an30888b Panasonic Corporation of North America, an30888b Datasheet - Page 24

• Manufacturer Part Number: an30888b
• Description: High Brightness Led Driver Ic
• Manufacturer: Panasonic Corporation of North America

(7) Setting output LED current and choosing current sense resistor R
The LED current in this IC can be set easily by selecting the appropriate R
For Boost Mode and Buck-Boost mode :
R
First is to calculate input current I
After which the peak input current, I
Lastly, R
Using numeric example of operating condition :
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[6] :
From Eq[7] :
From Eq[8] :
I
IN
PK
CS
IN
= (V
= I
= 6 V, V
= ——— ………………………………………………
V
V
I
V
IN
T
L = Inductor value found in part (6) inductor selection
V
V
I
V
I
V
I
OUT
LED
IN
PK
PK
OFF
OUT
D
IN
OUT
IN
FB
FB
+ ——————————— …………………… Eq[7]
= I
= Schottky diode forward drop voltage
is peak current found in Eq[7]
+ V
= Input supply voltage
= Input supply voltage
= Required LED current
is voltage at CS pin. Refer to data graphs for the V
= T
OUT
= Output voltage
= Output voltage
IN
(V
I
I
R
D
is input current found in Eq[6]
OFF
IN
PK
) × (I
= 10 V, I
CS
OUT
= (10 + 0.4) × (0.5 / 6) = 0.8667 A
= 0.8667 + ——————— = 0.9971 A
is fixed off time = 1 μs
= ———— = 100.8 mΩ
Eq[7]
- - - - - - - - - - - - - - - L * 2 P K
CS
I V FB
R =
- - - - - - - - - - - - PK
CS
I R =
IN
LED
– V
0.9917
at the required operating condition :
2L
PK
0.1
/ V
IN
LED
can be determine by adding I
) × T
IN
= 500 mA, T
) …………………………… Eq[6]
OFF
(10 – 6) × 1μ
2 × 16μ
OFF
= 1 μs, L = 16 μH, V
SDG00005AEB
IN
with half the peak to peak ripple current at the inductor.
Eq[8]
FB
CS
CS
voltage at different input voltage condition.
resistor to be used at CS pin of this chip.
D
= 0.4 V, V
FB
= 0.1 V@V
(Boost mode，Buck-Boost mode)
(Boost mode，Buck-Boost mode)
(Boost mode，Buck-Boost mode)
IN
= 6 V
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