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XC9223D01AL Datasheet(PDF) 9 Page - Torex Semiconductor |
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XC9223D01AL Datasheet(HTML) 9 Page - Torex Semiconductor |
9 / 25 page 9/25 XC9223/XC9224 Series ■OPERATIONAL EXPLANATION Each unit of the XC9223/XC9224 series consists of a reference voltage source, a ramp wave circuit, error amplifier, PWM comparator, phase compensation circuit, output voltage adjustment resistors, P-channel MOS driver transistor, N-channel MOS synchronous rectification switching transistor, current limiter circuit, U.V.L.O. circuit and others. The series compares, using the error amplifier, the internal reference voltage to the VOUT pin with the voltage feedback via 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 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 and can be selected from 1.0MHz and 2.0MHz. 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 resistors (RFB1 and RFB2). 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 current limiter circuit of the XC9223/XC9224 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. For the current limit values, please select the values either from 1.2A (MIN.) when the LIM pin is high level or 0.6A (MIN.) when the LIM pin is low level. 1When the driver current is greater than a specific level, the constant-current type current limit function operates to turn off the pulses from the Lx pin at any given time. 2When the driver transistor is turned off, the limiter circuit is then released from the current limit detection state. 3At the next pulse, the driver transistor is turned on. However, the transistor is immediately turned off in the case of an over current state. 4 When the over current state is eliminated, the IC resumes its normal operation. The IC waits for the over current state to end by repeating the steps 1 through 3. If an over current state continues for several msec and the above three steps are repeatedly performed, the IC performs the function of latching the OFF state of the driver transistor, and goes into operation suspension mode. After being put into suspension mode, the IC can resume operation by turning itself off once and then starting it up using the CE pin, or by restoring power to the VIN pin. Integral latch time may be released from a current limit detection state because of the noise. Depending on the state of a substrate, it may result in the case where the latch time may become longer or the operation may not be latched. Please locate an input capacitor as close as possible. VIN CE LX Current Limit LEVEL Limit < # mS Restart VSS 0mA Limit > # mS IOUT VOUT ms ms |
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