u6084b ATMEL Corporation, u6084b Datasheet - Page 3

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

3. Functional Description
3.1
3.1.1
3.2
3.3
3.4
3.4.1
3.5
4677C–AUTO–09/05
Pin1 – GND
Pin 2 – Enable/Disable
Pin 3 – Control Input
Pin 4 – Duty Cycle Reduction
Pin 5 – Attenuation
Ground-wire Breakage
Output Slope Control
To protect the FET in case of ground-wire breakage, a 820-k resistor between gate and source
is recommended to provide proper switch-off conditions.
The dimmer can be switched on or off with pin 2, independently of the set duty cycle.
Table 3-1.
The pulse width is controlled by means of an external potentiometer (47 k ). The characteristic
(angle of rotation/duty cycle) is linear. The duty cycle be varied from 0% to 100%. It is possible to
further restrict the duty cycle with resistors R
Pin 3 is protected against short-circuit to V
With pin 4 connected according to
V
brightness of the lamps is largely independent of the supply voltage range, V
The rise and fall time (t
is done with an integrator which controls a power MOSFET as source follower. The slope time is
controlled by an external capacitor C
Calculation:
With V
Capacitor C
t
V
> approximately 0.7V or open
< 0.7V or connected to pin 1
t
f
f
Batt
2
=
=
t
t
r
r
Batt
=
=
12.5V. This causes a power reduction in the FET and in the lamps. In addition, the
V
12V
= 12V, C
Batt
4
connected to pin 5 damps oscillation tendencies.
Pin 2 Function
470 pF
----------------- -
-------- -
I
40 µA
C
osc
4
4
= 470 pF and I
r
, t
141 µs
f
) of the lamp voltage can be limited to reduce radio interference. This
osc
4
Figure 7-1 on page
= 40 µA, the controlled slope is
and the oscillator current
Batt
1
and ground GND (V
and R
Function
Disable
Enable
2
(Figure 7-1 on page
9, the set duty cycle is reduced to
(Figure 7-1 on page
Batt
16.5V).
9).
Batt
= 12.5V to 16V.
U6084B
9).
3