an30888b Panasonic Corporation of North America, an30888b Datasheet - Page 25
an30888b
Manufacturer Part Number
an30888b
Description
High Brightness Led Driver Ic
Manufacturer
Panasonic Corporation of North America
Datasheet
1.AN30888B.pdf
(31 pages)
(7) Setting output LED current and choosing current sense resistor R
For Buck Mode :
R
First is to calculate the peak current I
current plus half of actual current ripple through the inductor.
Lastly, R
Using numeric example of operating condition :
Please note that for component deviation such as inductor, diodes, etc, these deviation can cause the designed I
than the calculated value.
Users may need to fine tune the value of R
Please take note of total impedance including parasitic impedance of PCB trace at CS pin to ground when designing the required R
value. This is especially important if the designed I
significant to the total impedance seen at CS pin
AN30888B
CS
Technical Data (continued)
resistor can be set in the following way :
Functions and properties descriptions (continued)
CS
I
resistor can be determine by using :
R
V
From Eq[9] :
From Eq[10] : R
PK
CS
IN
= I
= 12 V, V
= ——— ………………………………………………
LED
V
V
T
I
L = Inductor value found in part (6) inductor selection
V
I
V
LED
PK
I
OFF
OUT
IN
PK
FB
FB
+ ——————————— …………………… Eq[9]
is peak current found in Eq[9] .
= Input supply voltage
= LED output current
is voltage at CS pin. Refer to data graphs for the V
=T
= Output voltage
OUT
I
OFF
(V
PK
CS
= 2 V, I
IN
= 0.5 + —————— = 0.575 A
= Fixed off time design at 1 μs
= ———— = 348 mΩ
– V
2L
0.575
OUT
PK
0.2
LED
using Eq[9]. During buck mode, peak current sense correspond to the average output LED
(12 – 2) × 1μ
) × T
= 500 mA, T
CS
2 × 66μ
OFF
from the calculated values in order to obtain accurate I
LED
OFF
is high as R
= 1 μs, L = 66 μH, V
SDG00005AEB
CS
value will be small and in turn making parasitic impedance
Eq[10]
FB
CS
voltage at different input voltage condition.
(continued)
FB
= 0.2 V
(Buck mode)
(Buck mode)
LED
measurement.
PK
to be higher or lower
CS
25