L6364 datasheet(39/60 Pages) STMICROELECTRONICS

39 / 60 page

This results in a constant current output behavior with a variable frequency switching (see Figure 16). The

operating current and external components should be chosen to avoid this behavior under normal conditions.

Figure 16. Overcurrent operation

Coil

Current

ILIMIT

time

IOPMAX

ILIMIT

IOP

1/fSET

active

waiting

Overcurrent

operation

Normal

operation

For coil protection purposes, the maximum duty is further limited by the L6364 in relation to the supply voltage so

that the maximum coil current rise in one cycle is limited to:

DMAX

≾ 19.2 V / VVPLUS ⇒ Δ I ≾ 19.2V / (fSET × LCOIL)

For fSET= 1 MHz, LCOIL= 220 μH

⇒ ΔI<=87mA.

17.4.3

Capacitive blocking of DOUT

CDOUT provides capacitive isolation of the VPLUS supply from the DC-DC regulator. A minimum value, see

Table 5. Receiver CQ/DIO, is required to correctly supply the transient currents when the DC-DC converter

switches pin LOUT, and at low output currents where there is a negative current in the coil in part of the cycle. The

value may, however, be increased to provide additional isolation from input voltage ripple on VPLUS.

L6364

Converter external component consideration

DS13363 - Rev 4

page 39/60

L6364 데이터시트(PDF) 39 Page - STMicroelectronics