9511D to F series can be automatically switched to PWM/PFM
control. The PWM mode of the XC9511A to C series are controlled on a specified frequency from light loads through to
heavy loads. Since the frequency is specified, the composition of a noise filter etc. becomes easy. However, the
efficiency at the time of the light load may become low. The XC9511D to F series can switch to PWM/PFM automatic
switching control. With the automatic PWM/PFM switching control function, the series ICs are automatically switched
from PWM control to PFM control mode under light load conditions. The series cannot control only PFM mode. If
during light load conditions the coil current becomes discontinuous and on-time rate falls lower than 30%, the PFM
circuit operates to output a pulse with 30% of a fixed on-time rate from the Lx pin. During PFM operation with this fixed
on-time rate, pulses are generated at different frequencies according to conditions of the moment. This causes a
reduction in the number of switching operations per unit of time, resulting in efficiency improvement under light load
conditions. However, since pulse output frequency is not constant, consideration should be given if a noise filter or the
like is needed. Necessary conditions for switching to PFM operation depend on input voltage, load current, coil value
and other factors.
(ceramic, TAIYO YUDEN)
current.
diode is not normally needed. However, in cases where high efficiency is required when using the DC/DC converter during light
load while in non-synchronous operation, please connect a Schottky diode externally.
4.7μF
C
IN
Series
SOP-8 (TOP VIEW)
(ceramic, TAIYO YUDEN)
10μF
C
L1
OUT
pin through split resistors.
I
I
ROUT
ROUT
＜300mA
≧300mA
600KHz
1.2MHz
300kHz
FOSC
4.7μF (ceramic, TAIYO YUDEN)
10μF (ceramic, TAIYO YUDEN)
L
2 will be changed by the load
C
(CDRH4D28C, SUMIDA)
L2
(CDRH5D28, SUMIDA)
(CDRH6D28, SUMIDA)
*
Phase compensation is
2
4.7μH
10μH
22μH
L