
8/35
XC9511
Series
FOSC 
L 
1.2MHz 
4.7
μ
H  
(CDRH4D28C, SUMIDA) 
10
μ
H  
(CDRH5D28, SUMIDA) 
22
μ
H  
(CDRH6D28, SUMIDA) 
600KHz 
300kHz 
C
IN
4.7
μ
F 
C
L1
10
μ
F 
C
L2
 *
2
I
ROUT
<
300mA
I
ROUT
≧
300mA
4.7
μ
F (ceramic, TAIYO YUDEN)
10
μ
F (ceramic, TAIYO YUDEN)
(ceramic, TAIYO YUDEN) 
(ceramic, TAIYO YUDEN) 
■
TYPICAL APPLICATION CIRCUIT
SOP-8 (TOP VIEW) 
■
OPERATIONAL EXPLANATION
The XC9511 series consists of a synchronous step-down DC/DC converter, a high speed LDO voltage regulator, and a 
voltage detector. 
●
DC/DC Converter 
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
OUT
 pin through split resistors.  Phase compensation is 
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. 
SD *1: XB0ASB03A1BR (TOREX) 
*1 The DC/DC converter of the XC9511 series automatically switches between synchronous / non-synchronous.  The Schottky 
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. 
*2 Please pay much attention when external components are selected as recommended value of C
L
2 will be changed by the load 
current.