ZXLD1371QESTTC Diodes Inc. / Zetex, ZXLD1371QESTTC Datasheet - Page 26

• Manufacturer Part Number: ZXLD1371QESTTC
• Description: MOSFET LED Controller TSSOP TSSOP-16EP T&R 2.5K
• Manufacturer: Diodes Inc. / Zetex

Specifications of ZXLD1371QESTTC

• Rohs: yes

ZXLD1371
Document number: DS35436 Rev. 1 - 2
Applications Information
This will give small enough I
about 80mV. This means GI_ADJ should be greater than (1-D
There is also a maximum limit on V
133% of 225mV, the STATUS output may indicate an over-current condition. This will happen for larger D
together with the requirement of Equation 13 , the recommended range for GI_ADJ is
An optimum compromise for GI_ADJ has been suggested, i.e.
This value has been used for the “Automatic” setting of the web Calculator. If 1-D
0.2. If 1- D
Once GI_ADJ has been selected, a value of RGI1 can be selected from Equation 12 . Then RGI2 is calculated as follows,
rearranging Equation 2 :
For example to drive 12 LEDS at a current of 350mA from a 12V supply requires Boost configuration. Each LED has a
forward voltage of 3.2V at 350mA, so Vout = 3.2*12 = 38.4V. From Equation 6 , the duty cycle is approximately
From Equation 16 , we set GI_ADJ to 1 – D = 0.3125.
IF R
R
GI_ADJ =
Now we calculate Rs from Equation 11 . Assume ADJ is connected to REF.
R
A preferred value of R
selection.
Table 1 shows typical resistor values used to determine the GI_ADJ ratio with E24 series resistors.
Table 1
This completes the LED current setting.
GI2
SBoostBB
GI ratio
GI1
= 75kΩ. Now GI_ADJ is adjusted to the new value, using Equation 2 .
0.25
0.35
0.45
0.2
0.3
0.4
0.5
= 33kΩ, then from Equation 17 , R
0.355 ( 1-D
GI_ADJ
R
V
GI2
=
OUT
V
MAX
OUT
RGI1 +RGI2
= R
0.225
-V
I
LED
is greater than 0.5 then GI_ADJ is set to 0.5.
IN
RGI1
AUTO
GI1
MIN
=
GI_ADJ
100kΩ
= 1 - D
RGI1
30kΩ
33kΩ
39kΩ
30kΩ
51kΩ
30kΩ
) < GI_ADJ < 1.33 ( 1-D
1-GI_ADJ
38.4-12
SBoostBB
GI_ADJ
38.4
=
LED
MAX
33k +75k
V
V
REF
error for most practical purposes. Satisfactory operation will be obtained if V
33k
ADJ
=
= 0.2Ω will give the desired LED current with an error of 2% due to the preferred value
0.6875
(cont.)
RS
=
120kΩ
100kΩ
150kΩ
91kΩ
56kΩ
62kΩ
30kΩ
which gives a maximum limit for GI_ADJ. If V
=0.305
RG2
0.225
0.35
GI2
= 33000 * ( 1 -0.3125 ) / 0.3125 = 72.6kΩ. Let us choose the preferred value
* 0.305 = 0.196 Ω
MAX
)
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26 of 42
MIN
) * 80/225 = (1- D
Diodes Incorporated
MAX
MIN
A Product Line of
) * 0.355.
is less than 0.2, then GI_ADJ is set to
RS
exceeds approximately 300mV, or
Equation 15
Equation 16
Equation 17
© Diodes Incorporated
MAX
RS
February 2012
ZXLD1371
is more than
. Therefore,