XC9244 Series

400mA Synchronous Step-Down DC/DC Converters

The XC9244 series is a group of synchronous-rectification type step-down DC/DC converters with a built-in 0.65ΩP-ch MOS driver transistor and 0.45Ω N-ch MOS switching transistor, designed to allow the use of ceramic capacitors. Output current of 400mA (MAX.) to be configured using only a coil and capacitor connected externally.

The output voltage can be set from 0.8V to 4.0V in increments of 0.05V (±2.0%). With an internal switching frequency of 1.2MHz, small external components can be used. USPN-6 package is suitable for the application which requires low profile and small-footprint.

When stand-by mode, due to stop all operation, quiescent current is reduced to 1μA or less. The integrated CL discharge function which enables the electric charge at the output capacitor CL to be discharged via the internal discharge switch located between the VOUT and VSS pins. The CL discharge function prevents malfunction on VOUT connecting application during stand-by mode.

The XC9244 series has a high speed soft-start as fast as 0.25ms in typical for quick turn-on. Current limiter circuit (Constant Current & Latching) is built-in for preventing from thermal destruction.

With UVLO (Under Voltage Lock Out) function, the internal P channel driver transistor is forced OFF when input voltage becomes 2.25V or lower.

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Jul 27, 2011
Product News
【New Product Release】XC9244/XC9245 Series

Typical Application Circuit


Driver Transistor 0.65Ω P-ch Driver Transistor
0.45Ω N-ch Switching Transistor
Input Voltage Range 2.3V~6.0V
Output Voltage Range 0.8V~4.0V(0.05V increments)
High Efficiency 90%(TYP.)
Output Current 400mA
Oscillation Frequency 1.2MHz(±15%)
Maximum Duty Cycle 100%
Functions Current Limit(Constant Current & Latching),CL High Speed Auto Discharge,Soft-Start
Capacitor Low ESR Ceramic
Control Methods PWM
Operating Ambient Temperature -40℃~+85℃
Environmentally Friendly EU RoHS compliant, Pb free



Technical Document

Quality Reports


QuestionHow does the GO function of DC/DC converters work? Does it work just like a regulator?

Torex regard the PWM/PFM automatic switch control function as Green Operation (GO) in the case of DC/DC. The GO function is defined as the switching operation between the PFM mode for a small output current and the PWM mode for a large output current. The PFM control method controls the output current by increasing and decreasing the fall time according to the output current while keeping a pulse width. The PWM control method controls the output current by adjusting the pulse width of the rise time, which keeps the rise/fall time interval constant and increases the efficiency at a heavy load. By switching between the PFM control for a small output current and the PWM control for a large output current, the quiescent current can be controlled for both of heavy and light loads.

QuestionWhat is the soft-start function?

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

QuestionHow does the CL discharge function work?

The function rapidly releases the charge remained in the CL capacitor to make the VOUT pin voltage zero. The VOUT pin voltage does not reach zero immediately after being turned off by the CE function due to the charge remained in the connected CL capacitor. While the charge in the CL capacitor is gradually reaching zero, the LSI continues operating and does not work with the CE pin signal, which may cause a malfunction. This is why the discharge is required when turning off the CE pin. A larger capacitance of the capacitor needs longer time to be discharged.

QuestionWhat does CL mean?

Load capacitor. Other companies often refer to it as COUT.

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 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.