L6730B datasheet(18/52 Pages) STMICROELECTRONICS

номер детали	L6730B

подробное описание детали	Adjustable step-down controller with synchronous rectification

PDF	52 Pages

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производитель	STMICROELECTRONICS [STMicroelectronics]

домашняя страница	http://www.st.com

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18 / 52 page

Device description

L6730 - L6730B

18/52

Doc ID 11938 Rev 3

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 0.5 V and both

MOSFETs are off. When Vss is between 0.5 V and 1.1 V 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 1.1 V (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 pre-bias start-up applications. This means that when the startup occurs with output

voltage greater than 0V (pre-bias startup), even when Vss is between 0.5 V and 1.1 V the

low-side MOSFET is kept OFF (see Figure 9 and Figure 10).

The L6730B can always sink current and so it can be used to supply the DDR memory

termination BUS. If overcurrent is detected during the soft-start phase, the device provides

constant current-protection. In case there is short soft-start time and/or small inductor value

and/or high output capacitors value and thus, in case of high ripple current during the soft-

start, the converter can start-up in anyway and limit the current (Chapter 5.8: Monitoring and

Figure 9.

Start-up without pre-bias

Figure 10.

Start-up with pre-bias

LGate

VOUT

VSS

VOUT

LGate

L6730B датащи(PDF) 18 Page - STMicroelectronics