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XC9510
Series
<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
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
mode, operations can be resumed by either turning the IC off via the CE/MODE pin, or by restoring power to the
V
IN
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
XC9510 series can be set at 1.1A.
■
OPERATIONAL EXPLANATION (Continued)
<U.V.L.O. Circuit>
When the V
IN
pin voltage becomes 1.4 V or lower, the P-channel output driver transistor is forced OFF to prevent false
pulse output caused by unstable operation of the internal circuitry. When the V
IN
pin voltage becomes 1.8 V or higher,
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
IN
pin voltage falls momentarily below the
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.
●
High Speed LDO Voltage Regulator
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
OUT
pin, is then driven by the subsequent output signal. The
output voltage at the VR
OUT
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 error amplifier compares the reference voltage with the signal from VR
OUT
, and the amplifier controls the output of
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
OUT
and GND pin are shorted, the load current of about 30mA flows.