XC9206 / 9207/ 9208 Series

PWM, PWM/PFM Switchable Step-Down DC/DC Converters with Driver Transistor Built-In

# Instructions on Pattern Layout

< Reference Voltage Source >

The reference voltage source provides the reference voltage to ensure stable output voltage of the ICs.

< Ramp Wave Circuit >

< Error Amplifier >

< Current Limit >

4. Make sure that the PCB GND traces are as thick as possible, as

variations in ground potential caused by high ground currents at

the time of switching may result in instability.

2. Please mount each external component as close to the IC as

possible, and connect it to GND with the shortest possible PCB

traces.

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

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.

The ramp wave circuit determines switching frequency. The frequency is fixed internally and can be selected from 300kHz, 600 kHz and 1.2 MHz. Clock

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

1. In order to stabilize VDD's voltage level, we recommend that a

by-pass capacitor (CIN) be connected as close as possible to the

VIN & VSS pins.

3. Wire external components as close to the IC as possible and

use thick, short connecting traces to reduce the circuit impedance.

Each unit of the XC9206/9207/9208 series consists of a reference voltage source, ramp wave circuit, error amplifier, PWM comparator, phase

compensation circuit, output voltage adjustment resistors, driver transistor, current limiter circuit, U.V.L.O. circuit and others. The series ICs compare,

using the error amplifier, the voltage of the internal voltage reference source with the feedback voltage from the VOUT pin through resistors R1 and R2.

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.

12

3

4

5

VIN

CE/

MODE

GND

VOUT

Lx

( Through Hole to SD )

CIN

CL

SD

L

VIN Line

GND Line

Other Line

VIN

CE/MODE

LX

VOUT

IOUT

Current Limit LEVEL

Limit< #mS

Limit> #mS

Restart

VSS

0mA

Semiconductor Ltd.

The current limiter circuit of the XC9206/9207/9208 series monitors the current flowing through the P-channel MOS driver transistor connected to the Lx pin,

and features a combination of the constant-current type current limit mode and the operation suspension mode.

any given timing.

The IC waits for the over current state to end by repeating the steps

steps are repeatedly performed, the IC performs the function of latching the OFF state of the driver transistor, and goes into operation suspension mode.

Once the IC is in suspension mode, operations can be resumed by either turning the IC off via the CE /MODE pin, or by restoring power to the VIN pin. The

suspension mode does not mean a complete shutdown, but a state in which pulse output is suspended; therefore, the internal circuitry remains in operation.

The constant-current type current limit of the XC9206A/9207A/9208A series can be set at 600 mA.

Data Sheet

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