L6983 datasheet(11/63 Pages) STMICROELECTRONICS

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Functional description

The L6983 device is based on a “peak current mode" architecture with 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 is forced PWM control, or LCM (low consumption mode) to

increase the efficiency at light-load on the selected part number.

The main internal blocks shown in the block diagram in Figure 1. Block diagram and Figure 2. Pin connection (top

through view) are:

•

Embedded power elements

•

A fully integrated adjustable oscillator which is able to set eight different switching frequencies from 200 to

2200 kHz

•

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

•

The switchover capability of the internal regulator to supply a portion of the quiescent current when the

VBIAS pin is connected to an external output voltage

•

Enable/ disable dithering operation

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. Electrical characteristics)

The start-up threshold, VEN = 1.2 V (see Table 6. Electrical characteristics)

The following picture shows the device behavior.

L6983

Functional description

DS13116 - Rev 1

page 11/63

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