A6986F datasheet(28/72 Pages) STMICROELECTRONICS

28 / 72 page

Functional description

A6986F

28/72

DocID027739 Rev 1

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

transceiver 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

application.

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

prevent the battery discharge over the parking time. In order to minimize the regulator

quiescent 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).

In case the VBIAS pin is connected to the regulated output voltage (VOUT), the total current

drawn from the input voltage can be calculated as Equation 14.

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

capacitor value:

Equation 13

Figure 18. LCM operation over loading condition (part 1)

VOUT RIPPLE

Q

COUT

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

iL t dt





TBURST



COUT

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A6986F データシート(PDF) 28 Page - STMicroelectronics