XC9510A1333 TOREX [Torex Semiconductor], XC9510A1333 Datasheet - Page 9

• Manufacturer Part Number: XC9510A1333
• Description: Synchronous Step-Down DC/DC Converter With Built-In LDO Regulator Plus Voltage Detector
• Manufacturer: TOREX [Torex Semiconductor]

■OPERATIONAL EXPLANATION (Continued)
<PWM/PFM>
●Continuous Mode: Synchronous
The XC9510A to F series are PWM control, while the XC9510H to L series can be automatically switched between PWM
control and PWM/PFM control. The PWM of the XC9510A to F series are controlled on a specified frequency from light
loads through the 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 XC9510H to L series can switch in any timing between PWM control and PWM/PFM automatic switching control.
<Synchronous / Non-synchronous>
The XC9510 series automatically switches between synchronous / non-synchronous according to the state of the DC/DC
converter.
Highly efficient operations are achievable using the synchronous mode while the coil current is in a continuous state.
The series enters non-synchronous operation when the built-in N-ch switching transistor for 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.
required during light load current.
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.
●Discontinuous Mode: Non-Synchronous
Please use an external schottky diode if high efficiency is
XC9510
Series
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