TLE6389_07 datasheet(25/38 Pages) INFINEON

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TLE 6389

Datasheet Rev. 2.1

2007-08-13

Detailed circuit description

In the following, some internal blocks of the TLE6389 are described in more detail. For

the right choice of the external components please refer to the section application

information.

6.1

PFM/PWM Step-down regulator

To meet the strict requirements in terms of current consumption demanded by all Body-

and 42V PowerNet applications a special PFM (Pulse Frequency Modulation) - PWM

(Pulse Width Modulation) control scheme for highest efficiency is implemented in the

TLE 6389 regulators. Under light load conditions the output voltage is able to increase

slightly and at a certain threshold the controller jumps into PFM mode. In this PFM

operation the PMOS is triggered with a certain on time (depending on input voltage,

output voltage, inductance- and sense resistor value) whenever the buck output voltage

decreases to the so called WAKE-threshold. The switching frequency of the step down

regulator is determined in the PFM mode by the load current. It increases with increasing

load current and turns finally to the fixed PWM frequency at a certain load current

depending on the input voltage, current sense resistor and inductance. The diagram

below shows the buck regulation circuit of the TLE 6389 .

Figure 1

Buck control scheme

The TLE 6389 uses a slope-compensated peak current mode PWM control scheme in

which the feedback or output voltage of the step down circuit and the peak current of the

current through the PMOS are compared to form the OFF signal for the external PMOS.

VREF

VFB

BDS

GDRV

Current-

sense

Amplifier

MUX

Error

Amplifier

PWM

Comparator

Slope-

compensation

Blanking

Over-

Voltage

Lockout

Over-

Temp.

Shutdown

VREF

VFB, OV

VREF

VDIODE

Wake-

Comparator

VREF

VFB, WK

Oscillator

SYNC

MODE

Level-

shift

PFM

PWM

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