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XCL102/XCL103

Series

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OPERATIONAL EXPLANATION

The XCL102/XCL103 series consists of a reference voltage source, ramp wave circuit, error amplifier, PWM comparator, phase compensation

circuit, N-channel driver transistor, P-channel synchronous rectification switching transistor and current limiter circuit.

The error amplifier compares the internal reference voltage with the resistors RFB1 and RFB2. Phase compensation is performed on the

resulting error amplifier output, to input a signal to the PWM comparator to determine the turn-on time of the N-channel driver transistor 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 N-channel driver transistor’s turn-on 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, soft start function>

The reference voltage forms a reference that is used to stabilize the output voltage of the IC.

After “H” level is fed to CE pin, the reference voltage connected to the error amp increases linearly during the soft start interval. This allows the

voltage divided by the internal RFB1 and RFB2 resistors and the reference voltage to be controlled in a balanced manner, and the output voltage

rises in proportion to the rise in the reference voltage. This operation prevents rush input current and enables the output voltage to rise smoothly.

<Ramp Wave Circuit>

The ramp wave circuit determines switching frequency. The frequency is fixed internally at 3.0MHz. The Clock generated is 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 resistors (RFB1 and RFB2). When the FB is lower than the reference voltage, output voltage of the error amplifier increases. The

gain and frequency characteristics of the error amplifier are optimized internally.

<Shutdown function, load disconnection function>

The IC enters chip disable state by applying low level voltage to the CE pin. At this time, the N-channel and P-channel synchronous switching

transistors are turned OFF

and cathode: Lx during shutdown to break conduction from the input side to the output side by the parasitic diode of the P-channel synchronous

switching transistor.

<PWM/PFM control circuit>

When PFM operates, the N-channel driver transistor turns on at the timing of the signal sent from the PWM comparator. The N-channel driver

time of the N-channel driver transistor. This enables smooth switching between PWM and PFM. The XCL102 series directly outputs the signal

that is sent from the PWM comparator.

Load　Disconnect

Controller

CE Controller

Logic

PWM

Comparator

Buffer

Drive

Current sense

Short-circuit

protection

Latch Timer

Vref with

Soft Start

Inductor

GND

L2

L1

PFM/PWM

Controller Logic

CE

Discharge

Error Amp.

Phase

Compensation

RAMP Wave

Generator

OSC

FB

< BLOCK DIAGRAM (D type) >