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Axelite Confidential Materials, do not copy or distribute without written consent.

Rev.1.1 Nov.05, 2019

AX3984

Enable

The EN pin provides electrical on/off control of the regulator. Once the voltage of the EN pin

exceeds the threshold voltage, the regulator starts operation and the internal slow start begins to

ramp. If the voltage of the EN pin is pulled below the threshold, the regulator will stop switching

and the internal slow start reset. If the EN pin is open, it will be pulled to high by the internal circuit.

Under Voltage Lockout

The part incorporates an under voltage lockout circuit to keep the device disabled when VIN is

below the UVLO start threshold. During power-up, the internal circuit is held inactive until VIN

exceeds the UVLO start threshold voltage. Once this threshold voltage is reached, device start-up

begins. The device operates until VIN falls below the UVLO stop threshold voltage. The typical

hysteretic in the UVLO comparator is 250mV.

Soft-Start

The built-in soft-start function is to gradually raise the output voltage after power-on. The soft-start

period can be set by the external capacitor, which is between the SS pin and GND.

Css

Tss

10nF

2.8ms

100nF

28ms

Boost Capacitor

The BST pin and SW pin can be connected by a 10nF low ESR ceramic capacitor, providing the

gate drive voltage for the high side MOSFET.

Thermal Shutdown

The part protects itself from overheating with an internal thermal shutdown circuit. If the junction

temperature exceeds the thermal shutdown threshold, the voltage reference will be grounded and

high side MOSFET turned off.

Compensation

The system stability is controlled through COMP pin. It will present a general design procedure to

ensure a stable and operational circuit. The design in this data sheet is optimized for particular

requirements. Some components may need to be changed to ensure stability if there are different

requirements. First of all, the power components and their corresponding effects need to be

determined. Following are the compensation components, which are to produce stability.

The compensation steps for the converter are listed below: