AN2982 Datasheet, PDF (20/31 Pages) STMicroelectronics – This application note describes the STEVAL-ILB005V2 demonstration board equipped with the L6585DE lighting controller

Ballast stage design
2.4
End of life detection
In this design the blocking capacitor to ground configuration is chosen.
Figure 13. Blocking capacitor to ground topology
AN2982
!-V
The tracking configuration with a window of amplitude equal to 240 mV is selected,
connecting EOLP to ground with R_EOLP = 240 kΩ.
The EOL pin detects the blocking capacitor voltage by means of a voltage divider that, in
normal conditions, sets its voltage to the same value as the CTR pin:
Equation 50
V_CTR,0
=
V_out
R_ctrl
R_ctrl + R_ctrh
= 3.03 V ← V_EOL
Choosing the total upper resistor value equal to R_eol1 = 1.36 MΩ (2x680 kΩ), and with the
steady-state value of the blocking capacitor voltage equal to V_out/2, the lower resistor is
calculated as:
Equation 51
R_eol2
=
R_eol1
2V_EOL
V_OUT − 2V_EOL
= 19.9 kΩ → R_eol2
=
20 kΩ
A C_eol = 10 nF capacitor is used to filter the lamp frequency, maintaining the ripple. The
obtained cutoff frequency is calculated higher than 100 Hz, but lower than 49 kHz.
Equation 52
f_c,eol
≈
1
2π ⋅ R_eol2 ⋅ C_eol
= 796 Hz
20/31
Doc ID 15599 Rev 1