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

< Synchronous / Non-synchronous >

% Continuous Mode : Synchronous

% Discontinuous Mode : Non-Synchronous

< Current Limit >

XC9509 Series

The current limiter circuit of the XC9509 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.

the Lx pin at any given timing.

The IC waits for the over current state to end by repeating the steps

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 pin, or by restoring

power to the VIN 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 XC9509 series can be set at 1.2A.

The XC9509 series automatically switches synchronous / non synchronous according to the state of the DC/DC converter.

In the series, highly efficient operation using the synchronous mode while the coil current is in a continuation state.

The series enters non-synchronous operation when the built-in Nch switching transistor for synchronous operation is shutdown which happens

when the load current becomes low and the operation changes to a discontinuous state.

The IC can operate without an external schottky diode because the parasitic diode in the Nch switching transistor provides the circuit's step-

down operation. However, since Vf of the parasitic diode is high 0.6V, the efficiency level during non-synchronous operation shows a slight

decrease. Please use an external schottky diode if high efficiency is required during light load current.

0mA

ILmin

ILmax

Coil Current

LX

Wave Form

ILmax

0mA

Coil Current

LX

Wave Form

**

VIN

CE

LX

DCOUT

IDOUT

Current LimitLEVEL

Limit<8mS

Restart

VSS

0mA

Limit>8mS

*1.2MHz,Typical

Semiconductor Ltd.

Data Sheet

8