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XCL201/XCL202

Series

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OPERATIONAL DESCRIPTION

The XCL201/XCL202 series consists of a reference voltage source, ramp wave circuit, error amplifier, PWM comparator, phase compensation

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

switch, current limiter circuit, UVLO circuit with control IC, and an inductor. (See the block diagram below.) Using the error amplifier, the voltage

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 1.2MHz. 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

internal split resistors, R1 and R2. When a feed back voltage is lower than the reference voltage, the output voltage of the error amplifier is

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

CE/

CE

R2

R1

Error

Amp.

Vref with

Soft Start,

CE

Phase

Compensation

Current Feedback

Current Limit

PWM

Comparator

Logic

Synch

Buffer

Drive

R3

R4

UVLO

UVLO Cmp

Ramp Wave

Generator

OSC

Lx

CE

Control

Logic

VSHORT

FB

CFB

Inductor

L2

L1

PWM/PFM

Selector