xc9509c03cdr TOREX SEMICONDUCTOR LTD., xc9509c03cdr Datasheet - Page 9

• Manufacturer Part Number: xc9509c03cdr
• Description: Xc9509 Synchronous Step-down Dc/dc Converter With Built-in Ldo Regulator In Parallel Plus Voltage Detector
• Manufacturer: TOREX SEMICONDUCTOR LTD.

■OPERATIONAL EXPLANATION (Continued)
●DC/DC Converter (Continued)
●Continuous Mode: Synchronous
<PWM/PFM>
The PWM control of the XC9509A to F series are controlled on a specified frequency from light loads through the heavy
<Synchronous / Non-synchronous>
The XC9509 series automatically switches between synchronous / non-synchronous according to the state of the DC/DC
converter.
continuous state.
synchronous operation is shutdown, which happens when the load current becomes low and the operation changes to a
discontinuous state. The IC can operate without an external schottky diode because the parasitic diode in the N-ch
switching transistor provides the circuit's step-down operation. However, since Vf of the parasitic diode is a high 0.6V,
the efficiency level during non-synchronous operation shows a slight decrease.
if high efficiency is required during light load current.
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 XC9509H to L series can switch in any timing between PWM control
and PWM/PFM automatic switching control. The series cannot control only PFM mode. If needed, the operation can
be set on a specified frequency; therefore, the control of the noise etc. is possible and the high efficiency at the time of
the light load during PFM control mode is possible. 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. 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.
Highly efficient operations are achievable using the synchronous mode while the coil current is in a
The series enters non-synchronous operation when the built-in N-ch switching transistor for
●Discontinuous Mode: Non-Synchronous
Please use an external schottky diode
XC9509
Series
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