TLE6711_07 Datasheet, PDF (11/25 Pages) Infineon Technologies AG – Multifunctional Voltage Regulator and Watchdog

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 V_BOOST 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 V_BOOST guarantees accurate airbag firing,
even if the battery is disconnected by a car crash.
The boost inductance L_BO (typ. 100 µH) is PWM-switched by an integrated current limited power DMOS transistor
with a programmable (external resistor R_R) 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 V_BOFB from the
external divider network (determination of the output boost voltage V_BOOST).
Application note for programming the output voltage at pin V_BOOST:
V_BOOST
=
V_BO
FBTH
×
-⁽--^R----^B---^O----¹----+-----^R----^B---^O----²--⁾-
R_BO2
(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 V_{Boost &}
= V_thOV
38 V
L when
T_j > 175 ˚C
GND
V_Boost
V_thUV
4V
=
UV
COMP
+
-
H when
V_Boost < 4 V
H when
Overcurrent
GND
I _Pullup
H when
T_j > 175 ˚C
or OV at V_Boost
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
V_REF
2.8 V
=
Error
AMP
+
-
Error-Signal
Error-Ramp
PWM
COMP
H when
Error-Signal
<
Error-Ramp
OC
COMP
V_thOC
18 mV
R_Sense
14.5 mΩ
BOGND
Pin 13
GND
R
Pin 1
Oscillator
V_max
V_min
t_r t_f t_{r t}
Schmitt-trigger 1
Ramp Vhigh
V_low
t_r t_f t_r
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 V_BOOST undervoltage command.
Data Sheet
11
Rev. 3.4, 2007-08-16