A6986 datasheet(25/67 Pages) STMICROELECTRONICS

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A6986

Functional description

5.5.1

Low noise mode (LNM)

The low noise mode implements a forced PWM operation over the different loading

conditions. The LNM features a constant switching frequency to minimize the noise in the

final application and a constant voltage ripple at fixed VIN. The regulator in steady loading

condition never skip pulses and it operates in continuous conduction mode (CCM) over the

different loading conditions.

Figure 13. Low noise mode operation

Typical applications for the LNM operation are car audio, sensors.

5.5.2

Low consumption mode (LCM)

The low consumption mode maximizes the efficiency at light-load. The regulator prevents

the switching activity whenever the switch peak current request is lower than the ISKIP

threshold (700 mA typical). As a consequence the A6986 device works in bursts and it

minimizes the quiescent current request in the meantime between the switching operation.

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

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