Application Note
4 of 28
V 1.0
2019-01-23
ILD8150 80 V high side buck LED driver IC with hybrid dimming
Circuit description
2
Circuit description
2.1
Operation
VCC
GND
CS
VIN
SD
SW
BOOT
DIM
Cfltr
Rfltr
Rcs
Iout
Vin
Cout
L
Cin
Cboot
D
Vsd
V
DIM
IC
Vout
C
VCC
Figure 1
Typical application circuit
2.1.1
Current regulation
Figure 1 shows the typical application circuit. Current is controlled by the CS pin, which compares the voltage
drop on R
CS
to internal references. Output current is proportional to the voltage drop on R
CS
. When the CS
voltage drops below V
CSL
the MOSFET switches on. Current and voltage on R
CS
rise accordingly. When the CS
voltage achieves V
CSH
the MOSFET switches off, and stored energy in inductor L discharges through the diode D.
In this way, the system maintains a constant average output current as shown in Figure 2.
𝐼
𝐿𝐸𝐷,𝐴𝑉𝐺
=
𝑉
𝐶𝑆𝐻
+ 𝑉
𝐶𝑆𝐿
2𝑅
𝐶𝑆
The output ripple of the instantaneous current is:
∆𝐼
𝑂𝑈𝑇
=
𝑉
𝐶𝑆𝐻
− 𝑉
𝐶𝑆𝐿
𝑅
𝐶𝑆
time [s]
I
OUT
[A]
1/f
SW
t
ON
t
OFF
I
LED,AVG
I
OUT
Figure 2
Current regulation
Current never goes down to zero, so the system operates in Continuous Conduction Mode (CCM), where
