L5963 datasheet(24/45 Pages) STMICROELECTRONICS

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Functional Description

L5963

24/45

DocID028553 Rev 1

Both switching regulators can operate up to a 100% duty cycle. Once every four switching

periods, the PWM output is forced low for 100ns typ to refresh the bootstrap capacitor.

Their features include:



Wide input voltage range (from 3.5 V to 26 V)



Min output of 1 V



250 kHz free-run frequency and synchronization range from 250 kHz to 2 MHz. The

voltage feed forward is implemented in all frequency range



Internal 85 mΩ high-side and 105 mΩ low-side switching MOSFET



Up to 3 A load current capability



Power ok (SW1OK) output



Internal soft start function to minimize startup inrush current



Pulse-by-pulse current limiting (OCP)



Discontinuous mode detection (DMC)



Over temperature protection (OTP)



UVLO with stop threshold at 2.8 V (typ)



Load dump protection



Externally adjustable compensation



Stable with ceramic output capacitors

Oscillator/switching frequency

The internal oscillator provides a constant frequency clock of 250 kHz. The switching

frequency of DC/DC1 and DC/DC2 are determined by the internal frequency clock and the

external synchronization clock.

When no clock is applied to the SYNCIN pin or the synchronization clock is lower than

125 kHz (half of the internal clock), the two switching regulators work both with the internal

250 kHz clock. When the SYNCIN pin has a synchronization clock larger than 125 kHz, the

external synchronization clock is adopted.

There is a phase shift of 180° between PWM1 and PWM2, and the frequency of PWM2 can

be the same, 1/2, 1/4, 1/8 of PWM1 one. The division factor is programmed by FRDIV pin.

The switching clock of DC/DC1 can be sent out by pin SYNCOUT to synchronize another

device, in view of reducing EM disturbance.

Internal high-side and low-side Power MOSFET / Bootstrap structure

The two synchronous switching regulators don't need the external Schottky diode. Each of

them integrates a high-side and a low-side n-channel Power MOSFET, which allows a very

low drop voltage under high load current operation (up to 3 A).

The Bootstrap structure is used to drive the high-side n-channel Power MOSFET. A

Bootstrap capacitor of about 47 nF is needed.

Internal soft start function (SS)

To reduce the inrush current during startup, an internal soft start is implemented. The total

soft start time is about 400 μs and it doesn't change with operating frequency.

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