Synchronous Step-Down DC/DC Converter with Built-In LDO Regulator in Parallel plus Voltage Detector

< U.V.L.O. Circuit>

% High Speed LDO Voltage Regulator

< 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 VROUT, and the amplifier controls the output of the Pch driver transistor.

<Current Limit Circuit>

% Voltage Detector

The detector block of the XC9509 series detects output voltage from the VDOUT pin while sensing either VDD, DCOUT, or VROUT internally.

(N channel Open Drain Type)

<CE Pin Function>

<MODE Pin Function>

XC9509 Series

The operation of the XC9509 series' DC/DC converter block and voltage regulator block will enter into the shut down mode when a low level

signal is input to the CE pin. During the shut down mode, the current consumption occurs only in the detector and is 0.6

µA (TYP.), with a state

of high impedance at the Lx pin and the DCOUT pin. The IC starts its operation by inputting a high level signal to the CE pin. The input to the

CE pin is a CMOS input and the sink current is 0

µA (TYP.).

The operation of the XC9509A series' voltage detector block will enter into stand-by mode when a high level signal is input to the MODE pin.

When a low level signal is input, the voltage regulator block will enter into stand-by mode. However, if the IC enters into stand-by mode via the

CE pin, the voltage regulator block also shuts down. Likewise, if the XC9509B series enters into stand-by mode via the CE pin, the DC/DC

converter block can also shut down. With the XC9509C series control can be PWM control when the MODE pin is 'H' level and PWM/PFM

automatic switching control when the MODE pin is 'L' level.

When the VIN 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 VIN 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

VIN 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.

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

output current of the built-in P channel output driver transistor inside. 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 VROUT and GND pin are shorted, the load current of about

30mA flows.

The voltage regulator block of the XC9509 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 VROUT pin, is then driven by the subsequent output 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.

Semiconductor Ltd.

Data Sheet

9