ADT6780 ADTECH [ADTech], ADT6780 Datasheet - Page 11

• Manufacturer Part Number: ADT6780
• Description: Thermally enhanced Low VFB Step-Down LED Driver
• Manufacturer: ADTECH [ADTech]

Jul. 12. 2012 / Preliminary
APPLICATION INFORMATION
Table1 and Table2 list the typical values of compensation components and external components for general
applications.
Table 1. Components values for IRLED application
Table 2. Components values for WLED application
The output voltage is calculated by the below equation.
Where, n is the number of LEDs connected in series, VF is the forward voltage of the LED and VFB is the
voltage drop across the current sense resistor.
A general procedure to choose the compensation components for conditions is following:
1. Select the desired crossover frequency. Set the crossover frequency to be equal or less than 1/10 of
switching frequency.
2. Select R2 (compensation resistor) to operate the desired crossover frequency in a given condition. R2
value is calculated by the following equation:
3. Select C3 (compensation capacitor) to achieve the desired loop phase margin. C3 determines the desired
first system zero, f
calculated by:
4. If the ESR output zero (f
secondary compensation capacitor (C6) to cancel it. As f
VIN (V)
VIN (V)
12
24
12
24
# of series IRLEDs
# of series WLEDs
Z1
. Typically, set f
1 ~ 5
1 ~ 8
1 ~ 2
1 ~ 4
Thermally enhanced Low V
* This specifications are subject to be changed without notice
Z2
) is located at less than one-half the switching frequency, use the (optional)
VOUT
VOUT
Z1
below 1/4 of the Fc to provides sufficient phase margin. C3 value is
R2
10
16
16
MAX
MAX
8
(continued)
=
V
C3
C6
OUT
(V)
(V)
2π
G
≥
×
=
= n
EA
2π
F
11/13
C2
(Refer to the Typical Application Circuit, for other components.)
C
(Refer to the Typical Application Circuit, for other components.)
×
R2 ( ㏀ )
R2 ( ㏀ )
×
×
×
G
×
R2
V
F
C2
2
2
2
2
4
P3
C
FB
ESR
CS
F
=f
×
+
×
×
Step-Down LED Driver
R2
Z2
V
R
R1
, then:
FB
LED
C3 ( ㎋ )
C3 ( ㎋ )
8.2
8.2
8.2
8.2
C6 ( ㎊ )
C6 ( ㎊ )
None
None
None
None
http://www.ad-tech.co.kr
L1 (uH)
6.8 ~ 10
L1 (uH)
6.8 ~ 10
15 ~ 22
15 ~ 22
ADT6780
C2 ( ㎌ )
C2 ( ㎌ )
10
10
10
10