Datasheet

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 V

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 V

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

OUT

LGate