11

Data Sheet

ud200541

XC9508

Series

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DC/DC Converter (Continued)

<Current Limit>

The current limiter circuit of the XC9508 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.

①

When 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 timing.

②

When the driver transistor is turned off, the limiter circuit is then released from the current limit detection state.

③

At 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 8msec* 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. Once the IC is in suspension

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 XC9508 series

can be set at 1.1A for MSOP-10 package and 0.7A for USP-10 package

<U.V.L.O. Circuit>

switching operation takes place. By releasing the U.V.L.O. function, the IC performs the soft start function to initiate

U.V.L.O. operating voltage. The U.V.L.O. circuit does not cause a complete shutdown of the IC, but causes pulse

output to be suspended; therefore, the internal circuitry remains in operation.

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High Speed LDO Voltage Regulator

The voltage regulator block of the XC9508 series consists of a reference voltage source, error amplifier, and current

limiter circuit. The voltage divided by split resistors is compared with the internal reference voltage by the error

signal. The output voltage at the VROUT pin is controlled and stabilized by a system of negative feedback. A stable

output voltage is achievable even if used with low ESR capacitors as a phase compensation circuit is built-in.

<Reference Voltage Source>

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

<Error Amplifier>

the Pch driver transistor.

<Current Limit Circuit>

The voltage regulator block includes a combination of a constant current limiter circuit and a foldback circuit. When the

load current reaches the current limit level, the current limiter circuit operates and the output voltage of the voltage

regulator block drops. As a result of this drop in output voltage, the foldback circuit operates, output voltage drops

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OPERATIONAL EXPLANATION (Continued)