Application Note
12 of 28
V 1.0
2019-01-23
ILD8150 80 V high side buck LED driver IC with hybrid dimming
Circuit description
input capacitor, output capacitor and inductor. Place the input capacitor close to the IC, as parasitic
inductance can be minimized by minimizing trace lengths and using short and wide traces. Extra parasitic
inductance between the input capacitor’s terminals and the IC’s V
IN
and GND terminals creates high dV/dt due
to the switching process. This can lead to IC failure. Also, place the inductor as close as possible to the IC to
reduce radiated EMI.
The output capacitor completes the routing of all the power components. It is the final component connected
to the power ground terminal in the system. Improper output capacitor placement typically causes poor output
current regulation. To ensure optimal operation, take care to minimize the area of the power-current loop.
The small-signal control components consist of all analog and digital components indirectly related to the
power conversion, such the CS pin, which is sensitive to noise. To reduce the noise coupling from the power
stage to the control circuitry, it is necessary to keep the noisy switching traces far from the sensitive small-
signal traces. The magnetic field from the inductor may cause noise on the CS path that could in turn lead to
incorrect operation as double or triple pulses. To avoid this effect a shielded inductor should be used, but do
not place this inductor close to the sensitive CS path. To minimize noise and ensure good output current
regulation, it is critical to keep the V
CS
path as short as possible, and it is desirable to return the ground of the
small-signal component to a “clean” point. Poor routing of small-signal components may lead to poor output
current regulation. A power inductor placed close to the CS path can influence the regulation loop. An example
layout is shown in Figure 12.
1
2
3
4
SD
VCC
VIN
CS
5
6
7
8
DIM
BOOT
SW
GND
Thermal Via
LEDs
L
Cboot
D
Cin
Cvcc
Cout
Figure 12
Layout example
Keep separate grounds for power components, which are noisy, and for the small-signal components, which
are quiet. Then join these two grounds at one point, possibly the exposed pad under the IC, which is also the IC
ground. A grid of thermal vias should be placed under the exposed pad to improve thermal conduction. The
above guidelines ensure a well laid-out power supply design.
2.5
Design example
As an example, an LED driver with the following specification shall be designed:
V
IN
= 70 V
I
LED,AVG
= 1 A
V
LED
= 51 V (17 LEDs)
2.5.1
Determine R
CS
𝑅
𝐶𝑆
=
0.36 𝑉
1𝐴
= 𝟎. 𝟑𝟔 Ω
