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XC9248

Series

■OPERATIONAL EXPLANATION

The XC9248 series consists of a reference voltage source, an internal reference voltage source, ramp wave circuit, error

amplifier, PWM comparator, phase compensation circuit, Nch MOS driver transistor, current limiter circuit, UVLO, short

protection circuit, thermal shutdown circuit, over voltage protection and others. (See the block diagram below.)

By using the error amplifier, the FB pin voltage is compared with the internal reference voltage. The signal is input into the

PWM comparator to determine the on time of switching. The signal from the error amplifier is compared with the ramp wave

from the ramp wave circuit, and the resulting output is delivered to the output buffer circuit to provide on-time of the duty cycle at

the LX pin. This process is continuously performed to ensure stable output voltage.

The current feedback circuit monitors the Nch 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 using a low

ESR capacitor such as ceramic, which results in ensuring stable output voltage.

XC9248 Series

<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 500kHz internally. Clock pulses generated in

this circuit are used to produce ramp waveforms needed for PWM operation, and to synchronize all the internal circuits.

<Error Amplifier>

The error amplifier is designed to monitor output voltage. The amplifier compares the reference voltage with the feedback

voltage. When a voltage lower than the reference voltage is fed back, the output voltage of the error amplifier increases. The

gain and frequency characteristics of the error amplifier output are fixed internally to deliver an optimized signal to the mixer.

The error amplifier output signal optimized in the mixer is modulated with the current feedback signal. This signal is delivered to

the PWM comparator.