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XCL211/XCL212

Series

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OPERATIONAL DESCRIPTION

The XCL211/XCL212 series consists of a reference voltage source, ramp wave circuit, error amplifier, PWM comparator, phase compensation

circuit, output voltage adjustment resistors, P-channel MOS driver transistor, N-channel MOS switching transistor for the synchronous switch,

current limiter circuit, UVLO circuit and others. (See the BLOCK DIAGRAM below) The series ICs compare, using the error amplifier, the

voltage of the internal voltage reference source with the feedback voltage from the FB pin. 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.

<BLOCK DIAGRAM>

<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 1.2MHz or 2.4MHz.

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 divided by

the external split resistors, R1 and R2. 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.

<Current Limit>

The XCL211/XCL212 series includes a fold-back circuit, which aids the operation of the current limiter and circuit protection. The

XCL211/XCL212 series monitors the current flowing through the P-channel MOS driver transistor

①

②

The output voltage is automatically resumed if the load goes light. When it is resumed, the soft-start function operates.

LX

PVIN

GND

FB

AVIN

CE

L1

L2

R1

R2