ZXLD1370_11 DIODES [Diodes Incorporated], ZXLD1370_11 Datasheet - Page 14

• Manufacturer Part Number: ZXLD1370_11
• Description: 60V HIGH ACCURACY BUCK/BOOST/BUCK-BOOST LED DRIVER CONTROLLER
• Manufacturer: DIODES [Diodes Incorporated]

Set the appropriate GI ratio according to the circuit duty and the max switch current admissible cycle limitations
If the potential divider ratio is greater than 0.64, the device detects that buck-mode operation is desired and the output current
will deviate from the desired value.
For example, as in the typical application circuit, in order to get I
Setting R
ZXLD1370
Document number: DS32165 Rev. 3 - 2
Applications Information
Note that the average LED current for a boost or buck-boost converter is always less than the average sense resistor
current. For the ZXLD1370, the recommended potential divider ratio is given by:
It is possible to use a different combination of GI pin voltages and sense resistor values to set the LED current.
In general the design procedure to follow is:
-
-
-
Calculate the maximum duty-cycle as:
Buck mode
Boost mode
Buck-boost mode
- Set RGI1 as:
- Calculate RGI2 as:
When the ADJ pin is directly connected to the REF pin, this becomes:
-
Define input conditions in terms of V
Set output conditions in terms of LED current and the number of LEDs
Define controller topology – Buck, Boost or Buck-boost
Calculate the sense resistor as:
GI1
R
0
D
D
D
R
I
V
I
LED
R
V
RS
2 .
s
MAX
MAX
MAX
s
ADJ
GI
GI
= 33kΩ it results
=
=
≤
2
=
=
=
=
(R
=
≈
R (
(R
V
V
1
V
GI
V
GI
(R
LEDS
LEDS
GI
V
D
−
IN
V
R
LEDs
1
1
R
R
1
ADJ
MIN
D
GI
+
MAX
+
GI
GI
V
GI
V
+
GI
MAX
R
R
1
1
LEDS
R
LEDS
1
−
+
R
1
+
GI
=
GI
GI
V
V
GI
1
R
2
2
IN
IN
2
(R
x
)
)
)
GI
MIN
MIN
225
R
≤
GI
225
2
I
)
LED
R
1
GI
. 0
I
+
LED
≤
mV
1
GI
50
mV
1
R
1
GI
−
2
(Continued)
D
)
MAX
≈
. 0
23
IN
10
and I
k
Ω
≤
IN
R
www.diodes.com
GI
1
≤
14 of 35
200
LED
k
Ω
= 350mA with IRS=1.5A the ratio has to be set as:
Diodes Incorporated
A Product Line of
© Diodes Incorporated
ZXLD1370
February 2011