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L5989D：4 A continuous (more than 5 A pulsed) step-down switching regulator with synchronous rectification

The L5989D is a monolithic step down power switching regulator able to deliver a continuous output current of 4 A to the load in most of the application conditions limited only by the thermal performance. The device is able to deliver more than 5 A to the load for a maximum time which is dependent on the thermal impedance of the system and the specific operating conditions.

The input voltage can range from 2.9 V to 18 V. The device is capable of 100% duty cycle operation thanks to the embedded high side PMOS switch which doesn’t need external bootstrap capacitor to be driven.

The internal switching frequency is adjustable by external resistor and can be set continuously from 100 kHz to 1 MHz.

The multifunction UOS pin allows to set-up properly the additional embedded features depending on the value of the voltage level.

U (UVLO): two UVLO thresholds can be selected to match the 3.3 V and 5 V or 12 V input buses.

O (OVP): latched or not latched OVP protection selectable. In latched mode the switching activity is interrupted until an UVLO or INH event happens.

S (SINK): the sink capability is always disabled during soft-start time to support pre-biased output voltage. Afterwards the sink capability can be enabled or not depending on the voltage set on the multifunction pin.

During soft-start phase a constant current protection is active to deliver extra current necessary to load the output capacitor. The current limit protection is achieved by sensing the current flowing in both embedded switches to assure an effective protection even at extreme duty cycle operations. Finished the soft-start phase the current protection feature triggers the “HICCUP” mode forcing the soft-start capacitor to be discharged and recharged. The current thresholds of both switches can be adjusted in tracking by using an external resistor to dimension the current protection accordingly to the local application.

The soft-start time is based on a constant current charge of an external capacitor. As a consequence the time can be set accordingly to the value of the output capacitor.

The latest smart power technology BCD6 (Bipolar-CMOS-DMOS version 6) features a low resistance of the embedded switches (35 mΩ typical for a NMOS, 50 mΩ typical for a PMOS), achieving high efficiency levels.

The HTSSOP16 package with exposed pad accomplishes low R_thJA(40°C/W), useful in dissipating power internally generated during high output current / high frequency operations.

Key Features

• 4 A output current (more than 5 pulsed)
• Operating input voltage from 2.9 V to 18 V
• External 1.8 V ± 2% reference voltage
• Output voltage from 0.6 to input voltage
• MLCC compatible
• 200 ns TON
• Programmable UVLO matches 3.3 V, 5 V and 12 V bus
• FSW programmable up to 1 MHz
• Voltage feed-forward
• Zero load current operation
• Programmable current limit on both switches
• Programmable sink current capability
• Pre-bias start up capability
• Thermal shutdown

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