XC9128 Series

1A Driver Transistor Built-in, Step-Up DC/DC Converters

The XC9128 series are synchronous step-up DC/DC converters with a 0.2Ω (TYP.) N-ch driver transistor and a synchronous 0.2Ω (TYP.) P-ch switching transistor built-in. A highly efficient and stable current can be supplied up to 1.0A by reducing ON resistance of the built-in transistor. With a high switching frequency of 1.2MHz, a small inductor is selectable; therefore, the XC9128/XC9129 series are ideally suited for the applications required height limitation or space-saving. With the MODE pin, the XC9128/XC9129 series provide mode selection of PWM control or PFM/PWM automatic switching control. In the PWM/PFM automatic switching mode, the series enters from PWM to PFM to reduce switching loss when load current is small. When load current is large, the series enters automatically to the PWM mode so that high efficiency is achievable over a wide range of load conditions. The series provide small output ripple from light to large loads by using the built-in circuit which enables the transition between PWM and PFM smoothly.

When voltage higher than the input voltage is applied to the output during shut-down, the input and the output are isolated and the IC allows parallel drive with such as AC adaptor.

Typical Application Circuit


Output Current 150mA@VOUT=3.3V, VIN =0.9V
Input Voltage Range 0.8V~6.0V
Output Voltage Range 1.8V~5.3V (Externally set), Set up freely with a reference voltage, supply of 0.45V (±0.010V) & external, components
Oscillation Frequency 1.2MHz(±15%)
Input Voltage 1.0A
Maximum Current limit 1.2A(MIN.)2.0A(MAX.)
Control Methods PWM, PWM/PFM control, externally switching
Protection Circuits Thermal shutdown, Integral latch method (Over current limit)
Soft-Start 5ms (TYP.)
Capacitor Low ESR Ceramic
Functions Adaptor Enable Function
Error Flagout Output N-channel open drain



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