TLE6389_07 Datasheet, PDF (25/38 Pages) Infineon Technologies AG – Step-Down DC/DC Controller

TLE 6389
6
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 .
VS
CS
VFB, OV
VREF
VREF
VDIODE
+ - _Current-
sense
Amplifier
+ - _Over-
Voltage
Lockout
+ - _Over-
Temp.
Shutdown
VREF
+
+
-
VFB
Error
Amplifier
Slope-
compensation
Blanking
>1
PWM
Comparator
VREF
-
VFB, WK
Wake-
Comparator
PFM
MUX
PWM
R
SQ
&
Level-
shift
VS
GDRV
BDS
SYNC
Oscillator
MODE
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.
Datasheet Rev. 2.1
25
2007-08-13