U6083B_05 Datasheet, PDF (4/13 Pages) ATMEL Corporation – PWM Power Control IC with Interference Suppression

3. Functional Description
3.1 Pin 1, Supply Voltage, V_S or V_Batt
3.1.1 Overvoltage Detection
3.1.1.1
Stage 1
If overvoltages of V_Batt > 20V (typically) occur, the external transistor is switched off, and
switched on again at V_Batt < 18.5V (hysteresis).
3.1.1.2
Stage 2
If V_Batt > 28.5V (typically), the voltage limitation of the IC is reduced from V_S = 26V to 20V. The
gate of the external transistor remains at the potential of the IC ground, thus producing voltage
sharing between FET and lamps in the event of overvoltage pulses (e.g., load dump). The short-
circuit protection is not in operation. At V_Batt approximately < 23V, the overvoltage detection
stage 2 is switched off. Thus, during overvoltage detection stage 2, the lamp voltage V_lamp is cal-
culated as follows:
V_Lamp = V_Batt – V_S – V_GS
V_S = supply voltage of the IC at overvoltage detection stage 2
V_GS = gate - source voltage of the FET
3.1.2
Undervoltage Detection
In the event of voltages of approximately V_Batt < 5.0V, the external FET is switched off and the
latch for short-circuit detection is reset.
A hysteresis ensures that the FET is switched on again at approximately V_Batt ≥ 5.4V.
3.2 Pin 2, GND
3.2.1
Ground-wire Breakage
To protect the FET in the case of ground-wire breakage, a 1 MΩ resistor between gate and
source is recommended to provide proper switch-off conditions.
3.3 Pin 3, Control Input
The pulse width is controlled by means of an external potentiometer (47 kΩ). The characteristic
(angle of rotation/duty cycle) is linear. The duty cycle can be varied from 18 to 100%. It is possi-
ble to further restrict the duty cycle with the resistors R₁ and R₂ (see Figure 7-1 on page 11).
In order to reduce the power dissipation of the FET and to increase the lifetime of the lamps, the
IC automatically reduces the maximum duty cycle at pin 8 if the supply voltage exceeds
V₂ = 13V. Pin 3 is protected against short-circuit to V_Batt and ground (V_Batt ≤ 16.5V).
4 U6083B
4770B–AUTO–09/05