TLE6711G Ver la hoja de datos (PDF) - Infineon Technologies
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TLE6711G Datasheet PDF : 25 Pages
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TLE 6711
Circuit Description
4.3
Boost Converter
The TLE 6711 G/GL contains a fully integrated boost converter (except the boost-diode), which provides a supply
voltage for an energy reserve e.g. an airbag firing system. The regulated boost output voltage VBOOST is
programmable by a divider network (external resistors) providing the feedback voltage for the boost feedback pin
BOFB. The energy which is stored in the external electrolytic capacitor at VBOOST guarantees accurate airbag firing,
even if the battery is disconnected by a car crash.
The boost inductance LBO (typ. 100 µH) is PWM-switched by an integrated current limited power DMOS transistor
with a programmable (external resistor RR) frequency.
An internal bandgap reference provides a temperature independent, on chip trimmed reference voltage for the
regulation loop. An error amplifier compares the reference voltage with the boost feedback signal VBOFB from the
external divider network (determination of the output boost voltage VBOOST).
Application note for programming the output voltage at pin VBOOST:
VBOOST
=
VBO
FBTH
×
-(--R----B---O----1----+-----R----B---O----2--)-
RBO2
(1)
With a PWM (Pulse Width Modulation) comparator the output of the error amplifier is compared to a periodic linear
ramp, provided by a sawtooth signal of the oscillator connected to pin R. A logic signal with variable pulse width
is generated. It passes through the logic circuits (sets the output latch PWM-FF) and driver circuits to the power
switching DMOS. The Schmitt-trigger output resets the output flip-flop PWM-FF by NOR 2. The PWM signal is
gated by the NAND 2 to guarantee a dominant reset.
OV
COMP L when NAND 3
OV at VBoost &
= VthOV
38 V
L when
Tj > 175 ˚C
GND
VBoost
VthUV
4V
=
UV
COMP
+
-
H when
VBoost < 4 V
H when
Overcurrent
GND
I Pullup
H when
Tj > 175 ˚C
or OV at VBoost
NOR 1
1
Error
Gate
L when
Error
Error-FF
R& Q
H when NOR 2
Error
1
NAND1
&
&
S
Q
PWM-FF
R& Q
H=
OFF
INV
1
NAND 2
&
&
S
Q
H=
ON
Gate
Driver
BOI
Pin 14
Power
D-MOS
10 µA
BOFB
Pin 12
VREF
2.8 V
=
Error
AMP
+
-
Error-Signal
Error-Ramp
PWM
COMP
H when
Error-Signal
<
Error-Ramp
OC
COMP
VthOC
18 mV
RSense
14.5 mΩ
BOGND
Pin 13
GND
R
Pin 1
Oscillator
Vmax
Vmin
tr tf tr t
Schmitt-trigger 1
Ramp Vhigh
Vlow
tr tf tr
t Clock
Unlock
Detector
H when Outputcurrent > 1.2 A
OVL
Boost Status Pin 11
Low if Battery
Disconnected
GND
AEB02946
Figure 8 Boost Converter Block Diagram
Figure 8 shows the most important waveforms during operation; for low, medium and high loads up to overload
condition. The output transistor is switched off immediately if the overcurrent comparator detects an overcurrent
level at the power DMOS or if the sense output switches to low induced by a VBOOST undervoltage command.
Data Sheet
11
Rev. 3.4, 2007-08-16
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