TLE 6711

Circuit Description

Data Sheet

11

Rev. 3.4, 2007-08-16

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

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

even if the battery is disconnected by a car crash.

The boost inductance

L

with a programmable (external resistor

R

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

external divider network (determination of the output boost voltage

V

Application note for programming the output voltage at pin

V

(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.

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

+

()

-------------------------------------

×

=

AEB02946

Pin 1

R

V

min

t

f

r

t

t

Oscillator

V

max

V

low

t

r

t

r

high

Schmitt-trigger 1

t

Clock

Error-Ramp

Error-Signal

PWM

COMP

Error-Ramp

Error-Signal

H when

<

=

V

GND

2.8 V

REF

Error

-

+

AMP

Pin 12

BOFB

Pullup

I

10

=

GND

COMP

+

-

UV

4 V

thUV

V

Boost

V

GND

thOV

38 V

V

=

COMP

OV

NOR 1

1

&

OV at

L when

Boost

V

NAND 3

L when

> 175 ˚C

T

j

H when

Overcurrent

H when

< 4 V

Boost

V

H when

> 175 ˚C

j

T

V

NAND1

&

&

Error-FF

&

R

Q

S

Q

L when

Error

NOR 2

1

Error

H when

Error

Gate

Unlock

Detector

NAND 2

&

Q

R

&

S

Q

&

PWM-FF

H =

OFF

H =

ON

1

INV

D-MOS

Power

Gate

Driver

COMP

OC

V

thOC

18 mV

Sense

14.5 m

R

Ω

Pin 13

BOGND

H when Outputcurrent > 1.2 A

OVL

Pin 11

GND

BOI

Pin 14

Boost Status

Low if Battery

Disconnected