L6730C datasheet(17/50 Pages) STMICROELECTRONICS

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L6730C - L6730D

Device description

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

programmed value: 0.6V or 1.2V. During the soft-start phase the converter works in closed

loop. The L6730C can only source current during the soft-start phase in order to manage the

prebias start-up applications. The L6730D can always sink current and so it can be used to

supply the DDR Memory termination BUS. If an over current is detected during the soft-start

phase, the device provides a constant-current-protection. In this way, in case of 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 any case, limiting the current

(see section 4.5 Monitoring and protections) but not entering in HICCUP mode. The soft-start

phase ends when Vss reaches 3.5V. After that the over-current-protection triggers the HICCUP

mode (L6730C). With the L6730D there is the possibility to set the HICCUP mode or the

constant current mode after the soft-start acting on the multifunction pin CC/O/U. With the

L6730 the low-side MOSFET(s) management after soft-start phase depends on the S/O/U pin

state (see related section). If the sink-mode is enabled the converter can sink current after soft-

start (see figure 9) while, if the sink-mode is disabled the converter never sinks current (see

figure 10)..

Figure 8.

Sink-mode enabled: Inductor current during and after soft-start (L6730C).

VOUT

VSS

VCC

L6730C Arkusz danych(PDF) 17 Page - STMicroelectronics