XC9251 Series

30V Driver Transistor Built-In Step-Down DC/DC Converters

The XC9251 series are 30V operation step-down DC/DC converter ICs with an internal driver transistor. The internal Nch driver transistor is driven by bootstrap to achieve a stable, high-efficiency power supply up to an output current of 2.0A. Low ESR capacitors such as ceramic capacitors can be used for the load capacitor (CL).

A 0.8V reference voltage source is incorporated in the IC, and the output voltage can be set to a value from 1.2V to 12.0V using external resistors (RFB1, RFB2).

300kHz or 500kHz can be selected for the switching frequency. The generation of unneeded noise can be suppressed by synchronizing to an external CLK in a range of ±25% of the free running frequency using the SYNC pin. In automatic PWM/PFM control, the IC operates by PFM control when the load is light to achieve high efficiency over the full load range from light to heavy.

The soft start time can be set as desired by adding an external capacitance to the SS pin.

With the built-in UVLO function, the driver transistor is forced OFF when input voltage becomes 4.5V or lower.

Internal protection circuits include over current protection, integral latch protection, short-circuit protection, and thermal shutdown circuits to enable safe use.

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Jun 27, 2013
Product News
30V, 2A Step-Down DC/DC Converter Operates to 105℃ XC9250/XC9251 Series

Typical Application Circuit


Input Voltage Range 7V~30V
FB Voltage 0.8V±2%
Oscillation Frequency 300kHz
Maximum Output Current 2.0A
Control Methods PWM/PFM
Soft-Start Externally Set (set by external capacitor C)
Protection Circuits Over Current Protection 3.2A(TYP.)
Integral Latch Method(XC9251A)
Automatic return(XC9251B)
Thermal Shut Down
Low ESR Ceramic Capacitor Ceramic Capacitor
Operating Ambient Temperature -40℃~+105℃
Environmentally Friendly EU RoHS compliant, Pb free



Quality Reports


QuestionWhat is the soft-start function?

The function to soften the rise to prevent the inrush current.

QuestionWhat is the standby current?

The current that flows through the IC in the standby mode. The standby mode means the state where the IC has been turned off by the CE function.

QuestionWhat is PFM control and PWM control?

PFM control is a method to control the output current by maintaining a constant pulse width, and increasing and decreasing the OFF time according to the output current. Since the PWM control adjusts the pulse width of the ON time to control the output current, the cycle of the ON and OFF time becomes constant, which increases the efficiency during a heavy load. The current consumption during a heavy loading and light load is controlled by switching to PWM control when the output current is high, and to PFM control when the output current is low.

QuestionWhat does the FB product mean?

An IC for which any output voltage can be set by the reference voltage of the FB pins and the external dividing resistor. The output voltage is determined by the RFB1 and RFB2 values, using the following formula: VOUT = Vref × (RFB1 + RFB2)/RFB2

QuestionHow does UVLO (under voltage lockout) work?

This circuit forcibly turns off the driver transistor when VIN drops below the UVLO voltage. If the input voltage recovers to the value which is equal to the specified value or more, UVLO will be released to resume the switching operation. It is resumed by the soft-start function. The paused state by UVLO is not the shutdown. The pulse output is stopped, but the internal circuit is operating.