u6084b ATMEL Corporation, u6084b Datasheet - Page 5

• Manufacturer Part Number: u6084b
• Description: U6084b Pwm Power Control With Automatic Duty-cycle Reduction
• Manufacturer: ATMEL Corporation

3.7
3.8
3.9
3.9.1
3.9.2
3.10
4677C–AUTO–09/05
Pins 7, 8, 10 and 15
Pin 9 – Status Short Circuit Latch
Pins 11 and 12 – Short-circuit Protection and Current Sensing
Pins 13 and 14 – Charge Pump and Output
Short-circuit Detection and Time Delay t
Current Limitation
Not connected.
The status of the short-circuit latch can be monitored via pin 9 (open collector output).
Table 3-2.
The lamp current is monitored by means of an external shunt resistor. If the lamp current
exceeds the threshold for the short-circuit detection circuit (V
switched over to 100% and capacitor C
external FET is switched off after the cut-off threshold (V
of the FET is possible only after a power-on reset. The current source, I
tor C
Time delay, t
With C
The lamp current is limited by a control amplifier that protects the external power transistor. The
voltage drop across an external shunt resistor acts as the measured variable. Current limitation
takes place for a voltage drop of V
rent limitation occurs only when the short-circuit detection circuit has responded.
After a power-on reset, the output is inactive for half an oscillator cycle. During this time, the sup-
ply voltage capacitor can be charged so that current limitation is guaranteed in the event of a
short-circuit when the IC is switched on for the first time.
Pin 14 (output) is suitable for controlling a power MOSFET. During the active integration phase,
the supply current of the operational amplifier is mainly supplied by capacitor C
Additionally, a trickle charge is generated by an integrated oscillator (f
age doubler circuit. This permits a gate voltage supply at a duty cycle of 100%.
Pin 9
L
H
t
t
d
d
=
=
5
C
330 nF
is not charged by parasitic currents. Capacitor C
5
5
= 330 nF and V
------------------------------- -
V
I
11
ch
d
, is as follows:
---------------------------------- -
Pin 9 Function
–
–
9.8V 0.7V
0.7V
I
dis
20 A
–
Function
Short-circuit detected
No short-circuit detected
Batt
d
= 12V, we have
=
150 ms
T1
5
100 mV. Owing to the difference V
is charged by a current source of 20 µA (I
5
is discharged by I
T11
) is reached. Renewed switching on
T2
90 mV), the duty cycle is
13
dis
dis
T
, ensures that capaci-
– V
400 kHz) and a volt-
to typically 0.7V.
3
T2
(bootstrapping).
U6084B
ch
10 mV, cur-
– I
dis
). The
5