Product Specification

IXD3220/IXD3221

PS034101-0515

PRELIMINARY

5

Error Amplifier

The error amplifier compares reference voltage with the FB pin voltage. When a feedback voltage is lower than the

reference voltage, output voltage increases, resulting in longer ON time of the switching MOSFET.

The gain and frequency characteristics of the error amplifier are set internally to deliver an optimized signal to the

PWM comparator.

Control Methods

The IXD3220 series ICs utilize PWM control, while the IXD3221 series ICs use either PWM or PFM control

automatically changing mode.

The IXD3220 series ICs provide a constant switching frequency disregard to load. When a switching frequency

noise is a concern, it is easy to filter it, since the frequency is fixed. However, the efficiency at light load may fall.

The IXD3221 series IC provide high efficiency at wide range of load, using PFM mode at light and PWM mode at

heavy load, automatically changing mode.

If inductor current becomes discontinuous at light load and duty cycle intends to be less than 25%, the IXD3221

switches to PFM mode with duty cycle fixed at 25%. It increases efficiency at light load, but switching frequency at

this mode depends on load. If noise at switching frequency is a concern, filtering circuitry should be designed for full

specter of switching frequency.

UVLO (Under Voltage Lock Out)

When the input voltage falls to 2.3 V or lower, UVLO circuitry becomes active. It forces external P-channel

MOSFET in OFF state and resets internal circuitry. When input voltage restores above UVLO value, IC resumes

normal operation with internal soft start (disregard to the existence of the external soft start circuitry at

IXD3220/221B and D versions)

Soft-Start Time

The IXD3220/221B and D series can adjust the soft-start time externally via the CE pin. The soft-start function

operates until the CE pin voltage rises above 2.6 V. Please refer to the following equation for calculating the soft-

start time.

Minimum soft-start time is equal to the time set internally.