U6083B_05 Datasheet, PDF (7/13 Pages) ATMEL Corporation – PWM Power Control IC with Interference Suppression

U6083B
3.6 Interference Suppression
• “On-board” radio reception according to VDE 0879 part 3/4.81
• Test conditions referring to Figure 3-1
• Application circuit according to Figure 1-1 on page 2 or Figure 7-1 on page 11
• Load: nine 4W lamps in parallel
• Duty cycle = 18%
• V_Batt = 12V
• f_Osc = 100 Hz
Figure 3-1. Voltage Spectrum of On-board Radio Reception
3.7 Pins 5 and Pin 6, Short-circuit Protection and Current Sensing
3.7.1
Short-circuit Detection and Time Delay, t_d
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_T2 ≈ 90 mV), the duty cycle is
switched over to 100% and the capacitor C₅ is charged by a current source of I_ch – I_dis. The
external FET again is switched off after the cut-off threshold (V_T5) is reached. Switching on the
FET again is possible after a power-on reset only. The current source, I_dis, ensures that the
capacitor C₅ is not charged by parasitic currents.
The time delay, t_d, is calculated as follows:
t_d = C₅ × V_T5/(I_ch – I_dis)
With C₅ = 100 nF and V_T5 = 10.4V, I_ch =13 µA, I_dis = 3 µA, the time delay is as follows:
t_d = 100 nF × 10.4V/(13 µA – 3 µA)
t_d = 104 ms
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4770B–AUTO–09/05