L6730 datasheet(17/52 Pages) STMICROELECTRONICS

Part #	L6730

Description	Adjustable step-down controller with synchronous rectification

PDF	52 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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17 / 52 page

L6730 - L6730B

Device description

17/52

The output of the error amplifier is clamped with this voltage (Vss) until it reaches the

programmed value. No switching activity is observable if VSS is lower than 0.5V and both

MOSFETs are off. When Vss is between 0.5V and 1.1V the low-side MOSFET is turned on

because the output of the error amplifier is lower than the valley of the triangular wave and so

the duty-cycle is 0%. As VSS reaches 1.1V (i.e. the oscillator triangular wave inferior limit) even

the high-side MOSFET begins to switch and the output voltage starts to increase. The L6730 -

L6730B can only source current during the soft-start phase in order to manage the prebias

start-up applications. This means that when the startup occurs with output voltage greater than

0V (pre-bias startup), even when Vss is between 0.5V and 1.1V the low-side MOSFET is kept

OFF (see Figure 8. and Figure 9.).

Figure 8.

Start-up without prebias

Figure 9.

Start-up with prebias

LGate

VOUT

VSS

VOUT

LGate

L6730 Datasheet(PDF) 17 Page - STMicroelectronics