A6985F datasheet(28/77 Pages) STMICROELECTRONICS

28 / 77 page

Functional description

A6985F

28/77

DocID027738 Rev 2

Figure 17. LCM operation with ISKIPH = 100 mA typ. at zero load

The LCM operation satisfies the requirements of the unswitched car body applications

(KL30). These applications are directly connected to the battery and are operating when the

engine is disabled. The typical load when the car is parked is represented by a CAN trans-

ceiver and a microcontroller in sleep mode (total load is around 20 - 30 µA). As soon as the

transceiver recognizes a valid word in the bus, it awakes the µC and the rest of the applica-

tion.

The typical input current request of the module when the car is parked is 100 µA typ. to pre-

vent the battery discharge over the parking time. In order to minimize the regulator quies-

cent current request from the input voltage, the VBIAS pin can be connected to an external

voltage source in the range 3 V < VBIAS < 5.5 V (see Section 5.1: Power supply and voltage

reference on page 15).

Given the energy stored in the inductor during a burst, the voltage ripple depends on the

capacitor value:

Equation 13

VOUT RIPPLE

Q

COUT

--------------

iL t dt





TBURST



COUT

--------------------------------------------

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