L6982 datasheet(8/48 Pages) STMICROELECTRONICS

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Functional description

The L6982 device is based on a “peak current mode”, constant frequency control. Therefore, the intersection

between the error amplifier output and the sensed inductor current generates the PWM control signal to drive the

power switch.

The device features LNM (low noise mode) that implements a forced PWM control, or LCM (low consumption

mode) to increase the efficiency at light-load.

The main internal blocks shown in the block diagram in Figure 1 are:

•

Embedded power elements

•

The ramp for the slope compensation avoiding subharmonic instability

•

A transconductance error amplifier with integrated compensation network

•

The high-side current sense amplifier to sense the inductor current

•

A “Pulse Width Modulator” (PWM) comparator and the driving circuitry of the embedded power elements

•

The soft-start block ramps up the reference voltage on error amplifier thus decreasing the inrush current at

power-up. The EN pin inhibits the device when driven low

•

The EN/CLK pin section, which, for LNM versions, allows synchronizing the device to an external clock

generator

•

The pulse-by-pulse high side / low-side switch current sensing to implement the constant current protection

•

A circuit to implement the thermal protection function

•

The OVP circuitry to discharge the output capacitor in case of overvoltage event

6.1

Enable

The EN pin is a digital input that turns the device on or off.

In order to maximize both the EN threshold accuracy and the current consumption, the device implements two

different thresholds:

The Wake-Up threshold, VWAKE_UP = 0.5 V (see Table 6)

The Start-Up threshold, VEN = 1.2 V (see Table 6)

The following picture shows the device behavior.

Figure 4. Power up/down behavior

L6982

Functional description

DS13683 - Rev 1

page 8/48

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