XC9221 Series

16V Input Voltage, Step-Down DC/DC Controller

The XC9221 series is a group of multi-purpose step-down DC/DC controller ICs. The ICs enable a high efficiency, stable power supply with an output current up to 3A to be configured using only a transistor, a coil, a diode, and two capacitors connected externally.

Low ESR capacitors such as a ceramic capacitor can be used as an output capacitor.

The XC9221 series has a 0.9V (±1.5%) reference voltage, and using externally connected resistors, the output voltage can be set freely. With an internal switching frequency of 300kHz and 500kHz 1MHz, small external components can also be used. The As for the soft-start time, the XC9221A and C series is internally set to 4msec and the XC9221B and D series can be externally set-up. With the built-in UVLO (Under Voltage Lock Out) function, the external P-channel driver transistor is forced OFF when input voltage becomes 2.3V or lower. Two types of package, SOT-25 and USP-6, are available.

Typical Application Circuit


Operating Voltage Range 2.8V~16.0V
Output VoltageExternally Set 0.9V(Accuracy ±1.5V)
Oscillation Frequency 300k,500k,1.0MHz
Control Methods PWM/PFM automatic switching
Soft-Start 4ms, internally set(Types A)
Externally set (Types B)
Protection Circuits Integral protection 1.0ms(Types A,B), Short Circuit Protection
Low ESR Capacitor Ceramic Capacitor



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.

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.