XC9510 TOREX SEMICONDUCTOR LTD., XC9510 Datasheet - Page 10

• Manufacturer Part Number: XC9510
• Description: Xc9510 Synchronous Step-down Dc/dc Converter With Built-in Ldo Regulator In Series Plus Voltage Detector
• Manufacturer: TOREX SEMICONDUCTOR LTD.

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●High Speed LDO Voltage Regulator
■OPERATIONAL EXPLANATION (Continued)
XC9510
The voltage regulator block of the XC9510 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 amplifier.
The P-channel MOSFET, which is connected to the VR
output voltage at the VR
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 error amplifier compares the reference voltage with the signal from VR
the P-ch 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
further and the load current decreases. When the VR
<U.V.L.O. Circuit>
When the V
pulse output caused by unstable operation of the internal circuitry. When the V
switching operation takes place. By releasing the U.V.L.O. function, the IC performs the soft start function to initiate
output startup operation. The soft start function operates even when the V
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.
<Current Limit>
The current limiter circuit of the XC9510 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
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
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.
mode, operations can be resumed by either turning the IC off via the CE/MODE pin, or by restoring power to the
V
suspended; therefore, the internal circuitry remains in operation. The constant-current type current limit of the
XC9510 series can be set at 1.1A.
IN
to turn off the pulses from the Lx pin at any given timing.
case of an over current state.
pin. The suspension mode does not mean a complete shutdown, but a state in which pulse output is
IN
pin voltage becomes 1.4 V or lower, the P-channel output driver transistor is forced OFF to prevent false
Series
OUT
pin is controlled and stabilized by a system of negative feedback. A stable output voltage is
OUT
OUT
and GND pin are shorted, the load current of about 30mA flows.
pin, is then driven by the subsequent output signal. The
OUT
IN
pin voltage falls momentarily below the
, and the amplifier controls the output of
IN
pin voltage becomes 1.8 V or higher,
Once the IC is in suspension