ZXLD1371EST16TC Diodes Inc. / Zetex, ZXLD1371EST16TC Datasheet - Page 32

• Manufacturer Part Number: ZXLD1371EST16TC
• Description: MOSFET LED Controller TSSOP TSSOP-16EP T&R 2.5K
• Manufacturer: Diodes Inc. / Zetex

Specifications of ZXLD1371EST16TC

• Rohs: yes

ZXLD1371
Document number: DS35436 Rev. 1 - 2
Applications Information
Input Capacitor
The input capacitor can be calculated knowing the input voltage ripple ΔV
Buck
Boost
Buck-boost
The minimum RMS current for the output capacitor is calculated as follows:
Buck
Boost
Buck-boost
LED Current Dimming
The ZXLD1371 has 3 dimming methods for reducing the average LED current
DC Dimming
The ZXLD1371 has a clamp on the ADJ pin to prevent over-driving of the LED current which results in the maximum
voltage being applied to internal circuitry is the reference voltage. This provides a 10:1 dynamic range of dc LED current
adjustment.
The equation for DC dimming of the LED current is approximately:
One consequence of DC dimming is that as the ADJ pin
voltage is reduced the sense voltage will also be reduced
which has an impact on accuracy and switching frequency
especially at lower ADJ pin voltages.
I
LED_DIM
1.
2.
3.
I
C
C
C
I
I
=I
CIN
CIN
CIN
DC dimming using the ADJ pin
PWM dimming using the PWM pin
DC dimming for thermal protection using the TADJ pin.
Where
IN
IN
IN
LED_NOM
−
−
−
=
=
RMS
=
RMS
RMS
I
I
LED_DIM
LED_NOM
D
8
f
f
SW
SW
f x
x
=
=
=
1 (
SW
D
I
I
x
LED
I
V
V
Δ
LED
−
x
L
I x
Δ
−
12
ADJ
REF
I
is the LED current with V
Δ
D
L
x
PP
LED
V
is
−
V
x
Δ
)
x
IN
PP
IN
I x
V
−
Dx
LED
IN
−
1 (
PP
the
PP
−
−
1 (
D
PP
D
−
)
D
dimmed
)
(cont.)
Use D = 0.5 as worst case
Use D = D
use D=0.5 as worst case
Use D=D
LED
ADJ
= 1.25V
current
MAX
www.diodes.com
MAX
as worst case
32 of 42
as worst case
Figure 9. LED Current and switching frequency vs.
750
600
450
300
150
0
0
IN-PP
0.25
as follows:
Switching
Frequency
Diodes Incorporated
ADJ VOLTAGE (V)
A Product Line of
0.5
ADJ Voltage
0.75
T =25°C
V
2 LEDs
L=33µH
R =300m
A
AUX
S
1
=V =12V
IN
Ω
© Diodes Incorporated
February 2012
1.25
ZXLD1371
750
600
450
300
150
0